災(zāi)害天氣研究進(jìn)展

Advances in Research on Severe Weather

1 災(zāi)害天氣監(jiān)測(cè)

1 Severe weather monitoring technology

1.1 Establishment and preliminary application of the forward modeling method for Doppler spectral density of ice particles

Owing to the various shapes of ice particles,the relationships between fall velocity,backscattering crosssection,mass,and particle size are complicated.This affects the application of cloud radar Doppler spectral density data in the retrieval of the microphysical properties of ice crystals.In this study,under the assumption of six particle shape types,the relationships between particle mass,fall velocity,backscattering cross-section,and particle size were established based on existing research.Variations of Doppler spectral density with the same particle size distribution (PSD) of different ice particle types were discussed.The radar-retrieved liquid and ice PSDs,water content,and mean volume-weighted particle diameter were compared with airborne in situ observations in Xingtai,Hebei Province,China,in 2018.The results show the following:(1) For the particles with the same equivalent diameter (De),the fall velocity of the aggregates was the largest,followed by hexagonal columns,hexagonal plates,sector plates,and stellar crystals,with the ice spheres falling two to three times faster than ice crystals with the same De.Hexagonal columns had the largest backscattering crosssection,followed by stellar crystals and sector plates,and the backscattering cross-sections of hexagonal plates and the two types of aggregates were very close to those of ice spheres.(2) The width of the simulated radar Doppler spectral density generated by various ice crystal types with the same PSD was mainly affected by the particle’s falling velocity,which increased with the particle size.Turbulence had different degrees of influence on the Doppler spectrum of different ice crystals,and it also brought large errors to the PSD retrieval.(3)PSD comparisons show that each ice crystal type retrieved from the cloud radar corresponded well to aircraft observations within a certain scale range,when assuming that only a certain type of ice crystals existed in the cloud,which could fully prove the feasibility of retrieving ice PSDs from the reflectivity spectral density.(Ding Han,Liu Liping)

1.2 Improvement of X-band polarization radar melting layer recognition by the bayesian method and its impact on hydrometeor classification

Using the melting layer (ML) and non-melting layer (NML) data observed with the X-band dual linear polarization Doppler weather radar (X-POL) in Shunyi,Beijing,the reflectivity (ZH),differential reflectivity(ZDR),and correlation coefficient (CC) in the ML and NML are obtained in several stable precipitation processes.The prior probability density distributions (PDDs) of the ZH,ZDR and CC are calculated first,and then the probabilities of ZH,ZDR and CC at each radar gate are determined (PBB in the ML and PNB,in the NML) by the Bayesian method.When PBB > PNB,the gate belongs to the ML,and when PBB < PNB,the gate belongs to the NML.The ML identification results with the Bayesian method are contrasted under the conditions of the independent PDDs and joint PDDs of the ZH,ZDR and CC.The results suggest that MLs can be identified effectively,although there are slight differences between the two methods.Because the values of the polarization parameters are similar in light rain and dry snow,it is difficult for the polarization radar to distinguish them.After using the Bayesian method to identify the ML,light rain and dry snow can be effectively separated with the X-POL observed data.(Ma Jianli,Hu Zhiqun,Yang Meilin)

1.3 Integrated correction algorithm for X band dual-polarization radar reflectivity based on CINRAD/SA radar

The values of ratioaof the linear relationship between specific attenuation and specific differential phase vary significantly in convective storms as a result of resonance scattering.The best-linear-fit ratioaat X band is determined using the modified attenuation correction algorithm based on differential phase and attenuation,as well as the premise that reflectivity is unattenuated in S band radar detection.Meanwhile,the systemic reflectivity bias between the X band radar and S band radar and water layer attenuation (ZW) on the wet antenna cover of the X band radar are also considered.The good performance of the modified correction algorithm is demonstrated in a moderate rainfall event.The data were collected by four X band dual-polarization (X-POL)radar sites,namely,BJXCP,BJXFS,BJXSY,and BJXTZ,and a China’s New Generation Weather Radar(CINRAD/SA radar) site,BJSDX,in Beijing on 20 July 2016.Ratio a is calculated for each volume scan of the X band radar,with a mean value of 0.26 dB/(°) varying from 0.20 to 0.31 dB/(°).The average values of systemic reflectivity bias between the X band radar (at BJXCP,BJXFS,BJXSY,and BJXTZ) and S band radar(at BJSDX) are 0,?3,2,and 0 dB,respectively.The experimentally determinedZWis in substantial agreement with the theoretically calculated ones,and their values are an order of magnitude smaller than rain attenuation.The comparison of the modified attenuation correction algorithm and the empirical-fixed-ratio correction algorithm is further evaluated at the X-POL radar.It is shown that the modified attenuation correction algorithm in the present paper provides higher correction accuracy for rain attenuation than the empirical-fixedratio correction algorithm.(Wang Chao,Wu Chong,Liu Liping)

1.4 Method to retrieve aerosol extinction profiles and aerosol scattering phase functions with a modified CCD laser atmospheric detection system

Vertical distributions of ambient aerosols and their corresponding optical properties are crucial to the assessment of aerosol radiative effects.Traditionally,ambient aerosol phase function is assumed as a constant of input parameter in the retrieval of the vertical distribution of aerosol optical characteristics from remote sensing measurements (e.g.Lidar or camera-laser based instruments).In this work,sensitivity studies reveal that using constant aerosol phase function assumptions in the algorithm would cause large uncertainties.Therefore,an improved retrieval method was established to simultaneously measure ambient aerosol scattering phase functions and aerosol scattering function profiles with a modified charge-coupled device-laser aerosol detection system (CLADS),which are then combined to yield vertical profiles of aerosol extinction coefficients.This method was applied and evaluated in a comprehensive field campaign in the North China Plain during January 2016.The algorithm showed robust performance and was able to capture temporal variations in ambient aerosol scattering phase functions and aerosol scattering function profiles.Aerosol extinction coefficients derived with simultaneously measured aerosol phase functions agreed well with in-situ measurements,indicating that uncertainties in the retrieval of aerosol extinction vertical profiles have been significantly reduced by using the proposed method with the modified CLADS.The advantage of this modified CLADS is that it can accomplish these aerosol measurements independent of other supplementary instruments.Benefiting from its low cost and high spatial resolution (similar to 1 m on average) in the boundary layer,this measurement system can play an important role in the research of aerosol vertical distributions and its impacts on environmental and climatic studies.(Bian Yuxuan,Xu Wanyun,Hu Yaqiong)

1.5 Operational evaluation of the quantitative precipitation estimation by a CINRAD-SA dual polarization radar system

In this paper,a quantitative precipitation estimation based on the hydrometeor classification (HCA-QPE)algorithm was proposed for the first operational S band dual-polarization radar upgraded from the CINRAD/SA radar of China.The HCA-QPE algorithm,localized the Colorado State University-Hydrometeor Identification of Rainfall (CSU-HIDRO) algorithm,the Joint Polarization Experiment (JPOLE) algorithm,and the dynamic Z-R relationships based on variational correction QPE (DRVC-QPE) algorithm were evaluated with the rainfall events from March 1 to October 30,2017 in Guangdong Province.The results indicat that even though the HCA-QPE algorithm did not use the observed rainfall data for correction,its estimation accuracy was better than that of the DRVC-QPE algorithm when the rainfall rate was greater than 5 mm h?1; and the stronger the rainfall intensity,the greater the QPE improvement.Besides,the HCA-QPE algorithm worked better than the localized CSU-HIDRO and JPOLE algorithms.This study preliminarily evaluated the improved accuracy of QPE by a dual-polarization radar system modified from CINRAD-SA radar.(Chen Chao,Liu Liping,Hu Sheng)

1.6 Performance of a radar mosaic quantitative precipitation estimation algorithm based on a new data quality index for the Chinese polarimetric radars

The quality of radar data is crucial for its application.In particular,before radar mosaic and quantitative precipitation estimation (QPE) can be conducted,it is necessary to know the quality of polarimetric parameters.The parameters include the horizontal reflectivity factor,ZH; the differential reflectivity factor,ZDR; the specific differential phase,K-DP; and the correlation coefficient,rho (HV).A novel radar data quality index (RQI) is specifically developed for the Chinese polarimetric radars.Not only the influences of partial beam blockages and bright band upon radar data quality,but also those of bright band correction performance,signal-to-noise ratio,and non-precipitation echoes are considered in the index.RQI can quantitatively describe the quality of various polarimetric parameters.A new radar mosaic QPE algorithm based on RQI is presented in this study,which can be used in different regions with the default values adjusted according to the characteristics of local radar.RQI in this algorithm is widely used for high-quality polarimetric radar data screening and mosaic data merging.Bright band correction is also performed to errors of polarimetric parameters caused by melting ice particles for warm seasons in this algorithm.This algorithm is validated by using nine rainfall events in Guangdong Province,China.Major conclusions are as follows:ZHZDR,and K-DP in bright band become closer to those under bright band after correction than before.However,the influence of K-DP correction upon QPE is not as good as that ofZHandZDRcorrection in bright band.OnlyZHandZDRare used to estimate precipitation in the bright band affected area.The new mosaic QPE algorithm can improve QPE performances not only in the beam blocked areas and the bright band affected area,which are far from radars,but also in areas close to the two radars.The sensitivity tests show the new algorithm can perform well and stably for any type of precipitation occurred in warm seasons.This algorithm lays a foundation for regional polarimetric radar mosaic precipitation estimation in China.(Zhang Yang,Liu Liping,Wen Hao)

1.7 Statistical analysis of microphysical and dynamical parameters for clouds and precipitation over Naqu Tibetan Plateau in summertime using Ka-band cloud radar

A Chinese Ka-band solid-state transmitter cloud radar (CR) was employed to investigate clouds and precipitation over the Tibetan Plateau (TP) in summer 2014.After performing quality control and merging the output from the three work modes of CR,the Doppler spectral density data were analyzed to estimate the vertical air motion (Vair) and particle fall speed (Vfall) in clouds.The reproduced radar reflectivity was employed to retrieve the ice water content (IWC) and ice effective radius (Re).The cloud type classification algorithm was developed to classify cloud conditions into eight different categories.The vertical and daily variations of reflectivity,Vair,Vfall,IWC,andRewere then analyzed,and as a result,four conclusions were formulated.First,the clouds with reflectivity less than ?10 dBz were mainly located above 7 km,and the precipitable particles were formed below this layer (rain echo top) due to the abundant supercooled water therein.Second,the weak updraft in the range of 2?4 km caused the high occurrence of weak clouds during 04:00?12:00 Beijing local time (BT),and the rain echo top did not exceed 7 km due to the existing downdraft in 4?6 km.After 14:00 BT,convective clouds quickly developed,and the averaged updraft,reflectivity,and the echo top notably increased.Third,particular cloud types commonly exhibited weak reflectivity,low IWC,and less vertical variations,while the others more obvious vertical variations with larger IWC andRe.Last,compared with the radar sensitivity and range from radar,Vairbiases that were introduced by the Doppler spectra broadening due to turbulence,wind shear,and radar beam width,could be neglected.(Liu Liping,Gao Wenhua)

1.8 Uncertainties in retrieving microphysical properties of rain profiles using ground-based dualfrequency radar

Dual-frequency radar (DFR) could improve the accuracy of estimating the microphysical properties of rain profiles.Unfortunately,factors that cause inaccuracies in retrieved rain profiles include uncertainties in raindrop size distribution (DSD) parameterizations,DFR retrieval methods and radar measurement errors.The primary objective of this study was to assess the uncertainties in retrieving rain profiles to offer insight into application considerations for ground-based DFRs in China.The uncertainties caused by DSD models are assessed by comparing attenuation coefficients and rain rates from DFR algorithms with those directly derived from DSD spectra from disdrometers.Then,based on a DSD model,the impacts of retrieval methods,radar range resolution,measurement error and errors in temperature on DFR retrievals are explored by comparing the rain profiles obtained using DFR algorithms with those directly output from the Weather Research and Forecasting model.Overall,the impact of measurement error on the DFR retrievals is relatively significant for both the forward retrieval method and the iterative backward retrieval method and should be eliminated in practical applications.At an individual uncertainty level,the impact of DSD parameterizations on the retrievals from the dual-frequency technique is less than ± 10% bias when the shape factorμof the gamma distribution ranges from 2 to 4.The retrieved rain profiles from the forward retrieval method are relatively sensitive to radar range resolution and the retrieval performance can be improved with increasing the range resolution,while the iterative backward retrieval method exhibits stable retrieval performance.The impact of temperature errors on the retrieved rain profiles is negligible.(Wang Gaili,Liu Shengnan,Liu Liping)

1.9 Vertical structure and dynamical properties during snow events in middle latitudes of China from observations by the C-band vertically pointing radar

Data from the continuous observations of four shallow snow events (echo top 8 km) and two deep events( 10 km) were obtained using the C-band vertically pointing radar with frequency-modulation continuouswave technology with extremely high resolution during the winter of 2015?2016 in middle latitudes of China.Snow-generating cells (GCs) were found near the cloud top in each event.Reflectivity (Z),radial velocity,and the vertical gradients ofZ(dZ/dh,wherehis the vertical distance) andVr(dVr/dh) showed different vertical distribution characteristics between the upper GC and lower stratiform regions (St regions).Fall streaks (FSs)associated with GCs were embedded in the St regions.In the deep events,the proportions of GC regions were slightly larger,but the average contributions to the growth ofZ(33%) were lower than those in the shallow events (42%).The average dZ/dhvalues were usually two to three times larger inside GCs and FSs compared to outside.Bimodal Doppler spectra were used to establish the relationships betweenZand the reflectivityweighted particle fall speed (Vz) for the two regions.The vertical air velocity (Wa) andVzwere then retrieved,and the results show that both the updraft and the downdraft were alternately observed in GC regions.GC locations were usually accompanied by strong upward air motion,with average speeds mostly distributed around 1.2 m s?1,whereas downward air motion often appeared between GCs.In the St regions,the speeds ofWawere mainly within 0.5 m s?1.The upper areas of the St regions consisted primarily of weak upward motion,whereas weak downward motion dominated the lower areas.There was no apparent difference inWainside and outside the FSs.The averageVzwas slightly larger inside GCs and FSs compared to outside,with a difference of 0.1?0.3 m and 0.2?0.4 m s?1,respectively.(Cui Ye,Ruan Zheng,Wei Ming)

1.10 DSD參數(shù)對(duì)雙頻雷達(dá)估測(cè)降水的影響研究

雙頻雷達(dá)通過(guò)估計(jì)降水的雨滴譜分布（Rain Drop Size Distribution，DSD）參數(shù)來(lái)估測(cè)降水，相比多普勒天氣雷達(dá)利用Z-I關(guān)系估測(cè)降水的方法，估測(cè)結(jié)果更加準(zhǔn)確。真實(shí)的雨滴譜分布隨時(shí)空不斷變化，難以準(zhǔn)確描述。本研究的目的是評(píng)估將其描述成Gamma分布模型對(duì)雙頻雷達(dá)估測(cè)降水造成的誤差。研究中利用架設(shè)在廣東龍門(mén)和西藏那曲的雨滴譜儀觀測(cè)資料，計(jì)算Ku/Ka雙頻雷達(dá)的反射率因子，利用雙頻雷達(dá)算法反演降水率R和衰減系數(shù)k，并將其與雨滴譜儀直接計(jì)算的結(jié)果進(jìn)行比較，探討雙頻雷達(dá)反演算法中DSD模型對(duì)反演結(jié)果造成的影響，并對(duì)比反演誤差的地區(qū)差異性。研究結(jié)果表明：DSD參數(shù)對(duì)雙頻雷達(dá)反演降水的影響在那曲和龍門(mén)地區(qū)有一定的差異。從雙頻技術(shù)反演的質(zhì)量加權(quán)的粒子直徑(Dm)、Ka波長(zhǎng)衰減系數(shù)（k_Ka）、波長(zhǎng)衰減系數(shù)（k_Ku）和降水率（R）來(lái)看，當(dāng)Gamma分布的形狀因子μ分別取2、3和4時(shí)，龍門(mén)地區(qū)對(duì)四個(gè)參數(shù)的反演都能得到較為穩(wěn)定準(zhǔn)確的結(jié)果，相對(duì)誤差基本 10%。而就Ka和5～40 mm/h的降水率而言，那曲和龍門(mén)有很大的不同，在龍門(mén)當(dāng)μ取3時(shí)相對(duì)誤差最小，都在0值附近波動(dòng)，而那曲則要需要μ值在4和6附近才能使得相對(duì)誤差達(dá)到最小。(劉勝男，王改利)

1.11 Ka/Ku雙波段云雷達(dá)探測(cè)云降水滴譜和空氣垂直運(yùn)動(dòng)速度的能力模擬分析

由于湍流、雷達(dá)探測(cè)靈敏度等對(duì)單波長(zhǎng)云雷達(dá)探測(cè)回波強(qiáng)度譜密度的影響，造成了云雷達(dá)探測(cè)空氣垂直運(yùn)動(dòng)速度和雨滴譜的誤差，而雙波長(zhǎng)云雷達(dá)利用Mie散射造成的不同粒子后向散射大小差異來(lái)提高空氣上升速度探測(cè)精度，從而提高反演雨滴譜的能力，并且可提高訂正雨區(qū)衰減的能力。為此中國(guó)氣象科學(xué)研究院研發(fā)了Ka/Ku雙波段云雷達(dá)，并于2019年4月開(kāi)始在廣東龍門(mén)進(jìn)行了云降水觀測(cè)。本文針對(duì)該雙波段云雷達(dá)觀測(cè)模式和靈敏度等參數(shù)，在Gamma滴譜假設(shè)條件下，模擬分析了Ka、Ku波段功率譜及其比值與云降水參數(shù)、溫度和湍流的關(guān)系，研究了雷達(dá)靈敏度、湍流對(duì)空氣垂直速度、雨滴譜反演和衰減訂正的影響，并利用個(gè)例數(shù)據(jù)進(jìn)行了風(fēng)場(chǎng)反演試驗(yàn)，討論了雙波段探測(cè)微降水動(dòng)力和微物理參數(shù)的優(yōu)勢(shì)。結(jié)果表明：（1）溫度只能影響兩個(gè)波段功率譜比值(Ratio)的大小，對(duì)其峰值位置基本沒(méi)有影響，而湍流對(duì)其峰值位置的影響不超過(guò)0.5 m/s；（2）湍流、雷達(dá)靈敏度對(duì)單波段云雷達(dá)探測(cè)空氣垂直速度的影響比較明顯，湍流使空氣上升速度被高估，雷達(dá)最小可測(cè)回波強(qiáng)度隨高度的增加而增加使該參數(shù)被低估，其影響遠(yuǎn)遠(yuǎn)大于溫度和湍流對(duì)雙波段云雷達(dá)反演空氣垂直速度的影響；（3）對(duì)于單波段雷達(dá)來(lái)說(shuō)，雷達(dá)靈敏度和湍流明顯影響雨滴譜、含水量和衰減系數(shù)的探測(cè)，湍流使得雨滴譜拓寬，低估含水量和衰減系數(shù)；而雷達(dá)靈敏度卻使反演的雨滴譜變窄，增加小粒子數(shù)濃度，并高估了含水量和衰減系數(shù)；（4）選取2019年4月15—16日的個(gè)例進(jìn)行空氣上升速度的反演，并與模擬分析的結(jié)果進(jìn)行對(duì)比。結(jié)果顯示實(shí)際觀測(cè)數(shù)據(jù)反演的空氣上升速度與模擬分析結(jié)果中的趨勢(shì)較為一致。這項(xiàng)工作為單波段和雙波段云雷達(dá)的多普勒功率譜數(shù)據(jù)分析和云降水微物理和動(dòng)力參數(shù)的反演可提供參考。(鄭晨雨，劉黎平)

1.12 雙偏振雷達(dá)水凝物相態(tài)識(shí)別算法的參數(shù)改進(jìn)

雙偏振雷達(dá)的水凝物相態(tài)識(shí)別算法基于模糊邏輯方法建立，針對(duì)方法的可靠性和穩(wěn)定性問(wèn)題，利用2016—2017年暖季廣州S波段雙偏振雷達(dá)數(shù)據(jù)，從3個(gè)方面找出影響識(shí)別效果的關(guān)鍵因素并改進(jìn)。使用模糊邏輯的累加值為檢驗(yàn)依據(jù)，找出不合理的模糊規(guī)則，通過(guò)相態(tài)特征統(tǒng)計(jì)和權(quán)重矩陣修改加以改進(jìn)。使用誤差敏感性檢驗(yàn)法系統(tǒng)，評(píng)估誤差對(duì)識(shí)別效果的影響，發(fā)現(xiàn)反射率因子的誤差在?0.5～+0.5 dBz、差分反射率因子的誤差在?0.1～+0.1 dB、雷達(dá)相關(guān)系數(shù)的誤差在0～0.02、差分相移率的誤差在?0.3～+0.9 dB的范圍內(nèi)，識(shí)別結(jié)果穩(wěn)定性較好。此外，相態(tài)時(shí)空分布統(tǒng)計(jì)中發(fā)現(xiàn)底層冰雹面積異常增加，通過(guò)空間一致性檢驗(yàn)可訂正異常結(jié)果。(徐舒揚(yáng)，吳翀，劉黎平)

2 青藏高原天氣研究

2 Research on weather over the Tibetan Plateau

2.1 第二次青藏高原綜合科學(xué)考察研究

根據(jù)第二次青藏高原綜合科學(xué)考察研究任務(wù)一“西風(fēng)—季風(fēng)協(xié)同作用及其影響”年度計(jì)劃，中國(guó)氣象科學(xué)研究院災(zāi)害天氣國(guó)家重點(diǎn)實(shí)驗(yàn)室為牽頭單位，2020年任務(wù)一組織6個(gè)專題的科學(xué)家、專家組成的科研團(tuán)隊(duì)，開(kāi)展了數(shù)百人次科學(xué)考察與觀測(cè)試驗(yàn)，其中包括：（1）冰川、黃土、湖泊歷史演變環(huán)境指標(biāo)多類(lèi)型綜合科學(xué)考察：考察隊(duì)進(jìn)入巴基斯坦喀喇昆侖、三江源冰川、西昆侖區(qū)結(jié)則茶卡冰前湖、亞洲水塔區(qū)冰川地貌與湖泊、天山—帕米爾黃土區(qū)域，高質(zhì)量地完成歷史演變環(huán)境指標(biāo)多類(lèi)型（石筍、樹(shù)輪、冰芯鉆取等）科學(xué)考察任務(wù)；（2）藏東南區(qū)域飛機(jī)云降水過(guò)程探測(cè)試驗(yàn)：在三江源、祁連山與藏東南等地組織云降水過(guò)程飛機(jī)綜合觀測(cè)，獲取復(fù)雜地形下氣溶膠、云、降水宏微物理特征飛行探測(cè)及無(wú)人機(jī)組網(wǎng)觀測(cè)；實(shí)施了地面雷達(dá)、探空火箭、自動(dòng)站、降水現(xiàn)象儀、微波輻射計(jì)等多種觀測(cè)設(shè)備的綜合觀測(cè)；（3）構(gòu)建多圈層地氣相互作用立體綜合觀測(cè)試驗(yàn)網(wǎng)絡(luò)：在六個(gè)關(guān)鍵區(qū)（河湖源區(qū)、喜馬拉雅山區(qū)中段、江湖源區(qū)、中巴經(jīng)濟(jì)走廊、藏東南區(qū)、三江流域及橫斷山區(qū)）實(shí)施西風(fēng)—季風(fēng)區(qū)多圈層地氣相互作用立體綜合觀測(cè)組網(wǎng)建設(shè)級(jí)觀測(cè)（包括大氣邊界層塔、雙波段閃爍儀、風(fēng)溫廓線儀組網(wǎng)、微波輻射計(jì)、探空組網(wǎng)、風(fēng)吹雪、土壤溫濕度組網(wǎng)觀測(cè)等）；（4）西風(fēng)—季風(fēng)影響下多尺度地形特征——對(duì)流結(jié)構(gòu)觀測(cè)：在墨脫、珠峰、雅魯藏布江河谷區(qū)等水汽輸送通道關(guān)鍵區(qū)布設(shè)了相控陣?yán)走_(dá)超級(jí)站、云雷達(dá)等設(shè)備，結(jié)合衛(wèi)星遙感與探空、微波輻射計(jì)、邊界層通量站、GPS水汽觀測(cè)儀和自動(dòng)氣象站等，初步構(gòu)成了雅魯藏布江河谷區(qū)天—地—空—體化水汽輸送與云降水及水汽輸送通道的綜合觀測(cè)系統(tǒng)；（5）青藏高原氣候變化影響關(guān)鍵區(qū)科學(xué)考察：在天山—帕米爾高原等地區(qū)共開(kāi)展十余次野外科學(xué)考察；科考船完成1次印度洋科考計(jì)劃；（6）青藏高原環(huán)境生態(tài)綜合科考：2020年共派出17支科考分隊(duì)約160人次，開(kāi)展西風(fēng)—季風(fēng)協(xié)同作用下青藏高原亞洲水塔區(qū)和祁連山—阿爾金區(qū)水環(huán)境、植被環(huán)境、碳氮循環(huán)和大氣環(huán)境的野外考察。

基于上述綜合與立體觀測(cè)考察研究，評(píng)估了青藏高原及周邊地區(qū)過(guò)去和未來(lái)的氣候變化，發(fā)現(xiàn)西風(fēng)與季風(fēng)協(xié)同作用下青藏高原冰川歷史演化規(guī)律，揭示了東亞夏季風(fēng)在中世紀(jì)—小冰期過(guò)渡期快速衰退現(xiàn)象，并探討了過(guò)去2萬(wàn)年青藏高原及其毗鄰地區(qū)冰川演化規(guī)律及可能機(jī)制，其中“喀喇昆侖冰川科考與冰芯鉆取”成功入選中國(guó)科學(xué)院2020年第2季度科技創(chuàng)新亮點(diǎn)成果；研究了近代冰川變化與降水變率、水儲(chǔ)量變化格局的關(guān)聯(lián)性；獲得了藏東南飛機(jī)與地面綜合探測(cè)三維立體云物理觀測(cè)數(shù)據(jù)集；提出極端天氣氣候變異與生態(tài)環(huán)境影響效應(yīng)，高原西風(fēng)減弱或北移對(duì)青藏高原極端天氣氣候?yàn)?zāi)害具有決定性作用；首次定量給出青藏高原湖泊年蒸發(fā)總量，揭示出高原湖泊群在大氣水分循環(huán)過(guò)程中蒸發(fā)的巨大貢獻(xiàn)，揭示了亞洲水塔熱力驅(qū)動(dòng)下青藏高原水汽輸送“窗口”全球效應(yīng)；首次評(píng)估了青藏高原對(duì)流尺度模擬的降水及其對(duì)積雪的影響；研究高原科考關(guān)鍵區(qū)對(duì)流云高分辨率結(jié)構(gòu)動(dòng)態(tài)演變特征及其特殊規(guī)律，揭示出“世界屋脊”空氣低密度條件對(duì)高原對(duì)流云的觸發(fā)效應(yīng)，加深了對(duì)冰川與邊界層大氣間湍流的動(dòng)量及熱量輸送的認(rèn)知；揭示出西風(fēng)—季風(fēng)協(xié)同作用變化對(duì)植被環(huán)境趨好的影響效應(yīng)。上述研究成果為川藏鐵路工程提供數(shù)值預(yù)報(bào)新技術(shù)與決策服務(wù)。(徐祥德，徐柏青，馬耀明，陸日宇，郭學(xué)良，周廣勝，馬偉強(qiáng)，張勝軍)

2.2 Climate modulation of summer rainstorm activity in eastern China based on the Tibetan Plateau spring heating

Rainstorm intensity and frequency in the eastern China are closely associated with the Asian summer monsoon,one of the largest and most pronounced circulation systems on Earth.Changes in monsoon strength are linked to mechanical and thermal forcing by the Tibetan Plateau (TP),which,as an extensive elevated landmass,forms a vast heat source that protrudes into the free atmosphere.However,the impact of TP heating variability on rainstorm behavior in the eastern China remains unclear.By analyzing 50 years of climate data,significant interannual variability was identified in the occurrence of rainstorms (precipitation amounts of 50 mm),with decreased trend in the northern China and increased variability in the southern China.Results show that these changes are closely related with the springtime TP heating,indicating that recent changes in rainstorm distributions in the eastern China are consistent with interdecadal variability in TP thermal forcing.(Huang Wubin,Zhao Yang,Sun Chan)

2.3 Enhancement of the summer extreme precipitation over North China by interactions between moisture convergence and topographic settings

This study investigates the roles of atmospheric moisture transport under the influence of topography for summer extreme precipitation over North China (NC) during 1979?2016.Based on the rain gauge precipitation reanalysis and data,38 extreme precipitation days in NC during the 38 years were selected and associated moisture fluxes were estimated.The results show that there is a dominant moisture influx of 311.8 kg m?1s?1into NC along its southern boundary from tropical oceans,and a secondary influx of 107.9 kg m?1s?1across its western boundary carried by mid-latitude westerlies.The outflux across the eastern boundary is 206.9 kg m?1s?1and across the northern boundary is 76.0 kg m?1s?1,giving a net moisture gain over NC of 136.8 kg m?1s?1.During extreme precipitation days,the moisture flux convergence (MFC) was much larger,exceeding 4×10?5kg m?1s?1.The MFC maximum core,the pronounced moisture transport,and the striking extreme precipitation zone over NC are all anchored to the east of the steep slopes of the surrounding topography.Moreover,a remarkably high humidity and strong upward motion also occur near steep slopes,indicating the critical role of the adjacent topography on the extreme precipitations.Simulations with and without the topography in NC using the Weather and Research Forecasting model for the six selected out of the 38 extreme precipitation days demonstrate that the surrounding topography reinforces the MFC over NC by 16% relative to the case without terrain,primarily through enhanced wind convergence and higher moisture content,as well as stronger vertical motion induced by diabatic heating.The interactions between moisture convergence and topographic settings strengthen the extreme precipitation over NC.(Zhao Yang,Chen Deliang,Li Jiao)

2.4 Impact of “blocking” structure in the troposphere on the wintertime persistent heavy air pollution in northern China

In the winters of 2012?2018,a total of 25 “ultra-long” (≥6 days),wide-ranging pollution events occurred in the northern China.The results show that the atmospheric circulation pattern corresponding to 62.5% of the persistent “most serious” and “more serious” air pollution events in the northern China were the blocking structures,and that 43.75% of the 500-hPa atmospheric circulation anomalies in the middle and high latitudes of Eurasia were “dual-blocking”,18.75% of them were “single-blocking”.The abnormally stable blocking situation provided a special circulation background for the occurrence and maintenance of persistent heavy air pollution in the northern China.The Okhotsk blocking is significantly positively correlated with the persistent “most serious” air pollution events.“Stagnation” of the blocking system and its dynamic effect play an important role in regulating atmospheric environmental capacity and accelerating the accumulation of aerosols during the persistent heavy pollution episodes.Due to the synergy between the weak wind effect of the leeward slope on the eastern side of the Loess Plateau in this region and the downward airflow of the largescale blocking system,the effect of sustained suppression of atmospheric pollutant diffusion in the northern China is more significant.The downward air flow along the eastern leeward slope of the Loess Plateau is very important for accumulation of air pollutants,which is controlled by the tropospheric blocking high.In addition,the “subsidence (temperature) inversion” effect produced by the synergy between the downward airflow of the eastern leeward slope of the Loess Plateau and the large-scale blocking system creates a continuous and stable“warm-cover” structure in the middle of the troposphere on the eastern Loess Plateau; this effect strengthens the radiation effect of aerosols in the atmospheric pollutants,as well as the “two-way feedback” mechanism between adverse meteorological conditions in the boundary layer and atmospheric pollutants.(Cai Wenyue,Xu Xiangde,Cheng Xinghong)

2.5 Influence of satellite observation angle to tropical cyclone intensity estimation using the deviation angle variance technique

The deviation angle variance (DAV) method was developed to objectively estimate tropical cyclone(TC) intensity from geostationary infrared (IR) brightness temperature data.Here,we demonstrate that improvements of 25% root mean square error (RMSE) in major hurricane intensity estimation (relative to best track) can be obtained by considering the pixel-by-pixel satellite view angle in the estimation.Using data from the Chinese Fengyun 2E and 2F satellites for Super Typhoon Soudelor (2015),we demonstrate how the satellite observation angle can reduce the accuracy of intensity estimation,especially for the strongest TCs.Based on these results,an improved DAV estimator is developed using 12-year (2004?2015) Geostationary Operational Environmental Satellite (GOES)-East satellite IR images over the North Atlantic basin.(Hu Liang,Ritchie Elizabeth A,Tyo J Scott)

2.6 Influences of atmospheric ventilation on the composition of the upper troposphere and lower stratosphere during the two primary modes of the South Asia high

There are two key modes of the South Asia high (SAH) during the boreal summer:the Iranian Plateau (IP)and Tibetan Plateau (TP) modes.The anomalies of chemical constituents in the upper troposphere and lower stratosphere (UTLS) region within the SAH area largely depend on this bimodality.To better understand the underlying mechanisms of this dependence,the ensemble of 30-day backward trajectories,initialized in the UTLS region within the SAH,was simulated by a Lagrangian model FLEXPART.The comparative diagnostic was performed from the perspective of atmospheric ventilation.The results show that vertical transport from the lower troposphere to the UTLS during the TP mode was very efficient,resulting in tropospheric air mass transported into the UTLS within a shorter timescale than during the IP mode.Furthermore,the effect of SAH isolation during the TP mode was stronger than during the IP mode.This stronger trapping is likely to force the tropospheric air mass to reside in the SAH area for a longer period of time.In addition,compared to the IP mode,near-surface air mass sources during the TP mode overlapped more with areas of severe air pollution (CO emissions).The above three factors associated with the processes of atmospheric ventilation,i.e.,the efficiency of vertical transport,the strength of the SAH isolation,and the boundary layer sources,provide potential explanations as to why the anomalies of atmospheric constituents in the UTLS are different between the TP and the IP mode.(Yang Shuai,Wei Zhang,Chen Bin)

2.7 Remote moisture sources for 6-hour summer precipitation over the southeastern Tibetan Plateau and its effects on precipitation intensity

Using the Lagrangian moisture tracking methodology for 37-year reanalysis data,this study presents a quantitative climatology of remote moisture sources for 6-hour summer precipitation over the southeastern Tibetan Plateau (SETP) during the boreal summer for the 1980?2016 period.The connections between moisture sources and regional-scale precipitation intensity are also explored.Different from previous viewpoints,this study finds that the terrestrial and oceanic sources contribute approximately 70% and 30% to the moisture supply for the summer precipitation over the SETP,with the Indian continent and Arabian Sea acting as the most important providers,respectively.Enhanced regional-scale precipitation,particularly for extreme events,can largely be further attributed to the increased moisture uptake originating from these two predominant sources with transport time scales of 2?5 days prior to the onset of precipitation.The intensified precipitation events are more likely to be associated with the enhanced water vapor transport conveyed by the large-scale atmospheric circulations,together with the land evaporation over the remote source regions.(Yang Shuai,Zhang Wei,Chen Bin)

2.8 Roles of oceanic moisture exports in modulating summer rainfall over the middle-lower Yangtze River Basin:Inter-annual variability and decadal transition

Precipitation over the mid-lower reaches of the Yangtze River Basin (YRB),which is a typical East Asian monsoon region in China,is strongly impacted by oceanic moisture exports (OMEs) and feature variability at multiple spatial-temporal scales,resulting in frequent floods and droughts.We focus on two key issues of OME and its relevance to the summer rainfall variability over the YRB:determination of the individual contributions of OME from three specific oceanic sub-regions:the Arabian Sea (ARS),Bay of Bengal (BOB),and South China Sea (SCS),and their roles in the inter-annual variability and decadal changes in YRB summer rainfall.Using a Lagrangian forward trajectories tracing approach,we create a catalogue of OME-based diagnosed precipitation fields for three sub-regions spanning the summer seasons (May to August) of 1980?2013 with 6-hour resolution using ERA-Interim data.The results show that the pattern of the diagnosed OME-based precipitation resembles the observed pattern over the YRB in terms of climatology and temporal variation.Climatologically,the SCS region accounts for the largest relative contribution (60.7%),followed by the ARS(30.8%),whereas the contributions of the BOB (8.5%) are almost negligible.On the inter-annual scale,the variation in OME-based rainfall originated from the ARS,and the BOB is out of phase with that of the SCS.In contrast to climatology,the inter-annual changes in rainfall over the YRB are primarily modulated by the variation in the OME from the ARS.However,for the decadal changes,particularly in 1992/1993 over the YRB,the SCS and ARS are equivalent contributors to the summer precipitation over the YRB.These findings thus provide new insights into our understanding of the multi-scale variability of summer precipitation over the YRB region.(Chen Bin,Zhang Wei,Yang Shuai)

2.9 Short-term tropical cyclone intensity forecasting from satellite imagery based on the deviation angle variance technique

The deviation angle variance (DAV) is a parameter that characterizes the level of organization of a cloud cluster compared with a perfectly axisymmetric tropical cyclone (TC) using satellite infrared (IR) imagery,and can be used to estimate the intensity of the TC.In this study,the DAV technique is further used to analyze the relationship between satellite imagery and TC future intensity over the North Atlantic basin.The results show that the DAV of the TC changes ahead of the TC intensity change,and this can be used to predict short-term TC intensity.The DAV-IR 24-h forecast is close to the National Hurricane Center (NHC) 24-h forecast,and the bias is lower than those of NHC and other methods during weakening periods.Furthermore,an improved TC intensity forecast is obtained by incorporating all four satellite bands.Using SST and TC latitude as the other two predictors in a linear regression model,the RMSE and MAE of the DAV 24-h forecast are 13.7 and 10.9 kt (1 kt approximate to 0.51 m s?1),respectively,and the skill space of the DAV is about 5.5% relative to the Statistical Hurricane Intensity Forecast model with inland decay (Decay-SHIFOR) during TC weakening periods.Considering the DAV is an independent intensity technique,it could potentially add value as a member of the suite of operational intensity forecast techniques,especially during TC weakening periods.(Hu Liang,Ritchie Elizabeth A,Tyo J Scott)

2.10 Why are there more summer afternoon low clouds over the Tibetan Plateau compared to eastern China?

In this study,we analyze the relationships between summer afternoon low cloud cover and environmental conditions over the Tibetan Plateau (TP).Using in situ measurements,satellite data,and reanalysis,and based on theoretical analysis,we find that there is stronger thermal turbulence,lower temperature,and higher frequency of low cloud formation for the same surface relative humidity over the eastern and central TP compared with the eastern China.With the same sensible heat flux,the decreased air density enhances buoyancy flux,which increases the planetary boundary layer height and moisture vertical transport.At the same time,with the same near-surface relative humidity,the lower temperature over the TP decreases the lifting condensation level,which increases the probability of the air parcel reaching this level.Compared to the low-elevation region in the eastern China,these two mechanisms enhance low cloud occurrence in the afternoon over the TP.(Wang Yinjun,Zeng Xubin,Xu Xiangde)

2.11 1961—2016年秦嶺山區(qū)冷季積雪日數(shù)變化特征及其影響因子

根據(jù)1961—2016年秦嶺地區(qū)32個(gè)氣象站點(diǎn)的氣溫、降水及積雪等相關(guān)數(shù)據(jù)，運(yùn)用REOF、M-K檢驗(yàn)和小波分析等方法，對(duì)秦嶺地區(qū)冷季積雪日數(shù)的時(shí)空變化和影響因子進(jìn)行分析。結(jié)果表明:秦嶺地區(qū)冷季多年平均積雪日數(shù)表現(xiàn)為北坡比南坡積雪日數(shù)多。在全球氣候變暖的背景下，海拔越高積雪日數(shù)減少得越多。秦嶺冷季積雪日數(shù)呈現(xiàn)顯著減少的趨勢(shì)，5個(gè)區(qū)的積雪日數(shù)年代際變化特征顯著，在20世紀(jì)末到21世紀(jì)初發(fā)生了由積雪日數(shù)偏多到偏少的突變。各區(qū)冷季積雪日數(shù)的周期變化主要集中在10～20 a，秦嶺南坡同時(shí)也顯示了較為明顯的4 a左右的周期變化。西北太平洋海溫階段性增暖是導(dǎo)致秦嶺冷季積雪日數(shù)減少的外強(qiáng)迫因素。秦嶺地區(qū)冷季平均氣溫的顯著增暖和冷季降水量的顯著減少直接造成積雪日數(shù)的減少。秦嶺冷季積雪日數(shù)減少的突變要比氣溫增暖的突變滯后4～7 a。(李茜，魏鳳英，雷向杰)

2.12 2013—2017年氣象條件變化對(duì)中國(guó)重點(diǎn)地區(qū)PM2.5質(zhì)量濃度下降的影響

2013ü 2017年中國(guó)出臺(tái)《大氣污染防治行動(dòng)計(jì)劃》（簡(jiǎn)稱“大氣十條”），實(shí)施了系列污染減排措施，重點(diǎn)地區(qū)PM2.5質(zhì)量濃度下降明顯，這其中氣象條件變化起到了多大作用，是政府和公眾特別關(guān)心的問(wèn)題。本研究基于各類(lèi)氣象要素觀測(cè)、診斷、結(jié)合污染—?dú)庀髼l件指數(shù)等對(duì)PM2.5污染影響深入分析，發(fā)現(xiàn)“大氣十條”實(shí)施后的2014ü 2015年中國(guó)重點(diǎn)地區(qū)氣象條件相較2013年變差，2016和2017年氣象條件相較轉(zhuǎn)好。但在京津冀地區(qū)2017年相較2013年P(guān)M2.5質(zhì)量濃度下降的39.6%中，僅有約5%（約占總PM2.5降幅的13%）是來(lái)自氣象條件轉(zhuǎn)好的貢獻(xiàn)；在長(zhǎng)江三角洲地區(qū)下降的34.3%中，有約7%（約占總PM2.5降幅的20%）是來(lái)自氣象條件轉(zhuǎn)好的貢獻(xiàn)，由于氣象條件改善程度明顯低于此區(qū)域觀測(cè)到的PM2.5降幅，顯示出“大氣十條”實(shí)施五年減排仍然發(fā)揮了PM2.5污染改善的主導(dǎo)作用，天氣和氣候變化因素雖有影響但沒(méi)有起到控制性作用（本研究用PLAM指數(shù)來(lái)量化氣象條件變好或變差）。在珠江三角洲地區(qū)，氣象條件對(duì)2017年相較2013年的年均PM2.5濃度下降影響較弱，下降成效也主要來(lái)自減排的貢獻(xiàn)。2017年冬季氣象條件在京津冀和長(zhǎng)江三角洲區(qū)域相較2013年分別轉(zhuǎn)好約20%和30%，在兩區(qū)域冬季PM2.5分別約40.2%和38.2%的降幅中起到了明顯的“助推”作用。京津冀區(qū)域2016年冬季氣象條件好于2017年冬季約14%，但2017年冬季PM2.5降幅仍大于2016年，顯示出2017年更大力度的減排措施發(fā)揮了重要作用；在北京冬季持續(xù)性重污染期間選擇氣象條件相同的過(guò)程對(duì)比，也發(fā)現(xiàn)因減排導(dǎo)致的PM2.5下降幅度逐年增加，特別是2016和2017年下降的PM2.5濃度幅度更為明顯，表明“大氣十條”實(shí)施5年后空氣質(zhì)量改善的根本原因是各項(xiàng)控制措施取得了實(shí)質(zhì)性進(jìn)展，特別是2017年冬季污染物排放量得到了有效削減。中國(guó)大氣PM2.5持續(xù)性重污染主要發(fā)生在冬季，冬季京津冀地區(qū)僅因氣象條件不利就會(huì)導(dǎo)致PM2.5濃度較其他季節(jié)上升約40%～100%，這與冬季到達(dá)地面的太陽(yáng)輻射下降有關(guān)，與中國(guó)華北冬季受青藏高原大地形“背風(fēng)坡”效應(yīng)所導(dǎo)致的下沉氣流和“弱風(fēng)效應(yīng)”有關(guān)，與氣候變暖導(dǎo)致的區(qū)域邊界層結(jié)構(gòu)日趨穩(wěn)定有關(guān)。重污染形成是因?yàn)閰^(qū)域出現(xiàn)停滯—靜穩(wěn)的形勢(shì)，高空環(huán)流型主要可分為平直西風(fēng)和高壓脊型，污染形成后不斷累積的PM2.5污染還會(huì)進(jìn)一步導(dǎo)致邊界層氣象條件轉(zhuǎn)差、轉(zhuǎn)差氣象條件的反饋?zhàn)饔每刂屏薖M2.5的“爆發(fā)性增長(zhǎng)”現(xiàn)象，形成顯著的不利氣象條件與PM2.5累積之間的雙向反饋。表明在中國(guó)現(xiàn)今大氣氣溶膠污染程度仍然居高的情況下，不利氣象條件是持續(xù)性重污染形成、累積的必要外部條件。在重污染形成初期大幅降低區(qū)域污染排放，是消除和減少持續(xù)性重污染事件的關(guān)鍵手段。即使在有利氣象條件下，也不宜無(wú)限制地允許排放，因?yàn)楫?dāng)污染累積到一定程度后會(huì)顯著改變邊界層氣象條件、會(huì)“關(guān)閉”污染擴(kuò)散的“氣象通道”。（張小曳，徐祥德，丁一匯）

2.13 基于加密探空觀測(cè)的成都市一次重霾污染過(guò)程中大氣邊界層氣溶膠垂直結(jié)構(gòu)分析

基于2017年1月4—7日成都市一次重霾污染過(guò)程的系留汽艇探測(cè)的低層大氣氣象要素和大氣顆粒物垂直探空加密觀測(cè)資料，分析了大氣邊界層結(jié)構(gòu)及氣溶膠垂直分布。結(jié)果表明，此次重霾污染期間，大氣邊界層晝夜變化特征基本消失。穩(wěn)定邊界層結(jié)構(gòu)出現(xiàn)25次，對(duì)流邊界層結(jié)構(gòu)僅出現(xiàn)3次，大氣邊界層結(jié)構(gòu)趨于穩(wěn)定，邊界層高度普遍在700 m以下。霾污染發(fā)生、維持及消散階段大氣邊界層氣溶膠垂直結(jié)構(gòu)具有明顯差異。霾污染發(fā)生階段，大氣邊界層氣溶膠粗、細(xì)粒子主要集中在300 m高度以下，近地面層大氣氣溶膠粒子累積觸發(fā)霾污染事件；霾維持階段，大氣顆粒物粒子濃度數(shù)垂直方向趨于一致，大氣邊界層穩(wěn)定結(jié)構(gòu)中存在強(qiáng)的大氣垂直混合作用；在霾消散階段，較高處的氣溶膠粒子濃度最先下降，且下降幅度最大，表明對(duì)流層自由大氣作用對(duì)霾污染消散具有影響。大氣邊界層風(fēng)速的增大加劇了大氣傳輸擴(kuò)散。溫度與大氣顆粒物濃度在近地層呈負(fù)相關(guān)關(guān)系，在100 m高度以上呈正相關(guān)關(guān)系。大氣邊界層低層偏冷、高層偏暖的穩(wěn)定大氣熱力層結(jié)減弱了大氣污染物的垂直擴(kuò)散。相對(duì)濕度的增加有利于氣溶膠粒子的吸濕增長(zhǎng)和液相化學(xué)反應(yīng)，加劇了霾污染。(曹蔚，趙天良，徐祥德)

2.14 臺(tái)風(fēng)“溫比亞”(1818)影響遼東半島的預(yù)報(bào)分析

2018年第18號(hào)臺(tái)風(fēng)“溫比亞”北上引發(fā)遼東半島普降大暴雨，局部特大暴雨，但業(yè)務(wù)數(shù)值預(yù)報(bào)模式在其路徑、強(qiáng)度和降水預(yù)報(bào)方面均有一定偏差。利用中國(guó)氣象局熱帶氣旋年鑒、常規(guī)和非常規(guī)氣象觀測(cè)資料、FY-2G衛(wèi)星云頂亮溫（TBB）和歐洲中期數(shù)值預(yù)報(bào)中心ERA-Interim全球再分析資料(0.125°×0.125°)，對(duì)臺(tái)風(fēng)“溫比亞”影響遼東半島的預(yù)報(bào)進(jìn)行分析。結(jié)果表明：（1）“溫比亞”預(yù)報(bào)的難點(diǎn)是登陸后轉(zhuǎn)向點(diǎn)及轉(zhuǎn)向后路徑的預(yù)報(bào)，西風(fēng)槽和大陸高壓東移阻擋了“溫比亞”的西行;臺(tái)風(fēng)“蘇力”的西北移，導(dǎo)致副高位置偏北，其與東北地區(qū)高壓脊形成的高壓帶則有利于“溫比亞”的北抬。（2）“溫比亞”和“蘇力”2個(gè)臺(tái)風(fēng)與副高之間所形成的東南風(fēng)低空急流，提供了持續(xù)的水汽和能量，既有利于“溫比亞”強(qiáng)度的維持，又誘發(fā)遼東半島強(qiáng)降水的持續(xù)發(fā)生。（3）“溫比亞”在變性過(guò)程中與西風(fēng)槽以及低空急流相互作用有利于其北側(cè)螺旋云系的發(fā)展。強(qiáng)降水落區(qū)與臺(tái)風(fēng)低層環(huán)流北側(cè)輻合帶內(nèi)冷暖平流活動(dòng)密切相關(guān)，冷暖平流交匯處的能量鋒帶對(duì)強(qiáng)降水有較好的指示作用。（4）數(shù)值預(yù)報(bào)模式對(duì)轉(zhuǎn)向點(diǎn)和轉(zhuǎn)向后的路徑預(yù)報(bào)存在較大分歧，除了參考集合預(yù)報(bào)產(chǎn)品外，還可采用相似預(yù)報(bào)手段，對(duì)比分析相似個(gè)例和誤差小的數(shù)值預(yù)報(bào)模式的大尺度環(huán)境場(chǎng)，借助于數(shù)值預(yù)報(bào)產(chǎn)品和相似個(gè)例進(jìn)行訂正。(梁軍，馮呈呈，張勝軍)

2.15 影響我國(guó)霾天氣的多尺度過(guò)程

頻發(fā)的霾天氣是我國(guó)現(xiàn)階段面臨的最主要大氣環(huán)境問(wèn)題之一。霾期間高濃度大氣細(xì)顆粒物（PM2.5）是多種物理化學(xué)過(guò)程綜合影響的結(jié)果，包括排放、氣—粒轉(zhuǎn)化、大氣邊界層、局地環(huán)流、天氣與氣候等過(guò)程。上述過(guò)程的時(shí)空尺度跨越了幾個(gè)數(shù)量級(jí)，在空間尺度上涵蓋了納米尺度至上千千米尺度。多尺度過(guò)程本身的復(fù)雜性以及不同過(guò)程之間的相互影響是目前大氣環(huán)境領(lǐng)域面臨的最嚴(yán)峻挑戰(zhàn)，直接影響到對(duì)于霾天氣形成機(jī)制的科學(xué)認(rèn)識(shí)、預(yù)報(bào)技術(shù)與數(shù)值模式研發(fā)，以及相應(yīng)的大氣污染治理。文章綜述了在影響我國(guó)霾天氣的多尺度過(guò)程及其與氣溶膠的相互作用領(lǐng)域取得的研究進(jìn)展。研究表明：二次氣溶膠已經(jīng)成為我國(guó)大氣氣溶膠的主要部分，在霾過(guò)程后期，液相非均相過(guò)程對(duì)氣—粒轉(zhuǎn)化有重要貢獻(xiàn)；PM2.5呈現(xiàn)多時(shí)間尺度周期性振蕩，包括1，4～7 d以及40～60 d等，邊界層、天氣和氣候等多尺度過(guò)程是造成上述周期性變化的主因；已有證據(jù)表明，我國(guó)高氣溶膠已經(jīng)影響到該區(qū)域大氣光化學(xué)、大氣邊界層，甚至天氣和氣候過(guò)程。氣溶膠與上述過(guò)程的相互作用進(jìn)一步影響了氣溶膠濃度及其空間分布，但是此問(wèn)題極為復(fù)雜，尚存在很大不確定性。為此，今后需重點(diǎn)加強(qiáng)以下研究：加強(qiáng)包含氣溶膠理化性質(zhì)、大氣光化學(xué)、氣象要素在內(nèi)的多要素協(xié)同觀測(cè)，重點(diǎn)開(kāi)展對(duì)流層內(nèi)多要素協(xié)同垂直探測(cè)；增強(qiáng)跨學(xué)科領(lǐng)域研究，尤其是大氣物理—大氣化學(xué)—天氣/氣候等多學(xué)科間的交叉性研究；加強(qiáng)氣溶膠與大氣化學(xué)、邊界層、天氣氣候等過(guò)程相互作用的數(shù)值模擬研究。(權(quán)建農(nóng)，徐祥德，賈星燦)

3 暴雨和強(qiáng)對(duì)流研究

3 Research on heavy rainfall and strong convection

3.1 A dynamical-statistical-analog ensemble forecast model:Theory and an application to heavy rainfall forecasts of landfalling tropical cyclones

Combining dynamical models with statistical algorithms is an important way to improve weather and climate prediction.In this study,a concept of a perfect model,whose solutions are from observations,is introduced,and a dynamical-statistical-analog ensemble forecast (DSAEF) model is developed as an initialvalue problem of the perfect model.This new analog-based forecast model consists of the following three steps:(i) construct generalized initial value (GIV),(ii) identify analogs from historical observations,and (iii)produce an ensemble of predictands.The first step includes all appropriate variables,not only at an instant state but also during their temporal evolution,which plays an important role in determining the accuracy of each predictand.An application of the DSAEF model is illustrated through the prediction of accumulated rainfall associated with 21 landfalling typhoons occurring over South China during the years of 2012?2016.Assuming a reliable forecast of landfalling typhoon track,two different experiments are conducted,in which the GIV is constructed by including:(i) typhoon track only; (ii) both typhoon track and landfall season.Results show overall better performance in the second experiment than in the first one in predicting heavy accumulated rainfall in the training sample tests.In addition,the forecast performance of both experiments is comparable to the operational numerical weather prediction models currently used in China,the United States,and Europe.Some limitations and future improvements as well as comparisons with some existing analog ensemble models are also discussed.(Ren Fumin,Ding Chenchen,Zhang Da-lin)

3.2 An application of the LTP_DSEF model to heavy precipitation forecasts of landfalling tropical cyclones over China in 2018

Recently,a track-similarity-based Dynamical-Statistical Ensemble Forecast (LTP_DSEF) model has been developed in an attempt to predict heavy rainfall from Landfalling Tropical cyclones (LTCs).In this study,the LTP_DSEF model is applied to predicting heavy precipitation associated with 10 LTCs occurring over China in 2018.The best forecast scheme of the model with optimized parameters is obtained after testing 3452 different schemes for the 10 LTCs.Then,its performance is compared to that of three operational dynamical models.Results show that the LTP_DSEF model has advantages over the three dynamical models in predicting heavy precipitation accumulated after landfall,especially for rainfall amounts greater than 250 mm.The model also provides superior or slightly inferior heavy rainfall forecast performance for individual LTCs compared to the three dynamical models.In particular,the LTP_DSEF model can predict heavy rainfall with valuable threat scores associated with certain LTCs,which is not possible with the three dynamical models.Moreover,the model can reasonably capture the distribution of heavier accumulated rainfall,albeit with widespread coverage compared to observations.The preliminary results suggest that the LTP_DSEF model can provide useful forecast guidance for heavy accumulated rainfall of LTCs despite its limited variables included in the model.(Jia Zuo,Ren Fumin,Zhang Da-lin)

3.3 Boundary layer height as estimated from radar wind profilers in four cities in China:Relative contributions from aerosols and surface features

The turbulent mixing and dispersion of air pollutants is strongly dependent on the vertical structure of the wind,which constitutes one of the major challenges affecting the determination of boundary layer height(BLH).Here,an adaptive method is proposed to estimate BLH from measurements of radar wind profilers(RWPs) in Beijing (BJ),Nanjing (NJ),Chongqing (CQ),and Wulumuqi (WQ) of China,during the summer of 2019.Validation against simultaneous BLH estimates from radiosondes (RSs) yielded a correlation coefficient of 0.66,indicating that the method can be used to derive BLH from RWPs.Diurnal variations of BLH and the ventilation coefficients (VC) at four sites were then examined.A distinct diurnal cycle of BLH was observed over all four cities; BLH gradually increased from sunset,reached a maximum in the afternoon,and then dropped sharply after sunset.The maximum hourly average BLH (1.426 ± 0.46 km) occurred in WQ,consistent with the maximum hourly mean VC larger than 5000 m2s?1observed there.By comparison,the diurnal variation of VC was not strong,with values ranging between 2000 and 3000 m2s?1,likely owing to the highhumidity environment.Furthermore,surface sensible heat flux,latent heat flux,and dry mass of particulate matter with aerodynamic diameter≤2.5 μm (PM2.5) concentrations were found to somehow affect the vertical structure of wind and thermodynamic features,leading to a difference between RS and RWP BLH estimates.This indicates that the atmospheric environment can affect BLH estimates using RWP data.The BLH results from RWPs were better in some specific cases.These findings show great potential of RWP measurements in air quality research,and will provide key data references for policy-making toward emission reductions.(Liu Boming,Guo Jianping,Gong Wei)

3.4 Characteristics and causes of extreme rainfall induced by binary tropical cyclones over China

Binary tropical cyclones (BTC) often bring disastrous rainfall to China.From the viewpoint of the extreme of the BTC maximum daily rainfall,the characteristics of BTC extreme rainfall (BTCER) during 1960?2018 are analyzed using daily rainfall data,and some representative large-scale mean flows,in which the associated BTCs are embedded,are analyzed.Results show that the frequency of BTCER shows a decreasing trend (?0.49 per 10 years) and is mainly distributed within the BTC heavy rainstorm interval (100 mm≤BTCER 250 mm).BTCER occurs mostly from July to September with a peak in August.Three BTCER typical regions(Minbei,the Pearl River Delta (PRD),and Taiwan) are identified according to the clustering of stations with high BTCER frequency and large BTCER.A further analysis of the 850-hPa BTC composite horizontal wind and water vapor flux over the PRD region shows the existence of two water vapor transport channels,which transport water vapor to the western tropical cyclones.In the first of these channels,the transport takes place via the southwest monsoon,which accounts for 58% of the total moisture,and an easterly flow associated with the eastern tropical cyclones accounts for the remaining 42%.(Wang Mingyang,Ren Fumin,Xie Yanjun)

3.5 Characteristics and performance of wind profiles as observed by the radar wind profiler network of China

Wind profiles are fundamental to the research and applications in boundary layer meteorology,air quality and numerical weather prediction.Large-scale wind profile data have been previously documented from network observations in several countries,such as Japan,the USA,various European countries and Australia,but nationwide wind profiles observations are poorly understood in China.In this study,the salient characteristics and performance of wind profiles as observed by the radar wind profiler network of China are investigated.This network consists of more than 100 stations instrumented with 1290 MHz Doppler radar designed primarily for measuring vertically resolved winds at various altitudes but mainly in the boundary layer.It has good spatial coverage,with much denser sites in the eastern China.The wind profiles observed by this network can provide the horizontal wind direction,horizontal wind speed and vertical wind speed for every 120 m interval within the height of 0 to 3 km.The availability of the radar wind profiler network has been investigated in terms of effective detection height,data acquisition rate,data confidence and data accuracy.Further comparison analyses with reanalysis data indicate that the observation data at 89 stations are recommended and 17 stations are not recommended.The boundary layer wind profiles from China can provide useful input to numerical weather prediction systems at regional scales.(Liu Boming,Guo Jianping,Gong Wei)

3.6 Characteristics,physical mechanisms,and prediction of pre-summer rainfall over South China:Research progress during 2008-2019

The pre-summer rainy season (April to mid-June) over South China (SC) is characterized by a high intensity and frequent occurrence of heavy rainfall in the East Asian monsoon region.This review describes recent progress in the research related to this phenomenon.The mechanisms responsible for pre-summer rainfall consist of multiscale processes.Sea surface temperatures over the tropical Pacific and Indian Oceans are shown to have a great influence on the interannual variations of pre-summer rainfall over SC.Synoptic disturbances associated with regional extreme rainfall over SC are mainly related to cyclone- and troughtype anomalies.Surface sensible heating and mechanical forcing from the Tibetan Plateau can contribute to the formation and intensification of such anomalies.On a sub-daily scale,double rain belts often co-exist over SC.The northern rain belt is closely linked to dynamic lifting by a subtropical low pressure and its associated front/shear line,whereas westward extension of the western North Pacific high and intensification of the southwesterly monsoonal flows play important roles in providing high-equivalent potential temperature air to the west- and east-inland regions,respectively.The southern rain belt,with a smaller horizontal span,exists in the warm sector over either inland or coastal SC.The warm-sector rainfall over inland SC results from surface heating,local topographic lifting,and urban heat island effects interacting with the sea breeze.The warm-sector rainfall over coastal SC is closely associated with double low-level jets,land-sea-breeze fronts,and coastal mountains.A close relationship is found between convectively-generated quasi-stationary mesoscale outflow boundaries and continuous convective initiation in extreme rainfall events.Active warmrain microphysical processes can play an important role in some extreme rainfall events,although the relative contributions of warm-rain,riming,and ice-phase microphysical processes remain unclear.Moreover,to improve rainfall predictions,efforts have been made in convection-permitting modeling studies.(Luo Yali,Xia Rudi,Chan Johnny C L)

3.7 Convection-permitting regional climate simulation of warm-season precipitation over eastern China

Convection-permitting regional climate models have been shown to improve precipitation simulation in many aspects,such as the diurnal cycle,precipitation frequency,intensity and extremes in many studies over several geographical regions of the world,but their skill in reproducing the warm-season precipitation characteristics over the East Asia has not been robustly tested yet.Motivated by recent advances in computing power,model physics and high-resolution reanalysis,we use the convection-permitting weather research and forecasting (WRF) model configured with 3 km grid spacing to simulate the warm-season precipitation in the eastern China for 10 seasons (2008?2017).The hourly 31-km-resolution ERA5 reanalysis data are used to provide initial and boundary conditions for the simulations.The objectives are:(1) to evaluate the model skill in simulating warm-season precipitation climatology in the East Asian monsoon region,(2) to identify the promises and problems of the convection-permitting simulation,and (3) to investigate solutions for the model deficiencies.Results demonstrate that the 3-km-resolution WRF model reasonably reproduces the spatial characteristics of seasonal and sub-seasonal precipitation,the seasonal meridional migration associated with the summer monsoon activity,the diurnal variation phase and amplitude,and the propagating convection east of the Tibetan Plateau.The major deficiency is that the model overestimates precipitation amount,especially in the afternoon.Analysis and sensitivity experiments suggest that improved treatment of sub-grid cloud fraction and the aerosol effects may help to suppress the often-reported high precipitation bias.These results provide useful guidance for improving the model skill in simulating warm-season precipitation in East Asia.(Yun Yuxing,Liu Changhai,Luo Yali)

3.8 Elucidating the life cycle of warm-season mesoscale convective systems in eastern China from the Himawari-8 geostationary satellite

The life cycle of mesoscale convective systems (MCSs) in the eastern China is yet to be fully understood,mainly due to the lack of observations of high spatio-temporal resolution and objective methods.Here,we quantitatively analyze the properties of warm-season (from April to September of 2016) MCSs during their lifetimes using the Himawari-8 geostationary satellite,combined with ground-based radar and gauge measurements.Generally,the occurrence of satellite-derived MCSs has a noon peak over the land and an early morning peak over the ocean,which is several hours earlier than the precipitation peak.The developing and dissipative stages are significantly longer as total durations of MCSs increase.Aided by three-dimensional radar mosaics,we find the fraction of convective cores over the northern China is much lower when compared with those in the central United States,indicating that the precipitation produced by broad stratiform clouds may be more important for the northern China.When there exists a large amount of stratiform precipitation,it releases a large amount of latent heat and promotes the large-scale circulations,which favors the maintenance of MCSs.These findings provide quantitative results about the life cycle of warm-season MCSs in the eastern China based on multiple data sources and large numbers of samples.(Chen Dandan,Guo Jianping,Yao Dan)

3.9 Establishment of an objective standard for the definition of binary tropical cyclones in the western North Pacific

To develop an objective standard for defining binary tropical cyclones (BTCs) in the western North Pacific(WNP),two best-track datasets,from the China Meteorological Administration and the Joint Typhoon Warning Center,were adopted for statistical analyses on two important characteristics of BTCs-two TCs approaching each other,and counterclockwise spinning.Based on the high consistency between the two datasets,we established an objective standard,which includes a main standard for defining BTCs and a secondary standard for identifying typical/atypical BTCs.The main standard includes two requirements:two coexisting TCs are a pair of BTCs if (i) the separation distance is≤1800 km,and (ii) this separation maintains for at least 12 h.Meanwhile,the secondary standard defines a typical BTC as one,for which there is at least one observation when the two TCs approach each other and spin counterclockwise simultaneously.Under the standard,the ratio of typical BTCs increases as the BTC duration increases or the minimum distance between the two TCs decreases.Then,using the JTWC dataset,it was found that there are 505 pairs of BTCs during the period 1951?2014,including 328 typical BTCs and 177 atypical BTCs,accounting for 65.0% and 35.0% of the total,respectively.In addition,a study of two extreme phenomena—the maximum approaching speed and the maximum counterclockwise angular velocity in typical BTCs—shows that the configuration of the circulation conditions and the distribution of the BTCs favor the formation of these extreme phenomena.(Ren Fumin,Xie Yanjun,Yin Biwen)

3.10 Improvement in the forecasting of heavy rainfall over South China in the DSAEF_LTP model by Introducing the intensity of the tropical cyclone

The intensity of the tropical cyclone has been introduced into the Dynamical-Statistical-Analog Ensemble Forecast (DSAEF) for Landfalling Typhoon (or tropical cyclone) Precipitation (DSAEF_LTP)model.Moreover,the accumulated precipitation prediction experiments have been conducted on 21 target tropical cyclones with daily precipitation≥100 mm in South China from 2012 to 2016.The best forecasting scheme for the DSAEF_LTP model is identified,and the performance of the prediction is compared with three numerical weather prediction models (the European Centre for Medium-Range Weather Forecasts,the Global Forecast System,and T639).The forecasting ability of the DSAEF_LTP model for heavy rainfall (accumulated precipitation≥250 and≥100 mm) improves when the intensity of the tropical cyclone is introduced,giving some advantages over the three numerical weather prediction models.The selection of analog tropical cyclones with a maximum intensity (during precipitation over land) equaling to or higher than the initial intensity of the target tropical cyclone gives better forecasts.The prediction accuracy for accumulated precipitation is higher for tropical cyclones with higher intensity and higher observed precipitation,with in both cases positive linear correlations with the threat score.(Ding Chenchen,Ren Fumin,Liu Yanan)

3.11 Introducing TC intensity into the DSAEF_LTP model and simulating precipitation of supertyphoon Lekima (2019)

In this study,the Dynamical-Statistical-Analog Ensemble Forecast model for landfall typhoon precipitation (the DSAEF_LTP model),which has been developed by Ren et al.,in 2020,is applied to precipitation simulations for super-typhoon Lekima (2019),a tropical cyclone (TC) that produced heavy rainfall over the eastern China.A new variable,TC intensity,is introduced into the generalized initial value(GIV) of the DSAEF_LTP model.Two different groups of simulation experiments,one group including the new TC intensity variable in the GIV and the other group excluding it,have been conducted.Results show that,with TC intensity,the ability of the DSAEF_LTP model to forecast heavy rainfall (i.e.accumulated precipitation exceeding thresholds of 250 and 100 mm) for Lekima is improved.Its threat score (TS) ranks the second compared with those of three numerical weather prediction models (i.e.ECMWF,GRAPES and GFS).Further study shows that three factors prevent the DSAEF_LTP model from achieving more satisfactory results for Lekima:the historically rare occurrence of extreme precipitation in the northern China during Lekima,the increase of forecast track error when Lekima moved northwards,and the calculation of similarity between tracks of Lekima and historical TCs within an improper region (i.e.similarity region).To solve the third problem,new similarity region schemes are adopted and produce higher TS,in which the TS of precipitation greater than 100 mm (TS100) ranks first and the TS of precipitation greater than 250 mm (TS250) gets closer to the first place.(Jia Li,Jia Zuo,Ren Fumin)

3.12 Monsoonal influences on offshore rapid intensification of landfalling typhoons in a sheared environment over the South China Sea

Tropical cyclones (TCs) formed in the western North Pacific and South China Sea can undergo rapid intensification (RI) shortly before making landfall in China.Forecasting such offshore RI is a great challenge in operations.In this study,the offshore RI events in a sheared environment are examined for TCs that made landfall in China during 1979?2017.It is found that there were only three offshore RI events in a sheared environment,all of which occurred to the south of Hainan Island within the monsoon trough in early- to mid-July,coinciding with the termination of the Meiyu season.The specific geographic location and timing of the occurrence of the offshore RI in the sheared environment are associated with the adjustment of the East Asia summer monsoon system when the mei-yu season terminates in the Yangtze River valley.In addition to the adjustment favorable for TC intensification by enhancing the TC-trough interaction in the upper troposphere,this study suggests that two environmental factors also contribute to the offshore RI over the South China Sea in a sheared environment.One is the intrusion of dry air associated with the western North Pacific subtropical high (WNPSH) and the other is the penetration of the water vapor flux associated with the monsoon surge.The adjustment of the East Asia summer monsoon system allows the water vapor flux of the monsoon surge to penetrate the TC circulation and prevents the dry air of the WNPSH from intruding into the TC circulation.(Qiu Wenyu,Wu Liguang,Ren Fumin)

3.13 Novel models to estimate hourly diffuse radiation fraction for global radiation based on weather type classification

The diffuse radiation is well recognized as a key variable in solar energy assessment,albeit with sorely lacking ground-based measurements.Here,we proposed two novel models to estimate hourly diffuse radiation using the typical meteorological annual radiation data in Beijing as training samples.Model 1 was a combination of four classical models,including Liu & Jordan,Orgill & Hollands,Erbs and Reindl,in which the weight or coefficient was determined by weather types derived from clearness index.In Model 2,the weather type classification was refined by total cloud cover,and the principal component analysis (PCA) was further applied to determine the major meteorological variables for each weather type as model’s input,along with linear fitting.Using sub-typical annual radiation data as testing samples,the proposed models showed strong extrapolation ability with three statistical metrics:lower mean absolute percentage error and normalized root mean square error but relatively higher correlation coefficient,compared with other models.Finally,these models were verified by the observations in Wuhan.The results indicat that weather type classification and PCA effectively improved model’s performance by eliminating the collinearity between meteorological and environmental variables.Furthermore,both models performed better than any single classical model,irrespective of large-scale weather patterns.(Li Fen,Lin Yilun,Guo Jianping)

3.14 Roles of double low-level fets in the generation of coexistinginland and coastal heavy rainfall over South China during the presummer rainy season

In this study,the key dynamic factors influencing the formation of six heavy-rainfall events with coexisting inland and coastal rainfall over South China during May?June 2011?2017 are investigated using the global ensemble forecasts from the European Centre for Medium-Range Weather Forecasts.An ensemble sensitivity analysis and comparisons between the identified good and bad members are conducted.Results confirm the importance of the synoptic low-level jet (SLLJ) and boundary layer jet (BLJ),but with different contributions,in determining the generation of the inland and coastal rainbelts,respectively.The inland heavy rainfall is closely related to both SLLJ and BLJ,especially their meridional wind components.The more intense cold or quasi-stationary fronts,low-level vortexes,or shear lines accompanied by the stronger geostrophic southerly winds within both jets over inland and coastal South China are,the more rainfall over the inland region is favored.The ageostrophic southerly winds of the BLJ make limited contributions to the inland rainfall production,but exert greater impacts on the generation of extreme (yet localized) coastal rainfall.The geostrophic meridional winds and associated low-level fronts/vortexes also play a nonnegligible but indispensable role in producing the coastal rainfall.These findings add to our knowledge of heavy rainfall in the East Asian monsoon region.(Liu Xi,Luo Yali,Huang Ling)

3.15 Roles of synoptic to quasi-monthly disturbances in generating two pre-summer heavy rainfall episodes over South China

In this study,the power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of presummer heavy rainfall over South China.Two heavy rainfall episodes are selected during the months of April?June 2008?2015,which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances,respectively.Results show that the first heavy rainfall episode takes place in a southwesterly anomalous flow associated with an anticyclonic anomaly over the South China Sea (SCS) at the quasi-biweekly scale with 15.1% variance contributions,and at the synoptic scale in a convergence zone between southwesterly and northeasterly anomalous flows associated with a southeastwardmoving anticyclonic anomaly on the leeside of the Yungui Plateau and an eastward-propagating anticyclonic anomaly from higher latitudes with 35.2% variance contribution.In contrast,the second heavy rainfall episode takes place in southwest-to-westerly anomalies converging with northwest-to-westerly anomalies at the quasimonthly scale with 23.2% variance contributions to the total rainfall variance,which are associated with an anticyclonic anomaly over the SCS and an eastward-propagating cyclonic anomaly over North China,respectively.At the synoptic scale,it occurs in south-to-southwesterly anomalies converging with a cyclonic anomaly on the downstream of the Yungui Plateau with 49.3% variance contributions.In both cases,the lowertropospheric mean south-to-southwesterly flows provide ample moisture supply and potentially unstable conditions; it is the above synoptic,quasi-biweekly or quasi-monthly disturbances that determine the general period and distribution of persistent heavy rainfall over South China.(Jiang Zhina,Zhang Da-Lin,Liu Hongbo)

3.16 Science and prediction of heavy rainfall over China:Research progress since the reform and opening-up of new China

This paper reviews the major progress on development of the science and prediction of heavy rainfall over China since the beginning of the reform and opening-up of new China (roughly between 1980 and 2019).The progress of research on the physical mechanisms of heavy rainfall over China is summarized from three perspectives:(1) the relevant synoptic weather systems,(2) heavy rainfall in major sub-regions of China,and (3) heavy rainfall induced by typhoons.The development and application of forecasting techniques for heavy rainfall are summarized in terms of numerical weather prediction techniques and objective forecasting methods.Greatly aided by the rapid progress in meteorological observing technology and substantial improvement in electronic computing,studies of heavy rainfall in China have advanced to investigating the evolution of heavy-rain-producing storms and observational analysis of the cloud microphysical features.A deeper and more systematic understanding of the synoptic systems of importance to the production of heavy rainfall has also been developed.Operational forecast of heavy rainfall in China has changed from subjective weather event forecasts to a combination of both subjective and objective quantitative precipitation forecasts,and is now advancing toward probabilistic quantitative precipitation forecasts with the provision of forecast uncertainty information.(Luo Yali,Sun Jisong,Li Ying)

3.17 Sideswiping tropical cyclones and their associated precipitation over China

Tropical cyclone (TC) precipitation (TCP) has attracted considerable attention in recent decades because of its adverse socioeconomic impacts.In particular,considerable effort has been devoted to quantifying TCP and investigating the precipitation of TCs that make landfall.However,precipitation over land induced by TCs that do not make landfall (i.e.,offshore),the so-called “sideswiping” TCs (STCs),is an important component of TCP but has attracted little attention from the research community to date.Here,best-track and daily precipitation data from the China Meteorological Administration during the 59 years of 1960?2018 are used to study STC precipitation (STP).Results show that:(i) the annual number of STCs fluctuates significantly from 3 to 17,with a mean frequency of 8.8 STCs per year; (ii) there are decreasing trends in STC frequency and STP amount over the past 59 years; (iii) both STC frequency and STP are high from July to October,with maxima in August; (iv) the distribution of STP,covering most of China’s coastal regions,is dominated by intense STCs,and the annual STP decreases from southeast coastal regions to northwest inland areas,with a maximum value over the islands of Taiwan and Hainan; and (v) extreme STP events could appear not only over the island and coastal areas,but also over inland areas such as Zhumadian of Henan Province due to the influences of local orography and favorable large-scale forcing.(Feng Tian,Ren Fumin,Zhang Lin)

3.18 Statistical characteristics of pre-summer rainfall over South China and associated synoptic conditions

In this study,the climatological characteristics of pre-summer (April to June) rainfall over South China(SC) and the associated synoptic conditions are examined using 1980?2017 hourly rainfall observations and reanalysis data.The amount,frequency,and intensity of rainfall show pronounced regional variations and substantial changes between pre- and post-monsoon-onset periods.Owing to the more favorable thermodynamic conditions after monsoon onset over the South China Sea (SCS),rainfall intensifies generally over SC irrespective of the rainfall-event durations.Increased rainfall amounts in longer-duration ( 6 h)events were found over a designated west-inland region (west of 111°E),which are partially attributed to enhanced dynamic instability.In addition,rainfall events occur more frequently over the west-inland region,as well as coastal regions to the west of 118°E,but less over a designated east-inland region.Inland-region rainfall is closely linked to dynamic lifting driven by subtropical synoptic systems (low pressure and an associated front or shearline).The westward extension of the western North Pacific high and the eastward extension/movement of the front or shearline,interacting with the intra-period intensification of the southwesterly monsoonal flows,play important roles in providing high-θe,(equivalent potential temperature) air to the westand east-inland regions,respectively.Warm-sector coastal rain fall is closely related to the deceleration of the southerly boundary layer (BL) air flow over the northern SCS and associated convergence of BL high-θeair near the coast.Meanwhile,the southwesterly synoptic-system-related low-level jet in the lower-to-middle troposphere to the south of the inland cold front can contribute to the coastal rainfall occurrence by providing divergence above the BL convergence near the coast.The BL flow often simultaneously strengthens with the lower-troposphere horizontal winds,suggesting a close association between the BL flow and the synoptic systems.The quantitative statistics provided in this study complement previous case studies or qualitative results and,thus,advance our understanding about pre-summer rainfall over SC.(Li Zhenghui,Luo Yali,Du Yu)

3.19 Temperature inversion and clouds over the Arctic Ocean observed by the 5th Chinese National Arctic Research Expedition

The Arctic is of great significance to global weather and climate systems.However,its atmospheric conditions have not yet to be fully understood,partly because of the lack of intensive observations.Here we reported on the characteristics of lower troposphere over the Arctic Ocean using high-resolution radiosonde data collected during the 5th Chinese National Arctic Research Expedition from July to September 2014.Statistical analyses showed that temperature inversion (TI) occurred most frequently below 700 m,without apparent temporal variability between morning and noon.In contrast,the occurrence frequency of morning surface-based inversion (SBI) was always higher than that at noon in the whole boundary layer,whereas the elevated inversion (EI) frequency seemed much lower in the morning compared with that at noon.More frequent deeper clouds tended to occur in the morning than at noon,which led to more frequent EI than SBI.SBI was found to dominate the clear-sky condition,whereas EI was generally observed under cloudy conditions.Regarding the seasonal variation,deep TI and clouds dominated during the first intensive observational period (IOP-1; July 21?31) because of warm advection in combination with heating effects induced by long-range transported black carbon (BC).During IOP-2 (August 1?18),synoptic scale subsidence prevailed,with frequent EI and SBI partly caused by BC accumulation over the Arctic Ocean.In comparison,more clouds and less TI occurred during IOP-3 (from August 27 to September 11) largely due to the outbreaking polar vortex.These observations contribute to a better understanding of vertical temperature and cloud structures under global warming.(Wang Ding,Guo Jianping,Chen Aijun)

3.20 The effects of cloud-aerosol interaction complexity on simulations of presummer rainfall over the southern China

Convection-permitting simulations are used to understand the effects of cloud–aerosol interactions in a case of heavy rainfall over the southern China.The simulations are evaluated using radar observations from the Southern China Monsoon Rainfall Experiment (SCMREX) and remotely sensed estimates of precipitation,clouds and radiation.We focus on the effects of complexity in cloud–aerosol interactions,especially the depletion and transport of aerosol material by clouds.In particular,simulations with aerosol concentrations held constant are compared with a fully cloud–aerosol-interacting system to investigate the effects of twoway coupling between aerosols and clouds on a line of organised deep convection.It is shown that the cloud processing of aerosols can change the vertical structure of the storm by using up aerosols within the core of line,thereby maintaining a relatively clean environment which propagates with the heaviest rainfall.This induces changes in the statistics of surface rainfall,with a cleaner environment being associated with lessintense but more-frequent rainfall.These effects are shown to be related to a shortening of the timescale for converting cloud droplets to rain as the aerosol number concentration is decreased.The simulations are compared to satellite-derived estimates of surface rainfall,a condensedwater path and the outgoing flux of short-wave radiation.Simulations for fewer aerosol particles outperform the more polluted simulations for surface rainfall but give poorer representations of top-of-atmosphere (TOA) radiation.(Kalli Furtado,Paul Field,Luo Yali)

3.21 The impact of reforestation induced land cover change (1990-2017) on flood peak discharge using HEC-HMS hydrological model and satellite observations:A study in two mountain basins,China

Understanding the effect of land use and land cover (LULC) type change on watershed hydrological response is essential for adopting applicable measures to control floods.In China,the Grain to Green Program(GTGP) and the Natural Forest Conservation Program (NFCP) have had a substantial impact on LULC.We investigated the effect of these conservation efforts on flood peak discharge in two mountainous catchments.We used a series of Landsat images ranging from 1990 to 2016/2017 to evaluate the LULC changes.Further to this,the hydrological responses at the basin and sub-basin scale were generated by the Hydrologic Modeling System (HEC-HMS) under four LULC scenarios.Between 1990 and 2016/2017,both catchments experienced an increase in forest and urban land by 18% and 2% in Yanhe and by 16% and 8% in Guangyuan,respectively.In contrast,the agricultural land decreased by approximately 30% in Yanhe and 24% in Guangyuan,respectively.The changes in land cover resulted in the decrease in flood peak discharge ranging from 14%in Yanhe to 6% in Guangyuan.These findings provide a better understanding on the impact of reforestation induced LULC change on spatial patterns of typical hydrological responses of mountainous catchment and could help to mitigate flash flood hazards in other mountainous regions.(Kabeja Crispin,Li Rui,Guo Jianping)

3.22 The response of warm-season precipitation extremes in China to global warming:an observational perspective from radiosonde measurements

Consensus has been reached that precipitation extremes vary proportionally with global warming.Nevertheless,the underlying cause and magnitude of these factors affecting their relationships remain highly debated.To elucidate the complex relationship between precipitation extremes and temperature in China during the warm seasons (May through September),a 60-year (1958?2017) record of hourly rain gauge measurements,in combination with surface air temperature,RH,precipitable water (PW),and convective available potential energy (CAPE) collected from 120 radiosonde stations were examined.Spatially,the scaling relationship between precipitation extremes and temperature exhibits a large geographic difference across China.In particular,the Clausius-Clapeyron (CC) and sub-CC relationships tend to occur in Northwest (ROI-N)and Southeast China (ROI-S),whereas the super-CC relationship is found to mainly concentrate in the central China (ROI-C).Additionally,the response of precipitation extremes to temperature becomes more sensitive as precipitation intensity increases,shifting from CC to super-CC at a certain point of inflection that varies by geographic regions.This shift occurs at approximately 15℃ in ROI-C and ROI-N,but at around 20℃ in ROI-S.Within the temperature range of the super-CC slope,the PW rises with the increases in temperature,whereas the CAPE decreases with rising temperature,which is contrary to the monotonic scaling of precipitation with temperature.From the perspective of interannual variation,the precipitation extremes correlate positively with temperature.This further confirms the notion that global warming,through jointly affecting PW and CAPE,is able to considerably regulate precipitation extremes.(Guo Jianping,Yan Yan,Chen Dandan)

3.23 Urbanization enhanced summertime extreme hourly precipitation over the Yangtze River delta

An extensive urban agglomeration has occurred over the Yangtze River delta (YRD) region of East China as a result of rapid urbanization since the middle 1990s.In this study,a 44-year (i.e.,1975?2018) climatology of the summertime extreme hourly precipitation (EXHP; greater than the 90th percentile) over the YRD is analyzed,using historical land-use data,surface temperature,and hourly rain gauge observations,and then the relationship between rapid urbanization and EXHP changes is examined.Results show significant EXHP contrasts in diurnal variation and storm type roughly before and after middle July.That is,tropical cyclones(TCs) account for 16.4% of the total EXHP hours,80.5% of which occur during the late summer,whereas non-TC EXHP accounts for 94.7% and 66.2% during the early and late summer,respectively.Increasing trends in occurrence frequency and amount of the non-TC and TC-induced EXHP are detected over the urban agglomeration.Statistically significant larger increasing trends in both the EXHP and surface temperature are observed at urban stations than those at the nearby rural stations.An analysis of 113 locally developed non-TC extreme rainfall events during 2011?2018 summers also suggests the contribution of the urban heat island effects to the more occurrences of EXHP,especially over a band-shaped urban region where several major cities are distributed.This study reveals a significant correlation between rapid urbanization and increased EXHP during the past two decades over the YRD region.The results have important implications for understanding the impact of urbanization on EXHP changes in a warming climate.(Jiang Xiaoling,Luo Yali,Zhang Da-Lin)

3.24 High-resolution simulations of heavy rainfalls in association with monsoon systems and typhoons using cloud-resolving models

Monsoon systems and typhoons are major causes of heavy rainfall events in East Asia and occasionally give rise to serious disasters.Most heavy rainfall systems are composed of intense convective clouds.Cloudresolving models are,therefore,indispensable for studies of their mechanisms and processes,and also for accurate and quantitative predictions of heavy rainfall.Advances in computing now make it feasible to use cloud-resolving models for studies and predictions of heavy rainfalls associated with monsoon systems and typhoons.This chapter reviews recent studies of heavy rainfall events using regional cloud-resolving models such as MM5,WRF,JMA-NHM,and CReSS.As an example,the details of the CReSS model are summarized and two simulation experiments of heavy rainfall events are introduced:one caused by the Baiu front in Japan in 2017 and the other accompanying a typhoon in 2004.These high-resolution experiments,which successfully simulated the structure of heavy rainfall systems and provided quantitative predictions of rainfall,were performed with a horizontal resolution of 1 km.These results indicate that cloud-resolving models are very useful and indispensable for mechanism studies and quantitatively accurate predictions of heavy rainfall associated with monsoon systems and typhoons.(Kazuhisa Tsuboki,Luo Yali)

3.25 The Southern China Monsoon Rainfall Experiment (SCMREX)

During the pre-summer rainy season (April–June),South China often experiences frequent occurrences of extreme rainfall,leading to severe flooding and inundations.Although scientific understanding of the processes responsible for heavy rainfall production continues to advance (Schumacher 2017),quantitative precipitation forecasting is still a great challenge over the world including South China.To improve the quantitative precipitation forecasting (QPF) skill of the pre-summer rainy season rainfall,the China Meteorological Administration (CMA) initiated a nationally coordinated research project,the Southern China Monsoon Rainfall Experiment (SCMREX).With the participation and strong support of international experts,the SCMREX was approved by the World Meteorological Organization (WMO) as a World Weather Research Programme (WWRP) Research and Development Project (RDP).The scientific objectives of the SCMREX are:(1) to better understand the physical mechanisms governing the initiation,evolution,morphology,organization,and duration of the heavy-rain-producing MCSs that determine the precise timing and location and accumulative amount of rainfall; (2) to better understand the microphysical and kinematic structures of the heavy-rain-producing MCSs that determine the instantaneous rainfall amount and are of relevance when validating parameterization schemes representing cloud-precipitation microphysical processes in numerical weather prediction (NWP) models; and (3) to improve fine-scale quantitative precipitation forecasting (QPF)skills by better understanding the multi-scale precipitation processes,assessing the impact of assimilating highresolution observations into convection-permitting (horizontal grid spacing of 1–4 km) numerical models,and evaluating and improving cloud microphysical parameterization schemes in convection-permitting models.This article reviews the progress of SCMREX in 2016-2017 and briefly discusses future research opportunities.(Luo Yali,Bao Xinghua,Wang Hui)

3.26 LTP_DSEF模型對(duì)2018年登陸中國(guó)熱帶氣旋強(qiáng)降水預(yù)報(bào)的應(yīng)用

最近，一種基于路徑相似的登陸熱帶氣旋降水動(dòng)力統(tǒng)計(jì)集合預(yù)報(bào)（LTP_DSEF）模型被發(fā)展用來(lái)預(yù)報(bào)登陸熱帶氣旋（LTC）帶來(lái)的強(qiáng)降水。文章把LTP_DSEF模型應(yīng)用于2018年登陸中國(guó)的10個(gè)熱帶氣旋（TC）的強(qiáng)過(guò)程降水預(yù)報(bào)，通過(guò)測(cè)試模型的3452套預(yù)報(bào)方案確定了對(duì)這10個(gè)LTC的最佳方案，然后將其性能與3家動(dòng)力模式（ECMWF、GFS和GRAPES）進(jìn)行對(duì)比。結(jié)果表明：LTP_DSEF模型在預(yù)報(bào)LTC的較強(qiáng)過(guò)程降水方面與3家動(dòng)力模式相比很有優(yōu)勢(shì)，特別是預(yù)報(bào)250 mm以上量級(jí)的過(guò)程降水；對(duì)單TC，LTP_DSEF模型預(yù)報(bào)LTC過(guò)程降水的能力優(yōu)于或者略遜于3家動(dòng)力模式，特別在3家動(dòng)力模式對(duì)某些TC的強(qiáng)降水均無(wú)預(yù)報(bào)能力時(shí)，模型仍能提供寶貴的大于零的TS值；此外，雖然與實(shí)況相比該模型預(yù)測(cè)的強(qiáng)降水范圍傾向偏大，但它在多數(shù)情況下能合理地捕捉到強(qiáng)降水的落區(qū)。初步研究表明，盡管LTP_DSEF模型只引入了TC路徑和登陸時(shí)間兩個(gè)相似性變量，但它已能為L(zhǎng)TC的強(qiáng)過(guò)程降水預(yù)報(bào)提供非常有用的指導(dǎo)。（賈作，任福民，張大林）

3.27 1980—2017年南海季風(fēng)爆發(fā)前后華南前汛期降水統(tǒng)計(jì)特征對(duì)比分析

利用1980—2017年華南地區(qū)303 個(gè)國(guó)家級(jí)地面氣象站逐小時(shí)降水?dāng)?shù)據(jù)、ERA-Interim 再分析資料，分析華南前汛期（4—6月） 降水統(tǒng)計(jì)特征，定義站點(diǎn)上短時(shí)（1～6 h）、中等時(shí)長(zhǎng)（7～12 h）和長(zhǎng)時(shí)（ 12 h）降水事件，對(duì)比降水量、頻次和強(qiáng)度在南海季風(fēng)爆發(fā)前后的變化，以及所定義的西部?jī)?nèi)陸、東部?jī)?nèi)陸、沿海地區(qū)的異同。結(jié)果表明：（1） 南海季風(fēng)爆發(fā)后，研究區(qū)域平均而言，3類(lèi)降水事件的降水量增多、小時(shí)降水強(qiáng)度增強(qiáng)，短時(shí)、長(zhǎng)時(shí)降水事件發(fā)生頻次增多，而中等時(shí)長(zhǎng)降水事件發(fā)生頻次有所減少。（2） 從空間分布來(lái)看，南海季風(fēng)爆發(fā)后，小時(shí)降水強(qiáng)度在整個(gè)華南地區(qū)均增強(qiáng)，西部?jī)?nèi)陸時(shí)長(zhǎng)大于6 h 的降水事件尤為明顯；降水事件的發(fā)生頻次在西部?jī)?nèi)陸和沿海地區(qū)升高，而東部?jī)?nèi)陸時(shí)長(zhǎng)大于6 h 的降水事件發(fā)生頻次降低；因此，季風(fēng)爆發(fā)后西部?jī)?nèi)陸和沿海地區(qū)的總降水量均顯著增大，而東部?jī)?nèi)陸的總降水量變化不大。（3） 西部?jī)?nèi)陸降水事件主要在夜間開(kāi)始發(fā)生，持續(xù)時(shí)間越長(zhǎng)的事件越早開(kāi)始，且由西向東逐漸推遲；東部?jī)?nèi)陸短時(shí)降水事件主要在14:00 （北京時(shí)，下同）左右開(kāi)始，季風(fēng)爆發(fā)后更為明顯，而時(shí)長(zhǎng)大于6 h的降水事件的開(kāi)始時(shí)間和峰值時(shí)間無(wú)明顯的分布規(guī)律；沿海地區(qū)短時(shí)降水事件在季風(fēng)爆發(fā)前主要于05:00—08:00時(shí)開(kāi)始，季風(fēng)爆發(fā)后，在海岸線約50 km 以內(nèi)仍然如此，而較遠(yuǎn)離海岸線的短時(shí)降水事件主要于14:00開(kāi)始，沿海地區(qū)長(zhǎng)時(shí)降水事件在季風(fēng)爆發(fā)前、后都傾向于在夜間開(kāi)始，并在日間出現(xiàn)峰值。（李爭(zhēng)輝，羅亞麗）

3.28 1982—2016年云南省不同強(qiáng)度降水氣候態(tài)及其變化

基于1982—2016年云南省67個(gè)氣象站逐小時(shí)降水資料，利用百分位閾值法定義極端小時(shí)降水（大于第95百分位）、強(qiáng)小時(shí)降水（第80至95百分位之間）、中等—弱小時(shí)降水（小于第80百分位），并分析其35 a平均氣候態(tài)和變化趨勢(shì)。結(jié)果表明：（1）云南省年降水強(qiáng)度大值中心位于南部，年降水頻次大值中心位于西北部，分別對(duì)應(yīng)年降水量大值和次大值中心。云南省降水主要集中在夏秋季，同時(shí)云南省西北部存在春汛期，該地區(qū)2—4月降水頻次高、強(qiáng)度大、降水量多。（2）全省極端小時(shí)降水、強(qiáng)小時(shí)降水的閾值表現(xiàn)為從南向北、從西向東減小。（3）過(guò)去35 a全省大部分地區(qū)年降水量和小時(shí)降水頻次均表現(xiàn)為下降趨勢(shì)，且隨著降水強(qiáng)度等級(jí)降低而增強(qiáng)，秋季最為明顯，而小時(shí)降水強(qiáng)度表現(xiàn)為增強(qiáng)趨勢(shì)，夏秋兩季極端小時(shí)降水的增強(qiáng)趨勢(shì)通過(guò)顯著性檢驗(yàn)。（于淑婷，羅亞麗，李建）

3.29 地形作用下低空急流的演變與強(qiáng)降水對(duì)流風(fēng)暴系統(tǒng)的相互作用

利用雷達(dá)、衛(wèi)星、風(fēng)廓線雷達(dá)和地面加密區(qū)域自動(dòng)氣象站等觀測(cè)資料，分析了2016年入梅后發(fā)生在鄂東地區(qū)一次極端強(qiáng)降水事件的中尺度對(duì)流系統(tǒng)發(fā)生發(fā)展過(guò)程、結(jié)構(gòu)演變及其傳播特征，旨在揭示造成強(qiáng)降水過(guò)程中的3個(gè)中尺度對(duì)流系統(tǒng)（MCS）的觸發(fā)、發(fā)展、維持機(jī)理以及它們之間內(nèi)在的中尺度動(dòng)力學(xué)關(guān)系，尤其是地形作用下的低空急流的演變與強(qiáng)降水對(duì)流風(fēng)暴系統(tǒng)相互作用過(guò)程。研究表明：（1）與大多數(shù)梅雨鋒上的強(qiáng)降水帶與低空切變線平行分布不同，此次極端強(qiáng)降水雨帶呈傾斜的“n”字形，其中兩條主雨帶近乎與低空切變線垂直；此次極端強(qiáng)降水分別由大別山迎風(fēng)坡上西北—東南向MCS、湖北中東部平原地區(qū)西北—東南向MCS和桐柏—大洪山東側(cè)東北—西南向MCS造成。3個(gè)MCS移動(dòng)緩慢，都具有后向傳播的特征。（2）大別山迎風(fēng)坡上MCS初始雷暴是低空急流下邊界不斷向下擴(kuò)展過(guò)程中在地形抬升作用下觸發(fā)的，而湖北中東部平原地區(qū)的MCS和桐柏—大洪山東側(cè)MCS的觸發(fā)、發(fā)展、加強(qiáng)都與大別山迎風(fēng)坡上MCS形成的冷池加速推進(jìn)形成的出流邊界與環(huán)境氣流形成的強(qiáng)烈輻合抬升作用有關(guān)。（3）垂直于大別山的邊界層西南急流對(duì)山坡上的對(duì)流冷池產(chǎn)生的頂托作用不僅平衡了冷池密度流產(chǎn)生的向下作用力，而且進(jìn)一步強(qiáng)化了山區(qū)的輻合抬升強(qiáng)度，使得大別山迎風(fēng)坡上強(qiáng)降水風(fēng)暴系統(tǒng)得以長(zhǎng)時(shí)間維持和發(fā)展；當(dāng)山坡上的對(duì)流冷池堆積到足夠厚度，或者由于低空急流的下邊界迅速抬升時(shí)，這種平衡被打破，大范圍的冷池俯沖下山并在平原地區(qū)快速推進(jìn)，造成了湖北中東部平原地區(qū)大范圍的雷暴大風(fēng)和MCS發(fā)展加強(qiáng)，并沿冷池前沿逐步組織化，形成平原地區(qū)東南—西北向的強(qiáng)降水帶。（黃小彥，孫繼松，劉文婷）

3.30 海南島熱帶氣旋極端降水的特征及其成因

圍繞海南島熱帶氣旋（TC）極端降水的特征及其成因，利用國(guó)家氣象信息中心提供的海南島臺(tái)站日降水?dāng)?shù)據(jù)、上海臺(tái)風(fēng)所的TC最佳路徑數(shù)據(jù)集和NCEP/NCAR再分析數(shù)據(jù)，通過(guò)氣候統(tǒng)計(jì)、天氣診斷相結(jié)合的方法，探討了1958—2013年海南島TC極端降水的空間分布和時(shí)間變化特征，并進(jìn)一步診斷分析了極端降水產(chǎn)生的可能成因。結(jié)果表明，海南島TC極端降水在西北部出現(xiàn)最多，東南部出現(xiàn)較少。從長(zhǎng)期趨勢(shì)看，無(wú)論從TC極端降水量還是從TC極端降水頻數(shù)，TC極端降水的極端趨勢(shì)均在增加。充足的西南水汽通量輸送是產(chǎn)生TC極端降水的重要條件；當(dāng)南亞高壓和副熱帶高壓相距較近，即南亞高壓偏東偏強(qiáng)，副熱帶高壓偏西偏強(qiáng)時(shí)，海南島容易出現(xiàn)TC極端降水事件；在TC路徑和低層風(fēng)場(chǎng)結(jié)構(gòu)的配合下，海南島地形對(duì)極端降水的落區(qū)有關(guān)鍵影響。（蔣賢玲，任福民，蔡親波）

3.31 華北地區(qū)持續(xù)性極端暴雨過(guò)程的分類(lèi)特征

利用1960—2015年日降水資料，篩選出華北地區(qū)56次持續(xù)性極端暴雨過(guò)程?；诰嗥较嚓P(guān)系數(shù)的客觀聚類(lèi)分析方法和天氣學(xué)檢驗(yàn)，將它們進(jìn)行分類(lèi)，并使用NCEP（2.5°×2.5°）再分析資料進(jìn)行分類(lèi)合成，對(duì)比分析不同環(huán)流背景下華北地區(qū)持續(xù)性極端暴雨過(guò)程的基本特征。結(jié)果表明，這些持續(xù)性極端暴雨事件按照環(huán)流背景可分為經(jīng)向型、緯向型、減弱的登陸熱帶氣旋型和初夏型4類(lèi)。它們一般都與不同天氣系統(tǒng)配置結(jié)構(gòu)下的鋒面動(dòng)力學(xué)過(guò)程有關(guān)，由于鋒面結(jié)構(gòu)特征、環(huán)境大氣層結(jié)狀態(tài)以及與低空急流有關(guān)的暖濕氣流輸送通道和強(qiáng)度不同，造成不同環(huán)流形勢(shì)背景下，暴雨日的高頻站點(diǎn)與過(guò)程平均累計(jì)降水量在空間分布上存在差異。（1）緯向型對(duì)應(yīng)的鋒區(qū)強(qiáng)度明顯強(qiáng)于經(jīng)向型，但是其對(duì)應(yīng)的層結(jié)穩(wěn)定度與整個(gè)夏季狀態(tài)相當(dāng)，而經(jīng)向型存在弱的層結(jié)不穩(wěn)定異常，這表明，緯向型的對(duì)流活動(dòng)一般不如經(jīng)向型強(qiáng)，持續(xù)性鋒面降水特征更清晰，造成站點(diǎn)上日降水量超過(guò)50 mm的最大頻率明顯低于經(jīng)向型，但是過(guò)程累計(jì)平均最大降雨量卻比經(jīng)向型大。（2）從水汽輸送通道來(lái)看，源于西太平洋副熱帶高壓南側(cè)的水汽通道只在緯向型環(huán)流主導(dǎo)下的華北區(qū)域持續(xù)性極端暴雨過(guò)程中起主導(dǎo)作用。初夏型以及減弱的登陸熱帶氣旋與西風(fēng)帶系統(tǒng)相互作用造成的極端暴雨過(guò)程中，活躍的印度季風(fēng)造成25°N以南異常強(qiáng)盛的緯向低空西南氣流攜帶充沛的水汽，穿過(guò)中南半島后以西南低空急流或者通過(guò)減弱的登陸熱帶氣旋“中轉(zhuǎn)”，是這兩類(lèi)暴雨區(qū)的主要水汽供應(yīng)方式；經(jīng)向型環(huán)流背景下的水汽輸送也與這支源于青藏高原南側(cè)的西風(fēng)氣流異常有關(guān)。這可能是華北地區(qū)夏季降水與印度季風(fēng)降水的相關(guān)顯著強(qiáng)于中國(guó)東部其他地區(qū)的主要原因。（3）減弱的登陸熱帶氣旋與西風(fēng)帶系統(tǒng)相互作用造成的極端暴雨事件同樣由經(jīng)向型環(huán)流主導(dǎo)，但是，更充沛的水汽輸送、更強(qiáng)的上升運(yùn)動(dòng)和更深厚的大氣不穩(wěn)定層結(jié)狀態(tài)是它比一般的經(jīng)向型強(qiáng)度更大的直接原因；此外，中高緯度弱冷空氣侵入對(duì)減弱的登陸熱帶氣旋頂部形成持續(xù)性極端暴雨過(guò)程非常重要。（周璇，孫繼松，張琳娜）

3.32 強(qiáng)熱帶風(fēng)暴“碧利斯”（0604）極端降水研究回顧

強(qiáng)熱帶風(fēng)暴“碧利斯”于2006年7月14日在我國(guó)福建省登陸，登陸后一路西行，在福建、浙江、湖南、江西、廣東、廣西多個(gè)省份產(chǎn)生強(qiáng)降水，其陸上維持時(shí)間之長(zhǎng)、影響范圍之廣、降水極端性之強(qiáng)，在歷史上極為罕見(jiàn)。“碧利斯”引發(fā)的降水主要有3個(gè)極值中心，分別對(duì)應(yīng)著降水的3個(gè)階段，其中第2階段降水極端性最為突出，在湖南、江西和廣東交界處發(fā)生了暴雨增幅，造成嚴(yán)重的洪澇災(zāi)害。為了更加全面地認(rèn)識(shí)此次過(guò)程，本文對(duì)“碧利斯”產(chǎn)生極端降水的機(jī)制做了回顧總結(jié)，分別從有利的大尺度形勢(shì)、中尺度系統(tǒng)的影響、地形作用、云微物理過(guò)程以及動(dòng)力因子的診斷分析5個(gè)角度進(jìn)行，最后對(duì)“碧利斯”極端降水區(qū)別于其他極端降水個(gè)例的機(jī)理以及進(jìn)一步可能的研究方向進(jìn)行了討論。（馬蘊(yùn)琦，任福民，馮恬）

3.33 影響中國(guó)雙臺(tái)風(fēng)活動(dòng)氣候特征研究

在雙臺(tái)風(fēng)判定客觀標(biāo)準(zhǔn)的基礎(chǔ)上提出影響中國(guó)雙臺(tái)風(fēng)的定義：在雙臺(tái)風(fēng)活動(dòng)期間，雙臺(tái)風(fēng)中至少有一個(gè)臺(tái)風(fēng)對(duì)中國(guó)大陸或2個(gè)大島——海南島和臺(tái)灣島之一造成降水的雙臺(tái)風(fēng)，稱為影響中國(guó)雙臺(tái)風(fēng)。然后利用臺(tái)站逐日降水資料和臺(tái)風(fēng)最佳路徑資料，采用熱帶氣旋（TC）降水天氣圖客觀識(shí)別法（OSAT）和上述定義，對(duì)1960—2017年的影響中國(guó)雙臺(tái)風(fēng)進(jìn)行研究。結(jié)果表明：1960—2017年影響中國(guó)雙臺(tái)風(fēng)共有255對(duì)，年均4.4對(duì)，占西北太平洋雙臺(tái)風(fēng)總數(shù)的60.6%。影響中國(guó)雙臺(tái)風(fēng)年頻數(shù)表現(xiàn)為顯著下降趨勢(shì)。影響中國(guó)雙臺(tái)風(fēng)的影響期最長(zhǎng)可達(dá)10天，主要集中在1天、2天和3天，分別占18.8%，29.4%和24.3%。在地理分布上，影響中國(guó)雙臺(tái)風(fēng)主要分布在112°～138°E、12°～30°N范圍，頻發(fā)區(qū)在菲律賓北部附近洋面；受雙臺(tái)風(fēng)影響的年均頻次和年均降水均表現(xiàn)為由東南沿海向西北內(nèi)陸階梯遞減，主要影響區(qū)為中國(guó)的臺(tái)灣島、東南沿海和華南沿海，其中臺(tái)灣島受影響最大。進(jìn)一步分析發(fā)現(xiàn)，影響中國(guó)雙臺(tái)風(fēng)影響期內(nèi)出現(xiàn)單站最大日降水當(dāng)日兩TC平均位置主要表現(xiàn)為東—西向分布，西臺(tái)風(fēng)和東臺(tái)風(fēng)正好分別位于東亞夏季風(fēng)的西南風(fēng)水汽通道和副熱帶高壓西南側(cè)東南風(fēng)暖濕氣流中，不僅有利于西臺(tái)風(fēng)從西南風(fēng)水汽通道中獲得水汽，而且有利于東臺(tái)風(fēng)向西臺(tái)風(fēng)的水汽輸送，從而有利于西臺(tái)風(fēng)對(duì)中國(guó)臺(tái)灣島、東南沿海和華南沿海造成的強(qiáng)降水。（謝彥君，任福民，李國(guó)平）

3.34 中國(guó)暴雨的科學(xué)與預(yù)報(bào)：改革開(kāi)放40年研究成果

總結(jié)了改革開(kāi)放以來(lái)中國(guó)學(xué)者在暴雨科學(xué)與預(yù)報(bào)領(lǐng)域取得的重要研究進(jìn)展和主要成果。其中，暴雨機(jī)理研究成果從重要天氣系統(tǒng)、中國(guó)主要區(qū)域的暴雨、臺(tái)風(fēng)暴雨等3個(gè)方面分別進(jìn)行綜述，而暴雨預(yù)報(bào)技術(shù)研發(fā)與應(yīng)用則從中國(guó)數(shù)值天氣預(yù)報(bào)發(fā)展和暴雨預(yù)報(bào)客觀方法兩方面進(jìn)行歸納。（羅亞麗，孫繼松，李英）

4 臺(tái)風(fēng)研究

4 Typhoon research

4.1 A study of the effects of anthropogenic gaseous emissions on the microphysical properties of landfalling typhoon Nida (2016) over China

Using the Weather Research and Forecasting model with chemistry module (WRF-Chem),Typhoon Nida(2016) was simulated to investigate the effects of anthropogenic gaseous emissions on the vortex system.Based on the Multi-resolution Emission Inventory for China (MEIC),three certain experiments were conducted:one with base-level emission intensity (CTRL),one with one-tenth the emission of SO2(SO2_C),and one with one-tenth the emission of NH3(NH3_C).Results show that the simulations reasonably reproduced the typhoon’s track and intensity,which were slightly sensitive to the anthropogenic gaseous emissions.When the typhoon was located over the ocean,a prolonged duration of raindrop growth and more precipitation occurred in CTRL run.The strongest updraft in CTRL is attributed to the maximum latent heating through water vapor condensation.During the landfalling period,larger (smaller) differential reflectivities in the main-core of the vortex were produced in NH3_C (SO2_C) run.Such opposite changes of raindrop size distributions may lead to stronger (weaker) rainfall intensity,and the ice-related microphysical processes and the relative humidity in the lower troposphere were two possible influential factors.Moreover,additional ten-member ensemble results in which white noise perturbations were added to the potential temperature field,indicated that the uncertainty of the thermodynamic field in the current numerical model should not be ignored when exploring the impacts of aerosol on the microphysics and TC precipitation.(Deng Lin,Gao Wenhua,Duan Yihong)

4.2 Analysis of an ensemble of high-resolution WRF simulations for the rapid intensification of super typhoon Rammasun (2014)

Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification (RI) of Typhoon Rammasun.We show that the basic difference stems from subtle differences in initializations of (a) 500?850-hPa environmental winds,and (b) midlevel moisture and ventilation.We then describe how these differences impact the evolving convective organization,storm structure,and the timing of RI.As expected,ascent,diabatic heating and the secondary circulation near the inner-core are much stronger in the member that best forecasts the RI.The evolution of vortex cloudiness from this member is similar to the actual imagery,with the development of an inner cloud band wrapping inwards to form the eyewall.We present evidence that this structure,and hence the enhanced diabatic heating,is related to the tilt and associated dynamics of the developing inner-core in shear.For the most accurate ensemble member:(a) inhibition of ascent and a reduction in convection over the up-shear sector allow moistening of the boundary-layer air,which is transported to the down-shear sector to feed a developing convective asymmetry;(b) with minimal ventilation,undiluted clouds and moisture from the down-shear left quadrant are then wrapped inwards to the up-shear left quadrant to form the eyewall cloud; and (c) this process seems related to a critical down-shear tilt of the vortex from midlevels,and the vertical phase-locking of the circulation over upshear quadrants.For the member that forecasts a much-delayed RI,these processes are inhibited by stronger vertical wind shear,initially resulting in poor vertical coherence of the circulation,lesser moisture and larger ventilation.Our analysis suggests that ensemble prediction is needed to account for the sensitivity of forecasts to a relatively narrow range of environmental wind shear,moisture and vortex inner-structure.(Li Xun,Davidson Noel E,Duan Yihong)

4.3 Autumn tropical cyclones over the western North Pacific during 1949-2016:A statistical study

We used the tropical cyclone (TC) best track data for 1949?2016,provided by the Shanghai Typhoon Institute,China Meteorological Administration (CMA-STI),and a TC size dataset (1980?2016) derived from geostationary satellite infrared images to analyze the statistical characteristics of autumn TCs over the western North Pacific (WNP).We investigated TC genesis frequency,location,track density,intensity,outer size,and landfalling features,as well as their temporal and spatial evolution characteristics.On average,the number of autumn TCs accounted for 42.1% of the annual total,slightly less than that of summer TCs (42.7%).However,TCs classified as strong typhoons or super typhoons were more frequent in autumn than in summer.In most years of the 68-year study period,there was an inverse relationship between the number of autumn TCs and that of summer TCs.The genesis of autumn TCs was concentrated at three centers over the WNP:the first is located near (14°N,115°E) over the northeastern South China Sea and the other two are located in the vast oceanic area east of the Philippines around (14°N,135°E) and (14°N,145°E),respectively.In terms of intensity,the eight strongest TCs during the study period all occurred in autumn.It is revealed that autumn TCs were featured with strong typhoons and super typhoons,with the latter accounting for 28.1% of the total number of autumn TCs.Statistically,the average 34-knot radius (R34) of autumn TCs increased with TC intensity.From 1949 to 2016,164 autumn TCs made landfall in China,with an average annual number of 2.4.Autumn TCs were most likely to make landfall in Guangdong Province,followed by Hainan Province and Taiwan Island.(Yao Xiuping,Zhao Dajun,Li Ying)

4.4 Dependence of superintensity of tropical cyclones on SST in axisymmetric numerical simulations

This study revisits the superintensity of tropical cyclones (TCs),which is defined as the excess maximum surface wind speed normalized by the corresponding theoretical maximum potential intensity (MPI),based on ensemble axisymmetric numerical simulations,with the focus on the dependence of superintensity on the prescribed sea surface temperature (SST) and the initial environmental atmospheric sounding.Results show a robust decrease of superintensity with increasing SST regardless of being in experiments with an SSTindependent initial atmospheric sounding or in those with the SST-dependent initial atmospheric soundings as in nature sorted for the western North Pacific and the North Atlantic.It is found that the increase in either convective activity (and thus diabatic heating) in the TC outer region or theoretical MPI or both with increasing SST could reduce the superintensity.For a given SST-independent initial atmospheric sounding,the strength of convective activity in the TC outer region increases rapidly with increasing SST due to the rapidly increasing air–sea thermodynamic disequilibrium (and thus potential convective instability) with increasing SST.As a result,the decrease of superintensity with increasing SST in the SST-independent sounding experiments is dominated by the increasing convective activity in the TC outer region and is much larger than that in the SST-dependent sounding experiments,and the TC intensity becomes sub-MPI at relatively high SSTs in the former.Due to the marginal increasing tendency of convective activity in the TC outer region,the decrease of superintensity in the latter is dominated by the increase in theoretical MPI with increasing SST.(Li Yuanlong,Wang Yuqing,Lin Yanluan)

4.5 Differences in western North Pacific tropical cyclone activity among three El Ni?o phases

The impacts of El Ni?o on tropical cyclone (TC) activity over the western North Pacific (WNP) are examined through investigation of three types of tropical Pacific warming episodes according to where the maximum sea surface temperature (SST) anomalies occur in the equatorial Pacific:the eastern Pacific El Ni?o(EPE),the central Pacific El Ni?o (CPE),and the mixed El Ni?o (ME).More TCs form over the eastern part of the WNP in all the three El Ni?o types,whereas the frequency of TCs over the western part of the WNP increases as the peak SST anomalies migrate from east to west.Although TCs more frequently recurve at higher latitudes during EPE and CPE,the most frequent region for recurving is much closer to the East Asian continent in CPE years than in EPE years.In contrast,more TCs track westward and threaten the Philippines in ME years.The increased TC genesis over the western part of the WNP can be explained by enhanced lowlevel relative vorticity,reduced vertical wind shear,and increased maximum potential intensity during CPE and increased mid-level moisture during EPE and ME.This increase is further related to updraft anomalies near the date line driven by an anomalous Walker circulation and an anomalous low-level cyclonic circulation over the WNP.The TC track differences among the different El Ni?o types are linked to the east-west shift of the western Pacific subtropical high,possibly caused by an anomalous Hadley circulation from 120° to 130°E that is strongly coupled with the anomalous Walker circulation.(Song Jinjie,Klotzbach Philip J,Duan Yihong)

4.6 Different responses of tropical cyclone tracks over the western North Pacific and North Atlantic to two distinct sea surface temperature warming patterns

How future tropical cyclone (TC) activity could change under global warming is enormously important to society,which has been widely assessed using state-of-the-art climate models.However,these models were predominantly based on the projection of an El Ni?o-like warming pattern.Recent studies suggest that a La Ni?a-like warming pattern is also possible.Here we compare the responses of TC track density (TCTD) over the western North Pacific and North Atlantic to the two distinct global warming patterns.We find that the La Ni?a-like warming pattern reduces western North Pacific TCTD except in the South China Sea and along China coast and increases NA TCTD,while the El Ni?o-like warming pattern generally reduces TCTD in both basins.This is due to different responses of large-scale dynamic/thermodynamic conditions to the distinct zonal sea surface temperature gradients associated with the two warming patterns.These results help better understand potential future change in TC tracks.(Zhao Jiuwei,Zhan Ruifen,Wang Yuqing)

4.7 Effects of terrain and landmass near Fujian Province of China on the structure and propagation of a long-lived rainband in typhoon Longwang (2005):A numerical study

A similar to 14-hour long-lived spiral rainband in Typhoon Longwang (2005) produced catastrophic rainfall in Fujian Province of China on 2 October 2005.In this study,the effects of terrain and landmass near Fujian on the structure and propagation of this rainband are investigated through high-resolution numerical simulations.Results show that although the terrain and landmass near Fujian played a marginal role in the formation of the rainband,both greatly affected the structure and propagation of the rainband.Namely,convection in the upwind sector of the rainband tended to be maintained and locked up near the coastline in the control experiment with both the terrain and landmass near Fujian retained,but shrank more inland with the terrain near Fujian flattened,and further inland with the landmass near Fujian replaced by the virtual ocean.It is found that due to the land-sea surface roughness contrast,the upstream tangential winds from ocean would be substantially decelerated over land and thus induced a local subgradient force onshore near the coastline.The radially inward agradient force and the subsequent surface friction helped maintain the moisture convergence,and thus convection and the cold pool in the upwind sector of the rainband near the coastline.Although the orographic lifting and blocking effects were found to be marginal to the moisture convergence in the rainband,the terrains near Fujian enhanced the deceleration of surface winds,enhancing the effect of landsea surface roughness contrast on low-level moisture convergence and thus the lockup of the upwind sector of the rainband.(Li Yuanlong,Wang Yuqing,Lin Yanluan)

4.8 Factors affecting the weakening rate of tropical cyclones over the western North Pacific

In this study,based on the 6-hour tropical cyclone (TC) best track data and the ERA-Interim reanalysis data,statistical analyses as well as a machine learning approach,XGBoost,are used to identify and quantify factors that affect the overwater weakening rate (WR) of TCs over the western North Pacific (WNP) during 1980?2017.Statistical analyses show that the TC rapid weakening events usually occur when intense TCs cross regions with a sharp decrease in sea surface temperature (DSST) with relatively faster eastward or northward translational speeds,and move into regions with large environmental vertical wind shear (VWS) and dry conditions in the upshear-left quadrant.Results from XGBoost indicate that the relative intensity of TC (TC intensity normalized by its maximum potential intensity),DSST,and VWS are dominant factors determining TC WR,contributing 26.0%,18.3%,and 14.9% to TC WR,and 9,5,and 5 ms?1day?1to the variability of TC WR,respectively.Relative humidity in the upshear-left quadrant of VWS,zonal translational speed,divergence at 200 hPa,and meridional translational speed contribute 12.1%,11.8%,8.8%,and 8.1% to TC WR,respectively,but only contribute 2?3 m s?1day?1to the variability of TC WR individually.These findings suggest that the improved accurate analysis and prediction of the dominant factors may lead to substantial improvements in the prediction of TC WR.(Fei Rong,Xu Jing,Wang Yuqing)

4.9 How much does the upward advection of the supergradient component of boundary layer wind contribute to tropical cyclone intensification and maximum intensity?

Although the development of supergradient winds is well understood,the importance of supergradient winds in tropical cyclone (TC) intensification is still under debate.One view is that the spinup of the eyewall occurs by the upward advection of high tangential momentum associated with supergradient winds from the boundary layer.The other view argues that the upward advection of supergradient winds by eyewall updrafts results in an outward agradient force,leading to the formation of a shallow outflow layer immediately above the inflow boundary layer.As a result,the spinup of tangential wind in the eyewall by the upward advection of supergradient wind from the boundary layer is largely offset by the spindown of tangential wind due to the outflow resulting from the agradient force.In this study,the net contribution by the upward advection of the supergradient wind component from the boundary layer to the intensification rate and final intensity of a TC are quantified through ensemble sensitivity numerical experiments using an axisymmetric TC model.Results show that consistent with the second view above,the positive upward advection of the supergradient wind component from the boundary layer by eyewall updrafts is largely offset by the negative radial advection due to the outflow resulting from the outward agradient force.As a result,the upward advection of the supergradient wind component contributes little (often less than 4%) to the intensification rate and but it contributes 10%?15% to the final intensity of the simulated TC due to the enhanced inner-core air-sea thermodynamic disequilibrium.(Li Yuanlong,Wang Yuqing,Lin Yanluan)

4.10 Improved prediction of landfalling tropical cyclone in China based on assimilation of radar radial winds with new super-observation processing

This work explores the impact of assimilating radial winds from the Chinese coastal Doppler radar on track,intensity,and quantitative precipitation forecasts (QPF) of landfalling tropical cyclones (TCs) in a numerical weather prediction model,focusing mainly on two aspects:(1) developing a new coastal radar super-observation (SO) processing method,namely,an evenly spaced thinning method (ESTM) that is fit for landfalling TCs,and (2) evaluating the performance of the radar radial wind data assimilation in QPFs of landfalling TCs with multiple TC cases.Compared to a previous method of generating SOs (i.e.,the radially spaced thinning method),in which the density of SOs is equal within the radial space of a radar scanning volume,the SOs created by ESTM are almost evenly distributed in the horizontal grids of the model background,resulting in more observations located in the TC inner-core region being involved in SOs.The use of SOs from ESTM leads to more cyclonic wind innovation,and larger analysis increments of height and horizontal wind in the lower level in an ensemble Kalman filter data assimilation experiment with TC Mujigae (2015).Overall,forecasts of a TC’s landfalling position,intensity,and QPF are improved by radar data assimilation for all cases,including Mujigae and the other eight TCs that made landfall on the Chinese mainland in 2017.Specifically,through assimilation,TC landing position error and intensity error are reduced by 33% and 25%,respectively.The mean equitable threat score of extreme rainfall ( 80 mm per 3 hours)forecasts is doubled on average over all cases.(Feng Jianing,Duan Yihong,Wan Qilin)

4.11 Increasing destructive potential of landfalling tropical cyclones over China

This study investigates the trend in destructive potential of landfalling tropical cyclones (TCs) in terms of power dissipation index (PDI) over mainland China in the period of 1980?2018.Results show that both the accumulated PDI and averaged PDI after landfall show significant increasing trends.The increasing trends are found to be contributed primarily by the increasing mean duration of TCs over land and the increasing TC intensity at landfall.Further analyses indicate that the increase in landfalling TC intensity prior to and at landfall,the decrease in intensity weakening rate after landfall,and the northward shift of landfalling TC track density all contribute to the longer duration of TCs after landfall.Moreover,the conducive largescale conditions,such as the increases in coastal sea surface temperature and land surface temperature and soil moisture,the decrease in low-level vertical wind shear,and the increase in upper-level divergence,are all favorable for intense landfalling TCs and their survival after landfall,thus contributing to the increasing destructive potential of landfalling TCs over China.(Liu Lu,Wang Yuqing,Zhan Ruifen)

4.12 Increasing trend in rapid intensification magnitude of tropical cyclones over the western North Pacific

Rapid intensification (RI) refers to a significant increase in tropical cyclone (TC) intensity over a short period of time.A TC can also undergo multiple RI events during its lifetime,and these RI events pose a significant challenge for operational forecasting.The long-term tendency in RI magnitude of TCs over the western North Pacific is investigated in this study.During 1979?2018,a significant increasing trend is found in RI magnitude,which primarily results from the significant increasing number of strong RI events,defined as 24-hour intensity increases of at least 50 kt.Furthermore,there are significantly more (slightly fewer) strong RI occurrences west (east) of 155°E in 1999?2018 than in 1979?1998.Significant increases in strong RI occurrences are located over the region bounded by 10° similar to 20°N,120° similar to 150°E.These changes are likely induced by the warming ocean but appear uncorrelated with changes in the atmospheric environment.By contrast,there are slight decreases in strong RI occurrences over the region bounded by 12.5° similar to 22.5°N,155° similar to 170°E,likely due to the offset between RI-favorable influences of the warming ocean and RI-unfavorable influences of increasing vertical wind shear (VWS).(Song Jinjie,Duan Yihong,Klotzbach Philip J)

4.13 Infrared precipitation estimation using convolutional neural network

Infrared (IR) information is fundamental to global precipitation estimation.Although researchers have developed numerous IR-based retrieval algorithms,there is still plenty of scope for promoting their accuracy.This article develops a novel deep learning-based algorithm entitled infrared precipitation estimation using a convolutional neural network (IPEC).Based on the five-channel IR data,the IPEC first identifies the precipitation occurrence and then estimates the precipitation rates at hourly and 0.04°×0.04° resolutions.The performance of the IPEC is validated using the Stage-IV radar-gauge-combined data and compared to the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS) in three subregions over the continental United States (CONUS).The results show that the five-channel input is more efficient in precipitation estimation than the commonly used one-channel input.The IPEC estimates based on the five-channel input show better statistical performance than the PERSIANN-CCS with 34.9% gain in Pearson’s correlation coefficient (CC),38.0% gain in relative bias (BIAS),and 45.2% gain in mean squared error (MSE) during the testing period from June to August 2014 over the central CONUS.Furthermore,the optimized IPEC model is applied in totally independent periods and regions,and still achieves significantly better performance than the PERSIANN-CCS,indicating that the IPEC has a stronger generalization capability.On the whole,this article proves the effectiveness of the convolutional neural network (CNN) combined with the physical multichannel inputs in IR precipitation retrieval.This endto-end deep learning algorithm shows the potential for serving as an operational technique that can be applied globally and provides a new perspective for the future development of satellite precipitation retrievals.(Wang Cunguang,Xu Jing,Tang Guoqiang)

4.14 Location of the preferred region for tropical cyclogenesis in strong monsoon trough pattern over the western North Pacific

We examined the processes of tropical cyclogenesis in strong monsoon trough pattern over the western North Pacific (WNP) using reanalysis data and numerical experiments.Composite analysis showed that more tropical cyclones are likely to form in the central WNP (130°?165°E) and fewer tropical cyclones appear in the western (120°?130°E) and eastern (165°?180°E) WNP when monsoon trough extends southeastward.Numerical experiments with the same weak artificial vortices inserted into eight different regions of the monsoon trough showed that weak tropical disturbances tend to develop more rapidly in the central WNP near 140°?160°E,particularly near 150°?155°E when the monsoon trough extends eastward,whereas weak tropical disturbances tend to develop more slowly in the eastern WNP near 165°?170°E and do not form in the western WNP near 120°?137.5°E.Our modeling results are consistent with the observational analyses.The failure of tropical cyclogenesis in the western WNP is due to the decrease of the moisture and heat (including the sensible and latent heat) from the underlying ocean,whereas large vertical wind shear and dry conditions in the upper-level of the vortex reduce the gradient of intensification of tropical disturbances in the eastern WNP when the vortices have a similar initial intensity.(Cao Xi,Wu Renguang,Wei Na)

4.15 Occurrence and development of an extreme precipitation event in the Ili Valley,Xinjiang,China and analysis of gravity waves

We used observational data and the results from a high-resolution numerical simulation model to analyze the occurrence and development of an extreme precipitation event in the Ili Valley,Xinjiang,China on 26 June 2015.We analyzed the horizontal wavelength,period,speed,ducting,energy propagation and feedback mechanism of inertial gravity waves.A low-level convergence line was formed in the valley by the northerly and westerly winds as a result of Central Asian vortices and the trumpet-shaped topography of the Ili Valley.There was sufficient water vapor in the valley for the precipitation event to develop.A mesoscale vortex formed and developed on the low-level convergence line and the rainfall was distributed either near the convergence line or the mesoscale vortex.The low-level convergence line and the uplift caused by the terrain triggered convection,and then the convection triggered waves at lower levels.The combination of ascending motion induced by the lower level waves and the mesoscale vortex led to the development of convection,causing the precipitation to intensify.When the convection moved eastward to Gongliu County,it was coupled with the ascending phase of upper level waves,causing both the convection and precipitation to intensify again.We applied spectral analysis methods to verify that the waves were inertial gravity waves.The upper level inertial gravity waves propagated westward at a mean speed of -12 m s?1with periods of 73?179 min and horizontal wavelengths of 50?55 km.The lower level inertial gravity waves propagated eastward at a mean speed of 8 m s?1with periods of 73?200 min and a horizontal wavelength of 85 km.The more (less) favorable waveguide conditions determined whether the gravity waves persisted for a long (short) time and propagated for a longer(shorter) distance.Based on the mesoscale Eliassen-Palm flux theory,the wave energy of inertial gravity waves had an important effect on the maintenance and development of convection and precipitation by affecting wind strength and wind divergence.Feedback was mainly through the meridional and vertical transport of zonal momentum and the meridional transport of heat.(Huang Xin,Zhou Yushu,Liu Lu)

4.16 Recent increase in tropical cyclone weakening rates over the western North Pacific

This study investigates annual mean changes in 24-hour weakening rates of western North Pacific tropical cyclones (TCs) and annual number of rapid weakening (RW) events from 1982 to 2019.There is a significant increasing trend in the mean weakening rate,which correlates with a significant increase in RW number.Because stronger TCs are more likely to experience greater weakening rates and thus undergo RW,the increase in the ratio of intense TCs to all TCs can cause an increase in the weakening rate and RW frequency.Furthermore,the weakening rate and the RW number significantly increase over the region of 25°?35°N,120°?150°E from 1982?2000 to 2001?2019.Over this region,there are stronger sea surface temperature gradients in more recent years,likely contributing to a higher probability of TCs undergoing RW.Other environmental variables do not exhibit significant changes.Our study highlights inhomogeneous Pacific warming that may favor RW of TCs.(Song Jinjie,Klotzbach Philip J,Duan Yihong)

4.17 Relationship between spring tropical cyclone frequency over the western North Pacific and El Ni?o-Southern Oscillation

The number of tropical cyclones (TCs) over the western North Pacific (WNP) during spring (March-May)has a significant inverse correlation with concurrent El Ni?o-Southern Oscillation (ENSO) conditions during the period from 1979 to 2018.This relationship is different from the previously-documented weak relationship between TC frequency and ENSO during the climatologically most active portion of the TC season.In general,TCs seldom occur in El Ni?o years during March-May,whereas they frequently form over the western part of the WNP,particularly to the southeast of the Philippines,in La Ni?a years.This difference can be largely explained by ENSO-driven differences in the genesis potential index as derived from environmental variables.In La Ni?a years,the abnormally moist mid-troposphere,which relates to the strengthened vertical transport of water vapour induced by the enhanced Walker circulation,primarily favours TC development,while increased sea surface temperatures and positive low-level relative vorticity anomalies appear to play a lesser role in impacting TC formation.(Song Jinjie,Klotzbach Philip J,Duan Yihong)

4.18 Reply to “Comments on ‘How much does the upward advection of the supergradient component of boundary layer wind contribute to tropical cyclone intensification and maximum intensity?’”

This is a reply to the comments by Smith et al.(2020,hereafter SGM20) on the work of Li et al.(2020,hereafter LWL20) recently published in the Journal of the Atmospheric Sciences.All the comments and concerns by SGM20 have been well addressed or clarified.We think that most of the comments by SGM20 are not in line with the intention of LWL20 and provide one-sided and thus little scientifically meaningful arguments.Regarding the comment on the adequacy of the methodology adopted in LWL20,we believe that the design of the thought (sensitivity) experiment is adequate to address the scientific issue under debate and helps quantify the contribution by the upward advection of the supergradient component of boundary layer wind to tropical cyclone intensification,which is shown to be very marginal.Note that we are open to accept any alternative,better methods to be used to further address this scientific issue.(Li Yuanlong,Wang Yuqing,Lin Yanluan )

4.19 Revisiting the relationship between tropical cyclone size and intensity over the western North Pacific

This study revisits the nonlinear relationship between tropical cyclone (TC) size and intensity over the western North Pacific (WNP).Using best track data from the Japan Meteorological Agency for 2007?2019,we find that the statistical turning point on a fitted size-intensity curve only exists for TCs with greater lifetime peak intensities (e.g.,typhoons).The track and evolution type are two factors determining the statistical size-intensity relationship.The nonlinear size-intensity relationship is only observed for recurving typhoons reaching their peak intensities and sizes at different times,due to a nonmonotonic size change during the weakening stage.The slight size decrease in the initial weakening stage can be linked to a TC weakeninginduced shrinkage balanced by a baroclinic expansion when recurving typhoons move into higher latitudes.Finally,different evolution types for WNP typhoons can be determined by the ratio of intensity/size to its theoretical maximum.Tropical cyclone (TC) size and intensity are two primary metrics determining the destructive potential of a TC.Previous studies have reported a nonlinear size-intensity relationship,in which TC size substantially increases with intensity to an upper bound and then remains constant or even decreases with increasing intensity.Using best tracks from the Japan Meteorological Agency (JMA) for 2007?2019,we find that this statistical nonlinear size-intensity relationship only occurs for TCs with stronger lifetime maximum intensities (e.g.,typhoons).Whether the size-intensity relationship is linear or nonlinear is jointly determined by the track that the TC takes and its evolution type on a size-intensity diagram.There is a linear size-intensity relationship for recurving typhoons reaching their peak intensities and sizes simultaneously and for typhoons that are relatively straight moving.For other recurving typhoons,the nonlinear size-intensity relationship is primarily caused by a nonlinear size decrease during the weakening stage.We speculate that,as recurving typhoons move poleward,weakening TCs often begin to shrink,while the interaction between the TC and the midlatitude circulation leads to a baroclinic expansion of TC size.Finally,different evolution types for WNP typhoons can be determined by the ratio of intensity/size to its theoretical maximum.(Song Jinjie,Duan Yihong,Klotzbach Philip J)

4.20 Statistical and comparative analysis of tropical cyclone activity over the Arabian Sea and Bay of Bengal (1977-2018)

A statistical comparative analysis of tropical cyclone activity over the Arabian Sea (AS) and Bay of Bengal (BoB) has been conducted using best-track data and wind radii information from 1977 to 2018 issued by the Joint Typhoon Warning Center.Results show that the annual variation in the frequency and duration of tropical cyclones has significantly increased over time over the AS and insignificantly decreased over the BoB.The monthly frequency of tropical cyclones over the AS and the BoB shows a notable bimodal character,with peaks occurring in May,October and November,respectively.The maximum frequency of tropical cyclones occurs in the second peak as a result of the higher moisture content at mid-levels in the autumn.However,the largest proportion of strong cyclones (H1?H5 grades) occurs in the first peak as a result of the higher sea surface temperatures in early summer.Tropical cyclones over the AS break out later during the first peak and activity ends earlier during the second peak,in contrast with those over the BoB.This is related to the onset and drawback times of the southwest monsoon in the two basins.Tropical cyclones over the AS are mainly generated in the eastern basin,whereas in the BoB the genesis locations are meridionally (zonally) distributed in May?June (October?November) as a result of the seasonal movement of the low-level positive vorticity belt.The Arabian Sea is dominated by tropical cyclones that track west and northwest,accounting for about 74.6% of all the tropical cyclones there,whereas the tropical cyclones with a NE track account for only 25.4%.The proportions of the three types of tracks are similar in the BoB,with each accounting for about 33% of the tropical cyclones.The mean intensity and size of tropical cyclones over the AS are stronger and larger,respectively,than those over the BoB and the size of tropical cyclones over the North Indian Ocean in early summer is larger than that in the autumn.The asymmetrical structure of tropical cyclones over the North Indian Ocean is affected by topography and the longest radius of the 34 kt surface wind often lies in the eastern quadrant of the tropical cyclone circulation in both sea areas.(Fan Xiaoting,Li Ying,Lyu Aimin)

4.21 The effect of warm water and its weak negative feedback on the rapid intensification of typhoon Hato (2017)

Typhoon Hato (2017) went through a rapid intensification (RI) process before making landfall in Zhuhai,Guangdong Province,as the observational data shows.Within 24 hours,its minimum sea level pressure deepened by 35 hPa and its maximum sustained wind speed increased by 20m s?1.According to satellite observations,Hato encountered a large area of warm water and two warm core rings before the RI process,and the average sea surface temperature cooling (SSTC) induced by Hato was only around 0.73℃.Air-sea coupled simulations were implemented to investigate the specific impact of the warm water on its RI process.The results showed that the warm water played an important role by facilitating the RI process by around 20%.Sea surface temperature budget analysis showed that the SSTC induced by mixing mechanism was not obvious due to the warm water.Besides,the cold advection hardly caused any SSTC,either.Therefore,the SSTC induced by Hato was much weaker compared with that in general cases.The negative feedback between ocean and Hato was restrained and abundant heat and moisture were sufficiently supplied to Hato.The warm water helped heat flux increase by around 20%,too.Therefore,the warm water influenced the structure and the intensity of Hato.Although there might be other factors that also participated in the RI process,this study focused on air-sea interaction in tropical cyclone forecast and discussed the impact of warm water on the intensity and structure of a tropical cyclone.(Huo Zimo,Duan Yihong,Liu Xin)

4.22 Trends in landfalling tropical cyclone-induced precipitation over China

In this study,trends in landfalling TC-induced precipitation over China during 1980?2017 and the involved possible mechanisms are analyzed.Consistent with previous studies,it is found that the total annual TC precipitation shows a distinct spatial distribution with a significant increasing trend in the southeastern China but a decreasing trend in the southern China.This characteristic is found to be related to the increase in both the annual TC precipitation frequency and the precipitation intensity per TC over the southeastern China but to the decrease in the annual TC precipitation frequency over the southern China.A noticeable northward shift of total landfalling TC-induced annual precipitation has been identified.It is shown that the precipitation induced by strong TCs (STCs) significantly increased in the southern China,whereas that induced by weak TCs (WTCs) increased in the southeastern China,with the latter dominating the northward shift of total landfalling TC-induced precipitation over mainland China.The increasing trend of STC-induced precipitation in the southern China is found to be closely related to sufficient water vapor supply and the increase in average duration and intensity of STCs after landfall.The increasing trend of WTC-induced precipitation in the southeastern China is related to the northward shift of the average landfalling position of WTCs and changes in the environmental conditions that are more favorable for TC maintenance and precipitation.(Liu Lu,Wang Yuqing)

4.23 川藏地區(qū)雷暴大風(fēng)活動(dòng)特征和環(huán)境因子對(duì)比

利用2010—2017年中國(guó)氣象局重要天氣報(bào)、地面觀測(cè)和探空資料以及歐洲中期天氣預(yù)報(bào)中心ERA-Interim再分析資料，對(duì)川藏地區(qū)雷暴大風(fēng)的活動(dòng)特征、環(huán)境因子和環(huán)流形勢(shì)進(jìn)行統(tǒng)計(jì)分析，并對(duì)其中高原（海拔高度不低于1 km）和盆地（海拔高度低于1 km）區(qū)域雷暴大風(fēng)活動(dòng)進(jìn)行對(duì)比。結(jié)果表明：川藏高原區(qū)域雷暴大風(fēng)頻次呈5—6月和9月雙峰型分布，主要發(fā)生在午后；盆地區(qū)域主要發(fā)生在夏季，午后和夜間均較活躍。高原站雷暴大風(fēng)年平均頻次約為2次/站，在雷暴和大風(fēng)中分別約占4.5%和8%。盆地站年平均頻次僅為0.4次/站，雷暴中僅占1.5%，但在大風(fēng)中約占60%。高原站雷暴大風(fēng)的中低層環(huán)境溫度遞減率較大，一般呈上濕下干的逆濕垂直結(jié)構(gòu)；而盆地站雷暴大風(fēng)通常具有上干下濕的垂直結(jié)構(gòu)。分別對(duì)5—6月和9月高原站雷暴大風(fēng)兩個(gè)峰值時(shí)段的環(huán)流形勢(shì)進(jìn)行合成分析，發(fā)現(xiàn)5—6月受高空西風(fēng)槽影響，中層有弱冷平流侵入，高層位于高空急流入口區(qū)右側(cè)，環(huán)境垂直風(fēng)切變較大；而9月受副熱帶高壓邊緣影響，中高層較干，低層暖濕氣流明顯。這些均有利于雷暴大風(fēng)發(fā)生。（王黌，李英，宋麗莉）

4.24 華東登陸熱帶氣旋降水不同分布的對(duì)比分析

利用CMORPH降水資料，將熱帶氣旋（TC）登陸后的降水分為路徑左側(cè)降水（L型）和右側(cè)降水（R型）兩類(lèi)，并針對(duì)登陸華東地區(qū)TC的L型和R型降水的大氣環(huán)流場(chǎng)、環(huán)境水平風(fēng)垂直切變以及臺(tái)風(fēng)環(huán)流內(nèi)的動(dòng)熱力條件進(jìn)行對(duì)比分析，結(jié)果表明：2005ü 2014年間登陸華東地區(qū)的20例TC中包括12例L型和8例R型?？傮w來(lái)看，大氣環(huán)流因子對(duì)于登陸華東TC降水分布起主要作用。L型降水TC高層南亞高壓主要呈緯向帶狀分布，在登陸過(guò)程中路徑左側(cè)維持偏東風(fēng)高空輻散氣流，中層西風(fēng)槽偏東，西太平洋副熱帶高壓（簡(jiǎn)稱副高）偏南，環(huán)境水平風(fēng)垂直切變指向西南。R型降水TC高層南亞高壓斷裂，呈經(jīng)向分布。TC路徑左側(cè)風(fēng)場(chǎng)較均勻，右側(cè)東南風(fēng)高空輻散氣流明顯。副高的位置偏北呈塊狀，同時(shí)環(huán)境水平風(fēng)垂直切變指向東北，有利于路徑右側(cè)降水。臺(tái)風(fēng)環(huán)流內(nèi)，低層冷暖平流輸送以及水汽輻合與降水落區(qū)也有較好對(duì)應(yīng)關(guān)系。L型TC低層暖平流的輸送使TC西南象限低層增暖，大氣穩(wěn)定度降低。同時(shí)水汽輻合區(qū)也主要位于西南象限，有利于TC路徑左側(cè)降水。而R型TC副高位置偏北可將南側(cè)的東南暖濕氣流向臺(tái)風(fēng)環(huán)流更西部輸送，東北象限維持暖平流，有利于路徑右側(cè)降水發(fā)生。（卜松，李英）

4.25 熱帶氣旋過(guò)臺(tái)灣后再次登陸的路徑強(qiáng)度變化統(tǒng)計(jì)分析

登陸臺(tái)灣后再次登陸大陸的熱帶氣旋（TC）由于受復(fù)雜下墊面及中低緯天氣系統(tǒng)的共同影響，過(guò)島后在海峽內(nèi)的路徑、強(qiáng)度及結(jié)構(gòu)變化復(fù)雜，導(dǎo)致登陸大陸的精確化定位、定強(qiáng)及預(yù)報(bào)難度大。分析了1949—2017年二次登陸的81個(gè)熱帶氣旋路徑及強(qiáng)度變化特征，并對(duì)上海臺(tái)風(fēng)所（CMA/STI）、美國(guó)聯(lián)合臺(tái)風(fēng)警報(bào)中心（JTWC）及東京區(qū)域臺(tái)風(fēng)中心（RSMC-Tokyo）的熱帶氣旋最佳路徑數(shù)據(jù)中過(guò)島熱帶氣旋的定位定強(qiáng)進(jìn)行對(duì)比分析。結(jié)果表明：二次登陸大陸熱帶氣旋強(qiáng)度以減弱為主，少數(shù)熱帶氣旋在海峽內(nèi)增強(qiáng)；過(guò)島后熱帶氣旋路徑多數(shù)會(huì)發(fā)生明顯偏折，但3家最佳路徑資料判斷的偏折趨勢(shì)不一致；由于熱帶氣旋過(guò)島時(shí)結(jié)構(gòu)遭到破壞，定位定強(qiáng)難度增大，導(dǎo)致3個(gè)業(yè)務(wù)中心對(duì)其定位定強(qiáng)的差異較大，這種不確定性增大了其路徑和強(qiáng)度監(jiān)測(cè)預(yù)報(bào)的難度。（邢蕊，徐晶，林瀚）

4.26 熱帶氣旋研究和業(yè)務(wù)預(yù)報(bào)進(jìn)展——第九屆世界氣象組織熱帶氣旋國(guó)際研討會(huì)（IWTC-9）綜述

2018年12月3—7日在美國(guó)夏威夷召開(kāi)的第九屆世界氣象組織熱帶氣旋國(guó)際研討會(huì)對(duì)國(guó)際熱帶氣旋研究和預(yù)報(bào)預(yù)警業(yè)務(wù)的近期進(jìn)展進(jìn)行了充分回顧，并對(duì)未來(lái)的發(fā)展方向進(jìn)行了系統(tǒng)研討。過(guò)去4年（2015—2018年），在熱帶波動(dòng)和對(duì)流對(duì)熱帶氣旋生成的影響、復(fù)雜環(huán)境影響熱帶氣旋路徑轉(zhuǎn)向的機(jī)理、對(duì)流和風(fēng)垂直切變對(duì)熱帶氣旋強(qiáng)度變化的作用機(jī)制、雙眼墻形成和替換機(jī)理、熱帶氣旋變性過(guò)程對(duì)環(huán)境條件的響應(yīng)、熱帶氣旋氣候變化特征、熱帶氣旋多平臺(tái)觀測(cè)技術(shù)等諸多方面的研究取得了顯著進(jìn)展。同時(shí)，在熱帶氣旋生成概率預(yù)報(bào)、全球模式中熱帶氣旋強(qiáng)度預(yù)報(bào)改進(jìn)、熱帶氣旋活動(dòng)次季節(jié)業(yè)務(wù)預(yù)測(cè)技術(shù)發(fā)展以及熱帶氣旋預(yù)報(bào)不確定性理論等方面也取得積極進(jìn)展。在綜述此次會(huì)議的相關(guān)議題后，簡(jiǎn)要討論中國(guó)熱帶氣旋研究和業(yè)務(wù)發(fā)展方向。（端義宏，方娟，程正泉）

5 雷電研究

5 Lightning research

5.1 雷電野外科學(xué)試驗(yàn)

雷電團(tuán)隊(duì)克服新冠疫情的不利影響，于2020年6月中旬開(kāi)始組織人工觸發(fā)閃電試驗(yàn)。雖然受試驗(yàn)期雷暴系統(tǒng)明顯偏少的影響，未能成功觸發(fā)閃電，但團(tuán)隊(duì)進(jìn)一步強(qiáng)化了野外試驗(yàn)?zāi)芰?，包括：發(fā)展實(shí)現(xiàn)了低頻電場(chǎng)探測(cè)陣列（LFEDA）的實(shí)時(shí)定位技術(shù)，擴(kuò)充了廣東地區(qū)閃電成像陣列（LMA）站網(wǎng)，設(shè)計(jì)了未來(lái)5年人工引雷試驗(yàn)場(chǎng)的建設(shè)規(guī)劃和目標(biāo)。另一方面，團(tuán)隊(duì)在3—10月組織廣州高建筑物雷電觀測(cè)試驗(yàn)，在廣州粵大站補(bǔ)充了同步電磁場(chǎng)探測(cè)設(shè)備，在廣東省氣象局主站增設(shè)了雷電光譜觀測(cè)項(xiàng)目，獲得超過(guò)150例高建筑物觀測(cè)個(gè)例，并通過(guò)對(duì)歷史資料的整理，建立了包含有340余例高建筑物雷電的光學(xué)和電磁場(chǎng)同步綜合觀測(cè)數(shù)據(jù)集。（呂偉濤，張陽(yáng)，鄭棟，馬穎，樊艷峰）

5.2 雷電探測(cè)技術(shù)研發(fā)

研制了新一代精細(xì)化低頻全閃定位系統(tǒng)，形成了低功耗、一體化的閃電低頻信號(hào)探測(cè)子站，通過(guò)云平臺(tái)實(shí)現(xiàn)了全閃實(shí)時(shí)定位，定位數(shù)據(jù)豐富度相比業(yè)務(wù)系統(tǒng)有明顯提升。提出了基于雙向雙面鏡像延拓的集合經(jīng)驗(yàn)?zāi)B(tài)分解算法，實(shí)現(xiàn)了優(yōu)異的降噪性能，對(duì)弱信號(hào)的提取準(zhǔn)確度大幅提升，進(jìn)一步提升閃電定位系統(tǒng)性能。通過(guò)與TRMM/LIS閃電數(shù)據(jù)和WWLLN閃電數(shù)據(jù)的對(duì)比，揭示了FY-4A閃電成像儀（LMI）的閃電時(shí)空分布特征和光學(xué)輻射特性，評(píng)估了LMI的探測(cè)性能?？陀^評(píng)估了美國(guó)國(guó)家閃電探測(cè)網(wǎng)（NLDN）對(duì)高塔閃電的定位誤差，發(fā)現(xiàn)沿海地區(qū)系統(tǒng)偏差較內(nèi)陸大，定位結(jié)果整體偏向海洋一側(cè)。（張陽(yáng)，范祥鵬，劉恒毅）

5.3 雷電物理研究

發(fā)現(xiàn)當(dāng)建筑物高度確定，閃電回?fù)舴逯惦娏髟綇?qiáng)，對(duì)應(yīng)的閃擊距離越大，并探討了閃擊距離與上行連接先導(dǎo)起始時(shí)間的相關(guān)性。改進(jìn)閃電先導(dǎo)隨機(jī)模式，模擬研究指出600 m高的建筑物被雷擊的概率為100 m高的建筑物的3.6倍，高建筑物會(huì)使附近擊中地面的閃電的接地點(diǎn)向建筑物方向偏移。發(fā)現(xiàn)觸發(fā)閃電起始過(guò)程存在單次和多次兩種類(lèi)型，揭示了始發(fā)自持發(fā)展開(kāi)始的兩個(gè)關(guān)鍵物理過(guò)程——先驅(qū)放電簇和始發(fā)先驅(qū)放電簇的異同。提出長(zhǎng)時(shí)序電流由擊穿電流、電暈電流和準(zhǔn)穩(wěn)恒電流構(gòu)成的3組分模型，建立了基于PSO算法的長(zhǎng)時(shí)序觸發(fā)閃電回?fù)綦娏鞯姆植绞絽?shù)化重構(gòu)方法，實(shí)現(xiàn)了在400 μs的長(zhǎng)時(shí)間尺度上重構(gòu)回?fù)綦娏?，并給出各個(gè)分量的參數(shù)特征。首次解析出觸發(fā)閃電信號(hào)平靜期內(nèi)的磁場(chǎng)脈沖，明確了“梯級(jí)”傳播形式是上行正先導(dǎo)的一般發(fā)展特征；發(fā)現(xiàn)了甚高頻輻射脈沖簇出現(xiàn)在單個(gè)磁場(chǎng)脈沖產(chǎn)生的初始階段，揭示出不同頻段的輻射信號(hào)對(duì)應(yīng)了不同的放電過(guò)程。研究了上行負(fù)先導(dǎo)發(fā)展過(guò)程與母體雷暴電荷結(jié)構(gòu)的關(guān)系，估算了上行負(fù)先導(dǎo)的放電參數(shù)，明確了電荷結(jié)構(gòu)以及初始云內(nèi)過(guò)程對(duì)上行負(fù)先導(dǎo)始發(fā)的重要作用，提出了一種上行負(fù)先導(dǎo)的始發(fā)機(jī)理模型。（呂偉濤，樊艷峰，武斌）

5.4 雷暴電學(xué)研究

建立了云分檔電模型并改進(jìn)了融化起電物理過(guò)程的參數(shù)化方法，發(fā)現(xiàn)層云區(qū)融化層經(jīng)常觀測(cè)到的正電荷區(qū)是冰相粒子的非感應(yīng)融化起電產(chǎn)生的，同時(shí)層云區(qū)電荷主要源于對(duì)流核區(qū)的輸送。明確了中尺度對(duì)流系統(tǒng)層云區(qū)內(nèi)閃電的主要激發(fā)和傳播區(qū)域特征及其對(duì)應(yīng)的垂直反射率結(jié)構(gòu)，揭示了層云區(qū)閃電發(fā)生區(qū)域與回波亮帶區(qū)域之間特殊且密切的空間關(guān)系。利用WRFDA-3DVAR同化系統(tǒng)，通過(guò)調(diào)整模式相對(duì)濕度的方法，同化閃電資料，并利用臺(tái)風(fēng)進(jìn)行模擬檢驗(yàn)，發(fā)現(xiàn)在臺(tái)風(fēng)快速增強(qiáng)階段前期，同化眼壁區(qū)域閃電具有最好的預(yù)報(bào)效果。在暖云降水主導(dǎo)的暴雨過(guò)程中，發(fā)現(xiàn)主要閃電活動(dòng)偏離對(duì)流和強(qiáng)降水核心區(qū)以及閃電位置主要對(duì)應(yīng)干雪粒子的現(xiàn)象，建立了概念模型，從弱對(duì)流系統(tǒng)中電荷產(chǎn)生速率與電荷向外輸送速率的對(duì)比關(guān)系上對(duì)發(fā)現(xiàn)進(jìn)行了解釋。（鄭棟，張文娟，王飛）

5.5 雷電預(yù)警預(yù)報(bào)技術(shù)研發(fā)與應(yīng)用

構(gòu)建了融合WRF模式產(chǎn)品和閃電觀測(cè)數(shù)據(jù)的ADSNet和LightNet兩種雷電短時(shí)預(yù)報(bào)AI模型，設(shè)計(jì)并初步開(kāi)發(fā)完成了雷電短時(shí)預(yù)報(bào)系統(tǒng)，通過(guò)對(duì)AI模型的調(diào)用，給出未來(lái)0～12 h內(nèi)逐小時(shí)閃電活動(dòng)落區(qū)預(yù)報(bào)，并實(shí)現(xiàn)短時(shí)預(yù)報(bào)產(chǎn)品的自動(dòng)分析、生成、存儲(chǔ)、傳輸及顯示。經(jīng)過(guò)對(duì)比評(píng)估，該系統(tǒng)相比與單獨(dú)使用WRF_Elec模式，在4 km×4 km網(wǎng)格分辨率下，6 h閃電累積預(yù)報(bào)TS評(píng)分提高約3倍。（姚雯，孟青，徐良韜）

5.6 An improved hydrometeor identification method for X-band dual-polarization radar and its application for one summer hailstorm over northern China

Currently,the high-resolution severe storm observations obtained by vehicle-mounted mobile X-band dual-polarization radar (X-pol) are widely used in severe storm structure and dynamics studies; however,the identification of hailstones based on X-pol is still rare,leading to the limited application of X-pol in identifying hydrometeors in the microphysical processes of severe storms.Based on previous works,this study constructs an improved X-pol hydrometeor identification (HID) method for hailstorms; the hydrometeor categories include a rain-hail mixtures (RH) category indicating hailstones are melting or experiencing wet growth,and the correlation coefficient between horizontally and vertically polarized echoes is used to locate the local mixed phase region in storms to avoid misclassifications of hydrometeors resulted by environmental temperature in this local mixed phase region.The improved HID method can see liquid water information above the melting layer; it provides a possibility to observe the microphysical process of hailstones wet growth above the melting layer.Furthermore,this improved HID method was utilized to study the high spatiotemporal resolution data collected by the Institute of Atmospheric Physics of Chinese Academy of Sciences (IAP) X-pol for one summer hailstorm over the northern China.The results indicate that the identified RH is consistent with the surface hail record of National Weather Observatory of the China Meteorological Administration (CMA),the specific differential phase (K-DP) column is more sensitive than the differential reflectivity (ZDR) column for indicating the updraft zone movement,and we considered that the relative position between the key area of hail (KAH,where above theZDRcolumn,ZDRsimilar to -2 to 0 dBz,ZHsimilar to≥50 dBz) and the updraft zone (indicated by theZDR,K-DP column) will determine the evolution of hail.Furthermore,high-density graupels (HDGs) in the upper layer of the KAH may be the source of RH embryos,and these HDGs collect liquid droplets from the liquid water-rich (LWR) area located behind the KAH to form a large number of RH in the lower layer of the KAH.These characteristics are important for hailstone forecasting and warnings.(Zhao Chuanhong,Zhang Yijun,Zheng Dong)

5.7 Analysis of location errors of the US National Lightning Detection Network using lightning strikes to towers

The location accuracy of the US National Lightning Detection Network (NLDN) has been evaluated using as ground-truth rocket-triggered lightning data or video records but only at a few specific locations.In this study,by using the NLDN data for the events attributable to lightning strikes to towers,the location error of the NLDN across the entire contiguous United States was evaluated for the first time.We found that,on average,the NLDN median location error reduced from 198 to 84 m after the 2013 NLDN upgrade.The location error at the periphery of the network was significantly larger than that in its interior.In the coastal regions,there was directional location bias toward the water.Simulation results suggest that the bias is related to the lengthening of field waveform front due to electromagnetic wave propagation over lossy ground coupled with the asymmetrical sensor configuration relative to the strike point (lack of offshore sensors).(Zhu Yanan,Lyu Weitao,Cramer John)

5.8 Application of ensemble empirical mode decomposition in low-frequency lightning electric field signal analysis and lightning location

The application of empirical mode decomposition (EMD) in the analysis and processing of lightning electric field waveforms acquired by the low-frequency e-field detection array (LFEDA) in China has significantly improved the capabilities of the low-frequency/very-low-frequency (LF/VLF) time-of-arrival technique for studying the lightning discharge processes.However,the inherent mode mixing and the endpoint effect of EMD lead to certain problems,such as an inadequate noise reduction capability,the incorrect matching of multistation waveforms,and the inaccurate extraction of pulse information,which limit the further development of the LFEDA’s positioning ability.To solve these problems,the advanced ensemble EMD(EEMD) technique is introduced into the analysis of LF/VLF lightning measurements,and a double-sided bidirectional mirror (DBM) extension method is proposed to overcome the endpoint effect of EMD.EEMD can effectively suppress mode mixing,and the DBM extension method proposed in this article can effectively suppress the endpoint effect,thus greatly improving the accuracy of a simulated signal after a 25–500-kHz bandpass filter.The resulting DBM_EEMD algorithm can be used in the LFEDA system to process and analyze the detected electric field signals to improve the system’s lightning location capabilities,especially in terms of accurate extraction and location of weak signals from lightning discharges.In this article,a 3-D image of artificially triggered lightning obtained from an LF/VLF location system is reported for the first time,and methods for further improving the location capabilities of the LF/VLF lightning detection systems are discussed.(Fan Xiangpeng,Zhang Yijun,Paul R.Krehbiel)

5.9 Application of lightning data assimilation to numerical forecast of super typhoon Haiyan (2013)

Previous observations from World Wide Lightning Location Network (WWLLN) and satellites have shown that typhoon-related lightning data have a potential to improve the forecast of typhoon intensity.The current study was aimed at investigating whether assimilating TC lightning data in numerical models can play such a role.For the case of Super Typhoon Haiyan in 2013,the lightning data assimilation (LDA) was realized in the Weather Research and Forecasting (WRF) model,and the impact of LDA on numerical prediction of Haiyan’s intensity was evaluated.Lightning data from WWLLN were used to adjust the model’s relative humidity (RH) based on the method developed by Dixon et al.(2016).The adjusted RH was output as a pseudo sounding observation,which was then assimilated into the WRF system by using the three-dimensional variational (3DVAR) method in the cycling mode at 1-hour intervals.Sensitivity experiments showed that,for Super Typhoon Haiyan (2013),which was characterized by a high proportion of the inner-core (within 100 km from the typhoon center) lightning,assimilation of the inner-core lightning data significantly improved its intensity forecast,while assimilation of the lightning data in the rainbands (100?500 km from the typhoon center) led to no obvious improvement.The improvement became more evident with the increase in LDA cycles,and at least three or four LDA cycles were needed to achieve obvious intensity forecast improvement.Overall,the improvement in the intensity forecast by assimilation of the inner-core lightning data could be maintained for about 48 hours.However,it should be noted that the LDA method in this study may have a negative effect when the simulated typhoon is stronger than the observed,since the LDA method cannot suppress the spurious convection.(Zhang Rong,Zhang Wenjuan,Zhang Yijun)

5.10 Characterizing radio frequency magnetic radiation of initial upward leader stepping in triggered lightning with interferometric lightning mapping

In summer of 2019,the bandwidth of magnetic field sensor with relatively high sensitivity was extended to 1.2 MHz during the triggered lightning experiment of the Field Experiment Base on Lightning Sciences,the China Meteorological Administration (CMA-FEBLS) in Conghua,Guangdong Province.The measurements with the new magnetic fields reveal the presence of microsecond-scale magnetic pulses during the entire duration of upward positive leader (UPL),including the quiet stage when only few signals can be discerned in previous observations,which indicates that the UPL generally propagates in a stepwise manner during the initial stage of triggered lightning.Synchronous mapping observations from the broadband VHF interferometer shows that the VHF radiation corresponds to the onset of individual magnetic pulses,indicating that the VHF signals are radiated by the breakdown processes of individual stepping,and these breakdown events launch the meter-scale current pulses as the radiation source of individual magnetic pulses.(Fan Yanfeng,Lu Gaopeng,Zhang Yang)

5.11 Evolution characteristics during initial stage of triggered lightning based on directly measured current

The initiation of a leader is an important lightning discharge process,but how an upward positive leader(UPL) initiates is still not fully understood.The evolution characteristics of a UPL during its initial stage were systematically studied based on directly measured current data of 14 triggered lightning events in 2019.It was found that the initial stage of triggered lightning can be divided into two types:a single initial process form and a multiple initial process form,with percentages of 64.29% and 35.71%,respectively.Compared with the former,the latter usually lasts longer,and the corresponding lightning is often triggered under a lower groundlevel quasi-static electric field.In each initial process,precursor current pulses (PCPs),PCP clusters and initial precursor current pulses (IPCPs) are typical current waveforms,and the pulse durations and transferred charges of PCPs increase linearly with time.However,in the multiple initial process form,the pulse durations and transferred charges of PCPs will reduce significantly after each previous initial process and then continue to increase in the following initial process.In each initial process,when the pulse duration and transferred charge of a PCP increase to a certain extent,PCP clusters and IPCPs begin to appear.For the emergence of PCP clusters,the average values of the threshold are 3.48 μs and 19.53 μC,respectively.For the occurrence of IPCPs,the corresponding values are 4.69 μs and 27.23 μC,respectively.The average values of pulse durations and transferred charges of IPCPs are larger than those of PCP clusters.Compared with adjacent PCP clusters,IPCPs contain more pulses,with a critical range of 6?7.IPCPs also last longer,and have a critical range of 138?198 μs.(Chen Zefang,Zhang Yang,Fan Yanfeng)

5.12 FY-4A LMI observed lightning activity in super typhoon Mangkhut (2018) in comparison with WWLLN data

Using lightning observations from the Fengyun-4A Lightning Mapping Imager (FY-4A LMI),besttrack data from the Shanghai Typhoon Institute,bright temperature (TBB) data from Himawari-8 satellite,and composite reflectivity (CR) data from the South China radar network,we investigate the spatiotemporal distribution of lightning activity and convective evolution during the landfall of Super Typhoon Mangkhut,the strongest landing typhoon in China in 2018.Three stages of active total lightning are observed,and differences of lightning characteristics between the inner core and the outer rainbands are present.The onset of innercore lightning outbreak is about 4 hours ahead of the maximum intensity of the storm,providing indicative information on the change of typhoon intensity.Lightning rates in the outer rainbands increase rapidly 12 hours before the landfall,and lightning activity is mainly confined in the outer rainbands after the landfall.A good correlation in hourly variation is shown between lightning rates from the LMI and TBBs from the satellite.The averaged TBB within the inner core reaches its minimum (?80 ℃) when the inner-core lightning outbreak occurs,indicating the occurrence and enhancement of deep convection there.Lightning locations observed by the LMI has a good spatial correspondence with regions of low TBBs and high CRs,revealing the monitoring capability of the LMI to lightning activity and deep convection in landing typhoons.Comparisons between the World Wide Lightning Location Network (WWLLN) and the LMI reveal that the spatial distribution,temporal evolution,and radial pattern of lightning activity in Mangkhut observed by the two systems are consistent.Furthermore,due to the detection capability of total lightning,the LMI has advantages in revealing the higher ratio of intra-cloud lightning within the inner core in typhoon.The continuous and real-time observation of FY-4A LMI provides an unprecedented platform for monitoring total lightning and deep convection in landing typhoons in China,which will promote the generation of new research and applications in the future.(Zhang Wenjuan,Hui Wen,Lyu Weitao)

5.13 How does the melting impact charge separation in squall line? A bin microphysics simulation study

A new electrification and discharge model was developed based on a two-moment bin microphysical scheme coupled with the Weather Research and Forecasting (WRF) model.Based on the electrical model,the role of the noninductive charging mechanism associated with the melting processes of both snow and graupel(rimed particles) in the charge structure formation in the stratiform region of an organized convective system was examined.Our results show that the snow melting charging mechanism forms a substantial positive charge layer near and below 0 ℃ isotherm in the stratiform region of a squall line.It was also found that the graupel melting charging process mostly enhanced the positive charge layer in the convective region with little impact in the stratiform region.The in situ charging of noninductive collisional and melting processes and the charge transportation from the convective core all contribute to the charge structure formation in the stratiform region of a squall line.(Xu Liangtao,Xue Lulin,Geresdi Istvan)

5.14 Leader charges,currents,ambient electric fields,and space charges along downward positive leader paths retrieved from ground measurements in metropolis

An approach for retrieving the leader channel charge density,leader current,ambient electric field,and space charge along a leader channel path from ground observations with a complicated ground condition was presented.With this approach,properties of two downward positive leaders (DPL1 and DPL2) struck at highrise buildings were studied based on electric and optical measurements made on the roof of a 100 m high building in Guangzhou,China.It shows that the leader-produced electric field on the roof of the 100 m high building was about 4 times of that on flat ground.The 2-D speed for both leaders showed a general increasing trend as the leader going down,in the range of 1.8×105to 32.3×105and 1.7×105to 46.9×105m s?1,respectively.The channel line charge density for both leaders showed firstly a sharp increasing trend and then a decreasing trend as the leader going down,in the range of 0.4 to 8.6 and 0.4 to 15.2 mC m?1,respectively.The current of the two leaders varied in the range of 0.7 to 5.4 and 0.7 to 4.6 kA,respectively.The ambient electric field(downward is positive) for both leaders showed an alternating polarity along the leader path,in the range of ?120 to +176 and ?250 to +180 kV m?1,respectively.The space charge for both leaders showed also an alternating polarity along the leader path,in the range of ?12.3 to +4.2 and ?13.9 to +7.8 nC m?3,respectively,which may reflect the in-cloud electric structure and the corona charge distribution between the cloud and ground.(Gao Yan,Chen Mingli,Lyu Weitao)

5.15 Lightning activity and its associations with cloud structures in a rainstorm dominated by warm precipitation

Lightning activity and its associations with cloud structures during a rainstorm dominated by warm cloud precipitation were studied in Guangdong,China on May 7,2017,using three-dimensional lightning location and polarimetric radar data.The overall convection and lightning activities of the rainstorm were weak.The rainstorm generally showed a typical tripolar charge structure with the main negative charge core located between the ?15 ℃ and ?8 ℃ environmental isotherms in the first 4 hours.The height of the charge regions clearly decreased after this period,with the main negative charge core being below the ?8 ℃ isotherm.Lightning discharges were more concentrated in areas featuring relatively weak convection and relatively low precipitation intensity.Most of the locations with lightning discharges were dominated by dry aggregated snow and weak updrafts and downdrafts.This investigation demonstrated that the lightning discharges were spatially separated from the area of origin of charging in this rainstorm.It is proposed that,with weak convection in the rainstorm,the charging rate was lower than the speed of charge transfer from the area of origin,causing a relatively low charge density and a low frequency of lightning in the area of origin of charging.Meanwhile,the aggregation of small charged particles in regions away from the area of origin of charging might be conducive to the formation of a relatively high charge density and therefore relatively frequent lightning flashes.This situation is different from a typical thunderstorm with strong convection.(Liu Ze,Zheng Dong,Guo Fengxia)

5.16 Lightning and deep convective activities over the Tibetan Plateau

Lightning characteristics and its relationship with convection over the plateau are of great interest to researchers.High-density lightning is located near Naqu and the northeastern Qinghai.About 95% of the flashes occur during May to September.The ratio of intra-cloud lightning to cloud-to-ground (CG) lightning in the midsouthern plateau is approximately four.The lightning over the plateau is typically of shorter duration,smaller horizontal extent,and weaker optical radiance than that over the inland eastern China.The deep convective systems (DCSs,with 20-dBz echo tops exceeding 14 km) over the Tibet Plateau are of smaller horizontal scale and weaker convective intensity.The DCSs around the Naqu area have a mean area of about 120 km2,with mean 20- and 40-dBz echo tops of approximately 15.8 and 9.9 km,respectively.The corresponding values for intense DCSs (IDCSs,with 40-dBz echo tops exceeding 10 km) are approximately 196 km2,16.5 km,and 11.3 km,respectively.The average area and height of precipitation clouds with lightning are an order of magnitude larger and 2–4 km higher than those without lightning,respectively.On average,the thunderstorms over the eastern plateau tend to have larger horizontal extent and those over the south-bywest and southeastern parts of the plateau tend to a have higher top.The plateau thunderstorm tends to have a larger-than-usual lower positive charge center (LLPCC),which is suggested to be associated with the weak convection and low freezing level of the plateau.(Zheng Dong,Zhang Yijun,Zhang Yang)

5.17 Parametric reconstruction method for the long time-series return-stroke current of triggered lightning based on the particle swarm optimization algorithm

The lightning research group of the Chinese Academy of Meteorological Sciences has carried out observations and experiments with artificially triggered lightning for more than ten years,and it accumulated thousands of examples of channel base current data on the return stroke of artificially triggered lightning prior to 2020.Based on the current data,this paper explores ways of improving the constructed function of a long time-series (400 μs) return stroke and the parametric reconstruction of the current waveform.The long timeseries current can be divided into three components:the breakdown pulse current,corona current and quasiuniform current.The corona current and quasi-uniform current are constructed by a Heidler function,while the breakdown pulse current is determined by the waveform characteristics of the current peak,which can be divided into the Heidler type and high-order exponential type.According to the three-component model of the return-stroke current,a two-step parametric reconstruction method for the long time-series lightning returnstroke current based on the particle swarm optimization (PSO) algorithm is proposed.In this paper,the results of the parameterized reconstruction of 14 return strokes are given,and the results of the multidimensional error analysis of 13 long time-series return strokes are given to illustrate the accuracy of the improved parameterized model of the return-stroke current and the effectiveness of the two-step reconstruction method based on the PSO algorithm.(Fan Xiangpeng,Yao Wen,Zhang Yang)

5.18 Preliminary observations from the China Fengyun-4A lightning mapping imager and its optical radiation characteristics

The Fengyun-4A (FY-4A) Lightning Mapping Imager (LMI) is the first satellite-borne lightning imager developed in China,which can detect lightning over China and its neighboring regions based on a geostationary satellite platform.In this study,the spatial distribution and temporal variation characteristics of lightning activity over China and its neighboring regions were analyzed in detail based on 2018 LMI observations.The observation characteristics of the LMI were revealed through a comparison with the Tropical Rainfall Measuring Mission (TRMM)?Lightning Imaging Sensor (LIS) and World Wide Lightning Location Network (WWLLN) observations.Moreover,the optical radiation characteristics of lightning signals detected by the LMI were examined.Factors that may affect LMI detection were discussed by analyzing the differences in optical radiation characteristics between LMI and LIS flashes.The results are as follows.Spatially,the flash density distribution pattern detected by the LMI was similar to those detected by the LIS and WWLLN.Highflash density regions were mainly concentrated over the southeastern China and northeastern India.Temporally,LMI flashes exhibited notable seasonal and diurnal variation characteristics.The LMI detected a concentrated lightning outbreak over the northeastern India in the premonsoon season and over the southeastern China in monsoon season,which was consistent with LIS and WWLLN observations.LMI-observed diurnal peak flash rates occurred in the afternoon over most of the regions.There was a “stepwise” decrease in the LMI-observed optical radiance,footprint size,duration,and number of groups per flash,from the ocean to the coastal regions to the inland regions.LMI flashes exhibited higher optical radiance but lasted for shorter durations than LIS flashes.LMI observations are not only related to instrument performance but are also closely linked to onboard and ground data processing.In future,targeted improvements can be made to the data processing algorithm for the LMI to further enhance its detection capability.(Hui Wen,Zhang Wenjuan,Lyu Weitao)

5.19 Quantification of precipitation using polarimetric radar measurements during several typhoon events in the southern China

Accurate quantitative precipitation estimation (QPE) during typhoon events is critical for flood warning and emergency management.Dual-polarization radar has proven to have better performance for QPE,compared to traditional single-polarization radar.However,polarimetric radar applications have not been extensively investigated in China,especially during extreme events such as typhoons,since the operational dual-polarization system upgrade only happened recently.This paper extends a polarimetric radar rainfall system for local applications during typhoons in the southern China and conducts comprehensive studies about QPE and precipitation microphysics.Observations from S-band dual-polarization radar in Guangdong Province during three typhoon events in 2017 are examined to demonstrate the enhanced radar rainfall performance.The microphysical properties of hydrometeors during typhoon events are analyzed through raindrop size distribution (DSD) data and polarimetric radar measurements.The stratiform precipitation in typhoons presents a lower mean raindrop diameter and lower raindrop concentration than those of the convection precipitation.The rainfall estimates from the adapted radar rainfall algorithm agree well with rainfall measurements from rain gauges.Using the rain gauge data as references,the maximum normalized mean bias (NMB) of the adapted radar rainfall algorithm is 20.27%; the normalized standard error (NSE) is less than 40%; and the Pearson’s correlation coefficient (CC) is higher than 0.92.For the three typhoon events combined,the NSE and NMB are 36.66% and ?15.78%,respectively.Compared with several conventional radar rainfall algorithms,the adapted algorithm based on local rainfall microphysics has the best performance in the southern China.(Xia Qiulei,Zhang Wenjuan,Chen Haonan)

5.20 Quantifying the contribution of tropical cyclones to lightning activity over the Northwest Pacific

This study quantifies the impacts of tropical cyclones (TCs) to the geographical and seasonal lightning activity over the Northwest Pacific (5°?35°N,100°?160°E),and examines the connection between the occurrence of TC lightning and El Ni?o-Southern Oscillation (ENSO).Lightning data from the World Wide Lightning Location Network (WWLLN) and best-track data from the China Meteorological Administration are used to investigate 263 TCs for TC seasons (June?November) in the years 2005?2017.Results show that,on average,TCs account for about 4.9% of all lightning in the domain.The highest contributions occur in the northern South China Sea and the ocean northeast of the Philippines.The monthly TC contribution varies from 2.6% to 6.1% with the greatest in July and the lowest in June.The peak location of the lightning center contributed by TCs are observed a poleward shift from early summer (June?July) to late summer (August?September),and an equatorial shift from late summer to autumn (October?November).In terms of TC intensity,tropical storm strength TCs are the dominant lightning contributor (2.0%) over the Northwest Pacific.A greater likelihood of lightning activity in tropical storms than in typhoons is observed during the landfall,especially within the inner core region.Super typhoons produce lightning in more eastward longitude and more equatorward latitude than weaker strength TCs.The relationship between TC lightning and ENSO reveals that TCs contribute greater lightning during La Ni?a periods (5.0%) than El Ni?o periods (3.2%) over the Northwest Pacific.In El Ni?o years,super typhoons contribute the greatest lightning amounts (1.8%),while in La Ni?a years tropical storms contribute the greatest (2.2%).Infrared satellite observations indicate that the high contribution of lightning in tropical storms is due to the large occurrence of very deep convection in these storms during their landfall.(Zhang Wenjuan,Zhang Yijun,Zheng Dong)

5.21 Simulation of cloud-to-ground lightning strikes to structures based on an improved stochastic lightning model

An improved stochastic method for computer simulation of lightning leaders is developed based on the results from optical observation data.The development and attachment process of downward negative cloudto-ground lightning in the near-ground area is simulated.The distribution of lightning strike points influenced by tall structures is statistically analyzed.The results show that when downward negative leaders initiate at 1500 m height over a structure,the relative strike frequency for the structure increases at a decreasing rate as the structure height increases.The strike frequency for a 600-m tall structure is approximately 3.6 times that for a 100-m tall structure.Additionally,the structure may attract some lightning to hit itself and shift nearby ground strike points toward the structure.For taller structures,the deviation effect is more apparent.It is stipulated in this study that if the ground strike density in the vicinity of the structure is no more than 5% of the average density,then the structure has a sufficient protective effect on this area.The data indicate that there is a positive correlation between the protection distance and the height of the structure.The protection distances of structures of 100?600 m in height are 200 m,280 m,350 m,400 m,450 m,and 480 m approximatively,which show a declining rate of increase.(Jiang Ruijiao,Lyu Weitao,Wu Bin)

5.22 Vertical reflectivity structures near lightning flashes in the stratiform regions of mesoscale convective systems

Using an S-band Doppler radar and a very high frequency (VHF) radiation source location system,254 lightning flashes occurring in stratiform regions (stratiform lightning flashes) of 14 mesoscale convective systems (MCSs) in Chongqing,China,were observed and used to analyze the structure of vertical reflectivity in the area around the lightning channel.In most stratiform lightning flashes,the vertical reflectivity structures can be grouped into three general categories:single-layer,double-layer,and triple-layer.The single-layer structure flashes are the most numerous (65.0%),followed by the double-layer (26.8%) and triple-layer(1.2%) flashes.The regions with the single-layer structure and the double-layer structure are inferred to have mesoscale updrafts of different intensity in the middle of stratiform region.Around 62.3% of the singlelayer structure flashes initiate within 0?4 km above the vertical reflectivity core,and the main initiation range of these flashes widens with increasing value of the vertical reflectivity core.Around 49.2% and 12.7% of the double-layer structure flashes initiate within 3?6 km and 1?2 km above the vertical reflectivity core,respectively.The probability of lightning initiation at a greater distance to the vertical reflectivity core is higher than that at a shorter distance.This may imply that some electrifications occurring during the melting process are not as strong as expected and a non-riming non-inductive charging process occurring in a weak but broad mesoscale updraft in the middle of stratifom region may be more important for initiation of stratiform lightning flashes.(Wang Fei,Zhang Yijun,Liu Hengyi)

5.23 廣州高建筑物雷電觀測(cè)與研究10年進(jìn)展

作為中國(guó)氣象局雷電野外科學(xué)試驗(yàn)基地（CMA_FEBLS）的重要組成部分，廣州高建筑物雷電觀測(cè)站（TOLOG）始建于2009年，迄今已積累數(shù)百次高建筑物雷電資料。對(duì)于雷電連接過(guò)程，高建筑物會(huì)起到“放大鏡”的作用：TOLOG的觀測(cè)在國(guó)際上首次發(fā)現(xiàn)了連接過(guò)程中負(fù)—正先導(dǎo)之間“頭部—側(cè)面”連接的現(xiàn)象，給出了先導(dǎo)連接行為的兩種基本形態(tài)；揭示了負(fù)先導(dǎo)梯級(jí)發(fā)展過(guò)程的精細(xì)化結(jié)構(gòu)，給出了下行先導(dǎo)和上行先導(dǎo)的二維/三維發(fā)展特征；估算了不同高度建筑物上雷電的閃擊距離。高建筑物對(duì)雷電電磁場(chǎng)具有“放大器”的作用，且建筑物越高增強(qiáng)效應(yīng)越顯著。高建筑物是下行和上行閃電的“匯集點(diǎn)”：對(duì)下行閃電的吸引作用可保護(hù)高建筑物附近的其他物體免遭雷擊；正地閃的回?fù)?、延續(xù)電流和云內(nèi)放電過(guò)程均可在高建筑物上觸發(fā)負(fù)極性上行閃電。另外，高建筑物區(qū)域可作為閃電監(jiān)測(cè)系統(tǒng)的“標(biāo)校場(chǎng)”，TOLOG的觀測(cè)資料在地閃定位系統(tǒng)探測(cè)效率和定位精度的評(píng)估方面也得到了應(yīng)用。（呂偉濤，陳綠文，馬穎）

5.24 廣州兩座高建筑物上閃擊距離的二維光學(xué)觀測(cè)

利用廣州高建筑物雷電觀測(cè)站的高速攝像機(jī)在2012—2018年拍攝到的發(fā)生在兩座尖頂建筑物廣州塔（600 m高，12次）和廣晟國(guó)際大廈（360 m高，9次）上的21次下行地閃光學(xué)數(shù)據(jù)，結(jié)合廣東電網(wǎng)閃電定位系統(tǒng)提供的回?fù)舴逯惦娏鲾?shù)據(jù)，統(tǒng)計(jì)建筑物高度和回?fù)舴逯惦娏鲝?qiáng)度對(duì)閃擊距離的影響，并探討閃擊距離與上行連接先導(dǎo)起始時(shí)間的相關(guān)性。結(jié)果表明：更高的建筑物上雷電的閃擊距離更長(zhǎng)，廣州塔閃擊距離的中位數(shù)約是廣晟國(guó)際大廈閃擊距離中位數(shù)的2倍；對(duì)于確定高度的建筑物，閃擊距離有隨著回?fù)舴逯惦娏髟鰪?qiáng)而變長(zhǎng)的趨勢(shì)，且建筑物越高，對(duì)應(yīng)的回?fù)舴逯惦娏饕苍綇?qiáng)；在下行與上行先導(dǎo)連接前0.1 ms內(nèi)，二者的平均速率之比小于4，且速率比值在0～1這一區(qū)間的樣本最多，占比約65%。（齊奇，呂偉濤，武斌）

5.25 人工觸發(fā)閃電不同放電階段電流特征關(guān)系

分析了2019年夏季在廣州從化人工引雷試驗(yàn)場(chǎng)獲取的14次人工觸發(fā)閃電通道底部電流數(shù)據(jù)，以有無(wú)回?fù)簦≧S）和初始連續(xù)電流（ICC）持續(xù)時(shí)間長(zhǎng)短2個(gè)標(biāo)準(zhǔn)對(duì)數(shù)據(jù)進(jìn)行分類(lèi)，研究不同觸發(fā)閃電和不同放電階段的差異和規(guī)律。研究表明：相比無(wú)回?fù)舻挠|發(fā)閃電，產(chǎn)生回?fù)舻挠|發(fā)閃電具有更大的先驅(qū)放電脈沖（PCP）及初始先驅(qū)放電脈沖（IPCP）的平均峰值電流、更多的IPCP總體轉(zhuǎn)移電荷量、更大的ICC平均電流和總體轉(zhuǎn)移電荷量以及更長(zhǎng)的ICC持續(xù)時(shí)間；初始連續(xù)電流持續(xù)時(shí)間是回?fù)羝骄逯惦娏鞔笮　⑹状卫^后回?fù)艮D(zhuǎn)移電荷量大小和首次繼后回?fù)舴逯惦娏鞔笮〉闹匾绊懸蛩兀议L(zhǎng)初始連續(xù)電流的觸發(fā)閃電對(duì)應(yīng)的PCP及IPCP平均峰值電流也更大、平均轉(zhuǎn)移電荷量也更多；PCP和IPCP平均峰值電流與ICC持續(xù)時(shí)間相關(guān)性最強(qiáng)，是決定ICC放電持續(xù)時(shí)間的重要因素，未能產(chǎn)生初始連續(xù)電流的PCP脈沖簇其平均轉(zhuǎn)移電荷量小于初始先驅(qū)放電脈沖簇，其轉(zhuǎn)化的關(guān)鍵閾值之一是平均轉(zhuǎn)移電荷量大于25.91 μC。（王敬軒，張陽(yáng)，陳澤方）

5.26 人工觸發(fā)閃電初始連續(xù)電流的中低頻磁場(chǎng)特征

中國(guó)氣象局雷電野外科學(xué)試驗(yàn)基地開(kāi)展的人工觸發(fā)閃電試驗(yàn)是研究閃電電磁輻射效應(yīng)的有效手段，利用架設(shè)在試驗(yàn)場(chǎng)地周邊的多套磁場(chǎng)天線所獲取的高靈敏度磁場(chǎng)數(shù)據(jù)，針對(duì)初始連續(xù)電流階段的中低頻磁場(chǎng)特征開(kāi)展研究。得益于磁場(chǎng)天線帶寬的拓展，首次解析出了相對(duì)平靜期內(nèi)的磁場(chǎng)脈沖，單個(gè)脈沖的平均寬度約為1 μs，平均脈沖間隔約為14 μs，對(duì)應(yīng)了該階段中上行先導(dǎo)的小尺度擊穿發(fā)展形式；在近、遠(yuǎn)距離磁場(chǎng)測(cè)量中均觀測(cè)到了與先導(dǎo)通道頭部擊穿放電相關(guān)的爆發(fā)式磁場(chǎng)脈沖，其平均脈沖間隔（約為24.5 μs）明顯大于平靜期脈沖的統(tǒng)計(jì)值，而且在爆發(fā)式脈沖期間通道底部電流逐步增大到幾十至上百安培，上述現(xiàn)象表明此時(shí)電場(chǎng)條件更加有利于上行先導(dǎo)的發(fā)展。此外，高靈敏磁場(chǎng)天線能夠直觀地呈現(xiàn)出初始連續(xù)電流脈沖（ICCP）的電荷傳輸過(guò)程，且ICCP期間觀測(cè)到的規(guī)則磁場(chǎng)脈沖的脈沖間隔比其他類(lèi)型的磁場(chǎng)脈沖小一個(gè)量級(jí)，可能體現(xiàn)了正極性擊穿和負(fù)極性擊穿的特征差異。（樊艷峰，陸高鵬，張陽(yáng)）

5.27 雙向先導(dǎo)正端突然延展現(xiàn)象的高速攝像觀測(cè)

基于廣州高建筑物雷電觀測(cè)站的觀測(cè)設(shè)備，于2016年6月4日在廣州塔上發(fā)生的一次上行閃電過(guò)程中觀測(cè)到雙向發(fā)展的直竄先導(dǎo)正端在回?fù)羟?、后突然延展的現(xiàn)象。利用高時(shí)間分辨率的光學(xué)和電場(chǎng)變化同步數(shù)據(jù)，分析雙向先導(dǎo)正端突然延展現(xiàn)象的細(xì)節(jié)特征。結(jié)果表明：回?fù)羟爸备Z先導(dǎo)雙向發(fā)展時(shí)正端可能會(huì)出現(xiàn)多次突然延展的現(xiàn)象；突然延展現(xiàn)象有時(shí)由雙向先導(dǎo)的正端與已有懸空先導(dǎo)序列相連而引發(fā)，并促使雙向先導(dǎo)正端傳輸至未擊穿空氣中；在一次繼后回?fù)艉螅ǖ勒祟^部也觀測(cè)到兩次突然延展現(xiàn)象，但未沿回?fù)羟罢松煺雇ǖ纻鬏?，而是通過(guò)開(kāi)辟新通道進(jìn)入未擊穿空氣；回?fù)羟爸备Z先導(dǎo)正端3次突然伸展的二維平均速率約為2.3×106m/s，伸展長(zhǎng)度平均值約為115 m；回?fù)艉笸ǖ李^部?jī)纱瓮蝗谎诱沟亩S平均速率約為4.3×106m/s，伸展長(zhǎng)度平均值約為212 m。（武斌，呂偉濤，齊奇）

5.28 一次多回?fù)粲|發(fā)閃電全過(guò)程的連續(xù)干涉儀觀測(cè)

基于中國(guó)氣象科學(xué)研究院自主研發(fā)的閃電連續(xù)干涉儀，對(duì)2019年6月11日在中國(guó)氣象局雷電野外科學(xué)試驗(yàn)基地廣州從化人工引雷試驗(yàn)場(chǎng)成功觸發(fā)的一次多回?fù)糸W電放電全過(guò)程進(jìn)行觀測(cè)，結(jié)合通道底部電流數(shù)據(jù)和電場(chǎng)變化數(shù)據(jù)，共同揭示觸發(fā)閃電全放電過(guò)程：連續(xù)干涉儀能夠定位到最小為8 A的不連續(xù)的先驅(qū)電流脈沖輻射信號(hào)，初始先驅(qū)電流脈沖（IPCP）的平均轉(zhuǎn)移電荷量約為先驅(qū)電流脈沖（PCP）的2倍；上行正先導(dǎo)連續(xù)發(fā)展后為初始連續(xù)電流（ICC）過(guò)程，最初正流光通道以105m/s量級(jí)的速度繼續(xù)發(fā)展延伸，之后出現(xiàn)反沖先導(dǎo)放電；在ICC階段出現(xiàn)的經(jīng)典M分量，可由向前的106m/s量級(jí)速度的正流光（先導(dǎo)）產(chǎn)生，也可由已有通道頭部產(chǎn)生的反沖先導(dǎo)產(chǎn)生，且整個(gè)M分量過(guò)程中，多個(gè)反沖先導(dǎo)維持了放電過(guò)程的持續(xù)；之后的回?fù)糸g過(guò)程以反沖先導(dǎo)為主要放電形式，回?fù)綦娏髅}沖之前存在多次反沖先導(dǎo)過(guò)程，但多數(shù)未發(fā)展到接地通道，只處于企圖先導(dǎo)階段，直至成功的先導(dǎo)回?fù)舢a(chǎn)生；而前兩次回?fù)艟哂谐痰臅r(shí)間間隔，約為4.5 ms，這是由于兩次回?fù)羟暗南葘?dǎo)來(lái)源于云內(nèi)不同分支的反沖先導(dǎo)過(guò)程。（張陽(yáng)，陳澤方，王敬軒）

5.29 一次暖云強(qiáng)降水主導(dǎo)的對(duì)流單體閃電活動(dòng)特征

利用中國(guó)氣象局雷電野外科學(xué)試驗(yàn)基地（CMA_FEBLS）三維閃電觀測(cè)數(shù)據(jù)，結(jié)合廣州雙偏振雷達(dá)觀測(cè)數(shù)據(jù)，分析了2017年5月7日廣東一次暖云強(qiáng)降水對(duì)流單體的閃電活動(dòng)及其與云降水結(jié)構(gòu)的關(guān)系。該單體在4 h內(nèi)產(chǎn)生1250個(gè)閃電，地閃比例約24%。絕大多數(shù)閃電出現(xiàn)在4～12 km高度，對(duì)應(yīng)溫度層為0 ℃～-40 ℃；閃電放電活動(dòng)的峰值高度出現(xiàn)在8.5 km，對(duì)應(yīng)環(huán)境溫度約-19 ℃。分析的強(qiáng)降水單體宏觀上呈現(xiàn)上正、中負(fù)、下正的三極性電荷結(jié)構(gòu)，中部負(fù)電荷核心區(qū)約為-8 ℃～-15 ℃。在閃電活動(dòng)區(qū)域中，由干雪粒子主導(dǎo)區(qū)域占比約82%，霰粒子主導(dǎo)區(qū)域占比約11%，且大部分與閃電活動(dòng)關(guān)聯(lián)的霰粒子主要位于4～8 km高度?？傞W頻數(shù)與30 dBz雷達(dá)回波頂高、-20 ℃溫度層上大于20 dBz的回波體積具有較好的相關(guān)性。閃電活動(dòng)的平均位置高度與20 dBz雷達(dá)回波頂高和-20 ℃溫度層上大于30 dBz的回波體積具有較好的相關(guān)關(guān)系。閃電活動(dòng)與最大降水強(qiáng)度之間具有較好的時(shí)序?qū)?yīng)關(guān)系，單個(gè)閃電表征降水量的值為10～7 kg/fl量級(jí)。（劉澤，郭鳳霞，鄭棟）

5.30 粵港澳閃電定位系統(tǒng)對(duì)高建筑物雷電的探測(cè)

基于2016—2017年廣州高建筑物雷電觀測(cè)站獲取的資料對(duì)粵港澳閃電定位系統(tǒng)（簡(jiǎn)稱定位系統(tǒng)）的性能進(jìn)行評(píng)估，并根據(jù)2014—2018年定位系統(tǒng)歷史資料對(duì)廣州高建筑物區(qū)域的雷電活動(dòng)特征進(jìn)行初步分析，結(jié)果表明：定位系統(tǒng)對(duì)閃電的探測(cè)效率為93%（214/229），對(duì)回?fù)舻奶綔y(cè)效率為93%（449/481），對(duì)下行閃電首次回?fù)?、繼后回?fù)艏吧闲虚W電回?fù)舻亩ㄎ徽`差的平均值（中值）分別為361 m（188 m）、252 m（167 m）和294 m（173 m）；當(dāng)接地點(diǎn)高度低于200 m（不低于200 m）時(shí)，定位系統(tǒng)對(duì)下行負(fù)極性閃電首次和繼后回?fù)舻脑崎W/地閃識(shí)別正確率分別為99%（80%）和93%（35%），有83%的上行負(fù)地閃回?fù)舯欢ㄎ幌到y(tǒng)誤判為云閃，廣州高建筑物區(qū)域內(nèi)絕大部分負(fù)云閃定位記錄實(shí)際是高建筑物地閃；對(duì)定位系統(tǒng)得到的孤立高建筑物閃電密度中心進(jìn)行分析后發(fā)現(xiàn)，廣州塔（600 m）閃電密度中心200 m半徑范圍內(nèi)年均回?fù)舸螖?shù)約為中信廣場(chǎng)（390 m）和廣發(fā)證券大廈（308 m）的5倍，推測(cè)廣州塔閃電的主要類(lèi)型為上行閃電，而中信廣場(chǎng)和廣發(fā)證券大廈則為下行閃電。（陳綠文，呂偉濤，張義軍）

6 模式和再分析資料

6 Model and reanalysis data

6.1 A 100-m-scale modeling study of a gale event on the lee side of a long narrow mountain

In this study,a gale event that occurred on the lee side of a long narrow mountain was investigated,together with the associated mountain flows,using a realistic-case large-eddy simulation (LES) that is based on the Weather Research and Forecasting Model.The mountain is located on the southeastern Tibetan Plateau,where approximately 58 gales occur annually,mostly in the afternoons during the winter season.Benefitting from realistic topography and high horizontal resolution as fine as 111 m,the LES can replicate features similar to the wind fields observed during the gale period.Investigation of the early morning wind structure over the mountain revealed that weak inflows were blocked,reversed,and divided in the upstream area and that some weak lee waves,rotors,and two clear lee vortices were evident downstream.As the upstream wind accelerated and the boundary layer developed during the daytime,the lee waves became amplified with severe downslope wind and rotors.The interaction and coherent structure of the downslope wind,rotor,and vortices were investigated to show the severe wind distribution.The mountain drags associated with blocking and amplified lee waves were displayed to show the potential impact on the large-scale model.The linear lee-wave theory was adopted to explain the wave evolution during this event together with a discussion of the uncertainty around low-level nonlinear processes.(Xue Haile,Li Jian,Qian Tingting)

6.2 An improvement of convective precipitation nowcasting through lightning data dynamic nudging in a cloud-resolving scale forecasting system

A lightning data dynamic nudging (LDN) method was designed to adjust the dynamic field in convective clouds based on the physical relationship between lightning and vertical velocity.Under this framework,vertical velocity data retrieved from the Guangdong-Hongkong-Macau lightning location system were assimilated by a nudging approach using the Global/Regional Assimilation and Prediction System in mesoscale model (GRAPES-Meso).The effect of the assimilation on short-term ( 6 h) precipitation forecast was evaluated by simulating the squall line event on 7 May and a continuous experiment from May to August 2018.Firstly,a series of sensitivity experiments was carried out to adjust the configuration of the assimilation system based on the squall line event.The results show that LDN expanded the spatial distribution of the positive vertical velocity ( 1 m s?1) at 700 hPa by about 2%,and thus enlarged the spatial distribution of severe rainfall ( 40 mm h?1).It should be noted that LDN did not significantly change the intensity of the updraft (i.e.,the maximum vertical velocity) of the squall line relative to the simulation without assimilation.Overall,the equitable threat score (ETS) and fractions skill score (FSS) were increased by 0.04 and 0.13,respectively,and the positive effect lasted for 2?3 h after the data were assimilated.In view of the data assimilation frequency,using two successive nudging procedures with an interval of 12 min had the best effect on the forecast of severe precipitation.For the assimilation of both lightning and radar observations,the asynchronous assimilation of lightning and radar measurements performed slightly better than the synchronous assimilation.LDN improved the accuracy of severe precipitation forecast ( 40 mm h?1and 20 mm h?1for the squall line case and the continuous run,respectively),whereas assimilating radar data improved weak precipitation forecast (1?20 mm h?1in the squall line case and 1?10 mm h?1in the continuous run).(Wang Hong,Chen Dehui,Yin Jinfang)

6.3 Analysis of short-term cloud feedback in East Asia using cloud radiative kernels

Cloud radiative kernels were built by BCC_RAD (Beijing Climate Center radiative transfer model)radiative transfer code.Then,short-term cloud feedback and its mechanisms in East Asia (0.5°?60.5°N,69.5°?150.5°E) were analyzed quantitatively using the kernels combined with MODIS satellite data from July 2002 to June 2018.According to the surface and monsoon types,four subregions in East Asia—the Tibetan Plateau,Northwest,temperate monsoon (TM),and subtropical monsoon (SM)—were selected.The average longwave,shortwave,and net cloud feedbacks in East Asia are ?0.68 ± 1.20,1.34 ± 1.08,and 0.66 ± 0.40 W m?2K?1± 2 sigma),respectively,among which the net feedback is dominated by the positive shortwave feedback.Positive feedback in SM is the strongest of all subregions,mainly due to the contributions of nimbostratus and stratus.In East Asia,short-term feedback in spring is primarily caused by marine stratus in SM,in summer is primarily driven by deep convective cloud in TM,in autumn is mainly caused by land nimbostratus in SM,and in winter is mainly driven by land stratus in SM.Cloud feedback in East Asia is chiefly driven by decreases in mid-level and low cloud fraction owing to the changes in relative humidity,and a decrease in low cloud optical thickness due to the changes in cloud water content.(Wang Fei,Zhang Hua,Chen Qi)

6.4 Changes in anthropogenic PM2.5 and the resulting global climate effects under the RCP4.5 and RCP8.5 scenarios by 2050

Using an aerosolclimate model,we studied the temporal and spatial variations of anthropogenic PM2.5(aerodynamic diameter≤2.5 μm) and coarse particulate matter (CPM; aerodynamic diameter 2.5 μm) under Representative Concentration Pathway (RCP) 4.5 and RCP8.5 scenarios from 2014 to 2050.The corresponding radiative forcing and climate responses were also explored.The PM2.5burden decreases over most continents,especially East Asia.The CPM particles increase over the northern Asia,North America,and central Africa,in contrast to decrease over most regions of East Asia and North Africa.Relative to 2014,the global annual mean effective radiative forcing due to changes in PM2.5and CPM burden are 1.17 (1.10) and ?0.06 (?0.07) W m?2under RCP4.5 (RCP8.5),respectively.The reduction in PM2.5burden leads to apparent warming,especially over high latitudes of the Northern Hemisphere,with global annual mean surface air temperature increasing by 1.25 K under RCP4.5,and 1.22 K under RCP8.5.In contrast,changes in CPM result in apparent cooling over North America and the northern Asia,with global annual mean changes in surface air temperature of 0.10 K for both scenarios.The Northern Hemisphere Hadley cell weakens and moves northward due to changes in PM2.5after 2014,whereas the corresponding circulation in the Southern Hemisphere is strengthened,with the Intertropical Convergence Zone shifting to 10°N.Global annual mean precipitation increases by 0.10 mm per day under both scenarios.Generally,anthropogenic PM2.5contributes significantly to future changes in radiative forcing and climate.(Yang Dongdong,Zhang Hua,Li Jiangnan)

6.5 Development of a coupled atmosphere-ocean typhoon regional assimilation and prediction system for operational typhoon forecasting by the Chinese Academy of Meteorological Sciences-Part I:Experiments of western North Pacific typhoons in 2016

Typhoons can interact intensely with oceans,and the atmosphere-ocean interaction has an enormous impact on the intensity and structure of typhoons.To consider the impact of typhoon-ocean interactions,a regional coupled atmosphere-ocean system for operational forecasting of the western North Pacific typhoons is established in this paper based on a public coupled atmosphere-ocean framework and in accordance with the operational typhoon forecasting conditions and system settings of the Chinese Academy of Meteorological Sciences.The new coupled system is fully validated and used for hindcasting experiments on all typhoons in 2016.The results show that the computational cost associated with the proposed coupled system is approximately 5.33 as much as times that of the atmosphere-only system.A comparison of the hindcasts of the 2016 typhoons using the atmosphere-only system and the proposed coupled system reveals that the use of the coupled system can obviously reduce the forecasted intensity error by 10%?20% but not the typhoon track error.In addition,some of the intrinsic structural characteristics of typhoons influence the effectivity of the coupled system.Specifically,when typhoons have a high intensity and a low translational speed,move in an East?West or turning direction,and are at 20°?25°N latitude,the forecasts can be relatively significantly improved by the coupled system; otherwise,the improvement is not obvious.(Liu Xin,Duan Yihong,Huo Zimo)

6.6 Effects of microphysical latent heating on the rapid intensification of typhoon Hato (2017)

A 72-hour cloud-resolving numerical simulation of Typhoon Hato (2017) is performed by using the Weather Research and Forecasting (WRF) model with the Advanced Research WRF (ARW) core (V3.8.1)on a horizontal resolution of 2 km.To enhance the background tropical cyclone structure and intensity,a vortex dynamic initialization scheme with a terrain-filtering algorithm is utilized.The model reproduces reasonably well the track,structure,and intensity change of Typhoon Hato.More specifically,the change trend of simulated maximum wind speed is consistent with that of best-track analysis,and the simulated maximum wind of 49 m s?1is close to that (52 m s?1) of the best-track analysis,indicating that the model has successfully captured the rapid intensification (RI) of Typhoon Hato (2017).Analyses of the model outputs reveal that the total microphysical latent heating of the inner-core region associated with enhanced vertical upward motion reaches its maximum at 9-km height in the upper troposphere during the RI stage.The dominant microphysical processes with positive latent heat contributions (i.e.,heating effect) are water vapor condensation into cloud water (67.6%),depositional growth of ice (12.9%),and generation (nucleation) of ice from vapor (7.9%).Those with negative latent heat contributions (cooling effect) are evaporation of rain (47.6%),melting of snow(27.7%),and melting of graupel (9.8%).Sensitivity experiments further show that the intensification speed and peak intensity of this typhoon are highly correlated to the dominant heating effect.A significant increase in graupel over 5?10-km height and snow at 10?14-km height in the inner-core region of Typhoon Hato corresponds well with its RI stage,and the latent heating from nucleation and depositional growth is crucial to the RI of simulated Hato.(Zhao Dajun,Yu Yubin,Yin Jinfang)

6.7 Establishment of high-resolution aerosol parameterization and its influence on radiation calculations

To accurately simulate the effects of aerosols on the atmospheric radiation budget,we here establish an aerosol optical parameterization scheme with high spectral resolution (974-band) for radiative transfer model(BCC_RAD); this scheme includes sulfate (SF),black carbon (BC),organic carbon (OC),dust (SD),and sea salt (SS) aerosols.The results of the 974-band scheme are compared with those obtained using a lowresolution 17-band scheme.Our results show the 974-band scheme more accurate in its representation of the aerosols optical properties.The largest relative differences in the volume extinction coefficient (K-ex) between the 974-band and 17-band schemes range from 5.87% to 54.64%,with BC (41.13%) and SF (54.64%) showing the largest values at 1.91 and 2.7 μm,respectively.The single scattering albedo of hygroscopic aerosols (SF,SS,and OC) show minimal values at 2.84 and 6.01 μm,respectively,in the 974-band scheme due to light absorption; however,the low spectral resolution of the 17-band scheme prevents these features from being resolved.Specifically,the relative difference between the two schemes approaches 72.72% at 2.84 μm for SF.Thus,improved spectral resolution may be required for some aerosols.We also compare the effects of aerosols on the radiation budget in East Asia simulated by 974-band and 17-band BCC_RAD models.Under clear-sky conditions,the simulation results indicate a relative difference in the radiation flux of 0.28%?5.93% for the two schemes.The 974-band and 17-band schemes show daily mean direct radiative forcings (DRFs) due to all aerosols of ?16.97 and ?17.13 W m?2at the surface and ?7.12 and ?6.93 W m?2at the top of the atmosphere,respectively.Additionally,the 974-band model generally simulates a larger DRF for BC and smaller DRFs for scattering aerosols such as SF; these differences become greater for smaller zenith angles.(Zhang Hua,Zhu Sihong,Zhao Shuyun)

6.8 Evaluation of Noah-MP land-model uncertainties over parsely vegetated sites on the Tibetan Plateau

The water budget and energy exchange over the Tibetan Plateau (TP) region play an important role on the Asian monsoon.However,it is not well presented in the current land surface models (LSMs).In this study,uncertainties in the Noah with multiparameterization (Noah-MP) LSM are assessed through physics ensemble simulations in three sparsely vegetated sites located in the central TP.The impact of soil organic matter on energy flux and water cycles,along with the influence of uncertainties in precipitation are explored using observations at those sites during the third Tibetan Plateau Experiment from 1 August 2014 to 31 July 2015.The greatest uncertainties are in the subprocesses of the canopy resistance,soil moisture limiting factors for evaporation,runoff (RNF) and ground water,and surface-layer parameterization.These uncertain subprocesses do not change across the different precipitation datasets.More precipitation can increase the annual total net radiation (Rn),latent heat flux (LH) and RNF,but decrease sensible heat flux (SH).Soil organic matter enlarges the annual total LH by similar to 26% but lessens the annual total Rn,SH,and RNF by similar to 7%,7%,and 39%,respectively.Its effect on the LH and RNF at the Naqu site,which has a sand soil texture type,is greater than those at the other two sites with sandy loam.This study highlights the importance of precipitation uncertainties and the effect of soil organic matter on the Noah-MP land-model simulations.It provides a guidance to improve the Noah-MP LSM further and hence the land-atmosphere interactions simulated by weather and climate models over the TP region.(Zhang Guo,Chen Fei,Chen Yueli)

6.9 Fourth-order conservative transport on overset grids using multi-moment constrained finite volume scheme for oceanic modeling

With an increase in model resolution,the compact high-order numerical advection scheme can improve its effectiveness and competitiveness in oceanic modeling due to its high accuracy and scalability on massiveprocessor computers.To provide high-quality numerical ocean simulation on overset grids,we tried a novel formulation of the fourth-order multi-moment constrained finite volume scheme to simulate continuous and discontinuous problems in the Cartesian coordinate.Utilizing some degrees of freedom over each cell and derivatives at the cell center,we obtained a two-dimensional (2D) cubic polynomial from which point values on the extended overlap can achieve fourth-order accuracy.However,this interpolation causes a lack of conservation because the flux between the regions are no longer equal; thus,a flux correction is implemented to ensure conservation.A couple of numerical experiments are presented to evaluate the numerical scheme,which confirms its approximately fourth-order accuracy in conservative transportation on overset grid.The test cases reveal that the scheme is effective to suppress numerical oscillation in discontinuous problems,which may be powerful for salinity advection computing with a sharp gradient.(Gu Juan,Peng Xindong,Dai Yongjiu)

6.10 On the extreme rainfall event of 7 May 2017 over the coastal city of Guangzhou.Part I:Impacts of urbanization and orography

In this study,a nocturnal extreme rainfall event induced by the urban heat island (UHI) effects of the coastal city of Guangzhou in South China on 7 May 2017 is examined using observational analyses and 18-hour cloud-permitting simulations with the finest grid size of 1.33 km and the bottom boundary conditions nudged.Results show that the model reproduces convective initiation on Guangzhou’s downstream side (i.e.,Huashan),where a shallow thermal mesolow is located; the subsequent back-building of convective cells as a larger-scale warm-moist southerly flow interacts with convectively generated cold outflows,and their eastward drifting and reorganization into a localized extreme-rain-producing storm near Jiulong under the influences of local orography.In particular,the model produces the maximum hourly,3- and 12-hour rainfall amounts of 146,315,and 551 mm,respectively,at nearly the right location compared to their corresponding observed extreme amounts of 184,382,and 542 mm.In addition,the model reproduces an intense meso?gamma-scale vortex associated with the extreme-rain-producing Jiulong storm,as also captured by Doppler radar,with organized updrafts along cold outflow boundaries over a semicircle.A comparison of sensitivity and control simulations indicates that despite the occurrence of heavier rainfall amounts without the UHI effects than those without orography,the UHI effects appear to account directly for the convective initiation and heavy rainfall near Huashan,and indirectly for the subsequent formation of the Jiulong storm,while orography plays an important role in blocking cold outflows and enhancing cool pool strength for the sustained back-building of convective cells over the semicircle,thereby magnifying rainfall production near Jiulong.(Yin Jinfang,Zhang Da-Lin,Luo Yali)

6.11 Positive definite advection transport algorithm for conservation law equations on nonuniform irregular grids

The multidimensional positive definite advection transport algorithm (MPDATA) is an important numerical method for the computation of atmospheric dynamics.MPDATA is second-order accurate,positive definite,conservative,and computationally efficient.However,the method is problematic in which it results in a loss of precision when computing a nonuniform irregular grid.Furthermore,research revealed two reasons for this problem.On the one hand,numerical discretization of boundary derivatives of the finitevolume method is incompatible with nonuniform meshes (or grids); on the other hand,the up-wind scheme of staggered grids is not applicable to the calculation of irregular grids.We overcome these two problems by using the multipoint Taylor expansion method to obtain a boundary derivative numerical approximation scheme that does not depend on the grid structure.Furthermore,combined with the well-balance central-upwind scheme,a positive definite advection scheme for irregular meshes is proposed.Then,the positivity of the new numerical scheme is analyzed.Finally,the result of this study is verified by numerical simulation.(Yuan Xinpeng,Xiong Chunguang)

6.12 Quantifying contributions of uncertainties in physical parameterization schemes and model parameters to overall errors in Noah-MP dynamic vegetation modeling

Quantifying contributions of errors in model structure and parameters to biases in a land surface model(LSM) is critical for model improvement.This paper investigated the uncertainties in parameterizations and parameters in the Noah with multiparameterization (Noah-MP) LSM with dynamic vegetation using eddy flux data.First,we conducted full factorial experiments of eight land subprocesses,followed by sensitivity analysis(SA) to identify the subprocesses for which possible parameterizations made significant difference.Then,based on the full factorial experiments and SA results,we selected the statistically optimal parameterizations combination and the most biased parameterizations combination.Lastly,we calibrated the parameters in two selected parameterizations combinations.The results showed that five subprocesses—surface exchange coefficient,soil moisture beta threshold,radiation transfer,runoff and groundwater,and surface resistance to evaporation—had significant influence on the model performances,and the interactions were generally low but contributed up to 80% of the variation in the performance at some sites.In the optimization period,following the criterion by Moriasi et al.(2007,https://doi.org/10.13031/2013.23153),the parameter optimization improved the performance of both parameterizations combinations at most sites,which was satisfactory,and the superiority between two parameterizations combinations was preserved; in the validation period,adjusting the parameterizations was more robust than parameter optimization in improving LSMs.Finally,we found that uncertainty in soil parameters was much higher than that in vegetation parameters because the optimal soil parameters were significantly different among sites with the same soil types and recommended that spatially calibrating the soil parameters was a major issue for Noah-MP dynamic vegetation modeling.(Li Jianduo,Chen Fei,Lu Xingjie)

6.13 Statistical characteristics and synoptic situations of long-duration heavy rainfall events over North China

The spatiotemporal characteristics of long-duration heavy rainfall (LDHR) events are statistically analyzed using hourly surface observations over the central-southern North China during the warm seasons of 2011?2018,revealing pronounced variabilities in the frequency and amount of LDHR.Two accumulated rainfall peaks are found in the western (WHRR) and eastern (EHRR) regions of the central-southern North China.The LDHR occurrence frequency decreases westward,and the peaks of the LDHR amount,frequency and intensity in the WHRR and EHRR are observed at nighttime (21:00?02:00 Beijing Standard Time) or in the early morning (03:00?07:00 Beijing Standard Time).The rainfall amount exhibits a bimodal diurnal variation in the WHRR (determined mainly by the rainfall intensity),whereas a single rainfall frequencyrelated peak is found in the EHRR.Four types of LDHR events corresponding to different flow patterns,synoptic systems,and moisture transport mechanisms are classified according to their locations.The first is heavy rainfall in the WHRR with an upper-level jet favorable for an ascending motion near Taihang Mountain;topographic blocking of southerly flow is crucial for heavy rainfall formation.The second describes heavy rainfall in the EHRR attributable to the favorable configurations of upper- and lower-level systems.Heavy rainfall occurs over both the WHRR and the EHRR in the third type,including topographic blocking and convergence associated with low-pressure systems or shear lines and a mesoscale low vortex or shear line related to topographic effects and positive vorticity advection in front of a westerly trough.The fourth shows a scattered distribution of LDHR stations and is generally not comparable to the first three types.(Kang Yanzhen,Peng Xindong,Wang Shigong)

6.14 The change of cloud top height over East Asia during 2000-2018

In order to know how regional averaged cloud top height (CTH) responded to the past climatic change,the spatial and temporal variations of CTH based on MODIS data (MOD03_08_v6.0) from March 2000 to February 2018 are analyzed.The results show that the CTH in East Asia was higher in the southwest and lower in the northeast.The annual mean CTH was found to increase in East Asia at the rate of 0.020 km per year,of which,0.035 km per year over the eastern land and 0.034 km per year over the eastern sea.The CTH changes were statistically correlated with the sea surface temperature changes over the eastern sea (r=0.68),which indicates that the CTH changes may be affected by the underlying surface.Statistically significant increasing trend of annual mean CTH was found in the latitude zone of 30°?40°N.Furthermore,CTH showed decreasing trends of about ?0.030 km per year in the Middle-Lower Yangtze River Basin,Tarim Basin,Turpan Basin and northeastern Sichuan Basin in summer since more low cloud formations benefited to the decrease of CTH.In winter,the decreasing trend of CTH was found over the north of 40°N,whereas the increasing trend was found over the south of 40°N in East Asia.(Zhao Min,Zhang Hua,Wang Haibo)

6.15 Towards understanding multi-model precipitation predictions from CMIP5 based on China hourly merged precipitation analysis data

Large uncertainties still exist in the simulation and projection of precipitation from current climate models.Here,the newly released state-of-the-art China Hourly Merged Precipitation Analysis (CHMPA) data has been used to evaluate the ten models from the fifth phase of the Coupled Models Intercomparison Project(CMIP5).Particularly,the precipitation predictions under the Representative Concentration Pathways (RCP)4.5 and RCP8.5 scenarios in China are assessed for the period from 2008 to 2017.Interestingly,the ensemble mean precipitation under the two emission scenarios does not show systematic differences.Intercomparison analysis of precipitation between multi-model prediction and CHMPA yields a high correlation coefficient (0.85?0.95)on the annual timescale.However,most models tend to overestimate the precipitation in the northern China but to underestimate that in the southern China,due to the model-simulated monsoon precipitation extending to the north earlier.Relative to UKMO-HadGEM2AO model,other models overestimate precipitation at the southeastern edge of the Tibetan Plateau where the overestimation reaches up to 150%.In terms of the temporal evolution of predicted precipitation,the multi-model ensemble produces relatively small interannual variability except for more summer monsoon precipitation with biases over 0.3 mm/day,which indicates that models are not capable of reproducing the seasonal and meridional propagation of precipitation.Compared with the original model output,the precipitation corrected by quantile mapping algorithm better agrees with the observations for spatial and temporal distributions.The findings have great implications for better utilizing model-predicted precipitation in climate change studies.(Lyu Yanmin,Guo Jianping,Yim Steve Hung-Lam)

6.16 GRAPES_YY模式發(fā)展及其對(duì)梅雨鋒降水模擬的性能檢驗(yàn)

GRAPES_YY是在球面準(zhǔn)均勻陰陽(yáng)網(wǎng)格動(dòng)力框架基礎(chǔ)上發(fā)展起來(lái)的全球非靜力模式，目前已耦合全套物理過(guò)程參數(shù)化方案，具備了中期天氣預(yù)報(bào)能力。為了解模式對(duì)環(huán)流和降水的實(shí)際預(yù)報(bào)效果，檢驗(yàn)?zāi)Ｊ綄?duì)多尺度天氣系統(tǒng)的預(yù)報(bào)能力和誤差分布特征，以ERA-Interim資料和逐時(shí)地面融合降水產(chǎn)品為參考，對(duì)1個(gè)月（2018年6月中旬至7月中旬）批量試驗(yàn)結(jié)果和一次長(zhǎng)江流域梅雨個(gè)例（7月4—7日）模擬結(jié)果進(jìn)行分析。結(jié)果表明：在改進(jìn)上邊界條件基礎(chǔ)上，模式有較好的穩(wěn)定性，短期預(yù)報(bào)時(shí)效內(nèi)對(duì)全球環(huán)流和降水刻畫(huà)準(zhǔn)確，模式24 h累計(jì)降水緯向平均成功再現(xiàn)了低緯度和中緯度地區(qū)的兩個(gè)降水峰值，但對(duì)低緯度對(duì)流性降水和中緯度格點(diǎn)尺度降水預(yù)報(bào)偏強(qiáng)。其次，模式成功模擬出7月4—6日中國(guó)東部梅雨雨帶位置、走向及南北擺動(dòng)，整體上能正確反映主要天氣系統(tǒng)的移動(dòng)演變，但受分辨率限制以及濕物理過(guò)程影響，暴雨以上量級(jí)降水還存在強(qiáng)度預(yù)報(bào)偏弱、位置偏北的問(wèn)題。GRAPES_YY模式模擬結(jié)果基本合理可信，對(duì)中低緯度梅雨鋒降水的預(yù)報(bào)能力較GRAPES_GFS略有改善。（趙益帆，李曉涵，彭新東）

6.17 物理濾波初始化四維變分在臨近預(yù)報(bào)中的應(yīng)用

運(yùn)用WRF（Weather Research and Forecasting Model）天氣研究和預(yù)報(bào)模式以及WRFDA（WRF Data Assimilation）同化系統(tǒng)，探究采用物理濾波初始化四維變分同化方法提高數(shù)值預(yù)報(bào)在臨近預(yù)報(bào)時(shí)效的預(yù)報(bào)能力的可能性。通過(guò)采用12 min同化窗，在不顯著增加計(jì)算量的情況下，得到更協(xié)調(diào)的模式初始場(chǎng)，從而提高模式預(yù)報(bào)能力。選取2018年8月華北地區(qū)17個(gè)降水個(gè)例進(jìn)行研究。結(jié)果表明，采用物理濾波初始化四維變分同化技術(shù)能夠明顯改進(jìn)模式短時(shí)臨近降水預(yù)報(bào)能力，明顯提高對(duì)大量級(jí)降水預(yù)報(bào)的ETS評(píng)分，6 h累積降水大于25.0 mm量級(jí)的ETS評(píng)分由0.125提高到0.190，且6 h累積降水大于60.0 mm量級(jí)的ETS評(píng)分由0.016提高到0.081。研究還表明，同化雷達(dá)風(fēng)場(chǎng)通過(guò)改進(jìn)初始動(dòng)力場(chǎng)使次網(wǎng)格尺度降水過(guò)程（積云參數(shù)化）快速響應(yīng)，可提高短時(shí)臨近時(shí)段的降水預(yù)報(bào)能力。（姜文靜，梁旭東）

6.18 夏季白天中國(guó)中東部不同類(lèi)型云分布特征及其對(duì)近地表氣溫的影響

本文利用2001—2017年ERA5再分析資料以及CERES衛(wèi)星資料，探究夏季白天中國(guó)中東部不同類(lèi)型云的云量及其光學(xué)厚度的時(shí)空變化特征，并利用一維輻射對(duì)流模式定量分析不同類(lèi)型云對(duì)近地表氣溫的影響。觀測(cè)結(jié)果表明：夏季白天中國(guó)中東部總云量及其光學(xué)厚度整體呈由南向北逐漸減小的分布特征，且中高云量占主導(dǎo)地位?？傇屏空w呈?0.3%/a顯著減少趨勢(shì)，其中低云的貢獻(xiàn)（?0.27%/a）最大；總云光學(xué)厚度為0～0.1/a增加趨勢(shì)，其中低云光學(xué)厚度（0.06/a）和中低云光學(xué)厚度（0.03/a）呈增加趨勢(shì)，而中高云光學(xué)厚度（?0.08/a）和高云光學(xué)厚度（?0.03/a）呈減少趨勢(shì)。模式結(jié)果表明：四種不同類(lèi)型云的溫度效應(yīng)（Cloud Effect Temperature，CET）均為負(fù)值，表現(xiàn)為降溫效應(yīng)。低云、中低云、中高云和高云的年均CET值分別為?2.9 ℃、?2.7 ℃、?2.2 ℃和?1.7 ℃。其中，低云在華北平原降溫可達(dá)?5 ℃；中低云和中高云在四川盆地和云貴高原降溫可達(dá)?7.8 ℃。不同類(lèi)型云溫度效應(yīng)與近地表氣溫的年際變化具有較好的一致性，具體表現(xiàn)為：2004年前（后）近地表氣溫呈現(xiàn)下降（上升）趨勢(shì)，不同類(lèi)型云的CET在此期間呈下降（上升）趨勢(shì)，表現(xiàn)為云的降溫效應(yīng)增強(qiáng)（減弱）與近地表氣溫下降（上升）相對(duì)應(yīng)，體現(xiàn)了夏季白天中國(guó)中東部4種不同類(lèi)型云溫度效應(yīng)與近地表氣溫都呈正相關(guān)關(guān)系。特別地，夏季白天中國(guó)中東部中高云量占主導(dǎo)地位，其CET與近地表氣溫的相關(guān)系數(shù)高達(dá)0.63。綜上，夏季白天中國(guó)中東部不同類(lèi)型云溫度效應(yīng)對(duì)近地表氣溫的影響不同，但均呈正相關(guān)關(guān)系。定量分析不同類(lèi)型云對(duì)近地表氣溫的影響可以為定量研究云反饋對(duì)區(qū)域增暖的作用以及合理預(yù)估未來(lái)區(qū)域增暖情景提供必要的科學(xué)參考。（游婷，張華，王海波）

7 衛(wèi)星研究與應(yīng)用

7 Satellite research and application

7.1 A multivariable approach for estimating soil moisture from microwave radiation imager (MWRI)

Accurate measurements of soil moisture are beneficial to our understanding of hydrological processes in the earth system.A multivariable approach using the random forest (RF) machine learning technique is proposed to estimate the soil moisture from microwave radiation imager (MWRI) onboard Fengyun-3C satellite.In this study,soil moisture operational products system (SMOPS) products disseminated from NOAA are used as a truth to train the algorithm with the input of MWRI brightness temperatures (TBs) at 10.65,18.7,23.8,36.5,and 89.0 GHz,TB polarization ratios (PRs) at 10.65,18.7,and 23.8 GHz,height in digital elevation model (DEM),and soil porosity.The retrieved soil moisture is also validated against the independent SMOPS data,and the correlation coefficient is about 0.8 and mean bias is 0.002 m3m?3over the period from 1 August 2017 to 31 May 2019.Our retrieval of soil moisture also has a higher correlation with ECMWF ERA5 soil moisture data than the MWRI operational products.In the western part of China,the spatial distribution of MWRI soil moisture is much improved,compared to the MWRI operational products.(Zhang Sibo,Weng Fuzhong,Yao Wei)

7.2 Advanced radiative transfer modeling system (ARMS):A new-generation satellite observation operator developed for numerical weather prediction and remote sensing applications

(1) Urgent requirements for developing Fengyun satellite observation operators; (2) Capabilities of ARMS; (3) Preliminary results from ARMS simulations on Fengyun satellite observations; (4) The pathway for transitioning ARMS into operation and the plan for future development.(Weng Fuzhong,Yu Xinwen,Duan Yihong)

7.3 Advanced radiative transfer modeling system developed for satellite data assimilation and remote sensing applications

An advanced radiative transfer modeling system (ARMS) has been developed for satellite data assimilation and remote sensing applications.It inherits the capability of other fast radiative transfer models developed mainly for US and European satellite programs but focuses on the radiative transfer components that are specific for the assimilation of the Fengyun satellites and those sensors not included in existing models.The ARMS forward operator includes a fast transmittance module,a new particle absorption and scattering look-up table,surface emissivity and polarimetric radiative transfer solver.The particle optical properties of aerosols and ice clouds are calculated based on a super-spheroidal T-matrix model.The polarimetric twostream approximation is adopted as the preferred solver to simulate the Stokes vector and their Jacobians.The simulations of ARMS are compared with those of other models and observations of Fengyun satellites,respectively.The comparison shows close agreement between ARMS and other existing fast radiative transfer models.Therefore,ARMS has robust simulation capabilities for existing satellite sensors.(Yang Jun,Ding Shouguo,Dong Peiming)

7.4 Application and evaluation of the small-angle approximation on forward radiative transfer model

The small-angle approximation is used in solving the radiative transfer equation when the singlescattering phase function has a strong forward peak.The original vector radiative transfer equation is decomposed into three equations:the forward,the regular,and the correction ones.The forward equation can be efficiently solved using the small-angle approximation.The solution of the regular equation is given by the adding-doubling method in this study.The correction equation including cross terms between the forward and the regular quantities is given and analyzed.The combined model associated with the forward and regular equations is further verified in the forward radiative transfer model,where the molecular absorptions with respect to the standard atmospheric profiles are taken into consideration using the line-by-line method.Great agreements are given between the combined model and the model using the straight adding-doubling method.(Sun Bingqiang,Ding Shouguo)

7.5 Climatology of passive microwave brightness temperatures in tropical cyclones and their relations to storm intensities as seen by FY-3B/MWRI

A new database,the tropical cyclones passive microwave brightness temperature (TCsBT) database including 6273 overpasses of 503 tropical cyclones (TC) was established from 6-year (2011–2016) Fengyun-3B (FY-3B) microwave radiation imager (MWRI) Level-1 brightness temperature (TB) data and TC besttrack data.An algorithm to estimate the TC intensity is developed using MWRI TB’s from the database.The relationship between microwave TB and the maximum sustained surface wind (Vmax) of TCs is derived from the TCsBT database.A high correlation coefficient between MWRI channel TB and Vmax is found at the radial distance 50–100 km near the TC inner core.Brightness temperatures at 10.65,18.70,23.8,and 36.5 GHz increase but 89 GHz TB’s and polarization corrected TB at 36.5 GHz (PCT36.50) and PCT89 decrease with increasing TC intensity.The TCsBT database is further separated into the 5063 dependent samples (2010–2015) for the development of the TC intensity estimation algorithm and 1210 independent samples (2016)for algorithm verification.The stepwise regression method is used to select the optimal combination of storm intensity estimation variables from 12 candidate variables and four parameters (10.65h,23.80v,89.00v and PCT36.50) were selected for multiple regression models development.Among the four predictors,PCT36.50 contributes the most in estimating TC intensity.In addition,the errors are lower for estimating 6-hour and 12-hour future Vmax than estimating the current Vmax.(Qian Bo,Jiang Haiyan,Weng Fuzhong)

7.6 Detection of wind corridors based on “Climatopes”:A study in central Ji’nan

Wind corridor blueprints are an essential reference for climate planning that takes into account zones of fresh cold air,air channels as well as heat island alleviation zones.This article addresses the matter of how to plan urban wind corridors more efficiently by proposing a “ventilation potential coefficient” (VPC) as well as providing an index for natural cold sources.The study additionally proposes a surface urban heat island (SUHI)index as a means of evaluating the severity of the heat island effect.Based on these three indexes,a new method of categorizing urban climatic zones,called “Climatopes”,is developed.Using the above methods,data from 2016 meteorological observation stations and Landsat8 satellites,as well as urban planning materials and basic geographical information on a scale of 1:2000 are used to create an Urban Climate Analysis Map(UCAnMap) and formulate a plan for the construction of wind corridors in the urban centre of Ji’nan.The results reveal that the intensity of urban heat islands in Ji’nan is closely related to a lack of natural cold sources,the specific layout of different types of land use as well as poor planning of urban “function zones”.Moreover,there is a significant correlation between the VPC and other factors such as surface roughness length,building height,the density of building frontal area and floor area ratios.The potential wind corridors could also be determined based on the VPC.Based on an UCAnMap composed of 11 Climatopes and background wind environments,this article ascertains that it would be possible to construct a network of 3-level one corridor(each over 500 m wide) and 11-level two corridors (each over 80-m wide).Additionally,regulatory measures and protective legislation are proposed for the corridors,as well as for the city’s overall development.(Liu Yonghong,Cheng Pengfei,Chen Peng)

7.7 Development and application of ARMS fast transmittance model for GIIRS data

The Fengyun (FY)-4A geosynchronous interferometric infrared sounder (GIIRS) fast transmittance model has been developed as part of the advanced radiative transfer modeling system (ARMS) and applied to quantitative uses of the GIIRS data.To determine the accuracy of the fast transmittance model,one dataset that includes 83 atmospheric profiles generated by the European Center for Medium-Range Weather Forecasts(ECMWF) and another dataset that includes 48 atmospheric profiles developed at the University of Maryland at Baltimore County (UMBC) are utilized for training and testing,respectively.The radiative transfer simulations at six viewing angles are compared with the line-by-line results for dependent and independent evaluations of the fast transmittance model.It is shown that the profile dataset chosen for coefficient training has a substantial effect on the accuracy of the fast transmittance model.ARMS simulations using the fast transmittance model are compared with RTTOV simulations using the fast transmittance model (DiDi RTTOV) as well as GIIRS observations.The biases between the ARMS simulations and GIIRS measurements are less than 1.0 K and 1.5 K(in absolute value) for most channels of GIIRS band 1 and 2,respectively,and the difference between the two models is less than 0.7 K,except those near the strong absorption bands.There are some GIIRS channels with large biases,which are unusable.Several issues are also found during the comparison.The Jacobians with respect to different physical parameters are also calculated using both ARMS and DiDi RTTOV and compared for consistency.It is found that the temperature Jacobians of both models are similar; however,the water vapor and ozone Jacobians differ substantially between ARMS and DiDi RTTOV.(Kan Wanlin,Dong Peiming,Zhang Zhiqing)

7.8 Evaluation of the in-orbit performance of the microwave temperature sounder onboard the FY-3D satellite using different radiative transfer models

The in-orbit performance of the microwave temperature sounder (MWTS) onboard the Fengyun-3D (FY-3D) satellite is evaluated using the community radiative transfer model (CRTM) and the radiative transfer for the television infrared observation satellite operational vertical sounder (RTTOV) model.Both radiooccultation data from the Constellation Observing System for Meteorology,Ionosphere and Climate (COSMIC)Data Analysis and Archive Center and ERA-Interim analysis data from the European Centre for Medium-Range Weather Forecasts are taken as inputs to the two fast radiative transfer models.The radio-occultation data are quality controlled and the collocation criterion between the radio-occultation data and the MWTS measurements is defined such that the spatial and temporal difference is 50 km and 3 hours,respectively.The biases of MWTS channels 5?10 produced by both CRTM and RTTOV agree well over the oceans under clear sky conditions between 60°S and 60°N from July to December 2018.The mean biases simulated by the radio-occultation and ERA-Interim data are negative and the absolute values of the biases are 0.6 and 1.5 K for channels 5?10 of the MWTS,respectively.The biases at channels 4 and 11 between the CRTM and RTTOV simulations are inconsistent and require further investigation of the transmittance difference between the fast models.The standard deviation of the biases from the radio-occultation and ERA-Interim data are 0.5 and 1.8 K for the limited amount of collocated radio-occultation data.Asymmetrical patterns are detected for the MWTS through the scan angle-dependent bias.The long-term mean MWTS bias shows only a weak dependence on latitude,which suggests that biases do not vary systematically with brightness temperature.(Han Yang,Hou Xueyan)

7.9 Examining Asian dust refractive indices for brightness temperature simulations in the 650?1135 cm?1 spectral range

In this paper,we modeled dust impacts on atmospheric radiative transfer in the thermal infrared region of 650?1135 cm?1by using the radiative transfer for TOVs model (RTTOV).We assessed three sets of Asian dust refractive indices (the Volz refractive index implemented in the RTTOV as default,and the Gobi and Taklamakan refractive indices) for brightness temperature simulations.The US 76 standard profile was employed to represent the atmospheric status.Three scenarios of high (532.6 similar to 575.2 hPa),middle(661 similar to 703.6 hPa) and low (786.3 similar to 825.8 hPa) dust layers and four cases of aerosol optical thickness (AOT) (0.1,0.5,1.0,and 1.5 at 1000 cm?1) were considered in the simulations.It is found that the refractive indices have a clear impact on simulating the values and the spectral slope of brightness temperature in the mid-thermal infrared band.Brightness temperature difference (BTD) for different refractive indices(Gobi/Taklamakan-Volz) increases with the height of dust layer and the AOT.The BTD reaches about 4 K for the high dust layer (532.6 similar to 575.2 hPa) and the AOT of 1.5.Most BTDs (0.5?4 K) are much larger than the noise-equivalent temperature difference of high-spectral resolution infrared sounders.Even for the AOT of 0.1,BTDs for different refractive indices could be close to or larger than 0.2 K.This study emphasizes the requirement of accurate refractive indices according to dust origins for improving brightness temperature simulations and provides valuable references for potential improvement of dust retrievals.(Bi Lei,Ding Shouguo,Zong Ruirui)

7.10 Impacts of cloud scattering properties on FY-3D HIRAS simulations

Cloudy sky spectral radiance at the top of the atmosphere has always been an important while difficult variable to simulate for fast radiative transfer models.In this paper,we focus on examining the impacts of cloud scattering properties on the spectral radiance signature of the high-spectral resolution infrared atmospheric sounder (HIRAS) onboard the Fengyun-3D (FY-3D) satellite by using the advanced radiative transfer modeling system (ARMS) and the community radiative transfer model (CRTM).Cloud scattering properties used in the radiative transfer models are critical for modeling the spectral radiance under cloudy sky,which involves choices of appropriate cloud particle models and particle size distributions,etc.Multiple FY-3D HIRAS observations over the southern China and Southeast Asia with ice or liquid water cloud cover on 6 May 2018 are examined,respectively.Vertical atmospheric profiles are derived from the modern-Era retrospective analysis for research and applications,version 2 reanalysis product.Cloud property retrievals from the moderate resolution imaging spectroradiometer are used.Cloud scattering property parameterization schemes based on spherical and nonspherical cloud particle shapes are implemented for liquid water and ice clouds in ARMS and CRTM,respectively.Results show that both ARMS and CRTM can well simulate the radiance at the HIRAS spectral ranges under liquid water cloud condition as compared with the HIRAS observation with mean absolute error (MAE) of brightness temperature of less than 1 K.However,for ice cloud conditions,ARMS model using assumed spherical ice properties exhibits large biases between simulation and observation.CRTM with nonspherical ice properties using 16-stream approximation shows MAE less than 1 K and MAE of about 1 K using 2-stream approximation.(Yi Bingqi,Ding Shouguo,Bi Lei)

7.11 Multisource assessments of the Fengyun-3D microwave humidity sounder (MWHS) on-orbit performance

The microwave humidity sounder (MWHS) onboard the Fengyun-3D satellite is providing the data for profiling atmospheric temperature and moisture and has become an important data source for improving the weather forecasts.In this article,three data sources are utilized for assessing the MWHS on-orbit performance,including global navigation satellite system occultation sounder (GNOS),ECMWF (European Centre for Medium-Range Weather Forecasts) re-analysis (ERA)-interim reanalysis,and advanced technology microwave sounder (ATMS) data.GNOS-retrieved atmospheric profiles and the reanalysis data are used as inputs to the community radiative transfer model (CRTM) for simulating the MWHS brightness temperatures at the top of the atmosphere in July 2018 for characterizing the instrument performance.Since ATMS is a well-calibrated microwave sounding instrument onboard both Suomi NPP and NOAA-20 satellites,its measurements are also collocated with MWHS data for a consensus analysis using the simultaneous nadir overpasses (SNOs) method.In comparing GNOS simulations,MWHS upper air temperature sounding channels (36) have relatively larger biases (less than 2.5 K) than the water vapor sounding channels.However,the standard deviation of the difference between observations and simulations (O-B) is larger for water vapor sounding channels.For ERA simulations,MWHS sounding channels exhibit negative biases similar to GNOS results but the standard deviation of O-B at the water vapor channels is much smaller.When compared with ATMS water vapor channels,MWHS biases are mostly negative and agree with those from ERA simulation.Thus,the large uncertainty in simulating MWHS water vapor sounding channels from GNOS could result from the poor input water vapor profiles and high water vapor variability in the lower troposphere.(Kan Wanlin,Han Yang,Weng Fuzhong)

7.12 Preface for the special issue of radiative transfer models for satellite data assimilation

Satellite observations have a major positive impact on the accuracy of numerical weather prediction(NWP).They are used in NWP data assimilation systems through variational,ensemble and hybrid methods.For direct assimilation of satellite observations from passive infrared and microwave instruments,a radiative transfer model is typically required to compute the radiance at the top of the atmosphere from atmospheric state variables.In the past two decades,many countries have invested in developing the fast radiative transfer models through their space and NWP programs.The development of RTTOV (radiative transfer for TOVS) fast model in European community started in the 1990s and released in 1999.In the United States,the community radiative transfer model (CRTM) project was initiated at the Joint Center for Satellite Data Assimilation in earlier 2000s and CRTM was released to the United States NWP community in earlier 2010 for satellite radiance assimilation and remote sensing applications.An advanced radiative transfer modeling system (ARMS) is now being developed in China and it is now ready for uses in more broader applications including data assimilations.On April 2 to May 3,2019,the Chinese Academy of Meteorological Sciences State Key Laboratory of Severe Weather,the European Center for Medium-Range Weather Forecast (ECMWF)and US Joint Center for Satellite Data Assimilation (JCSDA) jointly hosted an international workshop in Tianjin,China on radiative transfer models in support of satellite data assimilation.More than 100 scientists from China,US,UK,Germany and Japan attended the workshop.A science steering committee for radiative transfer (SSC4RT) was also formed and 10 distinguished scientists were nominated as the SSC4RT members.The participants reported the major progresses in developing the fast radiative transfer models for satellite data assimilations.In the past,the NWP community primarily had used RTTOV (Europe) and CRTM (US).Now,China is developing the advanced radiative transfer modeling system (ARMS) for more satellite data applications.The SSC recognized the significance of ARMS development and ARMS will become a third pillar supporting NWP satellite data assimilation,after RTTOV and CRTM.This special issue solicits papers documenting research either reported at the workshop or pertaining to the main topics at the Tianjin workshop in solutions of radiative transfer equations,state-of-the art methods for computing the optical properties of aerosols,clouds,and precipitation,and surface reflectivity and emissivity modeling.It also addresses,where appropriate,shortcomings in the models that fast models are trained on,such as line-by-line transmittance models and surface dielectric property models.(Weng Fuzhong,Benjamin T.Johnson,Zhang Peng)

7.13 The long-term trend of upper-air temperature in China derived from microwave sounding data and its comparison with radiosonde observations

Currently,the satellite Microwave Sounding Unit (MSU/AMSU) datasets developed from three organizations—remote sensing systems (RSS),the University of Alabama at Huntsville (UAH),and the NOAA Center for Satellite Applications and Research (STAR)—are often used to monitor the global long-term trends of temperatures in the lower troposphere (TLT),midtroposphere (TMT),total troposphere (TTT),troposphere and stratosphere (TTS),and lower stratosphere (TLS).However,the trend in these temperatures over China has not been quantitatively assessed.In this study,the decadal variability and longterm trend of upper-air temperature during 1979?2018 from three MSU datasets are first evaluated over China and compared with the proxy MSU dataset simulated from homogenized surface and radiosonde profiles (EQU) at 113 stations in China.The regional mean MSU trends over China during 1979?2018 are 0.22?0.27 (TLT),0.15?0.22 (TMT),0.20?0.27 (TTT),0.02?0.14 (TTS),and 20.33?20.36 (TLS) K decade?1,whereas the EQU trends are 0.31(TLT),0.19 (TMT),0.24 (TTT),0.07 (TTS),and 20.26 (TLS) K decade?1.The trends from RSS generally show a better agreement with those from EQU.The trends from both MSU and EQU exhibit seasonal and regional difference with a larger warming in TLT in February and March,and stronger cooling in TLS from late winter to spring.The TLT and TMT over the Tibetan Plateau and northwestern China show larger warming trends.The variabilities from MSU and EQU agree well except TLT in Tibet and the southern China.The major difference in regional mean temperatures over China between MSU and EQU is related primarily to the satellite instrument changes during 1979?1998 and the radiosonde system changes in China in the 2000s.(Guo Yanjun,Weng Fuzhong,Wang Guofu)

7.14 Comparing the thermal structures of tropical cyclones derived from Suomi NPP ATMS and FY-3D microwave sounders

Accurate information on the thermal structures of tropical cyclones (TCs) is essential for monitoring and forecasting their intensity and location.In this study,a scene-dependent one-dimensional variation (SD1DVAR)algorithm is developed to retrieve atmospheric temperature and moisture profiles under all-weather conditions.In SD1DVAR,the background and observation error matrix varies according to the scattering intensity.Specifically,the observation error matrix increases in precipitating atmospheres due to a larger uncertainty in the forward operator.With the data from the advanced technology microwave sounder (ATMS) onboard the Suomi National Polar-orbiting Partnership (NPP) satellite,SD1DVAR can retrieve better thermal structures in the storm life cycle than NOAA microwave integrated retrieval system (MIRS).Comparing with the aircraft dropsonde observations,the temperature and humidity errors from SD1DVAR are about 3 K and 20%,respectively whereas those from MIRS are around 4?5 K and 30%,respectively.SD1DVAR is also applied for the microwave temperature sounder (MWTS) and microwave humidity sounder (MWHS) onboard FY-3D satellite.The MWTS and MWHS datasets are first combined into a single comprehensive microwave suite (CMWS) data stream and then used to retrieve the hurricane thermal structures.It is shown that the hurricane structure from CMWS is very similar to that from ATMS.However,due to the availability of 118 GHz measurements from the CMWS,the hurricane temperature vertical structure is better resolved,and the humidity error is also reduced by about 5%.(Hu Hao,Han Yang)

7.15 Retrieval of oceanic total precipitable water vapor and cloud liquid water from Fengyun-3D microwave sounding instruments

Fengyun-3D (FY-3D) satellite is the latest polar-orbiting meteorological satellite launched by China and carries 10 instruments onboard.Its microwave temperature sounder (MWTS) and microwave humidity sounder (MWHS) can acquire a total of 28 channels of brightness temperatures,providing rich information for profiling atmospheric temperature and moisture.However,due to a lack of two important frequencies at 23.8 and 31.4 GHz,it is difficult to retrieve the total precipitable water vapor (TPW) and cloud liquid water path(CLW) from FY-3D microwave sounder data as commonly done for other microwave sounding instruments.Using the channel similarity between Suomi National Polar-orbiting Partnership (NPP) advanced technology microwave sounder (ATMS) and FY-3D microwave sounding instruments,a machine learning (ML) technique is used to generate the two missing low frequency channels of MWTS and MWHS.Then,a new data set named as combined microwave sounder (CMWS) is obtained,which has the same channel setting as ATMS but the spatial resolution is consistent with MWTS.A statistical inversion method is adopted to retrieve TPW and CLW over oceans from the FY-3D CMWS.The inter-comparison between different satellites shows that the inversion products of FY-3D CMWS and Suomi NPP ATMS have good consistency in magnitude and distribution.The correlation coefficients of retrieved TPW and CLW between CMWS and ATMS can reach 0.95 and 0.85,respectively.(Han Yang,Yang Jun,Hu Hao)

7.16 A preliminary study on the influence of Beijing urban spatial morphology on near-surface wind speed

In order to explore the actual impact of urban spatial morphology on real near-surface wind speed on the urban scale,taking Beijing,China as an example，this study adopted an urban-rural ratio method to construct a WsR (wind speed ratio) to quantify the impact of urbanization on the near-surface wind speed.The spatial morphological parameters such as building height,building density (BD),building standard deviation,floor area ratio (FAR),frontal area index,roughness length,sky view factor (SVF) and fractal dimension at the 500 m spatial resolution were calculated,and further the relationship of these morphological parameters and WsR was analyzed.Results show that due to urbanization,the minimum and maximum average annual wind speed of urban areas are 56% and 160% of the suburban wind speed,and urbanization can reduce the wind speed in urban areas at different times by 3% to 27%.On the urban scale,there are significant spatial correlations between the eight morphological parameters and WsR.Except for the quadratic curve of BD and WsR,the other parameters are significantly linearly related to WsR.FAR,FAI and SVF,the three most significant impact factors,can individually explain 51%,48% and 48% of the change of WsR.(Liu Yonghong,Xu Yongming,Zhang Fangmin)

7.17 城市生態(tài)氣象監(jiān)測(cè)評(píng)估初步研究與實(shí)踐——以北京為例

氣象條件作為影響生態(tài)系統(tǒng)最活躍、最直接的驅(qū)動(dòng)因子，影響著生態(tài)系統(tǒng)的質(zhì)量和人類(lèi)生存的環(huán)境，關(guān)系著生態(tài)保護(hù)和建設(shè)的成果，而城市生態(tài)系統(tǒng)具有與其他系統(tǒng)不一樣的氣候特征，目前還未形成一套有關(guān)城市的生態(tài)氣象監(jiān)測(cè)評(píng)估方法?；谏鷳B(tài)氣象學(xué)理論，分別從城市氣候環(huán)境、與氣候相關(guān)的陸表環(huán)境、大氣環(huán)境、人居環(huán)境以及城市高影響天氣氣候事件等5個(gè)方面選擇不同的要素和指標(biāo)開(kāi)展了城市生態(tài)氣象監(jiān)測(cè)評(píng)估初步研究，并以北京為例，利用2018年國(guó)家和區(qū)域自動(dòng)氣象站資料、大氣成分觀測(cè)資料、2002—2018年MODIS衛(wèi)星資料、Landsat及環(huán)境一號(hào)衛(wèi)星資料，開(kāi)展了2018年北京城市生態(tài)氣象監(jiān)測(cè)評(píng)估。監(jiān)測(cè)評(píng)估顯示：（1）2018年北京城市“熱島”和“干島”氣候特征明顯，并在北京二環(huán)與五環(huán)之間存在一個(gè)“冂”形風(fēng)速低值區(qū)。（2）2018年北京陸表生態(tài)環(huán)境、大氣環(huán)境、人居環(huán)境進(jìn)一步好轉(zhuǎn)：其中植被覆蓋度達(dá)61.6%，創(chuàng)2002年以來(lái)新高，氣象條件貢獻(xiàn)率達(dá)50%，生態(tài)涵養(yǎng)區(qū)植被生態(tài)質(zhì)量處于正常偏好的面積比例達(dá)93.2%；中心城區(qū)陸表溫度為2011年以來(lái)最低值；重要水源地密云水庫(kù)、官?gòu)d水庫(kù)水體面積均為2000年以來(lái)最大值；氣溶膠光學(xué)厚度、霾日數(shù)、大氣靜穩(wěn)指數(shù)分別較過(guò)去4年平均值下降14%、31%和8%，大氣擴(kuò)散條件偏好，對(duì)霾日減少貢獻(xiàn)率達(dá)21%，外地污染傳輸對(duì)PM2.5貢獻(xiàn)達(dá)到53%；城市生態(tài)冷源較2013年明顯增加，城市“熱島”得到緩解。（3）歷史罕見(jiàn)的夏季高溫悶熱、冬季階段低溫、極端強(qiáng)降水以及持續(xù)無(wú)降水等高影響天氣氣候事件給城市安全運(yùn)行和生態(tài)環(huán)境帶來(lái)不利影響。綜合評(píng)估表明，2018年北京氣象條件總體利于陸表生態(tài)環(huán)境改善，有利的氣候條件提高了生態(tài)環(huán)境的質(zhì)量，但城市生態(tài)質(zhì)量仍面臨著極端天氣氣候事件、城市熱島、低風(fēng)速以及外來(lái)大氣污染輸送等風(fēng)險(xiǎn)。（劉勇洪，軒春怡，李梓銘）

7.18 基于1 km網(wǎng)格的北京暴雨洪澇災(zāi)害風(fēng)險(xiǎn)區(qū)劃

目前許多城市暴雨洪澇災(zāi)害綜合風(fēng)險(xiǎn)區(qū)劃對(duì)暴雨在復(fù)雜地形下可能引發(fā)的山洪與地質(zhì)災(zāi)害造成的高風(fēng)險(xiǎn)以及對(duì)城市交通安全風(fēng)險(xiǎn)估計(jì)不足，同時(shí)常規(guī)的氣象觀測(cè)資料已難以描述暴雨致災(zāi)危險(xiǎn)性精細(xì)化分布。本文基于自然災(zāi)害風(fēng)險(xiǎn)評(píng)估理論，利用遴選的293個(gè)北京氣象自動(dòng)站2006—2017年逐時(shí)降水觀測(cè)資料、北京2015年1:25萬(wàn)基礎(chǔ)地理信息、2016年Landsat8晴空遙感影像、災(zāi)情資料以及網(wǎng)格化的社會(huì)經(jīng)濟(jì)資料，在承災(zāi)體暴露度基礎(chǔ)上充分考慮了承災(zāi)體對(duì)暴雨引發(fā)的城市積澇、山洪與地質(zhì)災(zāi)害災(zāi)損敏感性差異，從暴雨致災(zāi)危險(xiǎn)性、孕災(zāi)環(huán)境敏感性、承災(zāi)體易損性3個(gè)方面開(kāi)展了北京地區(qū)暴雨災(zāi)害1 km分辨率的精細(xì)網(wǎng)格化風(fēng)險(xiǎn)評(píng)估與區(qū)劃，并結(jié)合實(shí)際案例進(jìn)行了分析。結(jié)果顯示：（1）基于高密度降水觀測(cè)資料提取的網(wǎng)格化短歷時(shí)暴雨頻次和暴雨量能較為精細(xì)地評(píng)估致災(zāi)危險(xiǎn)性；基于遙感與GIS提取的不透水蓋度、地形起伏度與河網(wǎng)密度可有效評(píng)估暴雨洪澇孕災(zāi)環(huán)境敏感性；基于1 km網(wǎng)格化的GDP、人口密度和路網(wǎng)密度以及災(zāi)損敏感系數(shù)可有效評(píng)估暴雨引發(fā)的積澇、山洪與地質(zhì)災(zāi)害對(duì)人員、財(cái)產(chǎn)和公路交通的易損性；（2）與已有成果比較，本次北京暴雨洪澇風(fēng)險(xiǎn)區(qū)劃不但凸顯了暴雨對(duì)城市的積澇風(fēng)險(xiǎn)，也凸顯了暴雨引發(fā)的山洪與地質(zhì)災(zāi)害風(fēng)險(xiǎn)，同時(shí)突出了暴雨對(duì)城市交通設(shè)施安全的影響；（3）風(fēng)險(xiǎn)區(qū)劃結(jié)果基本反映了北京市暴雨災(zāi)害的潛在風(fēng)險(xiǎn)，北京暴雨洪澇災(zāi)害防御的重點(diǎn)區(qū)域應(yīng)放在風(fēng)險(xiǎn)較高的3個(gè)區(qū)域。（軒春怡，劉勇洪，楊曉燕）