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 Applications of QC and merged Doppler spectral density data from Ka-band cloud radar to microphysics retrieval and comparison with airplane in situ observation

The new Chinese Ka-band solid-state transmitter cloud radar (CR) uses four operational modes with different pulse widths and coherent integration and non-coherent integration numbers to meet long-term cloud measurement requirements.The CR and an instrument-equipped aircraft were used to observe clouds and precipitation on the east side of Taihang Mountain in Hebei Province in 2018.To resolve the data quality problems caused by attenuation in the precipitation area,we focused on developing an algorithm for attenuation correction based on rain drop size distribution (DSD) retrieved from the merged Doppler spectral density data of the four operational modes following data quality control (QC).After dealiasing Doppler velocity and removal of range sidelobe artifacts,we merged the four types of Doppler spectral density data.Vertical air speed and DSD are retrieved from the merged Doppler spectral density data.Finally,we conducted attenuation correction of Doppler spectral density data and recalculated Doppler moments such as reflectivity,radial velocity,and spectral width.We evaluated the consistencies of reflectivity spectra from the four operational modes and DSD retrieval performance using airborne in situ observation.We drew three conclusions:First,the four operational modes observed similar reflectivity and velocity for clouds and lowvelocity solid hydrometeors; however,three times of coherent integration underestimated Doppler reflectivity spectra for velocities greater than 2 m s–1.Reflectivity spectra were also underestimated for low signal-tonoise ratios in the low-sensitivity operational mode.Second,QC successfully dealiased Doppler velocity and removed range sidelobe artifacts,and merging of the reflectivity spectra mitigated the effects of coherent integration and pulse compression on radar data.Lastly,the CR observed similar DSD and liquid water content vertical profiles to airborne in situ observations.Comparing the CR and aircraft data yielded uncertainty due to differences in observation space and temporal and spatial resolutions of the data.(Liu Liping,Ding Han,Dong Xiaobo)

1.2 Algorithms for Doppler spectral density data quality control and merging for the Ka-band solidstate transmitter cloud radar

The Chinese Ka-band solid-state transmitter cloud radar (CR) can operate in three different work modes with different pulse widths and coherent integration and non-coherent integration numbers to meet the requirement for long-term cloud measurements.The CR was used to observe cloud and precipitation data in the southern China in 2016.In order to resolve the data quality problems caused by coherent integration and pulse compression,which are used to detect weak clouds in the cloud radar,this study focuses on analyzing the consistencies of reflectivity spectra using the three modes and the influence of coherent integration and pulse compression,developing an algorithm for Doppler spectral density data quality control (QC) and merging based on multiple-mode observation data.After dealiasing Doppler velocity and artefact removal,the three types of Doppler spectral density data were merged.Then,Doppler moments such as reflectivity,radial velocity,and spectral width were recalculated from the merged reflectivity spectra.Performance of the merging algorithm was evaluated.Three conclusions were drawn.Firstly,four rounds of coherent integration with a pulse repetition frequency (PRF) of 8333 Hz underestimated the reflectivity spectra for Doppler velocities exceeding 2 m s–1,causing a large negative bias in the reflectivity and radial velocity when large drops were present.In contrast,two rounds of coherent integration affected the reflectivity spectra to a lesser extent.The reflectivity spectra were underestimated for low signal-to-noise ratios in the low-sensitivity mode.Secondly,pulse compression improved the radar sensitivity and air vertical speed observation,whereas the precipitation mode and coherent integration led to an underestimation of the number concentration of big raindrops and an overestimation of the number concentration of small drops.Thirdly,a comparison of the individual spectra with the merged reflectivity spectra showed that the Doppler moments filled in the gaps in the individual spectra during weak cloud periods,reduced the effects of coherent integration and pulse compression in liquid precipitation,mitigated the aliasing of Doppler velocity,and removed the artefacts,yielding a comprehensive and accurate depiction of most of the clouds and precipitation in the vertical column above the radar.The recalculated moments of the Doppler spectra had better quality than those merged from raw data.(Liu Liping,Zheng Jiafeng)

1.3 Statistical characteristics of raindrop size distribution in South China summer based on the vertical structure derived from VPR-CFMCW

The raindrop size distribution (DSD) characteristics during the precipitation season are analyzed using data collected by an OTT Particle Size Velocity (Parsivel) disdrometer and a Vertical Pointing Radar with C-band Frequency Modulation Continuous Wave (VPR-CFMCW) technology.The two datasets were collected at the same site in Longmen,Guangdong Province,which is the precipitation center of South China,from June to July in 2016 and 2017.We evaluate different fitting methods for the gamma model function and choose a nonlinear least-squares method to fit DSD.Based on the radar reflectance obtained by VPR-CFMCW,the precipitating clouds that occur during the summer precipitation season in South China are classified into four types (i.e.,convective,stratiform,mixture,and shallow).The characteristic parameters and the gamma model parameters of different precipitation types are compared.Avoiding the limitations of rainfall classification at the surface,the new classification quantifies the characteristics of mixture and shallow precipitation.The results show that the stratiform precipitation makes up 43.1% of the summer precipitation processes in South China,and the contribution of convective precipitation to total rainfall is 62.7%.The precipitation parameters of the four types of precipitation,such as the rain rate (R),the mass-weighted mean diameter (D-m),the radar reflectance (Z),and the liquid water content (LWC),follow the pattern:convective＞mixture＞stratiform＞shallow.The DSD characteristics of the four precipitating cloud types are investigated.For the DSD of convective and mixture precipitation,the spectra width is similar but the rain drop concentration of the mixture is smaller.For the DSD of stratiform and shallow clouds,the rain drop concentrations are similar,but the spectra widths of the shallow clouds are smaller.In addition,the relationships between mu-Lambda,D-m-N-w,D-m-R,and Z-R are obtained.These new relationships will help improve the accuracy of precipitation estimation and deepen the understanding of the characteristics of surface precipitation microphysical parameters for different types of precipitating clouds in South China.(Huo Zhaoyang,Ruan Zheng,Wei Ming)

1.4 Dual CCD detection method to retrieve aerosol extinction coefficient profile

The profile of aerosol extinction coefficient can help understand the air pollution transportation and development of the atmospheric boundary layer.The charge-coupled device (CCD)-laser aerosol detection system (CLADS) was widely used to measure the profile of aerosol extinction coefficient,which has excellent resolution near the ground.Traditionally,a constant aerosol scattering phase function and single scattering albedo (SSA) is assumed when retrieving the profile of aerosol extinction coefficient using the measured signals from CLADS.Sensitivity studies in this research show that aerosol scattering phase function leads to an uncertainty up to 462% of the retrieved profile of aerosol extinction coefficient,while SSA leads to an uncertainty up to 25%.A new method is proposed to derive the profile of aerosol extinction coefficient by using two CCD cameras.The aerosol scattering phase function can be determined by minimizing the difference between profiles of aerosol extinction coefficient from the two CCD cameras without any assumption.The profile of aerosol extinction coefficient can be retrieved with high accuracy by using our optimized aerosol scattering phase function.This method is validated by simulation studies where the relative difference between the pre-parameterized aerosol extinction profile and retrieved aerosol extinction profile is below 6%.This dual CCD detection system is employed in a field measurement and proved to be reliable.Our proposed method can obtain more accurate profile of aerosol extinction coefficient for further works about air pollution and atmospheric boundary layer development.(Lian Shaopeng,Bian Yuxuan,Zhao Gang)

1.5 Analysis of dual-polarimetric radar variables and quantitative precipitation estimators for landfall typhoons and squall lines based on disdrometer data in the southern China

Typhoon rainstorms often cause disasters in the southern China.Quantitative precipitation estimation (QPE) with the use of polarimetric radar can improve the accuracy of precipitation estimation and enhance the typhoon defense ability.On the basis of the observed drop size distribution (DSD) of raindrops,a comparison is conducted among the DSD parameters and the polarimetric radar observation retrieved from DSD in five typhoon and three squall line events that occurred in the southern China from 2016 to 2017.A new piecewise fitting method (PFM) is used to develop the QPE estimators for landfall typhoons and squall lines.The performance of QPE is evaluated by two fitting methods for two precipitation types using DSD data collected.Findings indicate that the number concentration of raindrops in typhoon precipitation is large and the average diameter is small,while the raindrops in squall line rainfall have opposite characteristics.The differential reflectivity (Z(DR)) and specific differential phase (K-DP) in these two precipitation types increase slowly with the reflectivity factor (Z(H)),whereas the two precipitation types have different Z(DR) and K-DP in the same Z(H).Thus,it is critical to fit the rainfall estimator for different precipitation types.Enhanced estimation can be obtained using the estimators for specific precipitation types,whether the estimators are derived from the conventional fitting method (CFM) or the PFM,and the estimators fitted using the PFM can produce better results.The estimators for the developed polarimetric radar can be used in operational QPE and quantitative precipitation foresting,and they can improve disaster defense against typhoons and heavy rains.(Zhang Yonghua,Liu Liping,Bi Shuoben)

1.6 青藏高原雅魯藏布大峽谷水汽通道入口處雨滴譜分布特征

利用墨脫2019年6—10月的雨滴譜儀數(shù)據(jù)，對(duì)雅魯藏布大峽谷水汽通道入口處的降水及雨滴譜特征進(jìn)行了統(tǒng)計(jì)分析。結(jié)果表明，雨強(qiáng)＜5 mm/h的降水占了降水頻次的98%，且占總降水量的80%。雨滴譜的譜寬隨著降水率的增加而增加，雨強(qiáng)大于1 mm/h的雨滴譜呈現(xiàn)雙模態(tài)結(jié)構(gòu)。從擬合的伽馬分布散點(diǎn)圖來看，墨脫地區(qū)的層狀云降水表現(xiàn)出較寬的滴譜范圍，log10Nw的范圍為2.1～4.6，Dm為0.4～1.7 mm。平均值分別為3.59和0.77 mm，與那曲、華北地區(qū)的平均值比較接近。而對(duì)流云降水具有海洋性降水的特征，表現(xiàn)出數(shù)濃度較大、質(zhì)量加權(quán)直徑較小的特點(diǎn)，log10Nw的范圍為3.1～4.7，Dm為0.9～2.4 mm。平均值分別為4.08和1.31 mm，接近于華東和華南的對(duì)流云伽馬參數(shù)分布平均值。對(duì)于層狀云來說，擬合的Z-R關(guān)系與那曲的接近，而對(duì)流云擬合的Z-R關(guān)系與墨脫的差異性較大，這與雨滴譜分布特征是一致的。（王改利，王志恩，劉黎平）。

1.7 基于災(zāi)情信息的1981—2017年北京地區(qū)降雹特征

對(duì)1981—2017年北京地區(qū)1010個(gè)高精度冰雹災(zāi)情信息進(jìn)行了統(tǒng)計(jì)分析。從年代際變化看，1981—1990年平均降雹日數(shù)為10 d，1991—2000年和2001—2010年年平均降雹日數(shù)均有所減少（5.67 d和4.33 d），而從2011年起，年平均降雹日數(shù)急劇增加到21 d。1981—1995年年平均最大冰雹直徑總體呈增加趨勢(shì)，2002年開始總體較小。從年變化看，冰雹日數(shù)的年變化呈明顯的單峰型即初夏峰型，4月起降雹日數(shù)逐漸增加并在6月達(dá)到峰值，其后緩慢下降。從空間分布看，北京地區(qū)的降雹分布十分廣泛，但高頻次降雹區(qū)域主要集中在北京西北部延慶區(qū)，平均每年至少發(fā)生兩次降雹，此外降雹高值區(qū)還出現(xiàn)在城區(qū)的海淀區(qū)。2010年后，降雹范圍明顯增大，同時(shí)降雹分布也由相對(duì)集中變?yōu)橄鄬?duì)均勻。（虎雅瓊，邊宇軒，黃夢(mèng)宇）

1.8 利用Ka波段毫米波雷達(dá)功率譜反演云降水大氣垂直速度和雨滴譜分布研究

利用中國(guó)氣象科學(xué)研究院2016年華南云降水試驗(yàn)中Ka波段毫米波雷達(dá)探測(cè)一次層狀云降水過程，開展了云內(nèi)大氣垂直速度和雨滴譜的反演研究，并與地面激光雨滴譜儀和微降水雷達(dá)的測(cè)量雨滴譜結(jié)果進(jìn)行對(duì)比分析。首先，采用小粒子示蹤法從功率譜密度中反演大氣垂直速度以得到靜止空氣條件下的功率譜密度，進(jìn)而利用粒子下落末速度-粒子直徑關(guān)系反演出雨滴譜，最后進(jìn)行標(biāo)準(zhǔn)化的Gamma分布擬合。研究表明：（1）云降水從零度層到地面1 km，主要由下沉氣流主導(dǎo)，近地面大氣浮游粒子和直流干擾造成的晴空雜波會(huì)影響雷達(dá)的功率譜分布；受動(dòng)態(tài)范圍限制，回波強(qiáng)度過飽和現(xiàn)象會(huì)影響近地面大氣垂直速度的反演結(jié)果。（2）毫米波雷達(dá)CR、微雨雷達(dá)MRR和地面雨滴譜儀測(cè)量回波強(qiáng)度存在一定差異，MRR相較于CR與地面雨滴譜儀測(cè)量偏差較?。辉诜€(wěn)定降水時(shí)CR和MRR功率譜密度對(duì)比較為一致。（3）CR和MRR反演雨滴譜對(duì)比試驗(yàn)中，雨滴譜反演對(duì)大氣垂直速度十分敏感，大氣垂直速度的變化會(huì)使CR反演雨滴譜隨著高度增加數(shù)濃度量級(jí)變大、粒子平均半徑變小。CR反演的雨滴譜與MRR反演結(jié)果基本一致，驗(yàn)證了CR功率譜反演雨滴譜方法的可靠性。（4）CR與地面雨滴譜儀雨滴譜擬合參數(shù)的對(duì)比表明，CR大氣垂直反演的雨滴譜與地面雨滴譜相比粒子平均直徑Dm較小，數(shù)濃度則較為一致。（馬寧堃，劉黎平，鄭佳鋒）

1.9 杭州“12·05”降雪天氣過程的偏振雷達(dá)觀測(cè)分析

國(guó)內(nèi)利用新一代多普勒天氣雷達(dá)已經(jīng)開展了較多冬季天氣過程的分析研究，但隨著國(guó)內(nèi)雷達(dá)網(wǎng)逐漸升級(jí)到雙線偏振雷達(dá)，如何將偏振參量應(yīng)用于冬季業(yè)務(wù)預(yù)報(bào)成為了目前需要解決的問題。利用杭州臨安C波段雙線偏振雷達(dá)觀測(cè)的2015年12月5日一次降雪過程資料及地面和探空資料，通過提出的基于零度層亮帶識(shí)別的降雪相態(tài)識(shí)別方法和降雪累計(jì)時(shí)間統(tǒng)計(jì)方法，分析了雷達(dá)參量、零度層亮帶的時(shí)空演變及統(tǒng)計(jì)的降雪累計(jì)時(shí)間分布特征，并與地面和探空資料對(duì)比，探索了雙線偏振雷達(dá)在冬季降雪預(yù)報(bào)中的優(yōu)勢(shì)。結(jié)果表明：（1）冬季降水相比夏季連續(xù)性降水回波強(qiáng)度偏弱，雨、雪的差分反射率因子、相關(guān)系數(shù)差別不大。（2）零度層亮帶在某些方位并不是水平的，大多數(shù)情況下為偏離雷達(dá)站的不規(guī)則環(huán)狀或者線狀，且某些時(shí)刻還有垂直零度層亮帶存在。（3）降雪累計(jì)時(shí)間分布與實(shí)際降雪厚度分布基本一致，統(tǒng)計(jì)方法為地區(qū)降雪厚度的估測(cè)提供了可能。（4）零度層亮帶的演變與地面和探空溫度的空間、時(shí)間變化一致，相比單極化雷達(dá)使用雙線偏振雷達(dá)觀測(cè)零度層亮帶更加可靠。（魏瑋，劉黎平，吳翀）

1.10 利用相控陣及雙偏振雷達(dá)對(duì)2016年6月3日華南一次強(qiáng)對(duì)流過程的分析

結(jié)合X波段相控陣?yán)走_(dá)（XPAR）和S波段雙偏振天氣雷達(dá)（SPOL）及地面和探空觀測(cè)資料，分析了2016年6月3日發(fā)生在華南的一次超級(jí)單體中小尺度特征。結(jié)果表明：（1）SPOL的多普勒參量和雙偏振參量可以觀測(cè)到超級(jí)單體的強(qiáng)度、速度和相態(tài)分布，以及超級(jí)單體的入流和出流影響鉤狀回波的形成。（2）XPAR可以獲取時(shí)空分辨率遠(yuǎn)高于SPOL的觀測(cè)資料，可以彌補(bǔ)SPOL仰角層嚴(yán)重不足的缺陷，觀測(cè)到超級(jí)單體完整的垂直結(jié)構(gòu)，可更精確地描述超級(jí)單體的短時(shí)演變。（3）超級(jí)單體鉤狀回波附近給地面帶來了降溫、大風(fēng)和強(qiáng)降水，超級(jí)單體經(jīng)過地區(qū)均有明顯降溫和風(fēng)區(qū)。研究結(jié)果證明相控陣?yán)走_(dá)和雙偏振雷達(dá)對(duì)認(rèn)識(shí)對(duì)流單體中小尺度系統(tǒng)的發(fā)展演變有較大幫助。（于明慧，劉黎平，吳翀）

1.11 風(fēng)廓線雷達(dá)資料在GRAPES-Meso模式中的同化應(yīng)用研究

以未來業(yè)務(wù)化應(yīng)用為目標(biāo)，進(jìn)行了業(yè)務(wù)數(shù)值預(yù)報(bào)模式GRAPES-Meso（Global/Regional Assimilation and Prediction System）中的風(fēng)廓線雷達(dá)資料同化應(yīng)用研究?；?015年7月的全國(guó)風(fēng)廓線雷達(dá)觀測(cè)數(shù)據(jù)，首先建立了面向同化應(yīng)用的風(fēng)廓線雷達(dá)資料兩步質(zhì)量控制方案。通過對(duì)比分析質(zhì)量控制前后風(fēng)廓線雷達(dá)觀測(cè)資料集與歐洲中期天氣預(yù)報(bào)中心再分析資料ERA-Interim的差值場(chǎng)特征，論證了質(zhì)量控制方案的合理性，兩步質(zhì)控后風(fēng)場(chǎng)誤差顯著減小，同時(shí)觀測(cè)背景差更接近高斯分布，符合數(shù)值同化應(yīng)用假設(shè)。將質(zhì)量控制后的風(fēng)廓線雷達(dá)資料應(yīng)用于GRAPES-3DVar系統(tǒng)，開展有、無風(fēng)廓線雷達(dá)資料同化的對(duì)比試驗(yàn)，通過批量試驗(yàn)和臺(tái)風(fēng)“蓮花”個(gè)例分析來探討風(fēng)廓線雷達(dá)資料同化對(duì)數(shù)值預(yù)報(bào)的影響。研究表明，在循環(huán)同化過程中加入風(fēng)廓線雷達(dá)資料對(duì)數(shù)值模式初始場(chǎng)有一定改善，風(fēng)場(chǎng)、溫度場(chǎng)、濕度場(chǎng)的分析誤差均有減小，從而使短期降水（0～12 h）的預(yù)報(bào)技巧得以提高。針對(duì)臺(tái)風(fēng)暴雨個(gè)例分析結(jié)果表明，風(fēng)廓線雷達(dá)資料同化能有效地調(diào)整臺(tái)風(fēng)降水區(qū)的動(dòng)力結(jié)構(gòu)和水汽分布，在模式中形成更有利于對(duì)流發(fā)展的環(huán)境條件，從而更好地預(yù)報(bào)降水的位置與強(qiáng)度。（王丹，阮征，王改利）

1.12 X波段雙線偏振雷達(dá)數(shù)據(jù)質(zhì)量分析及控制方法

利用雙偏振參量在弱降水過程中性質(zhì)均一、隨時(shí)空變化緩慢的特征，選取北京、佛山地區(qū)弱降水過程的觀測(cè)資料，通過將較長(zhǎng)時(shí)間觀測(cè)結(jié)果沿徑向或方位累積的方法，分析雙偏振參量測(cè)量精確度受地物、避雷針、旋轉(zhuǎn)及俯仰關(guān)節(jié)的影響，并提出相應(yīng)的質(zhì)控方法。得出以下結(jié)論：（1）差分反射率（ZDR）、相關(guān)系數(shù)（ρhv）及差分傳播相位（ΦDP）比水平反射率（Z）對(duì)地物更敏感，其中在地物處ρhv小于0.85，ZDR低于-1 dB。根據(jù)降雨與地物之間偏振參量特征的不同，將ρhv長(zhǎng)時(shí)間累積能有效地識(shí)別地物回波。（2）每根避雷針對(duì)雙偏振參量影響的方位和幅值是近似一致的。在以避雷針為中心的±15°的方位范圍內(nèi)，ZDR增大0.4～1.5 dB，ρhv降低0.01以下，Z降低1～2 dBz，且均在避雷針中心處影響達(dá)到極值。通過基于上述方位的統(tǒng)計(jì)訂正可以較好地去除避雷針對(duì)雙偏振參量的影響。（3）雷達(dá)旋轉(zhuǎn)關(guān)節(jié)的異常會(huì)導(dǎo)致ZDR在水平方向上不平穩(wěn)變化，而俯仰關(guān)節(jié)異常會(huì)使ZDR在高、低仰角差距較大，通過ZDR沿方位一段時(shí)間的累積得到各層仰角ZDR變化曲線，用此曲線來實(shí)現(xiàn)ZDR的誤差標(biāo)定。通過檢驗(yàn)，本文提出的質(zhì)量控制方法有效地提升了X波段雙偏振雷達(dá)的數(shù)據(jù)質(zhì)量，為其在業(yè)務(wù)中的進(jìn)一步推廣提供了支持。（王超，吳翀，劉黎平）

2 青藏高原天氣研究

2 Research on weather over the Tibetan Plateau

2.1 熱源驅(qū)動(dòng)下青藏高原云降水上游-下游對(duì)流“組織化”模型

青藏高原為“亞洲水塔”的對(duì)流云敏感區(qū)。高原南側(cè)來自低緯海洋“大三角扇形”水汽輸送構(gòu)成了高原云降水的水汽供應(yīng)源，且此“亞洲水塔”水汽源可跨越赤道追溯到南半球。夏半年，原上空大氣的物理屬性與赤道低緯地區(qū)有許多相似之處。有關(guān)文獻(xiàn)指出青藏高原東部夏季旺盛的中尺度對(duì)流活動(dòng)和巨大的積雨云“煙囪效應(yīng)”向上層大氣持續(xù)地輸送著熱量和水汽。從動(dòng)力學(xué)角度講，在對(duì)流邊界層中浮力是驅(qū)動(dòng)湍流的主要機(jī)制。這種湍流不是完全無規(guī)則的，而往往是有組織成熱泡和卷流之類可識(shí)別的結(jié)構(gòu)。青藏高原中部和東部爆米花狀組織化異常對(duì)流云系可揭示出與高原地形效應(yīng)、空氣密度小與湍流異常有關(guān)聯(lián)的特殊湍流—對(duì)流運(yùn)動(dòng)物理機(jī)制。

青藏高原是全球唯一的對(duì)流層中部“中空熱島”，隆升的高原地形和強(qiáng)大的表面輻射加熱形成了局地上升對(duì)流和高聳入對(duì)流層中部的熱源柱。統(tǒng)計(jì)發(fā)現(xiàn)1948—2018年青藏高原“熱島”（高溫“暖心”）氣溫緯向偏差值可達(dá)4.5 ℃以上。無疑，占中國(guó)約1/4面積持續(xù)存在如此強(qiáng)度的熱島已超越了世界上任何超級(jí)城市群落所產(chǎn)生的熱力效應(yīng)。通過流函數(shù)解析風(fēng)場(chǎng)分析發(fā)現(xiàn)，與視熱源相關(guān)的低層500 hPa渦度場(chǎng)高原區(qū)域呈逆時(shí)針旋轉(zhuǎn)氣旋環(huán)流，高層200 hPa則明顯為順時(shí)針旋轉(zhuǎn)反氣旋環(huán)流。從衛(wèi)星遙感動(dòng)態(tài)圖像可發(fā)現(xiàn)上層對(duì)流云團(tuán)往往圍繞高原中心順時(shí)針旋轉(zhuǎn)，顯然其與高原區(qū)域高層反氣旋環(huán)流系統(tǒng)相關(guān)聯(lián)。青藏高原“中空熱島”300～100 hPa呈高、低層互為反向環(huán)流結(jié)構(gòu)，其高層潛力釋放的類似臺(tái)風(fēng)“CISK”的自激反饋機(jī)制，導(dǎo)致高原高頻組織化異常對(duì)流云降水系統(tǒng)，顯然此類似臺(tái)風(fēng)結(jié)構(gòu)，大尺度三維立體渦旋系統(tǒng)與夏季高原特殊“空中熱島”的驅(qū)動(dòng)效應(yīng)亦密切相關(guān)。另外，全球 500 hPa以上整層水汽含量場(chǎng)亦可描述出青藏高原亦為全球唯一的“濕島”特征，這反映青藏高原亦是全球?qū)α鲗釉平邓诵膮^(qū)。通過分析1961—2015年夏季中國(guó)區(qū)域地面觀測(cè)站低云量資料可發(fā)現(xiàn)，雅魯藏布江、三江源與高原東南緣區(qū)域是中國(guó)區(qū)域低云量的極值區(qū)。有關(guān)青藏高原陡峭南坡水汽爬升的“熱驅(qū)動(dòng)力”研究發(fā)現(xiàn)，夏季青藏高原整層視熱源（熱源柱）導(dǎo)致高層輻散驅(qū)動(dòng)低層水汽流輻合，高原南坡—高原平臺(tái)“兩階梯耦合爬升模型”可實(shí)現(xiàn)源自低緯海洋暖濕氣流在陡峭南坡爬升的協(xié)同驅(qū)動(dòng)，為青藏高原對(duì)流組織化異常云降水提供強(qiáng)水汽源。

夏季高原特殊“空中熱島”的驅(qū)動(dòng)效應(yīng)印證了青藏高原這一熱驅(qū)動(dòng)形成的三維特殊的渦旋結(jié)構(gòu)對(duì)“亞洲水塔”大氣水分循環(huán)起著核心作用。這不僅可揭示出此特殊的渦旋結(jié)構(gòu)亦對(duì)“亞洲水塔”云降水活動(dòng)起著關(guān)鍵影響效應(yīng)，而且亦是青藏高原“世界屋脊”上游—下游云降水組織化對(duì)流觸發(fā)的重要機(jī)制。計(jì)算發(fā)現(xiàn)，長(zhǎng)江流域暴雨頻數(shù)與全國(guó)低云量相關(guān)分布特征呈現(xiàn)從青藏高原延伸至長(zhǎng)江下游地區(qū)帶狀高相關(guān)結(jié)構(gòu)。這充分表明長(zhǎng)江流域云降水組織化對(duì)流系統(tǒng)與上游高原“亞洲水塔”“熱驅(qū)動(dòng)”機(jī)制具有重要相關(guān)關(guān)系。

研究1979—2016年夏季青藏高原對(duì)流源東移軌跡發(fā)現(xiàn)，東移至下游長(zhǎng)江流域的對(duì)流系統(tǒng)可能源于青藏高原，也與前人的研究吻合。青藏高原大氣視熱源對(duì)局地與下游區(qū)域云降水過程水汽輸送流型等均呈顯著影響；夏季在高原熱力作用下對(duì)流層低層形成了輻合帶，隨后輻合帶在青藏高原東部邊緣激發(fā)出氣旋性渦旋，伴隨著充足的水汽輸送，氣旋性渦旋東移發(fā)展，在長(zhǎng)江中下游上空演變成為中尺度強(qiáng)對(duì)流云系統(tǒng)。統(tǒng)計(jì)分析發(fā)現(xiàn)，上述高層反氣旋相關(guān)環(huán)流系統(tǒng)向東延展，在長(zhǎng)江流域上空高層呈東—西反氣旋型輻散帶；中低層則為東—西輻合帶，此類三維環(huán)流相關(guān)結(jié)構(gòu)有助于在長(zhǎng)江流域產(chǎn)生組織化對(duì)流降水雨帶。有關(guān)研究結(jié)果表明，長(zhǎng)江流域暴雨與特大暴雨（23.4%）發(fā)生前期青藏高原上空水汽通量渦旋位移特征，統(tǒng)計(jì)發(fā)現(xiàn)存在明顯的水汽通量渦旋結(jié)構(gòu)東移影響到長(zhǎng)江流域異常降水事件。在長(zhǎng)江洪澇過程中，青藏高原地區(qū)中部和東部往往會(huì)出現(xiàn)爆米花狀對(duì)流云高頻突發(fā)現(xiàn)象，研究表明青藏高原水汽輸送通道及其對(duì)流云團(tuán)亦是影響中國(guó)區(qū)域旱澇形成的重要因素。上述研究可綜合描述出高原熱源驅(qū)動(dòng)相關(guān)環(huán)流渦旋，尤其高層帶狀向下游延伸的反氣旋型輻散結(jié)構(gòu)亦是“激發(fā)”下游“組織化”對(duì)流及東亞區(qū)域天氣災(zāi)害事件的關(guān)鍵動(dòng)力機(jī)制之一。（徐祥德）

2.2 冬季區(qū)域大氣重污染過程天氣氣候背景“大地形”“背風(fēng)坡”大氣動(dòng)力、熱力三維結(jié)構(gòu)綜合影響模型

京津冀及周邊地區(qū)位于青藏高原“二階梯”大地形的太行山東側(cè)和燕山南側(cè)的“半封閉”地形，是中國(guó)東部南—北向帶狀平原的最北端。深化京津冀秋冬季大氣重污染氣象成因認(rèn)識(shí)，為大幅減少重污染事件提供天氣、氣候變化影響的科學(xué)認(rèn)知，以回答京津冀地區(qū)大氣污染長(zhǎng)期變化趨勢(shì)的主要?dú)庀篁?qū)動(dòng)因素等關(guān)鍵科學(xué)問題，需從冬季京津冀特殊地理特征背景下大地形效應(yīng)及其氣候變化影響的視角，闡述區(qū)域大氣動(dòng)力、熱力三維結(jié)構(gòu)對(duì)大氣重污染生消過程的影響。研究表明，高原背風(fēng)坡垂直環(huán)流結(jié)構(gòu)季節(jié)性特征與中國(guó)區(qū)域霾日空間分布季節(jié)差異相吻合，西風(fēng)帶背景下秋冬季高原大地形東側(cè)存在類似的順時(shí)針下卷環(huán)流圈，類似背風(fēng)坡弱風(fēng)區(qū)“避風(fēng)港”效應(yīng)，其恰對(duì)應(yīng)霾日頻發(fā)峰值區(qū)。春夏季背風(fēng)坡則為逆時(shí)針垂直環(huán)流圈，其伴隨上升氣流特征；不同季節(jié)霾日頻數(shù)峰值大小依次為冬、秋、春、夏季。秋冬季盛行的西北季風(fēng)與大地形效應(yīng)協(xié)同作用是造成京津冀冬季霾年際變化顯著差異的重要因子。在冬季，值得注意的是高原大地形東側(cè)不僅背風(fēng)坡垂直環(huán)流出現(xiàn)“反轉(zhuǎn)”而且下游區(qū)域大氣垂直熱力結(jié)構(gòu)亦出現(xiàn)“逆轉(zhuǎn)”，大地形東側(cè)大氣對(duì)流層中層呈現(xiàn)了“上暖下冷”的大尺度“暖蓋”氣溫距平結(jié)構(gòu)特征，“背風(fēng)坡”地形效應(yīng)與“暖蓋”熱力結(jié)構(gòu)使中國(guó)東部上空大氣層結(jié)變得更加穩(wěn)定，由此有利于邊界層下壓、大氣逆溫頻次上升，為該區(qū)域大氣重污染過程形成提供了關(guān)鍵性氣候背景。

歷史數(shù)據(jù)分析表明，特別是從20世紀(jì)90年代中后期開始，到21世紀(jì)以來秋冬季盛行西北季風(fēng)作用和大氣擴(kuò)散能力減弱，且近年來受氣候變暖影響，對(duì)流層中層氣溫增幅，氣溫距平“暖蓋”結(jié)構(gòu)年代際特征更為顯著。研究表明，冬季青藏高原對(duì)應(yīng)冷源，其視熱源柱與中國(guó)東部區(qū)域平均霾日頻數(shù)存在顯著的相關(guān)性，我們?nèi)孕杷伎记嗖馗咴瓕?duì)氣候變暖響應(yīng)是否強(qiáng)化了上述“暖蓋”氣象條件，而與中國(guó)東部頻繁發(fā)生的霾事件是否存在關(guān)聯(lián)。敏感性模擬亦揭示出青藏高原變暖的熱力異常因素可影響中國(guó)東部霧霾發(fā)生頻率的機(jī)制，證實(shí)了氣候變暖背景下該區(qū)域霧霾頻發(fā)的年代際變化趨勢(shì)與青藏高原的熱源結(jié)構(gòu)變化呈顯著相關(guān)。通過分析研究亦進(jìn)一步證實(shí)了青藏高原的熱源結(jié)構(gòu)與對(duì)流層中層大尺度“暖蓋”特征存在十分明顯的關(guān)聯(lián)性。中國(guó)東部處于高原大地形東側(cè)，呈“半封閉”地理特征，京津冀為南-北向帶狀平原的最北端點(diǎn)。區(qū)域性大氣污染輸送亦是不可忽視的因素。從大氣環(huán)流形勢(shì)場(chǎng)上看，中國(guó)東部，尤其北方不利氣象條件往往污染區(qū)發(fā)生在低層，大多位于高壓系統(tǒng)后部或低壓系統(tǒng)主模態(tài)的控制下偏南氣流的強(qiáng)輻合區(qū)內(nèi)，且對(duì)流層中層氣溫距平“暖蓋”結(jié)構(gòu)和近地層高濕特征顯著。另外，統(tǒng)計(jì)表明持續(xù)性大范圍污染天氣過程與位勢(shì)高度距平場(chǎng)上中高層阻塞高壓的特殊氣象背景密切相關(guān)，這類特定阻塞高壓環(huán)流形勢(shì)的維持甚至可形成長(zhǎng)達(dá)5天持續(xù)性區(qū)域重污染天氣。由此，“大地形”“背風(fēng)坡”影響下不同尺度大氣環(huán)流模態(tài)與對(duì)流層“暖蓋”熱力結(jié)構(gòu)可構(gòu)成冬季區(qū)域大氣重污染過程特有的動(dòng)力、熱力三維結(jié)構(gòu)綜合影響模型。（徐祥德）

2.3 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 features 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,i.e.,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 the YRB summer rainfall.Using a Lagrangian forward trajectories tracing approach,we create a catalogue of OMEbased 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)

2.4 Identifying and contrasting the sources of the water vapor reaching the subregions of the Tibetan Plateau during the wet season

A Lagrangian approach is utilized to identify and compare the sources of water vapor transported to the four subregions of Tibetan Plateau (TP) during the wet season (May?August) of 1980?2016.We focus on the time scale and subseasonal variability of water vapor transport and the relationship between moisture supply and precipitation at the interannual scale.This study finds that:(1) The moisture sources for the four subregions differ significantly in both spatial pattern and magnitude and depend heavily on the combined effects of the summer monsoons,local recycling and the westerlies.(2) The spatial evolution of the moisture sources based on the backward trajectory analysis reveals that,although approximately 80% of the moisture is delivered to the target regions within 1–4 days,the individual subregions feature different transport pathways and associated time scales.(3) The subseasonal migration of the Indian summer monsoon regulates the importance of different moisture sources for the southern TP but not for the northern TP.Additionally,the subseasonal moisture source evolution differs greatly between the southeastern TP and the southwestern TP.(4) The interannual variability of precipitation over the whole TP during summer is negatively correlated with the variation in the moisture transported by the westerlies and is positively related to the moisture conveyed by the Indian summer monsoon for the northern TP and by adjacent moisture transport for the southern TP.(Chen Bin,Zhang Wei,Yang Shuai)

2.5 Evaluation of summer monsoon clouds over the Tibetan Plateau simulated in the ACCESS model using satellite products

Cloud distribution characteristics over the Tibetan Plateau in the summer monsoon period simulated by the Australian Community Climate and Earth System Simulator (ACCESS) model are evaluated using COSP [CFMIP (Cloud Feedback Model Intercomparison Project) Observation Simulator Package].The results show that the ACCESS model simulates less cumulus clouds at atmospheric middle levels when compared with observations from CALIPSO and CloudSat,but more ice clouds at high levels and drizzle drops at low levels.The model also has seasonal biases after the onset of the summer monsoon in May.While observations show that the prevalent high clouds at 9–10 km in spring shift downward to 7–9 km,the modeled maximum cloud fractions move upward to 12–15 km.The reason for this model deficiency is investigated by comparing model dynamical and thermodynamical fields with those of ERA-Interim.It is found that the lifting effect of the Tibetan Plateau in the ACCESS model is stronger than in ERA-Interim,which means that the vertical velocity in the ACCESS model is stronger and more water vapor is transported to the upper levels of the atmosphere,resulting in more high-level ice clouds and less middle-level cumulus clouds over the Tibetan Plateau.The modeled radiation fields and precipitation are also evaluated against the relevant satellite observations.(Hu Liang,Sun Zhian,Deng Difei)

2.6 The large-scale circulation patterns responsible for extreme precipitation over the North China Plain in midsummer

Extreme precipitation events over the North China Plain (NCP) in midsummer during 1979?2016 are classified into two types using objective cluster analysis:a northern pattern with heavy precipitation and a central-southern pattern with relatively moderate precipitation.The large-scale circulation patterns responsible for the midsummer extreme precipitation are then determined.In the northern NCP type,extreme precipitation accompanies a zonal gradient between an anomalous low-pressure system at high latitudes and the westward- and northward-extended western North Pacific subtropical high (WNPSH).Anomalous southwesterlies flow is driven by a trough that extended from the high latitudes to the northern NCP,where it encounters southeasterly wind flow induced by an anomalously northward-extended WNPSH and a southern low-pressure anomaly at low latitudes.Anomalous amounts of moisture are mainly transported from the tropical western Pacific by southeasterlies.In the central-southern NCP type,remarkable anomalous low-pressure systems control all of the northern China with centers over the Sichuan Basin and Northeast China.The westward-extended WNPSH occupies further south than that of the northern NCP type.The southwesterly low-level jet (LLJ) is more prevalent in the central-southern NCP type than in the northern NCP type.This southwesterly LLJ plays an important role in extreme precipitation over the central-southern NCP by transporting moisture primarily from the Bay of Bengal and the South China Sea and generating convergence.In addition,the upper-level anomalous strong divergence that is anchored over the right entrance of the westerly jet makes a greater contribution to extreme precipitation in the northern type than in the central-southern type.(Zhao Yang,Xu Xiangde,Li Jiao)

2.7 Effects of the Tibetan Plateau and its second staircase terrain on rainstorms over North China:From the perspective of water vapour transport

The effects of the Tibetan Plateau (TP) and its second staircase terrain (i.e.,the extension of the TP) on summer rainstorms over North China (NC) from the perspective of large-scale water vapour transport were investigated based on the frequency of summer rainstorms from 70 observational stations in NC and National Centers for Environmental Prediction reanalysis data from 1961 to 2010.Seven rainstorm cases over NC during 1981?2016 acquired from ERA-Interim reanalysis data and observational hourly precipitation data were selected.Two water vapour transport channels provided favourable backgrounds for rainstorms over NC.One channel flowed along the northern edge of the TP via westerlies.The other channel flowed along the eastern edges of the TP and its second staircase terrain accompanied with southerly monsoon airflow,with water vapour sources from the Bay of Bengal,South China Sea,and western Pacific.The abundant water vapour that was transported along the two channels not only offered a favourable moisture background for rainstorms over NC but also resulted in the development of water vapour flux vortexes that supplied convergence conditions for rainstorms in situ.At low levels,water vapour transport mainly flowed along the eastern edge of the TP second staircase terrain.The results from the Weather and Research Forecasting model simulation of a randomly selected rainstorm case originating from the TP to NC confirmed the vital effect of the TP second staircase terrain on rainstorms over NC accompanied with water vapour transport.(Zhao Yang,Xu Xiangde,Zhao Tianliang)

2.8 Trends in observed mean and extreme precipitation within the Yellow River Basin,China

We analyzed spatiotemporal precipitation trends within the Yellow River Basin (YRB) in China and examined the connection between the changes in average and extreme precipitation indices.Data from 423 weather stations recorded from 1961 to 2016 were analyzed using the Mann-Kendall test to explore the linear trends of relationships between various indices,along with a simple linear regression used to detect monotonic positive or negative trends in the annual and seasonal precipitation data.Moreover,we divided the YRB into three distinct topographic regions to better understand the effect of regional geography on precipitation patterns.Our results demonstrated that mean precipitation and extreme precipitation days in different areas of the YRB had different variation trends.Precipitation in the YRB overall showed a negative trend,as did extreme precipitation days in the lower YRB.Mean and extreme precipitation indices were significantly correlated both annually and seasonally.These results may be helpful in preparing for both drought and flood events.(Zhao Yang,Xu Xiangde,Huang Wubin)

2.9 The severity of drought and precipitation prediction in the eastern fringe of the Tibetan Plateau

The trend,severity,and duration of drought in the eastern fringe of the Tibetan Plateau (EFTP) have been investigated using the Mann-Kendall (M-K) trend test,standardized precipitation index (SPI),and generalized extreme value (GEV),using data obtained from 438 rainfall stations and reanalysis datasets for the period 1961?2014.A recent drought trend is evident from a decrease in rainfall,mainly occurring on the eastern slope of the TP (＜3000 m elevation); this is attributed to downward air flows over the eastern slope of the Tibetan Plateau (TP) induced by TP heating.Recent droughts have also been more severe,again mostly occurring on the eastern slopes.The duration of drought illustrates that extreme droughts are becoming more frequent.The study also predicted summer precipitation,due to its crucial role in drought research in the EFTP.Results show that the preceding May-June-July (MJJ) averaged column-integrated meridional water vapor transport (MWVT) from the South China Sea (SCS),Philippine Sea,and tropical western Pacific is a vital predictor of summer precipitation in the EFTP.A partial least squares (PLS) regression prediction model is therefore constructed,using the leading PLS components of preceding MJJ-averaged column-integrated MWVT.Compared to the observed summer rainfall,the PLS prediction model performs an excellent reconstructed skill with a correlation of 0.81 (1961–2006) and exhibits a promising forecast skill with a correlation of 0.67 (2007–2014).Results suggest that southerly moisture transport in early summer would help prevent summer drought in the EFTP.(Zhao Yang,Xu Xiangde,Liao Liufeng)

2.10 Precursory strong-signal characteristics of the convective clouds of the central Tibetan Plateau detected by radar echoes with respect to the evolutionary processes of an eastward-moving heavy rainstorm belt in the Yangtze River Basin

The integrated analysis was carried out of the data from a C-band frequency-modulated continuous-wave (C-FMCW) radar site in Naqu obtained during a rainstorm over the middle and lower reaches of the Yangtze River and the data concerning the three-dimensional structure of the circulation of the precipitation system that occurred over the lower reaches of the Yangtze River Basin during the Third Tibetan Plateau (TP) Atmospheric Experiment from August 15th to 19th,2014.The changes in the echo intensity at the C-FMCW radar site in Naqu were of regional indicative significance for the characteristics of the whole-layer apparent heat source Q1 in local areas and the region of the adjacent river source area,including the Yangtze River,Yellow River,and Lancang River (hereinafter referred to as the source area of three rivers),as well as to the vertical speeds due to the development of convection.This study indicates that the C-FMCW radar echo intensity of the plateau convection zone and the related power structures of the coupled dipole circulations in the middle layer of the atmosphere,as well as in the upper atmospheric level divergence and lower atmospheric level convergence,are important stimuli for convective clouds in this region.Furthermore,these radar data provided a physical image of the development and maintenance mechanisms of an eastward-moving heavy rainstorm belt.This study also shows that changes in the echo intensities at the C-FMCW radar site of Naqu can provide strong signals related to heavy rainstorm processes in the upper reaches of the Yangtze River.(Zhao Yang,Xu Xiangde,Ruan Zheng)

2.11 Diurnal variations in summer precipitation over the Yellow River Basin

The diurnal variations in summer precipitation over the Yellow River Basin (YRB) are investigated based on the National Centers for Environmental Prediction reanalysis dataset and hourly precipitation data from 481 gauge stations over the YRB during the time period 1981?2013.Three stair steps are identified to represent the upper,middle,and lower reaches of the YRB due to complex topography elevations over the different subregions of the YRB.The summer diurnal precipitation over the YRB shows significant spatial and temporal variations.The diurnal peaks in precipitation over the upper and middle reaches of the YRB occur in the evening and late afternoon,respectively.By contrast,double peaks in diurnal precipitation occur in the early morning and late afternoon over the lower reaches of the YRB.The diurnal peaks in summer precipitation along the YRB have an eastward transition,suggested to be associated with the westerlies transporting water vapor.Differing from the increasing tendency of summer hourly precipitation from west to east across the YRB with topography elevations decreased,a distinct reduction in hourly precipitation is observed over the transition region between the first and second stair steps in the YRB.Further analysis attributes this phenomenon to the regional descending airflow induced by the steep terrain along the slope of the Tibetan Plateau (TP).(Zhao Yang,Wang Minzhong,Li Jiao)

2.12 Linkage between moisture transport over the Yangtze River Basin and a critical area of the Tibetan Plateau during the Meiyu

Located downstream of the Tibetan Plateau (TP),the Yangtze River Basin (YRB) in China frequently experiences torrential rainfall and severe rainstorms within the zonally elongate Meiyu belt.Inter-annual variations in drought and flooding in the YRB are shown to be highly correlated with the upstream surface latent heat flux (SLHF) over the TP,suggesting that the SLHF over the TP can be a“strong signal”of Meiyu variability.Results show that the southeastern margin of the TP (SEMTP) is the most“sensitive area”of the“strong signal”.On inter-annual scales,low (high) SLHF over the SEMTP corresponds to high (low) humidity at upper levels,strong (weak) zonal moisture transport and a southerly (northerly) pattern of East Asian summer monsoon (EASM) moisture transport circulation in July.The anomalous moisture flow originating from the mid to low latitude oceans,converges in the east of the SEMTP and turns eastward (northward); thus,the SEMTP acts as the key area of redirection of moisture flow.The ridge of moisture transport is located at about 22.5°N (29.5°N) in East China for low (high) SLHF over the SEMTP.Under low SLHF conditions,the warm,humid airflow from the SEMTP creates favorable conditions for Meiyu rainfall and torrential rainstorms.Numerical simulation and sensitivity analyses using the mesoscale Weather Research and Forecasting (WRF) model further reveal that SLHF over the SEMTP shows pronounced“strong signal”features.The variation of intensity of SLHF over the SEMTP corresponds to the moisture transport structure of the Meiyu rain belt and the location of the ridge of the subtropical high in East China.An increase in the apparent heat source Q1 over the main body of the TP might explain the“strong signal”over the SEMTP.This apparent heat source plays an important role in modulating both the SLHF over the SEMTP and the location of the subtropical high circulation system.(Dong Lili,Xu Xiangde,Zhao Tianliang)

2.13 The causes of“vulnerable regions”to air pollution in winter in the Beijing-Tianjin-Hebei region:A topographic-meteorological impact model based on adaptive emission constraint technique

The Beijing-Tianjin-Hebei (BTH) region,with its complex terrain,has serious issues with air pollution.The northern and western parts of the BTH region are surrounded by the Yan Mountains and Loess Plateau (LP),and the south-central part of that region is a large open plain.Such special geographic configuration is prone to result in a concentrated pollution belt along the north-to-south direction on the eastern margin of the plateau,in addition to the influence of pollutant-emission sources and population distribution.In this study,based on an original adaptive nudging constraint method,we quantitatively analyzed the differences in the influence of emission sources under different dynamic and thermal conditions in the BTH region,which is impacted by a special large-scale leeward slope terrain.The mechanism of air pollution vulnerability and the comprehensive effects of terrain-meteorological conditions on air pollution in the BTH region were also discussed.The results indicated that the atmospheric diffusion conditions on the eastern side of the plateau were poor,and a subsynoptic-scale“vortex sequence”,which was composed of a series of linked vortices,was identified.The corresponding atmospheric pollution convergence line stretched from Beijing to Hebei to northern Henan in the lower atmosphere.On the eastern edge of the plateau,a“warm cover”formed by a temperature anomaly and a downdraft impeded the vertical diffusion of pollutants.Therefore,pollutants tended to converge at the eastern edge of the plateau,and the pollution belts would move longitudinally north and south along the topography of the eastern slope when south-westerly and north-easterly winds alternated.The movement generated a“train”of pollutants that were transported on the eastern edge of the plateau,which then caused air pollution to persist there.Such terrain-meteorological conditions amplified the effects of emissions by an average of 50% to 150% in the region,leading the eastern side of the LP to become a“naturally vulnerable region”to haze pollution region.(Meng Kai,Xu Xiangde,Xu Xiaobin)

2.14 青藏高原能量、水分循環(huán)影響效應(yīng)

青藏高原是世界上總輻射量最高的地區(qū)，也是全球超太陽(yáng)常數(shù)的極值區(qū)域之一。此處形成了一個(gè)“嵌入”對(duì)流層中部大氣的巨大的熱源，可以伸展到自由大氣，其超越了世界上任何超級(jí)城市群落所產(chǎn)生的中空熱島效應(yīng)，對(duì)全球與區(qū)域大氣環(huán)流系統(tǒng)變化的動(dòng)力“驅(qū)動(dòng)”產(chǎn)生了難以估計(jì)的效應(yīng)。與地形熱力過程季節(jié)變化密切相關(guān)的亞洲夏季風(fēng)是世界上范圍最廣和強(qiáng)度最強(qiáng)的季風(fēng)；從冬季到早春季節(jié)轉(zhuǎn)換過程中，由于太陽(yáng)輻射的影響造成青藏高原大地形感熱的“快速響應(yīng)”及其相對(duì)高值動(dòng)態(tài)移動(dòng)，在盛夏梅雨及其云降水帶前沿線恰好停滯于中國(guó)“三階梯”地形分布山地—平原過渡區(qū)。此現(xiàn)象表明，青藏高原可能扮演著夏季風(fēng)過程陸地—海洋—大氣相互作用的關(guān)鍵角色。中國(guó)區(qū)域低云量與總云量極值區(qū)均與青藏高原大江大河的源頭（長(zhǎng)江、瀾滄江、雅魯藏布江等）、中東部湖泊群與冰川集中區(qū)空間分布幾乎吻合，這表明“亞洲水塔”形成的關(guān)鍵因素與“世界屋脊”特有的云降水結(jié)構(gòu)不可分割。研究表明，青藏高原大氣熱源對(duì)局地與下游區(qū)域云降水過程水汽輸送流型等均有顯著影響。長(zhǎng)江流域降水與全國(guó)低云量存在一個(gè)明顯沿長(zhǎng)江流域的帶狀高相關(guān)結(jié)構(gòu)，充分表明長(zhǎng)江流域降水與上游“亞洲水塔”“熱驅(qū)動(dòng)”以及對(duì)流系統(tǒng)具有重要相關(guān)關(guān)系。從跨赤道經(jīng)向環(huán)流的視角可發(fā)現(xiàn)，夏季南、北半球跨赤道氣流低層強(qiáng)偏南、高層強(qiáng)偏北氣流出現(xiàn)在東亞地區(qū)和北美區(qū)域兩大地形對(duì)應(yīng)的赤道區(qū)，這2個(gè)跨赤道極值區(qū)恰與青藏高原、落基山高原位置相對(duì)應(yīng)。青藏高原緯向與經(jīng)向環(huán)流圈結(jié)構(gòu)與區(qū)域-全球大氣環(huán)流相關(guān)機(jī)制，印證了“世界屋脊”隆起大地形的“熱驅(qū)動(dòng)”及其對(duì)流活動(dòng)在全球能量、水分循環(huán)中的作用。青藏高原特殊水汽三維結(jié)構(gòu)分布和跨半球的緯向和經(jīng)向大氣垂直環(huán)流圖表明青藏高原對(duì)全球尺度大氣環(huán)流變化的貢獻(xiàn)顯著。文章進(jìn)一步以東亞、全球水循環(huán)的視角，提出了青藏高原作為全球性大氣“水塔”的觀念，認(rèn)為高原地區(qū)一個(gè)水塔的“供水”和“蓄水”循環(huán)體系，特別是高原地表冰川、積雪和湖泊作為“蓄水池”系統(tǒng)，使得所有的河流可作為“輸水管道”，將“水塔”的水向周邊區(qū)域輸送出去，高層大氣也提供向外輸送的渠道。青藏高原特殊的跨半球大氣水分循環(huán)可構(gòu)建“世界水塔”與其周邊地區(qū)獨(dú)特的水文功能概念，綜合描繪了青藏高原“世界水塔”及其地球上一個(gè)完整的行星尺度陸地-海洋-大氣水分循環(huán)物理圖像。（徐祥德，馬耀明，孫嬋）

2.15 青藏高原“亞洲水塔”效應(yīng)和大氣水分循環(huán)特征

青藏高原是東亞海陸氣相互作用最敏感的地區(qū)之一。青藏高原大氣水分循環(huán)結(jié)構(gòu)特征不僅反映了西風(fēng)氣流與“大三角扇形”影響域季風(fēng)水汽流的相互作用特征，而且凸現(xiàn)出該區(qū)域?yàn)槿蚰芰?、水汽的交換關(guān)鍵區(qū)，構(gòu)成“亞洲水塔”形成的重要背景。隆升的高原地形和強(qiáng)大的表面輻射加熱形成了局地上升對(duì)流和高聳入對(duì)流層中部中空“熱源柱”。研究揭示出此熱力驅(qū)動(dòng)下青藏高原高、低層互為反環(huán)流類似臺(tái)風(fēng)的自激反饋機(jī)制，其提供了“亞洲水塔”水汽匯流與抽吸動(dòng)力效應(yīng)。“亞洲水塔”熱源驅(qū)動(dòng)機(jī)制有助于“世界屋脊”大氣“熱島”“濕島”的形成和維持，使暖濕氣流從低緯海洋向高原輸送、匯聚。針對(duì)“世界屋脊”高原對(duì)流頻繁、云降水異常特征，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)。分析表明，低緯熱帶海洋成為“亞洲水塔”大氣水分循環(huán)的重要水汽源區(qū)，水汽源區(qū)可跨越赤道追蹤到南半球。提出了青藏高原熱力驅(qū)動(dòng)下大氣水分循環(huán)結(jié)構(gòu)類似全球性大氣水塔的觀點(diǎn)，青藏高原特殊的跨半球大氣水分循環(huán)構(gòu)建出“亞洲水塔”和其周邊地區(qū)獨(dú)特的大氣—水文功能體系。給出了西風(fēng)與季風(fēng)協(xié)同作用背景下青藏高原為核心區(qū)的陸地—海洋—大氣相互作用的“亞洲水塔”大氣水分循環(huán)物理圖像。（徐祥德，董李麗，趙陽(yáng)）

2.16 西北太平洋熱帶氣旋路徑異常偏折的分類特征

基于中國(guó)臺(tái)風(fēng)網(wǎng)CMA-STI熱帶氣旋（TC）最佳路徑資料，對(duì)1949—2016年西北太平洋TC路徑發(fā)生異常偏折的地理位置進(jìn)行K-means聚類分析，并將其分為5個(gè)區(qū)域。對(duì)各區(qū)TC路徑異常偏折的頻數(shù)、方向變化、周期及時(shí)間變率等特征進(jìn)行分析。結(jié)果表明：（1）不同分區(qū)TC異常偏折高頻月份不同，緯度較高區(qū)域主要發(fā)生在夏季，緯度較低區(qū)域則主要發(fā)生在秋季。（2）異常右折TC在發(fā)生偏折前移向主要為西北向，偏折后為北向；異常左折TC偏折前主要為北向，偏折后主要轉(zhuǎn)為西北向。（3）西北太平洋TC異常偏折總頻數(shù)存在準(zhǔn)2～4年、準(zhǔn)3～6年的年際變化周期，其長(zhǎng)期變化趨勢(shì)表現(xiàn)為20世紀(jì)80年代中期之前呈增加趨勢(shì)，其后呈減少趨勢(shì)，低緯區(qū)域年變化與之最為相似，中高緯區(qū)域變化趨勢(shì)不明顯。（4）將研究區(qū)域按5°×5°進(jìn)一步柵格化統(tǒng)計(jì)TC異常偏折頻數(shù)的時(shí)間變率，發(fā)現(xiàn)其地理分布表現(xiàn)為中國(guó)沿海為正、臺(tái)灣島以東海域?yàn)樨?fù)的變化特征。其中沿海的增加趨勢(shì)主要由異常右折的增加引起，臺(tái)灣島以東洋面的減弱趨勢(shì)主要由異常左折的減少引起。（5）異常右折TC強(qiáng)度增強(qiáng)的高頻中心主要位于菲律賓半島以東洋面，次中心位于中國(guó)南海中部，而強(qiáng)度減弱位于臺(tái)灣島西南區(qū)域；異常左折TC強(qiáng)度增強(qiáng)的高頻中心位于南海中部，強(qiáng)度減弱中心位于我國(guó)東南沿海。（王敏，徐祥德，李英）

2.17 臺(tái)風(fēng)Polly（9216）和Matmo（1410）對(duì)遼東半島降水影響的對(duì)比分析

臺(tái)風(fēng)Matmo（1410）和Polly（9216）影響遼東半島時(shí)的路徑近乎重合，但臺(tái)風(fēng)Polly造成了大范圍的暴雨和大暴雨，而臺(tái)風(fēng)Matmo僅造成個(gè)別測(cè)站出現(xiàn)暴雨。利用中國(guó)氣象局熱帶氣旋年鑒、FY-2D衛(wèi)星的黑體亮度溫度（TBB）產(chǎn)品（0.1°×0.1°）、日本氣象廳TBB資料、大連地區(qū)逐時(shí)自動(dòng)氣象站降雨量資料、常規(guī)觀測(cè)資料和歐洲中期數(shù)值預(yù)報(bào)中心ERA-Interim全球再分析資料（0.125°×0.125°），對(duì)2個(gè)臺(tái)風(fēng)影響遼東半島的降水過程進(jìn)行了對(duì)比分析。結(jié)果表明：（1）2個(gè)臺(tái)風(fēng)均進(jìn)入西風(fēng)槽區(qū)而變性，在其西側(cè)和北側(cè)分別具有冷鋒和暖鋒鋒生，遼東半島的降水均發(fā)生在臺(tái)風(fēng)低壓環(huán)流北側(cè)的鋒生區(qū)和環(huán)境風(fēng)垂直切變明顯增大過程中。但2個(gè)變性臺(tái)風(fēng)的大尺度環(huán)流背景卻差異顯著，臺(tái)風(fēng)Polly與西北側(cè)較強(qiáng)冷空氣相互作用，鋒區(qū)隨高度增加向西北傾斜，且與低空東南急流相連獲得豐富水汽供應(yīng)，強(qiáng)降水持續(xù)時(shí)間長(zhǎng)，而臺(tái)風(fēng)Matmo與東北部對(duì)流層低層冷空氣相互作用明顯，鋒區(qū)隨高度增加略向東北傾斜，但其低空急流水汽通道被快速隔斷，不穩(wěn)定度和動(dòng)力抬升條件減弱，強(qiáng)降水持續(xù)時(shí)間短。（2）臺(tái)風(fēng)Polly和Matmo的降水分布非對(duì)稱明顯，均出現(xiàn)在順垂直切變方向的左側(cè)，但臺(tái)風(fēng)相對(duì)于高空槽的位置不同，對(duì)流活動(dòng)發(fā)展的方位有所差異。臺(tái)風(fēng)Polly中尺度對(duì)流活動(dòng)在其北側(cè)發(fā)展旺盛，且向西南彎曲，而臺(tái)風(fēng)Matmo對(duì)流活動(dòng)僅發(fā)生在臺(tái)風(fēng)環(huán)流東北側(cè)。（3）臺(tái)風(fēng)的強(qiáng)降水落區(qū)還與其低層環(huán)流內(nèi)冷、暖平流的活動(dòng)密切相關(guān)。臺(tái)風(fēng)Polly西北側(cè)的冷平流加強(qiáng)，遼東半島位于臺(tái)風(fēng)北側(cè)低層冷暖平流交匯區(qū)，水平輻合加強(qiáng)，深厚的上升運(yùn)動(dòng)維持，而臺(tái)風(fēng)Matmo東北側(cè)的冷平流加強(qiáng)，遼東半島逐漸位于臺(tái)風(fēng)西側(cè)，低層為冷平流控制的下沉運(yùn)動(dòng)區(qū)，大氣層結(jié)趨于穩(wěn)定。（梁軍，張勝軍，馮呈呈）

3 暴雨和強(qiáng)對(duì)流研究

3 Research on heavy rainfall and strong convection

3.1 How accurate are modern atmospheric reanalyses for the data-sparse Tibetan Plateau region?

More than 6000 independent radiosonde observations from three major Tibetan Plateau experiments during the warm seasons (May?August) of 1998,2008,and 2015?2016 are used to assess the quality of four leading modern atmospheric reanalysis products (CFSR/CFSv2,ERA-Interim,JRA-55,and MERRA-2),and the potential impact of satellite data changes on the quality of these reanalyses in the troposphere over this data-sparse region.Although these reanalyses can reproduce reasonably well the overall mean temperature,specific humidity,and horizontal wind profiles against the benchmark independent sounding observations,they have nonnegligible biases that can be potentially bigger than the analysis-simulated mean regional climate trends over this region.The mean biases and mean root-mean-square errors of winds,temperature,and specific humidity from almost all reanalyses are reduced from 1998 to the two later experiment periods.There are also considerable differences in almost all variables across different reanalysis products,though these differences also become smaller during the 2008 and 2015?2016 experiment periods,in particular for the temperature fields.The enormous increase in the volume and quality of satellite observations assimilated into reanalysis systems is likely the primary reason for the improved quality of the reanalyses during the later field experiment periods.Besides differences in the forecast models and data assimilation methodology,the differences in performance between different reanalyses during different field experiment periods may also be contributed by differences in assimilated information (e.g.,observation input sources,selected channels for a given satellite sensor,quality-control methods).(Bao Xinghua,Zhang Fuqing)

3.2 Shift in the temporal trend of boundary layer height in China using long-term (1979–2016) radiosonde data

The knowledge regarding how the boundary layer height (BLH) changes over time is still poor.Here we analyze the spatial and temporal changes in radiosonde-derived measurements of BLH over China from 1979 to 2016.A qualitatively robust and abrupt change of BLH occurred in 2004.Over the former period (from 1979 to 2003) a spatially uniform increase was found in the BLH,while over the latter period BLH decreased in a spatially nonuniform way.Then,the meteorological influence on the rising BLH was determined to have a negative association with soil moisture,lower tropospheric stability and relative humidity,and a positive association with the near-surface temperature.Yet,there was a different influence of meteorology on the BLH over the latter period,where a negative association was revealed with T-sfc and relative humidity.These findings shed new light on the long-term changes in air pollution across China.(Guo Jianping,Li Yuan,Cohen Jason Blake)

3.3 Declining summertime local-scale precipitation frequency over China and the United States,1981–2012:The disparate roles of aerosols

The local-scale precipitation (LSP) is mainly driven by thermal convection.Here we reveal a decreasing trend in the summertime LSP frequency over both China and the United States (US) by utilizing the hourly rain gauge data from 1981 to 2012.The contrasting aerosol trend likely contributed to this same declining trend of LSP in both countries.As aerosol optical depth (AOD) goes beyond the turning zone of 0.25–0.30,the impact of aerosol on precipitation changes from invigoration to suppression.The mean AOD is generally less and larger than this range and of opposite trends in China and US,respectively,which likely accounts for the same declining trend of LSP hours in the two countries.The observed boomerang shape points to the importance of aerosol loading,which matters much,if not more than the AOD trend,thereby potentially serving as a constraint for climate model evaluation.(Guo Jianping,Su Tianning,Chen Dandan)

3.4 The trend reversal of dust aerosol over East Asia and the North Pacific Ocean attributed to large-scale meteorology,deposition,and soil moisture

The long-term trend in dust loading over East Asia remains under debate and is dependent on the study period chosen.In this study,the long-term trends in springtime dust over East Asia and the North Pacific Ocean (NPO) during 1980?2017 were examined based on the Modern-Era Retrospective Analysis for Research and Applications version 2 reanalysis.Results showed that there was a spatial gradient in dust aerosol loadings,with decreases from the western China eastward toward the NPO.This pattern was corroborated by Cloud-Aerosol Lidar with Orthogonal Polarization observations.Furthermore,the empirical orthogonal function method was used to reveal the leading modes of springtime dust aerosol optical depth (AOD) over East Asia and the NPO.An abrupt shift occurred in the dust AOD trend in 2010 for the empirical orthogonal function 1 mode.The dust AOD increased at a rate of approximately 2×10?4year?1during 1999?2009 and then decreased more sharply (around 5×10?4year?1) afterward.This trend reversal of dust AOD was closely associated with a decrease in 10-m wind velocity,which induces reduced dust emission.Compared with 10-m wind,the soil moisture is less correlated with the trend reversal in dust AOD.Additionally,the trends of dry (wet) deposition were closely associated with the trends of the dust AOD,especially for the period 2010?2016.Overall,our findings add new insights to the long-term nonlinear variability of dust.(Guo Jianping,Xu Hui,Liu Lin)

3.5 Retrieval of aerosol profiles by Raman lidar with dynamic determination of the lidar equation reference height

A reference height that often needs to be assumed in aerosol retrieval from Raman lidar tends to cause high uncertainty in retrieving the vertical distribution of aerosol optical properties.Here,a novel method is proposed to determine the height-revolved reference height,which is then used to retrieve aerosols from Raman lidar.This method can automatically avoid the atmospheric layers with the presence of aerosols,clouds and low signal to noise ratio (SNR).Based on elastic (at 355 nm) and inelastic (at 387 nm) signals collected during the period from 5 December 2016 to 5 March 2017 by a ground-based Raman lidar in Beijing,China,the aerosol optical properties,such as extinction coefficient,backscattering coefficient and lidar ratio have been successfully retrieved.Results show that the averaged nighttime aerosol optic depth (AOD) from Raman lidar is in good agreement with early morning AOD retrieved from a collocated sunphotometer.The AOD exhibits a strong diurnal variation with a peak at 15:00 Beijing Time.On average,the nighttime AOD at 355 nm is 0.32,whereas the daytime AOD is 0.72 over Beijing during the study period.The column averaged lidar ratio is 44 sr at 355 nm,roughly consistent with previous studies.Our findings shed light on the pathways towards improving the retrieval of vertical distribution of aerosols optical properties during nighttime.(Li Jian,Li Chengcai,Guo Jianping)

3.6 Dominant interannual covariations of the East Asian?Australian land precipitation during boreal winter

The present study applies the empirical orthogonal function (EOF) method to investigate the interannual covariations of East Asian?Australian land precipitation (EAALP) during boreal winter based on observational and reanalysis datasets.The first mode of EAALP variations is characterized by opposite-sign anomalies between East Asia (EA) and Australia (AUS).The second mode features an anomaly pattern over EA similar to the first mode,but with a southwest-northeast dipole structure over AUS.El Ni?o-Southern Oscillation (ENSO) is found to be a primary factor in modulating the interannual variations of land precipitation over EA and western AUS.By comparison,the Indian Ocean subtropical dipole (IOSD) mode plays an important role in the formation of precipitation anomalies over northeastern AUS,mainly through a zonally vertical circulation spanning from the southern Indian Ocean (SIO) to the northern AUS.In addition,the ENSO-independent cold sea surface temperature (SST) anomalies in the western North Pacific (WNP) impact the formation of the second mode.Using the atmospheric general circulation model ECHAM5,three 40-year numerical simulation experiments differing in specified SST forcings verify the impacts of the IOSD and WNP SST anomalies.Further composite analyses indicate that the dominant patterns of EAALP variability are largely determined by the out-of-phase and in-phase combinations of ENSO and IOSD.These results suggest that in addition to ENSO,IOSD should be considered as another crucial factor influencing the EAALP variability during the boreal winter,which has large implications for improved prediction of EAALP land precipitation on the interannual time scale.(Liu Lin,Guo Jianping,Chen Wen)

3.7 Contrasting influence of Gobi and Taklimakan deserts on the dust aerosols in the western North America

The dust generated in East Asia influences the western North America (WNA) through its trans-Pacific transport.This study investigates the distinct contribution between two main dust sources in East Asia on this remote influence based on Modern-Era Retrospective analysis for Research and Applications version 2 data set.Results show that the dust generated in Gobi Desert (GD) exerts a larger influence on the WNA compared to those in Taklimakan Desert (TD).This difference is attributed to the different terrain and background winds in GD and TD.GD is relatively flat and dominated by westerlies throughout the troposphere,which facilitates the trans-Pacific transport of dust to WNA.However,TD is located in the Tarim Basin and dominated by easterly wind in the lower troposphere.The uplifted dust is largely redeposited in TD.Moreover,the influence of GD on dust in WNA experiences decadal change around 1999,which is related to intrinsic change of dust loading in GD.(Liu Lin,Guo Jianping,Gong Hainan)

3.8 A three-dimensional wave activity flux of inertia-gravity waves and its application to a rainstorm event

A three-dimensional transformed Eulerian-mean (3D TEM) equation under a non-hydrostatic and nongeostrophic assumption is deduced in this study.The vertical component of the 3D wave activity flux deduced here is the primary difference from previous studies,which is suitable to mesoscale systems.Using the 3D TEM equation,the energy propagation of the inertia-gravity waves and how the generation and dissipation of the inertia-gravity waves drive the mean flow can be examined.During the mature stage of a heavy precipitation event,the maximum of the Eliassen-Palm (EP) flux divergence is primarily concentrated at the height of 10?14 km,where the energy of the inertia-gravity waves propagates forward (eastward) and upward.Examining the contribution of each term of the 3D TEM equation shows that the EP flux divergence is the primary contributor to the mean flow tendency.The EP flux divergence decelerates the zonal wind above and below the high-level jet at the height of 10 km and 15 km,and accelerates the high-level jet at the height of 12?14 km.This structure enhances the vertical wind shear of the environment and promotes the development of the rainstorm.(Liu Lu,Ran Lingkun,Gao Shouting)

3.9 Science and prediction of monsoon heavy rainfall

With the increasing incidence of heavy rainfall events,particularly over the monsoon regions,the highly dense populations are more vulnerable.Research initiatives on observation,modeling,and prediction of monsoon heavy rainfall have been promoted actively by the World Weather Research Programme’s (WWRP) Working Group on Tropical Meteorology Research (WGTMR) of the World Meteorological Organization (WMO) since 2010.Series of monsoon-heavy-rainfall workshops were held in Beijing (2011),Petaling Jaya (2012),and New Delhi (2015) to benefit scientists worldwide and forecasters from the National Meteorological and Hydrological Services.An international Research and Development Project,namely,the Southern China Monsoon Rainfall Experiment (SCMREX) was established in 2013 to coordinate field campaign experiments and to conduct scientific research on presummer (April?June) heavy rainfall processes in the southern China.The Fourth WMO Monsoon Heavy Rainfall Workshop (MHR-4) was held in Shenzhen in April 2019 to discuss recent advances in analysis,numerical weather prediction (NWP) studies,and development of techniques for observing/forecasting monsoon heavy rainfall,and to review the progresses of SCMREX.Innovated by the discussions in the MHR-4 Workshop,this paper highlights recent progresses on monsoon heavy rainfall research,including topics such as rainfall characteristics and physical mechanisms,field experiment,numerical simulations and model development,forecast methods,and tropical cyclone (TC) related heavy rainfall.Future research directions and some specific research topics are also proposed.(Luo Yali,Li Liye,Johnson Richard H)

3.10 An observational analysis of three extreme rainfall episodes of 19?20 july 2016 along the Taihang Mountains in North China

This study examines the synoptic- and mesoscale processes leading to the generation of three extreme rainfall episodes with hourly rates of greater than 100 mm h?1over the southern,middle,and northern portions of the eastern foothills of Mt.Taihang in North China on 19?20 July 2016.The extreme rainfall episodes took place over the 200?600-m elevation zones in the southern and northern portions but also over the lower elevations in the middle portion of the target region,sequentially during late morning,early evening,and midnight hours.Echo training accounted for the development of a linear convective system in the southern region after the warm and moist air carried by a southeasterly low-level jet (LLJ) was lifted to condense as moving across Mt.Yuntai.In contrast,two isolated circular-shaped convective clusters,with more robust convective cores in its leading segment,developed in the northern region through steep topographical lifting of moist northeasterly airflow,albeit conditionally less unstable.Extreme rainfall in the middle region developed from the convergence of a moist easterly LLJ with a northerly colder airflow associated with an extratropical cyclogenesis.Results reveal that the LLJs and associated moisture transport,the intensifying cyclone interacting with a southwest vortex and its subsequent northeastward movement,and the slope and orientation of local topography with respect to and the stability of the approaching airflows,played different roles in determining the timing and location,the extreme rainfall rates,and convective organizations along the eastern foothills of Mt.Taihang.(Xia Rudi,Zhang Da-Lin)

3.11 Importance of identifying tropical cyclone tornadoes in typhoon warning and defense systems

Tornado hazard produced by tropical cyclones (TCs) is an underestimated threat in China.A recent case concerns a tornado outbreak in Tianjin and Shandong associated with the landfalling typhoon Yagi (2018) on 13–14 August 2018.The cause of this tornado outbreak has aroused curious interest in the society and science community.This study presents first-hand observational facts and preliminary analyses on the vortex patterns from TC scale down to the tornado scale,using data from satellite,Doppler radar and onsite damage survey comprehensively.Damage swaths obtained from aerial photographs laid a solid foundation for the underestimated threat in China of tornado damage exerted by TCs.For weather forecasters and local governments in charge of the defense of severe weather hazards,this precious case strongly suggests that tornadoes may have been neglected based on the current Doppler radar network.Our preliminary findings calls for systematical investigations based on state-of-the-art tornado-resolvable radar observations and numerical simulations techniques,to illustrate the genesis mechanisms and predictability of tornadoes produced by TCs,towards the ultimate goal of effective prediction,warning,and defense against future tornado hazards.(Yao Dan,Liang Xudong,Meng Qing)

3.12 Genesis,maintenance and demise of a simulated tornado and the evolution of its preceding descending reflectivity core (DRC)

This study demonstrates the capability of a cloud model in simulating a real-world tornado using observed radiosonde data that define a homogeneous background.A reasonable simulation of a tornado event in Beijing,China,on 21 July 2012 is obtained.The simulation reveals the evolution of a descending reflectivity core (DRC) that has commonalities with radar observations,which retracts upward right before tornadogenesis.Tornadogenesis can be divided into three steps:the downward development of mesocyclone vortex,the upward development of tornado vortex,and the eventual downward development of condensation funnel cloud.This bottom-up development provides a numerical evidence for the growing support for a bottom-up,rapid tornadogenesis process as revealed by the state-of-the-art mobile X-band phase-array radar observations.The evolution of the simulated tornado features two replacement processes of three near-surface vortices coupled with the same midlevel updraft.The first replacement occurs during the intensification of the tornado before its maturity.The second replacement occurs during the tornado’s demise,when the connection between the midlevel mesocyclone and the near-surface vortex is cut off by a strong downdraft.This work shows the potential of idealized tornado simulations and three-dimensional illustrations in investigating the spiral nature and evolution of tornadoes.(Yao Dan,Meng Zhiyong,Xue Ming)

3.13 Influences of urban building complexes on ambient flows over the Washington-Reston region

This paper examines the collective impacts of urban building complexes on the planetary boundary layer (PBL) winds using both observations and a mesoscale model.Horizontal winds measured on the rooftops of federal buildings over the regions of Washington,D.C.,and a small city nearby (i.e.,Reston,Virginia) show the blocking effects of urban building complexes on the downstream winds during the daytime of 9 July 2007.A modeling study of the case using a coupled version of the Weather Research and Forecasting (WRF)—multilayer urban canopy model in which the observed building height and density information is implemented to advance the calculations of momentum and heat,and reproduces the rooftop-observed wind patterns and the related urban heat island effects,especially the wake flows on the downstream sides of the above-mentioned two cities.Results show that under daytime conditions the building complexes can collectively form a mesoscale wake on the downwind side of each city,about 2?10 km away,horizontally from the edge of the building complexes.The wake flow may extend to much higher levels than the building tops,depending on the incoming flow strength,the static stability in the PBL,the height of the building complexes,and the time of the day because of the strength of surface insolation.(Zhang Da-Lin,Jin Menglin S,Shou Yixuan)

3.14 Mesoscale convective systems in the Asian monsoon region from Advanced Himawari Imager:Algorithms and preliminary results

The knowledge of mesoscale convective system (MCS) in the Asian monsoon region remains still deficient due to the limited available data and less powerful algorithms.Here,by using the data from Advanced Himawari Imager onboard Himawari-8 (HW8),an improved algorithm combining the area overlapping with the Kalman filter is developed,which captures much smaller MCSs that are unavailable otherwise.Several influential factors like the overlapping rate and splitting/merging in the area overlapping method,and the initial state variable in the Kalman filter method,all of which were less appreciated,are handled explicitly.The occurrence frequency,and moving trajectory of two types of MCSs,including the ordinary MCS and superconvective system,has been comprehensively examined in the Asian monsoon region for the warm season (April to September) of 2016.Comparison analyses with ground precipitation and radar measurements confirm the good performance of our algorithm.In particular,the moving direction of MCS strongly depends on latitudes,so does the horizontal velocity.Compared with over ocean,the frequency of MCSs dominates over land or along coasts in the tropics,where strong moisture flux convergence is frequently observed in the low troposphere.In addition,the MCSs detected in the eastern China can roughly capture the meridional propagation over time,which corresponds well to the precipitation belts linked to Meiyu front systems.The superconvective systems dominate over the Bay of Bengal and South China Sea due to the large-scale circulation.Our findings provide new insights to spatiotemporal patterns of MCSs during warm season in the Asian monsoon region.(Chen Dandan,Guo Jianping,Yao Dan)

3.15 Tropopause trend across China from 1979 to 2016:A revisit with updated radiosonde measurements

The long-term trend in tropopause has profound implications for the expansion of tropical zone and the variation of large-scale circulation.However,the changes of tropopause in China have not been explicitly investigated as yet.In this study,the trend of lapse rate tropopause (LRT) height over China has been comprehensively revisited for the period of 1979?2016,using the newly released quality-controlled radiosonde data from China Meteorological Administration.Results show that the LRT height in most parts of China shows a significant upwards trend with a rate of 370 m/decade,most likely due to global warming.The fastest increase occurs in the northwest region,followed by the low-latitude regions (15°?25°N),while the slowest increase occurs in the high-latitude regions (45°?55°N).Overall,the LRT height varies with latitudes,exhibiting a south high and north low pattern.In particular,the high LRT height over low latitudes is found to be expanding rapidly polewards in recent years,in contrast to the almost constant LRT height over mid and high latitudes.In terms of the seasonality,the tropopause height reaches the peak in summer and bottom in winter.The frequency distribution in the vertical direction exhibits a bimodal pattern with the major peak mostly occurring at around 15 km and a secondary peak occurring between 8 and 12 km.This bimodal distribution is similar to the findings revealed in previous studies.Our findings offer important circumstantial observational evidences for the polewards expansion of the Tropics under global warming.(Chen Xinyan,Guo Jianping,Yin Jinfang)

3.16 Layer-wise formation mechanisms of an entire-troposphere-thick extratropical cyclone that induces a record-breaking catastrophic rainstorm in Beijing

A rarely seen entire-troposphere-thick (ETT) extratropical cyclone that induced a record-breaking catastrophic rainstorm in Beijing (the largest since 1963) on 20 July 2016 was reproduced reasonably by a convection-permitting Weather Research and Forecasting Model.This cyclone was the result of a vertical coupling of a lower,a middle,and an upper tropospheric cyclone,which formed at different times and locations.Dry air descending from the stratosphere through a tropopause folding process capped moist air to the middle and lower troposphere,making convection associated with the cyclone relatively shallow.Overall,cyclonic vorticity associated with the ETT cyclone enhanced much rapider than its wind kinetic energy (KE),and formation mechanisms of the ETT cyclone were characterized by layer-wise features:(i) The formation of the middle and upper tropospheric cyclones was dominated by cyclonic vorticity transport,instead of cyclonic vorticity production,whereas the lower tropospheric cyclone was generated through both cyclonic vorticity transport and convergence-related cyclonic vorticity production.(ii) Consistent with the cyclonic vorticity intensification,the formation of the lower and middle tropospheric cyclones featured an enhancement of rotational wind KE (in western section of the cyclone,this was mainly due to the work done by the pressure gradient force,but in eastern section,it was mainly due to the inward transport of wind KE by rotational wind),whereas the formation of the upper tropospheric cyclone featured a decrease in the rotational wind KE (particularly in its eastern section),which was in contrast to its increasing cyclonic vorticity.The export of wind KE by a southwesterly wind within the eastern section of the cyclone governed the rotational wind attenuation.(Li Wanli,Xia Rudi,Sun Jianhua)

3.17 Non-monotonic aerosol effect on precipitation in convective clouds over tropical oceans

Aerosol effects on convective clouds and associated precipitation constitute an important open-ended question in climate research.Previous studies have linked an increase in aerosol concentration to a delay in the onset of rainfall,invigorated clouds and stronger rain rates.Here,using observational data,we show that the aerosol effect on convective clouds shifts from invigoration to suppression with increasing aerosol optical depth.We explain this shift in trend (using a cloud model) as the result of a competition between two types of microphysical processes:cloud-core-based invigorating processes vs.peripheral suppressive processes.We show that the aerosol optical depth value that marks the shift between invigoration and suppression depends on the environmental thermodynamic conditions.These findings can aid in better parameterizing aerosol effects in climate models for the prediction of climate trends.(Liu Huan,Guo Jianping,Koren Ilan)

3.18 Observed link of extreme hourly precipitation changes to urbanization over coastal South China

Understanding changes in subdaily rainfall extremes is critical to urban planners for building more sustainable and resilient cities.In this study,the hourly precipitation data in 1971?2016 from 61 rain gauges are combined with historical land-use change data to investigate changes in extreme hourly precipitation (EXHP) in the Pearl River delta (PRD) region of South China.Also,120 extreme rainfall events (EXREs) during 2011?2016 are analyzed using observations collected at densely distributed automatic weather stations and the radar network.Statistically significant increase of hourly precipitation intensity leads to higher annual amounts of both total and extreme precipitation over the PRD urban cluster in the rapid urbanization period (about 1994?2016) than during the preurbanization era (1971 to about 1993),suggesting a possible link between the enhanced rainfall and the rapid urbanization.Those urbanization-related positive trends are closely related to more frequent occurrence of abrupt rainfall events with short duration (≤6 h) than the continuous or growing rainfall events with longer duration.The 120 EXREs in 2011?2016 are categorized into six types according to the originating location and movement of the extreme-rain-producing storms.Despite the wide range of synoptic backgrounds and seasons,rainfall intensification by the strong urban heat island (UHI) effect is a clear signal in all the six types,especially over the inland urban cluster with prominent UHIs.The UHI thermal perturbation probably plays an important role in the convective initiation and intensification of the locally developed extreme-rain-producing storms during the daytime.(Wu Mengwen,Luo Yali,Chen Fei)

3.19 Declining diurnal temperature range in the North China Plain related to environmental changes

The decreases in diurnal temperature range (DTR) observed in most regions are generally linked to the increase in cloud cover.However,declining clouds and rising aerosols observed over the North China Plain (NCP) of China make it elusive to elucidate the underlying mechanisms behind the declining DTR observed in this region.Here,we analyze the changes in DTR characteristics in the NCP based on 54-year surface temperature observations,in combination with collocated environmental variable measurements.Overall,there is a significant declining trend of DTR from 1960 to 2014 at a rate of ?0.12 /decade,largely due to a larger increase in minimum temperature during the night.The cloud effect on DTR is further explored by comparing DTR under clear-sky and overcast conditions,which exhibits a distinct annual cycle with a minimum in summer and a maximum in winter.The decreasing rate of DTR under overcast condition is ?0.30 /decade,much faster than the rate of ?0.17 /decade under clear-sky condition,indicating steady increases in the nighttime warming effect of middle- or high-clouds.Also,the elevated aerosol concentration could contribute to the declining DTR,due to the cooling effect of aerosols.Moreover,the effect induced by sunshine duration and water vapor on DTR cannot be ignored either.All of the aforementioned environmental variables combine to affect the long-term trend of DTR,despite their different roles in modulating DTR.Our findings call for better understanding of the influence of environmental factors on regional climate system at the diurnal timescale.(Xue Weitao,Guo Jianping,Zhang Yong)

3.20 A case study of the effects of a synoptic situation on the motion and development of warmsector mesoscale convective systems over South China

The effects of a synoptic situation on the motion and development of warm-sector mesoscale convective systems (MCSs) in a heavy rainfall event occurred in South China on 8 May 2014 are investigated using high-resolution observational data and ERA-Interim data.The results show that the blocking of an eastward moving low-level trough over the southwestern China by a stable anticyclone over the eastern China induced strong southerly winds ahead of the trough and an eastward vertical slant of the wind speed maximum.Consequently,a southeastward low-level wind shear formed in the region under the southerly jet,which caused a southeastward turning of the motion of a large inland MCS.Meanwhile,a northeastward/eastward low-level wind shear formed in the region under the east side of the southerly jet,leading to northeastward/eastward movement of some small MCSs in the coastal region.The continuous merging of the southeastward-moving MCS with the northeastward/eastward-moving MCSs resulted in heavy rainfall along the coastal region.On the other hand,the intensification and expansion of associated low and high mean-sea-level pressure (MSLP) centers caused southeastward migration of strong boundary-layer moisture flux convergence and high convective available potential energy zones,which promoted the persistent development of the large MCS and the later development of the small MCSs.Moreover,the strong boundary-layer southeasterly winds associated with the high MSLP center continuously enhanced the frontal ascent of the large MCS.These southeasterly winds also triggered the small MCSs through the convergence induced by differential surface friction between land and sea or the convergence of them with the southwesterly winds from the South China Sea.(Liang Zhaoming,Liu Ying,Yin Jinfang)

3.21 Characteristics and formation of a synoptic situation causing sudden turning of mesoscale convective systems over South China

The characteristics and formation of a synoptic situation that causes a sudden turning motion of warmsector mesoscale convective systems (MCSs) over South China are described,based on the collection and investigation of associated cases during April–June 2011–2017 using high-resolution observational data and ERA (ECMWF Re-Analysis)-Interim data.The results show that the blocking of a marked low-level high over the eastern China (eastern high) on a strengthening low-level trough over the southwestern China (southwestern trough) results in significant enhancement of southerly winds ahead of the trough,which produces a strong southeastward vertical wind shear at low levels near the western Guangdong Province.This low-level vertical wind shear results in sudden southeastward turning motion for the warm-sector MCSs entering into Guangdong Province from Guangxi Province.The formation of the eastern high is mainly attributable to the strong cyclonic wind anomaly over the northwestern Pacific Ocean,which continuously brings cold air from higher latitudes to the eastern China,where high synoptic-scale transient anomaly of geopotential height (SSTA-GH) forms.This cyclonic wind anomaly is induced by a low SSTA-GH,which travels from the north and south sides of the Tibetan Plateau to the northwestern Pacific Ocean and develops significantly as a result of a strong upper-level low SSTA-GH coupling with it or approaching it.On the other hand,the high SSTA-GH over the eastern China blocks the eastward extension of the low SSTA-GH originating from the Tibetan Plateau.Consequently,this low SSTA-GH turns to extend or move southeastward/southward to the southwestern China,leading to intensification of the southwestern trough.(Liang Zhaoming,Liu Ying,Yin Jinfang)

3.22 Observational analysis of characteristics of synoptic situation and evolution of organized warmsector rainfall in coastal region of South China in pre-summer rainy season

The characteristics of the synoptic situation and the evolution of the organized warm-sector rainfalls (OWSRs) in the coastal region of South China in the pre-summer rainy season were investigated,using the high-resolution observational data in the period of 2011–2016 and European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) data.The results show that a strong southwesterly lowlevel jet (LLJ) ahead of a trough over the southwestern China with a marked boundary-layer jet (BLJ) over the northern South China Sea (synoptic situation SWLLJ) or a prominent,low-level anticyclone over the Yangtze River Basin (synoptic situation ACR) is present when the OWSRs occur in the coastal region of South China.The OWSRs are prone to initiate on the windward side of the coastal mountains,owing to the convergence enhanced by the colliding of the BLJ with the mountains and the coupling of double LLJs near the coast (for SWLLJ),or due to the convergence between northerly and southeasterly winds near the coastal mountains (for ACR).The OWSRs present a long extension when the LLJ axis is nearby.The translation of the LLJ itself also promotes the long extension of the OWSRs.In contrast,the OWSRs show a short extension when the LLJ axis is farther away or ACR occurs.Meanwhile,the OWSRs are directed northeastward in Guangxi Province and more eastward in Guangdong Province,probably owing to the orientation difference of the LLJ in these two provinces.The rainfall systems in the ACR situation tend to move eastward,whereas those in the SWLLJ situation are prone to move eastward when equivalently strong or much-stronger upper-level winds overlay the LLJ,but move northeastward when much weaker upper-level winds couple with the LLJ.(Liang Zhaoming,Liu Ying)

3.23 BMA probability quantitative precipitation forecasting of land-falling typhoons in Southeast China

The probability of quantitative precipitation forecast (PQPF) of three Bayesian Model Averaging (BMA) models based on three raw super ensemble prediction schemes (i.e.,A,B,and C) are established,through calibration of their parameters using 1–3-day precipitation ensemble prediction systems (EPSs) from the China Meteorological Administration (CMA),the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) and observation during land-falling of three typhoons in Southeast China in 2013.The comparison of PQPF shows that the performance is better in the BMA than that in raw ensemble forecasts.On average,the mean absolute error (MAE) of 1-day lead time forecast is reduced by 12.4%,and its continuous ranked probability score (CRPS) of 1–3-day lead time forecast is reduced by 26.2%,respectively.Although the amount of precipitation prediction by the BMA tends to be underestimated,in view of the perspective of probability prediction,the probability of covering the observed precipitation by the effective forecast ranges of the BMA increased,which is of great significance for the early warning of torrential rain and secondary disasters induced by it.(Zhao Linna,Bai Xuemei,Qi Dan,Cheng Xing)

3.24 1949年以來我國(guó)臺(tái)風(fēng)暴雨及其預(yù)報(bào)研究回顧與展望

對(duì)1949年以來影響我國(guó)的臺(tái)風(fēng)暴雨及其預(yù)報(bào)研究的進(jìn)展，從臺(tái)風(fēng)暴雨形成機(jī)理、專題研究、預(yù)報(bào)研究和研究新動(dòng)向等4方面進(jìn)行回顧總結(jié)。首先，從環(huán)境場(chǎng)、下墊面和內(nèi)部條件3個(gè)角度對(duì)臺(tái)風(fēng)暴雨形成機(jī)理進(jìn)行簡(jiǎn)要回顧，并從“75·8”特大暴雨、“莫拉克”極端暴雨、遠(yuǎn)距離暴雨、臺(tái)風(fēng)暴雨的診斷分析和氣候特征等5個(gè)角度做了專題回顧。同時(shí)，簡(jiǎn)要回顧了臺(tái)風(fēng)暴雨預(yù)報(bào)研究進(jìn)展，并就臺(tái)風(fēng)暴雨研究新動(dòng)向給出了在云微物理、極端降水和預(yù)報(bào)方法3個(gè)方向上的初步判斷。在此基礎(chǔ)上，給出了小結(jié)與展望。（任福民，楊慧）

3.25 中國(guó)極端小時(shí)降水2010—2019年研究進(jìn)展

概述了近10年來關(guān)于中國(guó)極端小時(shí)降水的研究成果，為及時(shí)了解和掌握該領(lǐng)域研究進(jìn)展、開展相關(guān)科學(xué)研究和進(jìn)行強(qiáng)降水預(yù)報(bào)服務(wù)提供有價(jià)值的科學(xué)依據(jù)和參考?，F(xiàn)有的研究表明：（1）極端小時(shí)降水的閾值通常采用百分位和擬合經(jīng)驗(yàn)函數(shù)得到，閾值強(qiáng)度分布在中國(guó)的區(qū)域差異大，最強(qiáng)閾值位于華南沿海、海南島、臺(tái)灣島和華北平原，次大值位于四川盆地和長(zhǎng)江中下游地區(qū)。（2）根據(jù)中國(guó)極端小時(shí)降水發(fā)生的天氣背景特征，主要分為四大類型：熱帶氣旋型、鋒面型、低渦或切變線型、弱天氣尺度強(qiáng)迫型。每種類型極端小時(shí)降水的空間分布、季節(jié)變化和日變化特征各不相同。（3）定義“極端小時(shí)降水事件”為：站點(diǎn)連續(xù)觀測(cè)到降水大于等于0.1 mm/h的一段時(shí)間，其中最多只有1 h的降水間斷，且至少發(fā)生一次極端小時(shí)降水。中國(guó)極端小時(shí)降水事件維持時(shí)間在東南沿海、長(zhǎng)江中下游一帶較長(zhǎng)（超過12 h），而在中國(guó)北方則普遍較短（不到6 h）。極端小時(shí)降水事件具有不對(duì)稱性，即從降水開始到出現(xiàn)雨量峰值較為迅速，而從出現(xiàn)峰值至降水結(jié)束則變化較為緩慢，該特征在西部地形復(fù)雜地區(qū)更為明顯。（4）過去50多年，中國(guó)極端小時(shí)降水的變化趨勢(shì)呈現(xiàn)正負(fù)相間的空間分布特征。觀測(cè)分析表明，上海和珠三角城市地區(qū)極端小時(shí)降水在城市化迅速發(fā)展的近30年間具有區(qū)別于周圍地區(qū)的顯著增長(zhǎng)趨勢(shì)，而觀測(cè)和模擬均表明北京城市強(qiáng)熱島效應(yīng)有利于增強(qiáng)小時(shí)降水。（吳夢(mèng)雯，羅亞麗）

3.26 不同強(qiáng)度熱帶氣旋對(duì)中國(guó)降水變化的影響

基于1960—2017年2000多個(gè)氣象臺(tái)站逐日降水?dāng)?shù)據(jù)和中國(guó)氣象局熱帶氣旋（TC）最佳路徑資料集，采用客觀天氣圖分析法（OSAT）識(shí)別得到TC降水。研究表明，中國(guó)TC降水總體呈顯著下降趨勢(shì)，較12年前的研究結(jié)果下降趨勢(shì)變緩；TC盛期（7—9月）降水占到TC總降水的78.5%，TC盛期降水和TC非盛期降水均呈顯著下降趨勢(shì)。TC降水氣候趨勢(shì)在空間分布上以減少為主要特征，并表現(xiàn)出明顯的地域差異，自南向北呈“減少—增多—減少”的分布型，減少趨勢(shì)中心位于廣東和海南。按TC影響期最大強(qiáng)度分級(jí)（弱TC、中等強(qiáng)度TC和強(qiáng)TC）研究不同強(qiáng)度TC降水變化的結(jié)果顯示，強(qiáng)TC降水表現(xiàn)出顯著減少趨勢(shì)，主要決定著TC總降水的影響范圍和趨勢(shì)等主要特征。進(jìn)一步分析發(fā)現(xiàn)，影響TC頻數(shù)在1960—2017年呈顯著減少趨勢(shì)，并在1995年發(fā)生突變；對(duì)1995年前后2個(gè)時(shí)期的對(duì)比研究顯示，與前一時(shí)期（1960—1994年）相比，后一時(shí)期（1995—2017年）影響TC活動(dòng)頻次在20°N以南的海域呈現(xiàn)出顯著的減少趨勢(shì)，減少大值中心位于南海北部，而且這一特征也主要由影響TC中的強(qiáng)TC所決定；強(qiáng)TC的這一變化趨勢(shì)導(dǎo)致了華南地區(qū)尤其是廣東和海南TC降水日數(shù)的減少，進(jìn)而使得TC降水減少。（楊慧，任福民，楊明仁）

3.27 2類不同風(fēng)災(zāi)個(gè)例超級(jí)單體特征對(duì)比分析

采用分鐘級(jí)加密自動(dòng)氣象站觀測(cè)資料，鹽城、淮安和岳陽(yáng)、荊州雷達(dá)探測(cè)數(shù)據(jù)，以及歐洲中期天氣預(yù)報(bào)中心（ECMWF）高分辨率的ERA-Interim全球再分析數(shù)據(jù)，對(duì)比分析了2016年6月23日江蘇阜寧龍卷災(zāi)害和2015年6月1日湖北監(jiān)利下?lián)舯┝鞔箫L(fēng)災(zāi)害的環(huán)境特征與超級(jí)單體的結(jié)構(gòu)特征。結(jié)果表明：（1）2次強(qiáng)對(duì)流大風(fēng)災(zāi)害發(fā)生在相似的低空環(huán)流背景下。風(fēng)災(zāi)發(fā)生在低空急流出口區(qū)左側(cè)的暖區(qū)內(nèi)、850 hPa低渦中心東側(cè)6～7個(gè)經(jīng)距的位置；環(huán)境大氣的對(duì)流有效位能大于2000 J/kg。但是風(fēng)災(zāi)的類型不同，江蘇阜寧大風(fēng)災(zāi)害主要由超級(jí)單體龍卷造成，監(jiān)利“東方之星”沉船事故主要由超級(jí)單體觸發(fā)的下?lián)舯┝髟斐?。短時(shí)強(qiáng)降水中心與風(fēng)災(zāi)中心的相對(duì)位置不同：阜寧龍卷移動(dòng)方向的左側(cè)伴隨著最強(qiáng)短時(shí)降水；湖北監(jiān)利沉船事件發(fā)生期間，風(fēng)災(zāi)中心與短時(shí)強(qiáng)降水中心基本重合。鑒于不同性質(zhì)的對(duì)流大風(fēng)位置與超級(jí)單體母體的中心位置對(duì)應(yīng)關(guān)系上存在差異，通過比較地面觀測(cè)的瞬時(shí)大風(fēng)與瞬時(shí)強(qiáng)降水中心的相對(duì)位置將有助于區(qū)分強(qiáng)對(duì)流大風(fēng)的性質(zhì)。（2）環(huán)境風(fēng)垂直切變強(qiáng)度對(duì)對(duì)流風(fēng)暴結(jié)構(gòu)、發(fā)展、維持有重要影響。阜寧龍卷發(fā)生時(shí)，其上空0～6 km風(fēng)垂直切變達(dá)4×10-3/s，超級(jí)單體有明顯的向前傾斜結(jié)構(gòu)，形成有界弱回波區(qū)；而監(jiān)利強(qiáng)對(duì)流沉船位置0～6 km風(fēng)垂直切變只有2.3×10-3/s左右，風(fēng)暴單體中的上升氣流近乎于垂直。阜寧超級(jí)單體中氣旋，首先出現(xiàn)在0～1.5 km風(fēng)垂直切變和0～3 km風(fēng)暴相對(duì)螺旋度帶狀大值區(qū)，在向抬升凝結(jié)高度更低的環(huán)境移動(dòng)過程中，其底部不斷下降，形成龍卷；而在監(jiān)利沉船區(qū)，中低層風(fēng)切變和風(fēng)暴相對(duì)螺旋度相對(duì)要弱得多，對(duì)應(yīng)風(fēng)暴單體中的中氣旋強(qiáng)度、持續(xù)性較弱，中氣旋底部高度維持在1.6 km左右。（3）環(huán)境濕度垂直結(jié)構(gòu)特征不同可能是風(fēng)暴單體形成不同類型災(zāi)害大風(fēng)的重要環(huán)境因子。監(jiān)利下?lián)舯┝髟斐傻娘L(fēng)災(zāi)發(fā)生時(shí)，在地面氣溫迅速下降過程中，氣壓變化呈現(xiàn)快速跳升又快速下降的“尖錐”形，氣壓峰值比降水峰值提前4 min出現(xiàn)。它與對(duì)流層中高層環(huán)境大氣中較為深厚的干空氣卷入對(duì)流風(fēng)暴中造成水物質(zhì)強(qiáng)烈蒸發(fā)、冷卻過程有關(guān)。而阜寧風(fēng)災(zāi)過程中，環(huán)境大氣中層僅存在非常淺薄的干層，加之低層較為深厚的飽和大氣環(huán)境，對(duì)應(yīng)的地面冷池效應(yīng)相對(duì)較弱。（楊波，孫繼松，劉鑫華）

3.28 湖北3類組織形態(tài)強(qiáng)對(duì)流系統(tǒng)造成的地面強(qiáng)對(duì)流大風(fēng)特征

利用湖北省2012—2017年區(qū)域自動(dòng)站、天氣雷達(dá)和周邊探空站觀測(cè)資料，對(duì)3類不同組織形態(tài)的中尺度對(duì)流系統(tǒng)（MCS）（線性MCS、非線性MCS和孤立對(duì)流風(fēng)暴）造成的地面強(qiáng)風(fēng)（極大風(fēng)速≥17 m/s）的時(shí)空分布、移動(dòng)與傳播、對(duì)流環(huán)境特征等方面進(jìn)行了統(tǒng)計(jì)對(duì)比分析，并結(jié)合個(gè)例討論了地面入流大風(fēng)的成因及其對(duì)對(duì)流系統(tǒng)發(fā)展、組織的影響。結(jié)果表明：（1）大量的非線性MCS可能是由更早發(fā)生在山區(qū)和丘陵的孤立對(duì)流風(fēng)暴向平原地區(qū)移動(dòng)過程中組織形成的，孤立對(duì)流風(fēng)暴造成的地面大風(fēng)出現(xiàn)的峰值時(shí)間在17：00（北京時(shí)，下同）前后，非線性MCS地面大風(fēng)的峰值時(shí)間在19：00左右，線性MCS造成的強(qiáng)對(duì)流大風(fēng)主要出現(xiàn)在平原地區(qū)。（2）非線性MCS和孤立對(duì)流風(fēng)暴是造成湖北省地面大風(fēng)的主導(dǎo)系統(tǒng)，其中，非線性MCS造成的地面大風(fēng)站次數(shù)占強(qiáng)對(duì)流大風(fēng)站次總數(shù)的41.9%，而39.3%的地面強(qiáng)對(duì)流大風(fēng)站次是由孤立對(duì)流風(fēng)暴造成的。（3）雖然大于17 m/s的地面入流大風(fēng)占所有強(qiáng)對(duì)流大風(fēng)的比例很小，但存在地面入流大風(fēng)的強(qiáng)對(duì)流系統(tǒng)的影響范圍、持續(xù)時(shí)間均遠(yuǎn)大于同一類型對(duì)流系統(tǒng)的平均值?；谝淮伍L(zhǎng)生命史線性MCS（颮線）造成強(qiáng)對(duì)流大風(fēng)事件的分析表明，雷暴系統(tǒng)前側(cè)的地面入流大風(fēng)是由對(duì)流強(qiáng)烈發(fā)展造成，這支暖濕入流又進(jìn)一步增強(qiáng)了對(duì)流風(fēng)暴的發(fā)展，同時(shí)地面入流大風(fēng)的形成進(jìn)一步加強(qiáng)了垂直風(fēng)切變，因而強(qiáng)的地面入流更有利于對(duì)流系統(tǒng)的組織化發(fā)展。（4）雖然暖季強(qiáng)對(duì)流系統(tǒng)的平均引導(dǎo)氣流均以西南風(fēng)為主，但線性MCS主要自西向東移動(dòng)、非線性MCS以自西南向東北移動(dòng)為主、孤立對(duì)流風(fēng)暴的移動(dòng)方向則更具多樣性，也更易出現(xiàn)后向傳播現(xiàn)象。孤立對(duì)流風(fēng)暴相對(duì)組織化的強(qiáng)對(duì)流系統(tǒng)而言，往往發(fā)生在更不穩(wěn)定或更干的層結(jié)大氣中，且環(huán)境垂直風(fēng)切變更弱、風(fēng)速更小。（郭英蓮，孫繼松）

3.29 一次超級(jí)單體雹暴的中尺度對(duì)流特征和形成條件分析

北京2014年7月16日一次超級(jí)單體風(fēng)暴造成了罕見大冰雹、短時(shí)大風(fēng)和局地暴雨等強(qiáng)天氣。利用雷達(dá)、自動(dòng)站、探空、基于雷達(dá)觀測(cè)的四維變分同化系統(tǒng)（VDRAS）等資料針對(duì)中尺度對(duì)流特征和形成條件進(jìn)行了分析。結(jié)果表明：（1）這次超級(jí)單體風(fēng)暴有穹窿回波和懸垂、中氣旋、三體散射等典型大冰雹雹暴云特征。（2）降雹屬于西北氣流型，雹區(qū)出現(xiàn)在低層切變線和地面輻合區(qū)（輻合線）附近，低層很好的水汽條件是這種類型下降雹的必要條件。此外，1500 J/kg以上的高CAPE以及上干下濕的不穩(wěn)定層結(jié)、850 hPaθse360 K的高能舌中心均有利于強(qiáng)對(duì)流的發(fā)生，“喇叭口”形探空、適宜的0 ℃層和-20 ℃層高度以及這兩個(gè)特性層之間厚度變小是大冰雹出現(xiàn)的典型環(huán)境。（3）有利的地形、雷暴下山冷池增強(qiáng)導(dǎo)致前側(cè)輻合增強(qiáng)是超級(jí)單體發(fā)展并向南移動(dòng)的有利條件。（雷蕾，孫繼松，喬林）

4 臺(tái)風(fēng)研究

4 Typhoon research

4.1 Landfalling tropical cyclone research project (LTCRP) in China

Landfalling tropical cyclones (TCs) often experience drastic changes in their motion,intensity,and structure due to complex multiscale interactions among atmospheric processes and among the coastal ocean,land,and atmosphere.Because of the lack of comprehensive data and low capability of numerical models,understanding of and ability to predict landfalling TCs are still limited.A 10-year key research project on landfalling TCs was initiated and launched in 2009 in China.The project has been jointly supported by the China Ministry of Science and Technology,China Meteorological Administration (CMA),Ministry of Education,and Chinese Academy of Sciences.Its mission is to enhance understanding of landfalling TC processes and improve forecasting skills on track,intensity,and distributions of strong winds and precipitation in landfalling TCs.This article provides an overview of the project,together with highlights of some new findings and new technical developments,as well as planned future efforts.(Duan Yihong,Wan Qilin,Huang Jian)

4.2 Impact of different types of ENSO years on intensity changes of landfalling tropical cyclones over China

This study examines whether there are significant differences in intensity and destructiveness of landfalling tropical cyclones (TCs) over China in central Pacific warm (CPW),eastern Pacific warm (EPW) and La Ni?a (LA) years.By analyzing different seasons and locations of TCs making landfall over China,it was found that TCs in LA years generally had a larger power dissipation index (PDI) and may cause more disasters in China,while TCs in EPW years had a larger PDI over South China in autumn.A larger PDI of TCSC (landing location in Southern China) usually occurred in EPW years and a larger PDI of TCEC (landing location in Eastern China) occurred in LA years,compared with CPW years.The TCs in LA years were generally stronger,more frequent,and of longer duration over China,because of the positive relative humidity (RH) anomalies,the significant anomalous cyclones that occupied the South China Sea (SCS),and the easterly wind anomalies providing a beneficial steering flow for TCs making landfall.In EPW years,although TCs were less frequent,they had stronger intensity when making landfall and a longer lifetime over land which was mainly caused by a broad band of anomalous westerlies over the SCS giving rise to a belt of positive relative vorticity anomalies,as well as the slow translation speed of TCs before landfall supplying more energy for TCs to survive over land.Overall,we conclude that greater caution is warranted when TCs occur in LA and EPW years,as they may result in more serious disasters in China.(Liu Lu)

4.3 Contribution of recycling of surface precipitation to landfalling tropical cyclone rainfall:A modeling study for Typhoon Utor (2013)

Surface evaporation is an important factor in the hydrological cycle.It is unknown however how much the recycling of surface precipitation contributes to rainfall in a landfalling tropical cyclone.In this study,ensemble simulations were performed using the Weather Research and Forecasting model to quantify the contribution of re-evaporation of surface precipitation to rainfall in Typhoon Utor (2013) during and after its landfall over South China.Two sets of ensemble simulations were conducted,one with all default model settings (CTRL) and the other with the surface precipitation rate in the land surface model being set to zero within a radius of 500 km from the storm center so that the re-evaporation of surface precipitation was removed.Results show that the re-evaporation of surface precipitation contributed about 15%?20% to the total rainfall in the inner core within a 100-km radius from the storm center after landfall.It is found that the removal of surface precipitation in the land surface model reduced soil moisture and thus surface latent heat flux,which led to a slightly weaker storm,thus the weaker boundary layer inflow and reduced inward moisture transport into the inner-core region of the storm.The results demonstrate that the reduced surface evaporation and inward moisture transport contributed about 30%?40% and 60%?70%,respectively,to the decrease in precipitation in the inner-core region in the experiment with the re-evaporation of surface precipitation removed.(Liu Lu,Xu Jing,Wang Yuqing)

4.4 Parameterizing sea surface temperature cooling induced by tropical cyclones:1.Theory and an application to Typhoon Matsa (2005)

Sea surface temperature cooling (SSTC) induced by tropical cyclones (TCs) could produce a significant impact on the TC intensity.Although a coupled atmosphere-ocean model could provide such SSTC,various challenges associated with coupled modeling often lead many TC researchers to continue to use atmosphereonly models.Therefore,the main goal of this study is to develop a fast,robust,and effective parameterization scheme for TC-induced SSTC that can be used in atmosphere-only TC models.The following three steps are taken to achieve this goal:(i) results from an idealized ocean simulation,together with theoretical and temperature budget analyses,are analyzed to isolate each major mechanism causing TC-induced SSTC,which is then used as a basis for the parameterization; (ii) building upon the idealized ocean simulation,a new SSTC parameterization scheme including vertical mixing,advection,and SST recovery processes under the influences of sea surface height anomalies and ocean subsurface temperature is developed; and (iii) this SSTC parameterization scheme is evaluated through numerical simulations of Typhoon Matsa (2005) and validated against remote sensing data.Results show significant improvements in the simulated TC intensity and SST changes after applying this parameterization scheme.Although further testing with more TC cases is needed,these results are promising,and the parameterization scheme should be compatible with any TC weather prediction model.It is well known that tropical cyclones (TCs) may induce local cooling in sea surface temperature (SST),through upwelling of cold water from underneath,which would in turn act to slow down TC intensification.So it is highly desirable to incorporate the fine-scale structures of the TC-induced SST cooling into numerical TC models in order to improve the prediction of TC intensity.In this study,we developed an easy-to-use,fast,and effective parameterization scheme for TC-induced SST cooling that can be used in atmosphere-only TC models.Results show significant improvements in the simulated TC intensity and SST changes after applying this parameterization scheme.Although further testing with more TC cases is needed,the parameterization scheme should be compatible with any TC weather prediction model.(Liu Xin,Wei Jun,Zhang Da-Lin)

4.5 Parameterizing sea surface temperature cooling induced by tropical cyclones:2.Verification by ocean drifters

This study analyzes sea surface responses to tropical cyclones (TCs),based on sea surface temperature (SST) and ocean surface current (V-OS) data from 57 buoy drifters,together with satellite SST and sea surface height anomaly data,associated with nine TCs during the year of 2016 in order to validate the TC-induced SST cooling (SSTC) parameterization scheme developed in Part 1.Results show that the drifters-measured SSTs compare favorably to the satellite detected,except near the coastline and at high latitudes,and that SSTCs are negatively correlated with sea surface height anomaly.During TC passage,V-OS usually rotate clockwise on the right-hand side of TC tracks,but their rotating directions cannot be specified on their left-hand side.After TC passage,most drifters,located on both sides,show clockwise rotation.These results help characterize the responses of SST and V-OS to TCs into the following three modes:(i) significant increases in V-OS during TC passage,followed by strong SSTC; (ii) decreases or little changes in V-OS,followed by SSTC; and (iii) little changes in both V-OS and SSTC.All the three response modes are reasonably included in the SSTC parameterization scheme.After optimizing three empirical constants,based on the drifters’ data,the scheme’s performance is evaluated by comparing the parameterized SSTC to the drifters-measured SSTs,showing satisfactory results in terms of the starting time,duration,strength,and rate of SSTCs.An error analysis shows a mean value of about 20% of the observed SSTC with a small standard deviation,confirming the effectiveness of the SSTC parameterization scheme.In this study,we examine sea surface responses to the passage of tropical cyclones (TCs),based on observational data taken from ocean buoy drifters,in order to validate the TC-induced sea surface temperature (SST) cooling parameterization scheme presented in Part 1 of this series of papers.Results show some interesting features in ocean surface currents during TC passage.These features have been more or less included in our TC-induced SST cooling theory.An error analysis shows a mean value of about 20% of the observed SST cooling with a small standard deviation,which confirms the effectiveness of the SST cooling parameterization scheme.(Liu Xin,Zhang Da-Lin,Guan Jian)

4.6 The axisymmetric and asymmetric aspects of the secondary eyewall formation in a numerically simulated tropical cyclone under idealized conditions on an f-Plane

The axisymmetric and asymmetric aspects of the secondary eyewall formation (SEF) in a numerically simulated tropical cyclone (TC) under idealized conditions were analyzed.Consistent with previous findings,prior to the SEF,the tangential wind of the TC experienced an outward expansion both above and within the boundary layer near and outside the region of the SEF later.This outward expansion was found to be closely related to the top-down development and inward propagation of a strong outer rainband,which was characterized by deeper and more intense convection upwind and shallower and weaker convection downwind.In response to diabatic heating in the outer rainband was inflow in the mid-to-lower troposphere,which brought the absolute angular momentum inward and spun up tangential wind in the inflow region and also in the convective region because of vertical advection.As a result,as the outer rainband intensified and spiraled cyclonically inward,perturbation tangential and radial winds also spiraled cyclonically inward and downward along the rainband.As it approached the outer edge of the rapid filamentation zone outside the primary eyewall,the downwind sector of the rainband in the boundary layer was rapidly axisymmetrized.Continuous inward propagation and axisymmetrization and secondarily the merging with inner rainbands led to the spinup of tangential wind in the boundary layer,enhancing surface enthalpy flux and convection and eventually leading to the simulated SEF.Our results demonstrate that the simulated SEF was a top-down process and was mainly triggered by asymmetric dynamics.(Wang Hui,Wang Yuqing,Xu Jing)

4.7 Evolution of the warm-core structure during the eyewall replacement cycle in a numerically simulated tropical cyclone

This study examines the evolution of the warm-core structure during the secondary eyewall formation (SEF) and the subsequent eyewall replacement cycle (ERC) in a numerically simulated tropical cyclone (TC) under idealized conditions.Results show that prior to the SEF,the TC exhibited a double warm-core structure centered in the middle and upper troposphere in the eye region,and as the storm intensified with a rapid outward expansion of tangential winds,the warm core strengthened and a secondary off-center warm ring developed between 8- and 16-km heights near the outer edge of the eye.During the SEF,both the upper-level warm core and the secondary off-center warm ring rapidly strengthened.As the secondary eyewall intensified and contracted and the primary eyewall weakened and dissipated,the off-center warm ring extended inward and merged with the inner warm core to form a warm core typical of a single-eyewall TC.Results from the azimuthal-mean potential temperature budget indicate that the warming in the eye is due to subsidence and the warming above 14-km height outside the eye is largely contributed by radial warm advection in the outflow.The development of the off-center warm ring is largely due to the subsidence warming near the inner edge of the primary eyewall and in the moat area and the warming by diabatic heating in the upper part of the inner eyewall below 14-km height.Further analysis indicates that the eddy advection also played some role in the warming above 12-km height in the upper troposphere.(Wang Hui,Wang Yuqing,Xu Jing)

4.8 Factors affecting the variability of maximum potential intensity (MPI) of tropical cyclones over the North Atlantic

Contributions of atmospheric factors to the variability of the calculated theoretical maximum potential intensity (MPI) of tropical cyclones (TCs) over the North Atlantic are explored using the 6-hour atmospheric reanalysis and TC best track data from 1980 to 2015.The results show that for a given sea surface temperature (SST),the calculated theoretical MPI between the medians of top 10% and bottom 10% samples can vary by as large as 10?15 m s?1,which accounts for 20%?25% of the median of the MPI.It is shown that the drier (moister) and colder (warmer) environment favors higher (lower) MPI,and the TC-MPI is more sensitive to atmospheric temperature at lower SSTs,but more sensitive to atmospheric humidity at higher SSTs.Results from sensitivity experiments show that the tropospheric temperature and humidity profiles and the outflow layer temperature are all responsible for the MPI variability,but their relative importance varies with SST.The atmospheric humidity accounts for 12?13 (7?11) m s?1at SSTs over (below) 28 ,the tropospheric temperature accounts for about 7?12 (5?6) m s?1at SSTs below (above) 28 ,and the outflow temperature accounts for 7?8 m s?1almost independent of SST.These results strongly suggest that the modulation of MPI by synoptic variability needs to be considered when MPI is calculated and used as a predictor/parameter in operational TC intensity prediction schemes,especially for strong TCs.(Xu Jing,Wang Yuqing,Yang Chi)

4.9 Interbasin differences in the median and variability of tropical cyclone MPI in the Northern Hemisphere

Using the 1980?2017 6-hour best-track tropical cyclone data and global reanalysis data,we studied the interbasin differences in the median and variability of tropical cyclone maximum potential intensity (MPI) as a function of sea surface temperature (SST) in the North Atlantic (NA),eastern North Pacific (ENP),western North Pacific (WNP),and North Indian Ocean (NI).Results show that the MPI median increases by 4.8,7.7,6.4,and 4.4 m s?1per degree increase in SST in the NA,ENP,WNP,and NI,respectively.The MPI is the largest in the NI at SST between 27 and 28.5 and in the ENP at SST above 28.5 ,while is the smallest at SST below 29.5 in the WNP.The environmental factors that contribute to such interbasin differences were compared among basins.The greatest MPI in the ENP is largely contributed by the colder troposphere and drier boundary layer.The warmer troposphere and wetter boundary layer are responsible for the smallest MPI in the WNP.In the NA,the warmer outflow layer reduces the thermodynamic efficiency and partly offsets the positive contributions by the colder troposphere and drier boundary layer,resulting in the moderate MPI.In the WNP,the variability in MPI decreases with increasing SST across all four basins and is the largest.The large variability at low SSTs is largely contributed by the variability in air temperature,which includes both the airsea temperature difference and the outflow layer temperature,while the variability at relatively high SSTs is dominantly contributed by boundary layer moisture.(Xu Jing,Wang Yuqing,Yang Chi)

4.10 Microphysical properties of rainwater in Typhoon Usagi (2013):A numerical modeling study

A 2-km resolution simulation using the Weather Research and Forecasting model with Morrison microphysics was employed to investigate the rainwater microphysical properties during different stages of Typhoon Usagi (2013) in the inner-core and outer region.The model reproduced the track,intensity,and overall structure of Usagi (2013) reasonably.The simulated raindrop size distribution showed a rapid increase in small-size raindrop concentration but an oscillated decrease in large-size ones in the inner-core region,corresponding well with the upward motion.It was found that there existed two levels (1.25 and 5.25 km) of maximum number concentration of raindrops.The ice-related microphysics at high levels was stronger than the warm-rain processes at low levels.The larger raindrops formed by self-collection in the inner-core suffered from significant breakup,but the raindrops outside the eyewall did not experience evident breakup.Model results indicated that the dominant terms in the water vapor budget were the horizontal moisture flux convergence (HFC) and local condensation and deposition.The evaporation from the ocean surface (PBL) was similar to 10% of the HFC in the inner core,but up to 40% in the outer region as the air therein was far from saturation.Furthermore,water vapor in the outer region was obtained equally through evaporation from the cloud and inward transportation from the environment.An earlier start of cloud microphysical processes in the inner-core region was evident during the intensification stage,and the continuous decreasing of condensation in both the inner-core and outer regions might imply the beginning of the storm weakening.(Deng Lin,Gao Wenhua,Duan Yihong)

4.11 Effect of unidirectional vertical wind shear on tropical cyclone intensity change:Lower-layer shear versus upper-layer shear

In this study,a quadruply nested,nonhydrostatic tropical cyclone (TC) model is used to investigate how the structure and intensity of a mature TC respond differently to imposed lower-layer and upper-layer unidirectional environmental vertical wind shears (VWSs).Results show that TC intensity in both cases decrease shortly after the VWS is imposed but with quite different subsequent evolutions.The TC weakens much more rapidly for a relatively long period in the upper-layer shear than in the lower-layer shear,which is found to be related to the stronger storm-relative asymmetric flow in the middle-upper troposphere and the larger vertical vortex tilt in the former than in the latter.The stronger storm-relative flow in the former imposes a greater ventilation of the warm core in the middle-upper troposphere,leading to a more significant weakening of the storm.The storm in the lower-layer shear only weakens initially after the VWS is imposed but then experiences a quasi-periodic intensity oscillation with a period of about 24 h.This quasi-periodic behavior is found to be closely related to the boundary layer thermodynamic discharge/recharge mechanism associated with the activity of shear-induced outer spiral rainbands.There is no significant intensity oscillation for the storm embedded in the upper-layer shear,even though outer spiral rainbands develop quasi-periodically also.The boundary layer inflow is very weak in that case and the low equivalent potential temperature air induced by downdrafts in outer spiral rainbands therefore cannot penetrate into the inner core but remains in the outer region.(Fu Hao,Wang Yuqing,Riemer Michael)

4.12 A method for diagnosing the secondary circulation with saturated moist entropy structure in a mature tropical cyclone

Under the adiabatic,axisymmetric and steady assumption,a relationship between the saturated moist entropy structure and the secondary circulation in a tropical cyclone (TC) is derived from the continuity equation.It is found that the isentropic surfaces coincide with the streamlines,and the streamfunction can be expressed with saturated moist entropy.The secondary circulation and the saturated moist entropy structure depend on each other.Thus,a method for diagnosing the secondary circulation with the structure of saturated moist entropy is proposed.The method is verified with a simulated intense idealized TC with a highly axisymmetric structure.The diagnosed secondary circulation reproduces well the moist inflow in the boundary layer and the moist updraft in the eyewall.This method facilitates secondary circulation diagnosis in theoretical or mature TCs that satisfy the adiabatic,axisymmetric and steady approximations.(Huang Yiwu,Duan Yihong,Chan Johnny C L)

4.13 Revisiting the dynamics of eyewall contraction of tropical cyclones

The dynamics of eyewall contraction of tropical cyclones (TCs) has been revisited in this study based on both three-dimensional and axisymmetric simulations and dynamical diagnostics.Because eyewall contraction is closely related to the contraction of the radius of maximum wind (RMW),its dynamics is thus often studied by examining the RMW tendency in previous studies.Recently,Kieu and Stern,et al.,proposed two different frameworks to diagnose the RMW tendency but had different conclusions.In this study,the two frameworks are evaluated first based on theoretical analysis and idealized numerical simulations.It is shown that the framework of Kieu is a special case of the earlier framework of Willoughby,et al.,if the directional derivative is applied.An extension of Stern et al.’s approach not only can reproduce but also can predict the RMW tendency.A budget of the azimuthal-mean tangential wind tendency indicates that the contributions by radial and vertical advections to the RMW tendency vary with height.Namely,radial advection dominates the RMW contraction in the lower boundary layer,and vertical advection favors the RMW contraction in the upper boundary layer and lower troposphere.In addition to the curvature,the increase of the radial gradient of horizontal mixing (including the resolved eddy mixing in three dimensions) near the eyewall prohibits eyewall contraction in the lower boundary layer.Besides,the vertical mixing including surface friction also plays an important role in the cessation of eyewall contraction in the lower boundary layer.(Li Yuanlong,Wang Yuqing,Lin Yanluan)

4.14 Characteristics of tropical cyclone extreme precipitation and its preliminary causes in Southeast China

Extreme precipitation induced by a tropical cyclone (TC) is of great concern to Southeast China.Regional characteristics of daily TC-induced extreme precipitation (TCEP) between 1958 and 2016 and the associated preliminary causes over Southeast China (Zhejiang,Fujian,and Shanghai) were examined by applying the objective synoptic analysis technique,TC track similarity area index,daily precipitation observations,and reanalysis data.The intensity and frequency of high-intensity TCEP (≥100,≥200,≥300 mm) have had an increasing trend over recent decades.Most of TCEP occurs from July to September,with frequency peaking in August for TCEP at all intensity levels,apart from the frequency for TCEP≥300 mm that peaks in September.Regions with high frequency and large TCEP (R-HFLTs) (relatively high frequency for TCEP≥100 mm) were concentrated along the coastline of the southern coastal Fujian (Southern R-HFLT),the regions from northern coastal Fujian to southernmost coastal Zhejiang (Central R-HFLT),and central coastal Zhejiang (Northern R-HFLT),decreasing from the coastline to inland.The Central R-HFLT region had the highest TCEP intensity and frequency for TCEP≥100 mm compared with the other R-HFLTs.Further analysis showed that the special terrain of Southeast China matched the spatial distribution of TCEP,which highlights the significance of the topography of Southeast China.To discover other factors responsible for the heavy TCEP,we compared two TC groups that influence Central R-HFLT.Under a more northerly direction and slow movement combined with the unique terrain,TCs with stronger vortex circulation generated heavier TCEP during landfall in Central R-HFLT.Heavy TCEP occurred with easterly and southeasterly winds interacting with terrain over the eastern coast for Central R-HFLT.Although large changes in the internal and external environment were sensitive to the observed TCEP intensity,the interaction between TC circulation and the complex topography in Southeast China under the northerly track was the dominant factor.(Qiu Wenyu,Ren Fumin,Wu Liguang)

4.15 Contributions of SST anomalies in the Indo-Pacific Ocean to the interannual variability of tropical cyclone genesis frequency over the western North Pacific

This study attempts to evaluate quantitatively the contributions of sea surface temperature (SST) anomalies in the Indo-Pacific Ocean to the interannual variability of tropical cyclone (TC) genesis frequency (TCGF) over the western North Pacific (WNP).Three SST factors in the Indo-Pacific Ocean are found to play key roles in modulating the interannual variability of WNP TCGF.They are summer SST anomaly in the east Indian Ocean (EIO),the summer El Ni?o-Southern Oscillation Modoki index (EMI),and the spring SST gradient (SSTG) between the southwestern Pacific and the western Pacific warm pool.Results show that the three factors together can explain 72% of the total variance of WNP TCGF in the typhoon season for the period 1980?2015.Among them,the spring SSTG and the summer EIO contribute predominantly to the interannual variability of TCGF,followed by the summer EMI,with respective contributions being 39%,38%,and 23%.Further analysis shows that the summer EMI was affected significantly by the spring SSTG and thus had a relatively lower contribution to the TCGF than the spring SSTG.In addition,a statistical model is constructed to predict the WNP TCGF in the typhoon season by a combination of the May EIO and the spring SSTG.The new model can reproduce well the observed WNP TCGF and shows an overall better skill than the ECMWF Seasonal Forecasting System 5 (SEAS5) hindcasts.This statistical model provides a good tool for seasonal prediction of WNP TCGF.(Zhan Ruifen,Wang Yuqing,Zhao Jiuwei)

4.16 Coastal ocean response and its feedback to Typhoon Hato (2017) over the South China Sea:A numerical study.

The coastal ocean response and feedback to Typhoon Hato (2017) were studied based on high-resolution numerical simulations using both a coupled and an uncoupled cloud-resolving model.As a category 3 landfalling typhoon that moved west-northwestward across the northern South China Sea,Hato (2017) rapidly intensified prior to its landfall and induced significant impacts on the coastal water column,causing warm and cold patches in sea surface temperature (SST) over the continental shelf to the right of the track.This feature was well captured in an air-sea coupled model experiment.The coastal SST warming was found to be related to a two-layer oceanic circulation across the continental shelf forced by the onshore surface wind stress to the right of the storm track.The associated onshore surface currents imposed a warm temperature advection and downwelling,leading to the SST warming in the inner sea shelf,as diagnosed from an ocean temperature budget analysis.A sensitivity experiment,in which the typhoon vortex was removed from the initial conditions,further confirmed that it was the strong onshore wind stress to the right of the storm track that forced the onshore surface currents and the SST warming in the inner sea shelf.Results from an atmosphere-only model experiment with the typhoon-forced coastal warm SST anomalies removed demonstrate that the typhooninduced coastal warm SST anomalies contributed partly to the rapid intensification of Typhoon Hato prior to its landfall over South China and also slowed down the weakening of Hato at and shortly after its landfall.(Zhang Ze,Wang Yuqing,Zhang Weiming)

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

Recently,a track-similarity-based the 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)

4.18 我國(guó)大風(fēng)機(jī)理研究和預(yù)報(bào)技術(shù)進(jìn)展

大風(fēng)作為常見且影響嚴(yán)重的天氣現(xiàn)象，可在各類天氣系統(tǒng)和地形綜合影響下產(chǎn)生。全面認(rèn)識(shí)其機(jī)理和預(yù)報(bào)方法，對(duì)風(fēng)災(zāi)防御和風(fēng)能利用都有很大幫助。本文梳理了我國(guó)氣象觀測(cè)和業(yè)務(wù)預(yù)報(bào)關(guān)于大風(fēng)定義、大風(fēng)分布特征以及雷暴、臺(tái)風(fēng)等主要災(zāi)害性系統(tǒng)大風(fēng)分布情況。之后簡(jiǎn)述雷暴、臺(tái)風(fēng)、冷空氣等系統(tǒng)產(chǎn)生大風(fēng)的機(jī)理，以及復(fù)雜地形下墊面的熱力和動(dòng)力作用對(duì)局地大風(fēng)的影響，概括了不同系統(tǒng)大風(fēng)預(yù)報(bào)技術(shù)的研究進(jìn)展。最后總結(jié)大風(fēng)研究現(xiàn)狀和不足。（王黌，李英，吳哲紅）

4.19 西北太平洋熱帶氣旋變性過程中的風(fēng)及降水分布變化特征分析

利用中國(guó)氣象局上海臺(tái)風(fēng)研究所（CMA/STI）整編的熱帶氣旋最佳路徑資料、美國(guó)颶風(fēng)聯(lián)合警報(bào)中心（JTWC）最佳路徑資料、美國(guó)國(guó)家海洋與大氣管理局（NOAA）的全球多平臺(tái)熱帶氣旋風(fēng)場(chǎng)資料（MTCSWA）和CMORPH降水資料、日本衛(wèi)星云頂黑體輻射溫度（TBB）資料等，分析1987—2016年30年間西北太平洋228個(gè)變性熱帶氣旋（ETTC）的活動(dòng)規(guī)律、風(fēng)與降水分布及其演變特征。結(jié)果表明：（1）ETTC年均7.6個(gè)，除1—2月，各月均有分布，峰值在9月。約90.4%的ETTC變性位置在30°N以北，僅約9.6%在30°N以南較低緯度，且多發(fā)生于春夏和秋冬交替季節(jié)。（2）TC（熱帶氣旋）變性通常發(fā)生在其轉(zhuǎn)向后，半數(shù)以上移速加快，大多數(shù)中心氣壓升高或維持，僅10.5%降低。（3）變性過程中ETTC近中心最大風(fēng)速減小，最大風(fēng)速半徑增大，內(nèi)核趨于松散。其34節(jié)風(fēng)圈半徑北側(cè)明顯大于南側(cè)，風(fēng)場(chǎng)結(jié)構(gòu)非對(duì)稱性增強(qiáng)。（4）ETTC強(qiáng)風(fēng)和強(qiáng)降水呈顯著非對(duì)稱性分布，其強(qiáng)風(fēng)區(qū)主要出現(xiàn)在ETTC中心東側(cè)，即路徑右后方；強(qiáng)降水區(qū)主要出現(xiàn)在北側(cè)，且變性后在東北象限向外擴(kuò)張。（5）較強(qiáng)的環(huán)境水平風(fēng)垂直切變（VWS）是影響ETTC風(fēng)及降水分布的重要因子。強(qiáng)降水主要出現(xiàn)在順風(fēng)切方向及其左側(cè)，強(qiáng)風(fēng)（去除TC移速時(shí)）出現(xiàn)在切變左側(cè)。（王佳琪，李英）

4.20 高空冷渦影響臺(tái)風(fēng)Meranti（1010）北翹路徑的集合預(yù)報(bào)分析

路徑突變是臺(tái)風(fēng)路徑預(yù)報(bào)中的一個(gè)難題。2010年第10號(hào)臺(tái)風(fēng)Meranti（1010）在臺(tái)灣島南部海域西移過程中突然北折，而歐洲中期天氣預(yù)報(bào)中心（ECMWF）集合預(yù)報(bào)對(duì)其北翹路徑存在較大分歧。選取預(yù)報(bào)成功與不成功兩組集合成員各8例，對(duì)比分析臺(tái)風(fēng)Meranti路徑變化的主要原因。結(jié)果表明：（1）一個(gè)來自熱帶對(duì)流層上部槽的切斷高空冷渦（UTCL）是該臺(tái)風(fēng)路徑變化的一個(gè)重要影響系統(tǒng)。Meranti北翹路徑跟它與UTCL的南北向耦合有關(guān)。（2）UTCL通過改變臺(tái)風(fēng)上層的環(huán)境氣流影響臺(tái)風(fēng)引導(dǎo)氣流。在UTCL移至臺(tái)風(fēng)北部過程中，臺(tái)風(fēng)的偏南風(fēng)引導(dǎo)氣流明顯加強(qiáng)，有利于其路徑北翹。（3）UTCL對(duì)臺(tái)風(fēng)Meranti北翹路徑的影響還與其自身結(jié)構(gòu)有關(guān)。水平環(huán)流寬且氣旋性渦旋向下垂直伸展更深的UTCL對(duì)臺(tái)風(fēng)路徑變化影響更明顯。（4）位渦傾向方程的診斷分析表明，在TC與UTCL南北向耦合過程中，臺(tái)風(fēng)北部的正位渦水平平流項(xiàng)輸送顯著，有利于臺(tái)風(fēng)向北運(yùn)動(dòng)，且UTCL影響下產(chǎn)生的非對(duì)稱風(fēng)場(chǎng)在其中起主要作用。（溫典，李英，魏娜）

4.21 基于路徑相似的登陸熱帶氣旋降水之動(dòng)力-統(tǒng)計(jì)集合預(yù)報(bào)模型

過去幾十年，數(shù)值天氣預(yù)報(bào)（NWP）在熱帶氣旋（TC）預(yù)報(bào)方面的最大進(jìn)步是越來越準(zhǔn)確的路徑預(yù)報(bào)。對(duì)于登陸TC降水的預(yù)報(bào)，目前以數(shù)值模式為代表的技術(shù)手段預(yù)報(bào)能力還十分有限。圍繞動(dòng)力-統(tǒng)計(jì)結(jié)合之方法研究，初步發(fā)展了登陸熱帶氣旋降水（LTP）預(yù)報(bào)的一種新方法——基于路徑相似的登陸熱帶氣旋降水之動(dòng)力統(tǒng)計(jì)集合預(yù)報(bào)（LTP_DSEF）模型。該方法主要分為5步：TC路徑預(yù)報(bào)、相似路徑TC識(shí)別、其他特征相似性的判別、TC降水集合預(yù)報(bào)和最佳預(yù)報(bào)方案選擇。涉及兩個(gè)關(guān)鍵技術(shù)：TC降水分離的客觀天氣圖分析法（OSAT）和TC路徑相似面積指數(shù)（TSAI）。LTP DSEF模型對(duì)2012—2016年影響華南地區(qū)出現(xiàn)最大日降水量≥100 mm的21個(gè)TC的定量降水預(yù)報(bào)（QPF）試驗(yàn)結(jié)果顯示，該模型對(duì)登陸TC過程降水的預(yù)報(bào)結(jié)果優(yōu)于動(dòng)力模式。登陸TC過程降水≥50 mm情況下，建模樣本和獨(dú)立樣本平均TS評(píng)分均高于動(dòng)力模式（EC、GFS、T639）相應(yīng)的最好表現(xiàn)。對(duì)LTP_DSEF模型3個(gè)最佳方案的參數(shù)取值分析顯示，起報(bào)時(shí)刻參數(shù)設(shè)定為最臨近影響時(shí)刻即TC對(duì)陸地產(chǎn)生降水的前一天12：00 UTC、集合參數(shù)取最大值時(shí)預(yù)報(bào)效果穩(wěn)定趨好。（丁晨晨，任福民，邱文玉）

5 雷電研究

5 Lightning research

5.1 雷電野外科學(xué)試驗(yàn)

“中國(guó)氣象局雷電野外科學(xué)實(shí)驗(yàn)基地”觀測(cè)條件進(jìn)一步改善，開展了廣州野外雷電綜合觀測(cè)試驗(yàn)以及那曲高原雷電觀測(cè)試驗(yàn)。（1）針對(duì)廣州高建筑物雷電觀測(cè)增加了2個(gè)光學(xué)觀測(cè)點(diǎn)，本年度獲得的閃電個(gè)例數(shù)＞200。（2）新建了48 m2的人工引雷控制和觀測(cè)室，成功引雷次數(shù)39次，創(chuàng)歷史新高。（3）引進(jìn)的閃電成像陣列（LMA）實(shí)現(xiàn)試運(yùn)行，連續(xù)干涉儀的閃電通道精細(xì)化解析能力獲得提升，捕獲了幾十例高質(zhì)量閃電觀測(cè)個(gè)例。（4）在廣東和高原持續(xù)開展了基于閃電探測(cè)陣列的雷暴閃電活動(dòng)觀測(cè)試驗(yàn)，獲得了一手的觀測(cè)數(shù)據(jù)。（呂偉濤，張陽(yáng)，鄭棟，馬穎）

5.2 雷電探測(cè)技術(shù)研發(fā)

提出了一種應(yīng)用于閃電低頻信號(hào)的到達(dá)時(shí)差—時(shí)間反轉(zhuǎn)定位算法，其具有對(duì)定位最小站數(shù)要求低、抗干擾能力強(qiáng)、對(duì)時(shí)間精度要求不高的優(yōu)勢(shì)，并取得良好的定位效果?；诘皖l電場(chǎng)變化探測(cè)陣列的三維定位結(jié)果，對(duì)一次致人死亡的“晴天霹靂”閃電進(jìn)行了分析，指出旁絡(luò)閃擊和多回?fù)籼卣魇窃斐扇藛T死亡的直接原因?；陲L(fēng)云四衛(wèi)星的閃電成像儀（LMI）對(duì)我國(guó)登陸臺(tái)風(fēng)全閃電的觀測(cè)，檢驗(yàn)了LMI閃電活動(dòng)觀測(cè)的連續(xù)性、實(shí)時(shí)性和有效性。（張陽(yáng)，張文娟，范祥鵬，樊艷峰）

5.3 雷電物理研究

明確了觸發(fā)閃電中爆發(fā)式磁場(chǎng)脈沖的普遍性，并揭示了其輻射來源和放電強(qiáng)度。利用廣州高建筑物雷電過程的觀測(cè)資料，明確了廣州塔對(duì)下行閃電的影響范圍和程度；揭示了閃電反沖先導(dǎo)的確切始發(fā)位置和雙向傳輸細(xì)節(jié)特征；給出了同一次閃電中沿著相同路徑的首次和繼后回?fù)舻墓鈱W(xué)和電磁波形差異；分析了正地閃觸發(fā)的并發(fā)上行閃電特征，結(jié)果表明正地閃回?fù)艏爸笤苾?nèi)負(fù)先導(dǎo)朝建筑物頂端方向快速伸展均會(huì)激發(fā)上行閃電；基于我們獲取的最高時(shí)間分辨率的自然下行閃電的光學(xué)觀測(cè)資料，解析了一次近距離閃電的連接過程。采用3D-FDTD電磁場(chǎng)數(shù)值算法，研究了海陸混合傳播路徑對(duì)風(fēng)力發(fā)電機(jī)上的閃電回?fù)舢a(chǎn)生的雷電電磁場(chǎng)傳播的影響，揭示了海陸界面影響雷電電磁場(chǎng)的主要因素；構(gòu)建了多個(gè)建筑物雷擊模型，發(fā)現(xiàn)建筑物屏蔽效應(yīng)對(duì)屏蔽體高度的依賴性比屏蔽體的距離、相對(duì)距離和長(zhǎng)度等參數(shù)更強(qiáng)。（張陽(yáng)，呂偉濤，武斌，齊奇）

5.4 雷暴電學(xué)研究

明確了層云區(qū)閃電始發(fā)和傳播位置的反射率特征，發(fā)現(xiàn)了層云區(qū)閃電的始發(fā)與亮帶區(qū)域之間空間上緊密、實(shí)則在因果關(guān)系上相對(duì)疏遠(yuǎn)的現(xiàn)象。明確了閃電初始階段的通道發(fā)展規(guī)律，揭示了不同類型雷暴以及雷暴不同區(qū)域閃電初始先導(dǎo)發(fā)展特征的差異，建立了電荷區(qū)分布形態(tài)和電荷密度不同配置影響閃電初始先導(dǎo)發(fā)展的概念模型。揭示了冬季雷暴電荷結(jié)構(gòu)的多樣性特征，指出部分冬季雷暴存在較大的下部正電荷區(qū)；發(fā)現(xiàn)冬季雷暴的閃電尺度和閃電初始擊穿能量大于夏季。揭示了東亞以及西太平洋地區(qū)閃電的持續(xù)時(shí)間、空間擴(kuò)展尺度和輻射能等特征，發(fā)現(xiàn)閃電空間擴(kuò)展與雷暴對(duì)流強(qiáng)度之間的反向關(guān)聯(lián)。建立了基于云分檔微物理方案的起放電模型，相比于一般電學(xué)模型，該模型可以更為精細(xì)地模擬云內(nèi)電過程，是研究起電機(jī)制和雷暴電荷結(jié)構(gòu)形成的重要工具。基于模擬研究，揭示高原雷暴中獨(dú)特的環(huán)境條件，如弱上升運(yùn)動(dòng)和低凍結(jié)層高度，是促使高原雷暴中頻繁出現(xiàn)下部大正電荷中心的根本原因。（鄭棟，王飛，徐良韜）

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

開發(fā)了“雷電臨近預(yù)警系統(tǒng)V2.1版本”，完成與國(guó)家級(jí)短時(shí)臨近預(yù)報(bào)系統(tǒng)（SWAN）系統(tǒng)集成，實(shí)現(xiàn)對(duì)大區(qū)域范圍的雷電活動(dòng)進(jìn)行臨近預(yù)警，并通過業(yè)務(wù)轉(zhuǎn)化認(rèn)證評(píng)審。發(fā)展了基于人工智能技術(shù)融合應(yīng)用WRF模式產(chǎn)品和閃電實(shí)測(cè)數(shù)據(jù)的雷電短時(shí)預(yù)報(bào)模型，初步完成了“人工智能和WRF模式相結(jié)合的閃電短時(shí)預(yù)報(bào)模塊”的模塊開發(fā)工作。為做好雷電監(jiān)測(cè)、預(yù)警服務(wù)保障工作，2019年對(duì)雷電監(jiān)測(cè)預(yù)警的各個(gè)系統(tǒng)軟件進(jìn)行了更新和完善。在70周年國(guó)慶期間，保障了雷電監(jiān)測(cè)產(chǎn)品、雷電預(yù)警產(chǎn)品每天24 h實(shí)時(shí)上傳到中國(guó)天氣網(wǎng)，及時(shí)提供了雷電活動(dòng)服務(wù)產(chǎn)品。順利完成了大興安嶺雷擊森林火災(zāi)服務(wù)系統(tǒng)的運(yùn)行及維護(hù)工作，其監(jiān)測(cè)預(yù)警產(chǎn)品實(shí)時(shí)上傳到國(guó)家林業(yè)局森林防火預(yù)警監(jiān)測(cè)信息中心，為各級(jí)林業(yè)管理部門開展雷擊火監(jiān)測(cè)提供了支持。（姚雯，孟青，馬穎，陸天舒）

5.6 Characteristics of a multi-stroke“bolt from the blue”lightning-type that caused a fatal disaster

Observational data from the low-frequency electric-field detection array (LFEDA) and radar were used to study the precise location of a fatal accident caused by a lightning in Conghua,Guangzhou,China,2017.Based on a comprehensive analysis,the lightning was concluded to be a negative“bolt from the blue”ground flash with seven return strokes.The first return stroke was on June 3 at 16:36:49 with a peak current intensity of ?30.9 kA.The LFEDA system mapped the development of the lightning channel.The horizontal distance from the edge of the cloud anvil area (0 dBz) to the return stroke point was about 0.3 km; the horizontal distance from the edge of the precipitation area (18 dBz) to the return stroke point was about 1.8 km; and the return stroke channel extended as far as 3 km out of the cloud.There was no cloud cover above the head of the victim.The electric field waveform of the return strokes detected by the LFEDA system showed multi-peak characteristics,and all seven return strokes were multiple-termination strokes.The most probable mechanism for the lightning injuries was the side flash.(Fan Xiangpeng,Zhang Yijun,Yin Qiyuan)

5.7 Measurements of magnetic pulse bursts during initial continuous current of negative rockettriggered lightning

During the Shandong Triggering Lightning Experiment (SHATLE) in summer of 2014 and 2015 and the Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD) campaign in 2018,we have conducted the observations of the magnetic pulse bursts (MPBs) during the initial continuous current in negative rocket-triggered lightning.The MPBs are commonly recorded at the main site of SHATLE (970 m from the rocket launch site),but the synchronous magnetic field (B-field) measurements at the close site of SHATLE (78 m from the rocket launch site) show the slow variations with small MPBs superposing on them.Note that both the charge transfer and the relative brightness increase notably during the appearance of the MPBs.After shifting up the operation frequency of the magnetic sensor,the MPBs can be observed at close distance (80 m from the rocket launch site) obviously in GCOELD.Observations show that the radiation sources of MPBs originate from the breakdown in the vicinity of the leader tip,but the sources of the initial magnetic pulses (IMPs) measured at the very initial stage of triggered lightning are from the radiation of the whole steel wire.The continuous current measured at the channel base during the MPBs cannot reflect the characteristics of breakdown current,because the current is attenuated and dispersed when propagating along the high-impedance leader channel.The average peak current associated with the MPBs is estimated to be on the order of kiloamperes.(Fan Yanfeng,Lu Gaopeng,Li Xiao)

5.8 Observations of the magnetic pulses in rocket-triggered lightning with sensitive magnetic sensor

With the observations in SHandong Triggering Lightning Experiment (SHATLE) and Comprehensive Observation Experiment on Lightning Discharge (GCOELD) in China,we investigate the magnetic pulses associated with the upward positive leaders during the initial stage of negative triggered lightning.The initial magnetic pulses (IMPs) measured at the very initial stage are corresponding to the sustained upward positive leaders,and can be divided into two categories (i.e.,impulsive and ripple pulses) according to the discernibility of separation between individual pulses.The IMPs are generated by leader current pulses propagating downward along the steel wire.For the magnetic pulses measured during the stage of initial continuous current or called magnetic pulse bursts (MPBs) since these pulses last longer than IMPs,they are commonly observed both in SHATLE and in GCOELD,even though the associated signals of electrical fields are not obvious.The heights of rocket upon the inception of the MPBs are at least about 268 m in our observations,and the average inter-pulse intervals are affected by the height significantly.The cases with higher height usually have shorter inter-pulse intervals.In comparison with the IMPs,the inter-pulse intervals of the MPBs contain more small time scale (＜20 μs) cases,since the speed of upward leaders shows an accelerating tendency with height and time.MPBs are derived from the breakdown near the leader tip.(Fan Yanfeng,Lu Gaopeng,Li Xiao )

5.9 Development of lightning nowcasting and warning technique and its application

The Chinese Academy of Meteorological Sciences Lightning Nowcasting and Warning System (CAMS_LNWS) was designed to predict lightning within the upcoming 0?1 h and provide lightning activity potential and warning products.Multiple remote sensing data and numerical simulation of an electrification and discharge model were integrated in the system.Two core algorithms were implemented:(1) an area identification,tracking,and extrapolating algorithm; (2) a decision tree algorithm.The system was designed using a framework and modular structure,and integrated warning methods were applied in the warning program.Two new algorithms related to the early warning of the first lightning and thunderstorm dissipation were also introduced into the system during the upgrade process.Thunderstorms occurring in Beijing,Tianjin,and Hebei during 2016?2017 were used to evaluate the CAMS_LNWS by the low-frequency cloud to ground lightning detection data,and the results show that the system has good forecasting and warning ability for local lightning activities.The TS score in 0?1 h ranged from 0.11 to 0.32,with a mean of 0.20.Operational experiments and promotional work for the CAMS_LNWS are now in progress.(Meng Qing,Yao Wen,Xu Liangtao)

5.10 High-speed video observations of natural lightning attachment process with framing rates up to half a million frames per second

Using high-speed video cameras operating with framing rates of 20 and 525 kfps,we imaged the attachment process of a natural negative cloud-to-ground flash,occurring at a distance of 490 m.Nine upward leaders were observed.A total of 12 space stems/leaders in 47 steps of the downward negative stepped leader were captured.The two-dimensional length of them was between 2.0 and 5.9 m,with an average of 3.0 m.The average interstep interval,step length,and two-dimensional speed of the downward negative leader and that of upward positive leader were statistically analyzed.The last step of the downward negative leader making contact with the upward connecting leader was recorded.The two-dimensional length of the final imaged gap between the tips of opposite-polarity leaders was estimated to be about 13 m.(Qi Qi,Lyu Weitao,Ma Ying)

5.11 Numerical simulation of the formation of a large lower positive charge center in a Tibetan Plateau thunderstorm

Numerical modeling is applied to elucidate the formation mechanism of the large lower positive charge centers (LPCCs) observed during thunderstorms over the Tibetan Plateau based on the simulation of a storm at the northeastern boundary of the plateau.Four sensitivity tests were carried out to explore the impacts of inductive charging,reversal temperature,and the choice of noninductive charging scheme.The results show that the unique environmental conditions of the Qinghai-Tibet Plateau,which include weak convection and low freezing level,are fundamental to the formation of large LPCC.A weakened charge density in the upper positive charge center highlights the role of a LPCC in lightning initiation although the charge density of the LPCC has no obvious change compared to that in the LPCC of the typical tripole structure.This accounts for Tibetan Plateau thunderstorms having low frequencies of lightning flashes,which occur mainly in the lower dipole.Inductive electrification,which provided more than 50% of the positive charge on graupel and increased the positive and negative charge on cloud drops by 2 orders of magnitude,is an important complement to the lower dipole of the tripole charge structure originally established by noninductive electrification.The inductive electrification also evidently enhances the LPCC and the middle negative charge center while slightly reducing the upper positive charge center.Subsequently,the lightning activity is strengthened,and lightning flashes are more likely to be initiated at the lower dipole.Varying the reversal temperatures and noninductive charging scheme does not fundamentally affect the formation of the LPCC.(Wang Fei,Deng Xiaohua,Zhang Yijun)

5.12 Radar reflectivity of lightning flashes in stratiform regions of mesoscale convective systems

A total of 254 flashes observed in 14 mesoscale convective systems in Chongqing,China,during the summers of 2014?2015 was used to investigate the characteristics of lightning flashes in stratiform regions (stratiform lightning flashes).The data were analyzed and combined with data from an S-band Doppler radar system.The results show that the reflectivity characteristics of stratiform lightning flashes are different from those of convective lightning flashes.More than 90% of the stratiform lightning flashes had close spatial relationship with the areas in which bright bands were identified in the vertical direction.The reflectivity at the first detected very-high-frequency sources of most stratiform lightning flashes decreased with increasing core reflectivity within the lightning extension area.Further investigations show that only a small proportion (≤10%) of the stratiform lightning flashes were directly initiated by the charge corresponding to the reflectivity cores.It suggests that the reflectivity cores (mostly bright bands) and stratiform lightning flashes are close in space,but different in causality.Some in situ electrifications in stratiform regions,such as nonriming noninductive electrification and melting electrification,are inferred to cause this relationship.The stratiform lightning flashes initiated from lower altitudes tended to have a lower maximum reflectivity within their lightning areas,but a higher maximum reflectivity in the vertical direction of their initiation locations than the flashes initiated at higher altitudes.(Wang Fei,Liu Hengyi,Dong Wansheng)

5.13 High-speed video observations of recoil leaders producing and not producing return strokes in a Canton-Tower upward flash

High-speed video and electric field change data have been used to examine the initiation and propagation of 21 recoil leaders,7 of which evolved into dart (or dart-stepped) leaders (DLs) initiating return strokes and 14 were attempted leaders (ALs),in a Canton-Tower upward flash.Three DLs and two ALs clearly exhibited bidirectional extension.Each DL was preceded by one or more ALs and initiated near the extremity of the positive end of the preceding AL.The positive end of each bidirectional DL generally appeared to be inactive (stationary) or intermittently propagated along the positive part of the preceding AL channel and extended into the virgin air.A sequence of two floating channel segments was formed ahead of the approaching positive end of one DL,causing its abrupt elongation.In this paper,we presented high-speed video observations of recoil leaders (RLs) which were not obscured by the cloud.We examined the initial positions,morphology,and dynamics of RLs in a Canton-Tower upward flash.Out of a total of 21 RLs,7 evolved into dart (or dartstepped) leaders,attaching to the Tower and producing return strokes,and 14 failed to reach the Tower,that is,were attempted dart (or dart-stepped) leaders.We infer that all the RLs were bidirectional with the negative end steadily extending toward the Tower and the positive end generally being stationary or showing intermittent propagation.Each dart (or dart-stepped) leader initiated near the extremity of the positive end of the preceding bidirectional attempted leader.The positive end of one dart (or dart-stepped) leader extended abruptly via connection of at least one floating channel to the positive channel tip.(Wu Bin,Lyu Weitao,Qi Qi)

5.14 Synchronized two-station optical and electric field observations of multiple upward lightning flashes triggered by a 310-kA +CG flash

A positive cloud-to-ground (+CG) lightning flash containing a single stroke with a peak current of approximately +310 kA followed by a long continuing current triggered seven upward lightning flashes from tall structures.The flashes were observed on 4 June 2016 at the Tall Object Lightning Observatory in Guangzhou,Guangdong Province,China.The optical and electric field characteristics of these flashes were analyzed using synchronized two-station data from two high-speed video cameras,one total-sky lightning channel imager,two lightning channel imagers,and two sets of slow and fast electric field measuring systems.Three upward flashes were initiated sequentially in the field of view of high-speed video cameras.One of them was initiated approximately 0.35 ms after the return stroke of +CG flash from the Canton Tower,the tallest structure within a 12-km radius of the +CG flash,while the other two upward flashes were initiated from two other,more distant tall objects,approximately 18 ms after the +CG flash stroke.The initiation of the latter two upward flashes could be caused by the combined effect of the return stroke of +CG flash,its associated continuing current,and K process in the cloud.Each of these three upward flashes contained multiple downward leader/upward return stroke sequences,with the first leader/return stroke sequence of the second and third flashes occurring only after the completion of the last leader/return stroke sequence of the preceding flash.The total number of strokes in the three upward flashes was 13,and they occurred over approximately 1.5 s.(Wu Bin,Lyu Weitao,Qi Qi)

5.15 Simulation of inverted charge structure formation in convective regions of mesoscale convective system

The charge structure evolution of a mesoscale convective system with an anomalous or inverted charge structure,observed in the Severe Thunderstorm Electrification and Precipitation Study,a field project on the Colorado-Kansas border in summer 2000,is simulated using the Weather Research and Forecasting (WRF) model coupled with electrification and discharge processes.Two noninductive electrification schemes are used,based on the liquid water content (LWC) and the graupel rime accretion rate (RAR).The simulation with the LWC-based electrification scheme cannot reproduce the inverted charge structure with a positive charge region sandwiched by two negative charge layers,while the RAR-based electrification scheme produces the evolution process of a normal-inverted-normal charge structure in the convective region,which is consistent with the observations.In the low RAR (＜2 g m?2s?1) region,graupel is mainly negatively charged when it bounces off ice crystals,while the ice crystals take up positive charge.However,in the zone where the inverted charge structure forms,a strong updraft (＞16 m s?1),high LWC (＞2 g m?3),and high RAR (＞4.5 g m?2s?1) region appears above the height of the ?20 layer,so that a positive graupel charging region is generated above the ?20 layer of the convective region,resulting in a negative dipole charge structure with negatively charged ice crystals above the positively charged graupel.The negative dipole is superposed on the positive dipole (positive above negative) charge structure at the lower position to form an inverted tripole charge structure.(Xu Liangtao,Zhang Yijun,Wang Fei )

5.16 Inner-core lightning outbreaks and convective evolution in super Typhoon Haiyan (2013)

Using lightning data from the World Wide Lightning Location Network,infrared satellite imagery,and micro-wave observations,this study investigates lightning outbreaks and convective evolution in the inner core (0?100 km) of super Typhoon Haiyan (2013),the strongest storm on record to make landfall in the northwest Pacific.This storm was characterized by intense lightning activity with half of the strokes occurring in the inner core.Three major inner-core lightning outbreaks and convective bursts (CBs) were observed during rapid intensification (RI),maximum intensity (MI),and weakening stages.These outbreaks coincided with favorable large-scale environmental conditions for TC development with higher sea surface temperature (29?30 ),higher relative humidity (75%?80%),and weaker deep-layer vertical wind shear (3?8 m s?1),compared to the climatological averages for the month of November in the northwest Pacific.The RI lightning outbreak occurred primarily in the downshear quadrants and CBs were located inside the radius of maximum wind (RMW).The MI lightning outbreak occurred just after the eyewall replacement cycle,inducing marked depression of brightness temperature at 91-GHz.The lightning outbreak during Haiyan’s weakening stage preferred the upshear-left quadrant outside the RMW.In contrast,relative lack of cloud-to-ground lightning in the rainbands was observed during all three main outbreaks.The radial and azimuthal distributions of lightning outbreak within the inner core provided indicative information on the relationships between convective structure and intensity changes of Haiyan.(Zhang Wenjuan,Rutledge Steven A,Xu Weixin)

5.17 Initial leader properties during the preliminary breakdown processes of lightning flashes and their associations with initiation positions

The properties of initial leaders (ILs) of 1056 flashes in two thunderstorms in Guangzhou,China,are analyzed.The median values of IL properties are 11.1 ms for duration,2.2 km for vertical distance,2.7 km for 3-D distance,1.9×105m s?1for vertical displacement speed,2.4×105m s?1for 3-D displacement speed,28° for angle between the IL’s displacement direction and the vertical direction,1.1 per ms for pulse rate,179 m for vertical step length,and 224 m for 3-D step length.All the IL properties follow lognormal distributions.Strong monotonic relationships of IL duration with speed and pulse rate and pulse rate with speed and step length are revealed.With increasing initiation altitude,IL duration and step length tend to increase,and IL speed and pulse rate tend to decrease.The ILs initiated at approximately ?20 isotherm are more vertically orientated on average than those initiated at lower or higher levels.The ILs initiated in the strong kinematic areas generally had a greater speed and pulse rate but smaller duration,distance,and step length relative to those initiated in the weak kinematic areas.The possible impacts of the charge distribution patterns and density on the IL properties in different types of thunderstorms or thunderstorm areas are discussed.(Zheng Dong,Shi Dongdong,Zhang Yang)

5.18 Charge regions indicated by LMA lightning flashes in Hokuriku’s winter thunderstorms

The charge distribution of some cells in three winter thunderstorms in the Hokuriku region of Japan is investigated based on lightning mapping array (LMA) flash data.The vertical arrangements of charge regions involved in lightning discharges suggest diverse charge patterns,including quad-polar,tripole,positive dipole,inverted dipole,and inverted tripole.The riming electrification between graupel and ice crystals or their aggregations are thought to be responsible for the electrification of most cells.The charging process between snow/aggregates and ice crystals may be responsible for some inverted charge structure that occurred above 0 isotherm and accompanied with weak radar echoes.Convection indicated by the vertical development of radar reflectivity appears crucial to shaping the diverse charge distribution patterns by determining which charging mechanisms occur and where; it also influences changes in height or even the disappearance of the charge regions.The charged cores are distributed from 0.7 to 5.3 km heights and 2 to ?31 temperatures,while the distances between adjacent charged cores with opposite polarities change between 0.2 and 3.4 km,with a mean of 1.3 km.The mean flash duration and horizontal distance are 425.0 ms and 19.8 km,respectively.The average height,temperature,and power of flash initiations are 2.8 km,?11.9 ,and 15.6 dBW,respectively.(Zheng Dong,Wang Daohong,Zhang Yijun)

5.19 Correlated luminosity and magnetic field peaks produced by Canton Tower-strokes

Simultaneously measured luminosity and magnetic field induced by the return strokes in typical upward and downward flashes occurring on the 600-m tall Canton Tower were presented.The correlation between peak relative luminosity and peak relative magnetic field induced by return strokes were examined for 4 upward and 4 downward flashes.All the flashes contained 3 or more return strokes and all the return strokes in a same flash followed the same path.Luminosity of the lightning channel close to the top of the Canton Tower exhibited characteristics of pronounced initial peak with 20%?90% rise time of about 5.2 μs (arithmetic mean value,based on 43 samples) for subsequent strokes,which was inferred to be related to the secondary (typically largest) peak current at the top of the Canton Tower.The magnetic field induced by subsequent strokes exhibited characteristics of pronounced initial peak with 20%?90% rise time of about 1.2 μs (arithmetic mean value,based on 47 samples).The initial peak magnetic field was modified to proportionally represent the largest peak current at the top of the Canton Tower.Roughly linear and quadratic relation between the initial peak luminosity and modified peak magnetic field were found for subsequent strokes in both upward and downward flashes.The quadratic relation fit the data slightly better than the linear relation.The ratios of peaks of luminosity to magnetic field of the downward first stroke were considerably larger than those of the subsequent strokes,and the possible reasons were also discussed.(Chen Lyuwen,Lyu Weitao,Zhang Yijun)

5.20 A method of three-dimensional location for LFEDA combining the time of arrival method and the time reversal technique

Based on fast electric field waveforms of the Low-frequency E-field Detection Array (LFEDA),we introduce the time reversal technique into lightning three-dimensional location for the first time and propose a new algorithm for the three-dimensional location of lightning low-frequency discharges.Without using complex filtering algorithms to remove higher-frequency component,this method obtains similar results to the newly reported LFEDA refinement algorithm.The new algorithm can obtain finer,more continuous,and richer positioning results with a minimum of four stations,5-dB signal-to-noise ratio,and 500-ns time error compared with the low-frequency signal time of arrival three-dimensional positioning method.These results indicate that the new algorithm has the advantages of low requirements on the number of stations,certain antiinterference ability,and low requirements on time accuracy.The standard deviations in theXandYdirections for return strokes of triggered lightning flashes are both approximately 90 m.During the last 20 years,besides the location of return stroke,finer and more accurate positioning of total lightning based on lightning lowfrequency discharge signals can be achieved by using the time of arrival method.The Chinese Academy of Meteorological Sciences developed a lightning Low-frequency E-field Detection Array (LFEDA),consisting of ten substations in Conghua,Guangzhou,since 2014,which is capable of determining the three-dimensional locations of lightning discharge events.With the application of empirical mode decomposition algorithm in the past research of LFEDA,the fine structure of lightning channel can be obtained.This paper proposes a new lightning low-frequency discharge three-dimensional location algorithm based on the multistation waveform data of the LFEDA system.This is the first time that the time reversal method has been applied to total lightning three-dimensional location.This method can obtain accurate lightning three-dimensional location results without using a complex filtering algorithm.Compared with the time of arrival method,the new algorithm not only can yield positioning results similar to those of the fine positioning algorithm (Fan et al.,2018) but also has the advantages of low requirements on the number of stations,certain anti-interference ability,and low requirements on time accuracy.(Chen Zefang,Zhang Yang,Zheng Dong)

5.21 Lightning electromagnetic fields along an ocean-land mixed propagation path generated by return strokes to wind turbines

We evaluate lightning electromagnetic fields along an ocean-land mixed propagation path generated by return strokes to wind turbines (WTs) using a three-dimensional finite-difference time domain method.In these simulations,we consider the following three cases:strikes to onshore WTs,strikes to offshore floating WTs,and strikes to onshore WTs in the presence of horizontally stratified ground.Also,we investigate the effect on lightning electromagnetic fields of the following two parameters:distancedbetween the WT and the observation point,and distancedlbetween the coastline and the observation point.Generally,the lightning electromagnetic fields are affected by the ocean-land interface,anddanddlplay an important role in the effect degree.For onshore WTs,the effect of a mixed path is visible on magnetic field and vertical electric field fordless than 300 m and horizontal electric field fordexceeding 300 m.The effect fordl=10 m is stronger than that fordl=50 m.For offshore WTs,the effect of a mixed path is significant and the effect fordl=10 m is almost the same as that fordl=50 m.(Su Zhiguo,Lyu Weitao,Chen Lyuwen)

5.22 Shielding effect of surrounding buildings on the lightning-generated vertical electric field at the top of a tall building

We have evaluated the vertical electric field E-z on the roof of a 100-m tall building considering the shielding effect of surrounding buildings (the shields) due to nearby lightning return strokes to flat ground by using the 3-D finite-difference time-domain method.Also,we have investigated the influences on the vertical electric field E-z and corresponding enhancement factors of the following parameters:the distancedbetween the strike point and the field point; the lengthlof plan area,the heighth,and the conductivity is of the shields; and the relative position and relative distancerdbetween the field point and those shields in its vicinity.In general,vertical electric fields and enhancement factors at the field point can be reduced because of the effect of the shields in its vicinity.The effect for the shield located in front of the field point is much stronger than that for the shield located in any other positions.Moreover,the dependence of shielding effect on heighthof the shield is stronger than any other parameters such as distanced,relative distancerd,and lengthlof the shield.(Su Zhiguo,Lyu Weitao,Chen Lyuwen)

5.23 Duration,spatial size and radiance of lightning flashes over the Asia-Pacific region based on TRMM/LIS observations

The geographical distributions of flash duration,length,footprint and radiance,as well as their correspondence with thunderstorm structures,are investigated for the first time in the Asia-Pacific region ranging from 70°E to 160°E and from 18°N to 36°N and in six specially chosen regions by employing flash data collected by the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite and TRMM-based radar precipitation feature (RPF) data from 2002 to 2014.The flash length,footprint and radiance values are,on average,the largest over the deep ocean,followed by offshore waters and land.Flash duration is the longest over the offshore waters near the east coast of China,followed by the deep ocean and land.The Tibet Plateau and the northern part of the Indian Peninsula have the weakest flash properties in the study region.Furthermore,the geographic distributions of the flash properties exhibit evident seasonal changes.The monotonic relationship between flash spatial size and radiance is stronger than the monotonic relationships between flash duration and spatial size or radiance.Based on a comparison of the seasonal and regional changes in flash properties with RPF properties,convective intensity is proposed to play a crucial role in characterizing the flash spatial size and radiance,according to their inverse correlation in most regions.However,the climatological correspondence between flash duration and thunderstorm structures remains poorly constrained.We have launched a discussion of the possible association between thunderstorm structures and flash properties.(You Jin,Zheng Dong,Zhang Yijun)

5.24 Analysis of radiation evolution characteristics of the artificial triggered lightning channel

The spectrum of one triggered lightning with time resolution of 20 s was observed by using the slitless spectrograph and the current intensity at the channel bottom was obtained,based on which the radiation characteristics of the lightning spectrum under different current intensities were analyzed.The duration of the spectral line was analyzed according to the excitation energy of the spectral line and the change of the channel current.As a result,the spectral lines were divided into three types.Furthermore,mechanisms of the continuous background radiation of short wavelength and long wavelength were analyzed,respectively.The influences of two radiation mechanisms on continuous background radiation attenuation were researched.(Zhang Huaming,Lyu Weitao,Zhang Yang)

5.25 Development and assessment of quantitative preciptitation estimation algorithms for S-,C-,and X-band dual-polarization radars based on disdrometer data from three regions of China

The accuracy of quantitative precipitation estimation (QPE) for dual-polarization radars can be improved by using a localized rainfall estimation algorithm derived from the raindrop size distribution (DSD).In the present study,DSDs observed at Suzhou City,Jiangsu Province; Yangjiang City,Guangdong Province; and Naqu City,Tibet are analyzed during the rainy season together with the corresponding polarimetric variables for the above three regions.Most importantly,these DSD data are used to develop optimal“synthetic”QPE algorithms for S-,C-,and X-band dual-polarization radars,which will be built or upgraded in the three regions.Meanwhile,a new piecewise fitting method (PFM) is proposed.It has been found that the number concentrationNDof small raindrops (D＜1 mm) is the highest in Suzhou,while that of larger raindrops (D＞1 mm) is the highest in Yangjiang.The characteristics of the differential reflectivityZDRand specific differential phase (K-DP) are significantly different in the three locations,suggesting that different rainfall estimators are needed for different locations.Further performance assessment of the QPE based on DSD data indicates that the PFM QPE algorithm (LDSD) performs better than the conventional fitting method (CFM),and the localized QPE algorithm can improve the QPE accuracy.Observations from S-band dualpolarization radars and rain gauges in the Southern China Monsoon Rainfall Experiment are implemented to verify the performances of the QPE algorithms proposed in the present study.It is found that compared with non-localized algorithms,the localized LDSD algorithm yields the best results with at least 7.66% and 8.43% reductions in the RMSE and NE,respectively,which implies that while polarimetric variables can reflect DSD characteristics,the localized QPE algorithm remains necessary.(Zhang Yang,Liu Liping,Wen Hao)

5.26 一套雙頻段三維全閃電定位系統(tǒng)及其初步觀測(cè)結(jié)果

介紹了一套同時(shí)工作在甚高頻（VHF）和甚低頻/低頻（VLF/LF）頻段的三維閃電定位系統(tǒng)，并給出了初步觀測(cè)結(jié)果。系統(tǒng)使用到達(dá)時(shí)間差法對(duì)2個(gè)頻段的閃電輻射源進(jìn)行定位，能連續(xù)地給出雷暴過程中閃電活動(dòng)空間位置，并詳細(xì)給出單次閃電的發(fā)展路徑，在使用2個(gè)頻段輻射波形參數(shù)進(jìn)行定位的同時(shí)還可以保存原始波形用于深入研究。VHF、VLF/LF 2個(gè)頻段閃電定位結(jié)果的時(shí)間分辨率分別為100 μs和1 ms，定位精度在站網(wǎng)覆蓋范圍可優(yōu)于200 m。2個(gè)頻段的定位結(jié)果都能很好地描述雷暴中的閃電活動(dòng)，但表現(xiàn)出的特征有一定差異。2個(gè)頻段定位結(jié)果對(duì)單個(gè)閃電發(fā)生路徑進(jìn)行描繪時(shí)，VLF/LF頻段的大部分定位結(jié)果能與VHF定位結(jié)果重疊。（劉恒毅，董萬勝，蔡力）

5.27 一次正地閃觸發(fā)兩個(gè)并發(fā)上行閃電的光電觀測(cè)

廣州高建筑物雷電觀測(cè)站光電同步觀測(cè)系統(tǒng)于2017年6月16日記錄到一次峰值電流達(dá)+141 kA的單回?fù)粽亻W觸發(fā)兩個(gè)并發(fā)上行閃電過程。利用高速攝像、普通攝像和電場(chǎng)變化數(shù)據(jù)分析了觸發(fā)型上行閃電的始發(fā)特征和機(jī)理。結(jié)果表明：正地閃回?fù)艉蠹s0.8 ms內(nèi)，在距正地閃接地點(diǎn)約3.9 km的廣州塔（高600 m）和4.1 km的東塔（高530 m）分別有上行閃電始發(fā)。正地閃回?fù)暨^程中和大量正電荷以及之后可能有云內(nèi)負(fù)先導(dǎo)朝高塔方向快速伸展造成塔頂局部區(qū)域的電場(chǎng)發(fā)生突變是兩個(gè)上行閃電激發(fā)的原因。兩個(gè)上行閃電在353 ms內(nèi)發(fā)生7次回?fù)簦渲?次在廣州塔上，僅1次在東塔上，且廣州塔回?fù)舴逯惦娏髌骄担?21.4 kA）約為東塔回?fù)舴逯惦娏鳎?7.3 kA）的3倍，表明廣州塔上行閃電通道可能比東塔上行閃電通道伸展至分布范圍更廣、電荷量（或電荷密度）更大的負(fù)電荷區(qū)。兩個(gè)上行閃電先導(dǎo)的二維速率變化范圍為9.4×104～1.8×106m/s，平均值為6.9×103m/s。（武斌，呂偉濤，齊奇）

5.28 一次“晴天霹靂”致死事件分析

對(duì)2017年廣州從化地區(qū)一次“晴朗”天氣下的閃電致死事件進(jìn)行調(diào)查分析發(fā)現(xiàn)，這次事件是閃電首先擊中一棵大樹，然后擊中附近人員頭頂致死。根據(jù)目擊者描述的時(shí)間和位置，利用閃電低頻電場(chǎng)變化探測(cè)陣列的定位數(shù)據(jù)和廣東電力等系統(tǒng)的雷電定位數(shù)據(jù)，結(jié)合廣州番禺雷達(dá)觀測(cè)資料，確定此事件是由一次含有7 次回?fù)舻牡亻W過程的首次回?fù)粼斐?，其電流峰值?qiáng)度為-30.9 kA。閃電起始于13.0 km高度的云內(nèi)，經(jīng)約600 ms云內(nèi)發(fā)展過程后閃電通道從云體延伸出來，云砧區(qū)邊緣（0 dBz）到回?fù)酎c(diǎn)水平距離約300 m，降水區(qū)邊緣（18 dBz）到回?fù)酎c(diǎn)水平距離約1.8 km。使用雷擊現(xiàn)場(chǎng)等效電路模型，計(jì)算旁絡(luò)閃擊空氣擊穿場(chǎng)強(qiáng)可擊穿空氣與人頭部連接為通路，根據(jù)電路分流原理，如果雷電流擊中13 m高的大樹后流經(jīng)到“跳點(diǎn)”（樹干上方1/4）處后，則有13.2 kA雷電流直接閃擊到受害者身上，同時(shí)還承受了78.3 kV跨步電壓傷害，而距離雷擊點(diǎn)10 m遠(yuǎn)的目擊者僅承受1.3 kV跨步電壓。（殷啟元，范祥鵬，張義軍）

5.29 廣東省雷電傷亡事故特征分析

通過1995—2016年廣東雷電災(zāi)害匯編記錄的雷災(zāi)傷亡事件資料和1999—2016年廣東省電力雷電定位系統(tǒng)數(shù)據(jù)，對(duì)廣東省雷電傷亡事故特征進(jìn)行了分析。結(jié)果如下：（1）1075起雷災(zāi)傷亡事件中，死亡人數(shù)約是受傷人數(shù)的1.2倍，1起雷災(zāi)事件最多傷亡數(shù)為17個(gè)，2人以上的多人受傷概率要遠(yuǎn)大于多人死亡；雷災(zāi)傷亡高于全省平均水平的農(nóng)村地區(qū)政府更應(yīng)重視防御工作。（2）每月的雷電災(zāi)情特征與閃電活動(dòng)年變化相關(guān)；雷電災(zāi)情的時(shí)間特征與人們的作息時(shí)間相關(guān)，尤其對(duì)于戶外活動(dòng)較集中的農(nóng)村地區(qū)更應(yīng)關(guān)注雷電頻發(fā)時(shí)段。（3）雷災(zāi)傷亡事件發(fā)生在農(nóng)田的最多，造成群死群傷事件主要是發(fā)生在未做雷電防護(hù)措施的建筑物內(nèi)和大樹旁。（4）雷災(zāi)傷亡人員中男女比例相當(dāng)，但男女同時(shí)遭受雷擊時(shí)女性更易遭受身亡。由于不同年齡段從事不同種類的工作，導(dǎo)致壯年年齡段（25～64歲）男性傷亡高于女性，但是在傷亡最多的31～40歲年齡段中女性傷亡是男性的1.46倍?？傊?，雷電引起的傷亡事故大部分發(fā)生在農(nóng)村地區(qū)，提高農(nóng)村農(nóng)民防雷減災(zāi)意識(shí)和加強(qiáng)鄉(xiāng)村振興防雷減災(zāi)服務(wù)的工作迫在眉睫。（殷啟元，范祥鵬，陳綠文）

5.30 基于光學(xué)資料的廣州塔附近下行地閃特征

利用2009—2014年廣州高建筑物雷電觀測(cè)站的光學(xué)觀測(cè)資料，結(jié)合雷聲和電磁場(chǎng)變化波形，對(duì)廣州塔（高度為600 m）西北部60°扇形區(qū)域3 km范圍內(nèi)的119次下行地閃分布特征進(jìn)行統(tǒng)計(jì)分析，結(jié)果表明：43.7%（52/119）的地閃發(fā)生在區(qū)域內(nèi)4個(gè)最高的建筑物上；除了直接擊中廣州塔的20次地閃（16.8%），距離廣州塔附近0～1 km的區(qū)域未觀測(cè)到地閃，觀測(cè)到的距廣州塔最近的地閃離廣州塔約1.2 km；距廣州塔1～2 km的區(qū)域共觀測(cè)到35次地閃（29.4%），其中每個(gè)高度低于300 m的建筑物被擊中的次數(shù)不超過1次；距離廣州塔2～3 km區(qū)域共觀測(cè)到64次地閃（53.8%），其中有些高度低于300 m的建筑物被地閃擊中1次以上，最多達(dá)5次。廣州塔對(duì)附近區(qū)域下行地閃的吸引作用使其附近1 km左右范圍內(nèi)未觀測(cè)到地閃，且1～3 km范圍內(nèi)隨距離增加下行地閃密度（扣除擊中其他高度不低于300 m的建筑物的地閃）有逐漸增加趨勢(shì)，說明高建筑物對(duì)下行地閃的吸引作用隨著距離的增加而逐漸減弱。（吳姍姍，呂偉濤，齊奇）

5.31 東亞和西太平洋閃電時(shí)空尺度及光輻射能

利用2002—2014年的熱帶測(cè)雨衛(wèi)星/閃電成像儀TRMM/LIS閃電觀測(cè)數(shù)據(jù)分析了18°～36°N和70°～160°E范圍內(nèi)閃電尺度和光輻射能空間分布特征，并選取6個(gè)區(qū)域（區(qū)域1～6），探討09：00—14：00（地方時(shí)，下同）和18：00至次日06：00兩個(gè)時(shí)段閃電上述屬性的逐月變化和參數(shù)分布特征。研究指出：閃電空間尺度和光輻射能在深海最大，次之為近海和陸地，持續(xù)時(shí)間在中國(guó)東部近海最大，次之為深海和陸地。不同閃電屬性大值分布區(qū)域差異明顯，小值則分布在區(qū)域1和區(qū)域2。多數(shù)區(qū)域分析時(shí)段內(nèi)閃電空間尺度和光輻射能的逐月變化趨勢(shì)較一致，陸地上它們與閃電活動(dòng)逐月變化的反向?qū)?yīng)關(guān)系較明顯。分析時(shí)段內(nèi)閃電時(shí)空尺度和光輻射能均呈對(duì)數(shù)正態(tài)分布，陸地閃電各屬性值比海洋閃電更向小值方向集中。在LIS觀測(cè)性能較高的18：00至次日06：00，各區(qū)域內(nèi)閃電持續(xù)時(shí)間中值為0.18～0.29 s，通道延展距離中值為12～21 km，光輻射能中值為0.11～0.52 J/(m2·sr·μm）。分析時(shí)段內(nèi)閃電空間尺度與光輻射能的相關(guān)性明顯優(yōu)于它們與持續(xù)時(shí)間的相關(guān)性。（尤金，鄭棟，姚雯）

6 模式和再分析資料

6 Model and reanalysis data

6.1 Assessment and reduction of the physical parameterization uncertainty for Noah-MP land surface model

The community Noah land surface model with multiparameterization options (Noah-MP) provides a plethora of model configurations with varying complexity for land surface modeling.The practical application of this model requires a basic understanding of the relative abilities of its various parameterization configurations in representing spatiotemporal variability and hydrologic connectivity.We designed an ensemble of 288 experiments from multiparameterization schemes of six physical processes to assess and reduce the structural uncertainty for land surface modeling over 10 hydrologic regions in China for the period 2001?2010.The observed latent heat (LH) was well reproduced by the ensemble.Meanwhile,most experiments underestimated sensible heat (SH) throughout the year and overestimated the cold season but underestimated the warm season terrestrial water storage anomaly (TWSA).The sensitive processes and best-performing schemes varied not only with regions but also among variables.The LH and SH were most sensitive to runoff-groundwater (RUN),surface heat exchange coefficient (SFC),and radiation transfer (RAD).The TWSA was dominated by RUN and RAD while largely influenced by soil moisture factor for stomatal resistance (BTR) and frozen soil permeability (INF) over some limited regions.By contrast,supercooled liquid water (FRZ) had little influence on all variables.Our optimization for individual variables produced high mean Taylor skill scores that ranged from 0.95?0.99 for LH,0.82?0.99 for SH,and 0.63?0.95 for TWSA depending on regions.The simultaneous optimization made trade-off among the three variables,which improved TWSA performance at the cost of reducing the skill for LH and SH over a few regions.(Gan Yanjun,Liang Xinzhong,Duan Qingyun)

6.2 Improving land surface temperature simulation in CoLM over the Tibetan Plateau through fractional vegetation cover derived from a remotely sensed clumping index and model-simulated leaf area index

Parameterizations of fractional vegetation cover (FVC) in land surface models have important effects on simulations of surface energy budget,especially in arid and semiarid regions.This study uses a FVC scheme in which FVC is derived from leaf area index and a remotely sensed clumping index.The performance of the new scheme (SMFVC) is evaluated against Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and in situ soil temperature observations,together with two other FVC schemes,a general FVC scheme (CTL) based on land cover map and a climatology-based FVC scheme (RSFVC) that uses longterm remotely sensed Normalized Difference Vegetation Index of MODIS.The three FVC schemes were implemented in the Common Land Model (CoLM) and applied in the Tibetan Plateau using the same forcing data and default parameters.Our results demonstrate that FVC schemes have significant influence on the CoLM performance:(1) the RSFVC and SMFVC schemes significantly reduce the LST biases found in CTL,particularly in grassland and during summer; (2) soil temperature evaluation by in situ observations from three networks on the Tibetan Plateau corroborates the LST results; and (3) the improvements are mainly related to representing temporal (seasonal) variability and subgrid heterogeneity of FVC,which improves surface albedo and surface energy balance.In other words,by including more vegetation characteristics,such as using a clumping index,land surface models may better simulate surface vegetation condition and further better represent the land surface energy budget over the Tibetan Plateau.(Li Chengwei,Lu Hui,Leung L Ruby)

6.3 Evaluation of land surface subprocesses and their impacts on model performance with global flux data

Study on the uncertainties in land surface models (LSMs) helps us understand the differences and errors in climate models.Meanwhile,uncertainty in model structure,derived from the many possible parameterization schemes for the same physical subprocess,is a primary source of land model uncertainties.To attribute structural errors and model parameterization scheme uncertainties,it is critical to identify the key subprocesses involved and investigate the interactions of these subprocesses on LSM behavior,which will ultimately help us identify the optimal parameterization schemes for various plant functional types,soil types,and different locations.Here,we conduct physical ensemble simulations for multiple sites from FLUXNET and then apply a variance-based sensitivity analysis method to quantitatively assess the impacts of uncertainties in the parameterization schemes of subprocesses in the Noah with multiparameterization (Noah-MP) LSM on model performance.The results show that three subprocesses—surface exchange coefficient,runoff and groundwater,and surface resistance to evaporation—have the most significant impacts on the performance of the simulated sensible heat flux,latent heat flux,and net absorbed radiation in the Noah-MP LSM.The interaction between two subprocesses could contribute up to 50% of the variation in model performance for some sites,which highlights the need for taking into consideration the interactions of subprocesses to improve LSMs.Finally,a statistical optimal combination of the parameterization schemes is recommended for global land modeling,although it is noticed that the optimal schemes vary with regions and can be different even for neighboring sites.(Li Jianduo,Zhang Guo,Chen Fei)

6.4 An IVAP-based dealiasing method for radar velocity data quality control

Dealiasing is a common procedure in radar radial velocity quality control.Generally,there are two dealiasing steps:a continuity check and a reference check.In this paper,a modified version that uses azimuthal variance of radial velocity is introduced based on the integrating velocity-azimuth process (IVAP) method,referred to as the V-IVAP method.The new method can retrieve the averaged winds within a local area instead of averaged wind within a full range circle by the velocity-azimuth display (VAD) or the modified VAD method.The V-IVAP method is insensitive to the alias of the velocity,and provides a better way to produce reference velocities for a reference check.Instead of a continuity check,we use the IVAP method for a fine reference check because of its high-frequency filtering function.Then a dealiasing procedure with two steps of reference check is developed.The performance of the automatic dealiasing procedure is demonstrated by retrieving the wind field of a tornado.Using the dealiased radar velocities,the retrieved winds reveal a clear mesoscale vortex.A test based on radar network observations has also shown that the two-step dealiasing procedure based on V-IVAP and IVAP methods is reliable.(Liang Xudong,Xie Yanxin,Yin Jinfang)

6.5 Diurnal characteristics of turbulent intermittency in the Taklimakan Desert

A case study is performed to investigate the behavior of turbulent intermittency in the Taklimakan Desert using an intuitive,direct,and adaptive method,the arbitrary-order Hilbert Spectral Analysis (arbitrary-order HSA).Decomposed modes from the vertical wind speed series confirm the dyadic filter-bank essence of the empirical mode decomposition processes.Due to the larger eddies in the CBL,higher energy modes occur during the day.The second-order Hilbert spectra L-2 (omega) delineates the spectral gap separating fine-scale turbulence from large-scale motions.Both the values of kurtosis and the Hilbert-based scaling exponent xi(q) reveal that the turbulence intermittency at night is much stronger than that during the day,and the stronger intermittency is associated with more stable stratification under clear-sky conditions.This study fills the gap in the characteristics of turbulence intermittency in the Taklimakan Desert area using a relatively new method.(Wei Wei,Wang Minzhong,Zhang Hongsheng)

6.6 Generalized Z-grid model for numerical weather prediction

Z-grid finite volume models conserve all-scalar quantities as well as energy and potential enstrophy and yield better dispersion relations for shallow water equations than other finite volume models,such as C-grid and C-D grid models; however,they are more expensive to implement.During each time integration,a Z-grid model must solve Poisson equations to convert its vorticity and divergence to a stream function and velocity potential,respectively.To optimally utilize these conversions,we propose a model in which the stability and possibly accuracy on the sphere are improved by introducing more stencils,such that a generalized Z-grid model can utilize longer time-integration steps and reduce computing time.Further,we analyzed the proposed model’s dispersion relation and compared it to that of the original Z-grid model for a linearly rotating shallow water equation,an important property for numerical models solving primitive equations.The analysis results suggest a means of balancing stability and dispersion.Our numerical results also show that the proposed Z-grid model for a shallow water equation is more stable and efficient than the original Z-grid model,increasing the time steps by more than 1.4 times.(Xie Yuanfu)

6.7 Coupling the common land model to ECHAM5 atmospheric general circulation model

The ECHAM5 model is coupled with the widely used common land model (CoLM).ECHAM5 is a stateof-the-art atmospheric general circulation model incorporated into the integrated weather and climate model of the Chinese Academy of Meteorological Sciences (CAMS-CSM).Land surface schemes in ECHAM5 are simple and do not provide an adequate representation of the vegetation canopy and snow/frozen soil processes.Two AMIP (Atmospheric Model Intercomparison Project)-type experiments using ECHAM5 and ECHAM5-CoLM are run over 30 years and the results are compared with reanalysis and observational data.It is found that the pattern of land surface temperature simulated by ECHAM5-CoLM is significantly improved relative to ECHAM5.Specifically,the cold bias over Eurasia is removed and the root-mean-square error is reduced in most regions.The seasonal variation in the zonal mean land surface temperature and the in situ soil temperature at 20- and 80-cm depths are both better simulated by ECHAM5-CoLM.ECHAM5-CoLM produces a more reasonable spatial pattern in the soil moisture content,whereas ECHAM5 predicts much drier soils.The seasonal cycle of soil moisture content from ECHAM5-CoLM is a better match to the observational data in six specific regions.ECHAM5-CoLM reproduces the observed spatial patterns of both sensible and latent heat fluxes.The strong positive bias in precipitation over land is reduced in ECHAM5-CoLM,especially over the southern Tibetan Plateau and middle-lower reaches of the Yangtze River during the summer monsoon rainy season.(Xin Yufei,Dai Yongjiu,Li Jian)

6.8 Understanding the Asian summer monsoon onset in terms of catastrophe theory

Monsoon has been puzzling that the monsoon occurrence is sudden with the rapid onset observed while the evolution of the differentiating heating is gradual with time of year.Here,focusing on the Asian summer monsoon,we use catastrophe theory to show how gradual changes in the atmospheric heating source with time will cause an abrupt variation of the relevant South Asian High (SAH) to atmospheric circulations and thus lead to the monsoon onset.This argumentation illustrates that the Asian summer monsoon is essentially caused by temporal changes in the differentiating heating owing to surface inhomogeneites such as land-sea contrasts,and the monsoon onset results,in nature,from the nonlinearity of the complex atmospheric system itself.Employing the cusp catastrophe (one of the elementary catastrophes) model,we found that a sudden change like the rapid monsoon onset is an inevitable outcome when the control parameters such as the differentiating heating exceed a threshold though the parameters evolve gradually.(Yin Jinfang,Liu Chongjian)

6.9 The development of an atmospheric aerosol/chemistry-climate model,and simulated effective radiative forcing of nitrate aerosols

This study developed a next-generation atmospheric aerosol/chemistry-climate model,the BCC_AGCM_CUACE2.0.Then,the performance of the model for nitrate was evaluated,and the nitrate direct radiative forcing (DRF) and effective radiative forcing (ERF) due to aerosol-radiation interactions were simulated for the present day (2010),near-term future (2030),and middle-term future (2050) under the Representative Concentration Pathway 4.5,6.0,and 8.5 scenarios relative to the preindustrial era (1850).The model reproduced the distributions and seasonal changes in nitrate loading well,and simulated surface concentrations matched observations in Europe,North America,and China.Current global mean annual loading of nitrates was predicted to increase by 1.50 mg m m?2relative to 1850,with the largest increases occurring in East Asia (9.44 mg m m?2),Europe (4.36 mg m m?2),and South Asia (3.09 mg m?2).The current global mean annual ERF of nitrates was ?0.28 W m m?2relative to 1850.Due to global reductions in pollutant emissions,the nitrate ERF values were predicted to decrease to ?0.17,?0.20,and ?0.24 W m m?2in 2030 and ?0.07,?0.18,and ?0.19 W m m?2in 2050 for Representative Concentration Pathway 4.5,6.0,and 8.5 relative to 1850,respectively.Although global mean nitrate values showed a declining trend,future nitrate loading remained high in East Asia and South Asia.Nitrate aerosols are effective at scattering solar radiation.Many studies have shown that NOx(NO2and NO) and NH3emissions,the main precursors of nitrates,have continued to increase,resulting in a greater proportion of the total anthropogenic aerosols being composed of nitrates.So,it is very likely that nitrate will become an important climate forcing factor at regional and seasonal scales in the future.Although some studies have investigated the DRF values of nitrate,few have used the optical properties of nitrates in atmospheric chemistry-climate online models.This study developed a next-generation atmospheric aerosol/chemistry-climate model,the BCC_AGCM_CUACE2.0.We evaluated the performance of the model and the nitrate direct radiative forcing and effective radiative forcing due to aerosol-radiation interactions for the present day (2010),near future (2030),and middle future (2050) under different Representative Concentration Pathway scenarios,based on the real nitrate optical properties.Our results are useful for understanding the role of nitrate forcing in future climate change.(An Qi,Zhang Hua,Wang Zhili)

6.10 Half-a-degree matters for reducing and delaying global land exposure to combined daytimenighttime hot extremes

The Paris Agreement has motivated rapid analysis differentiating changes in frequency/intensity of weather and climate extremes in 1.5 versus 2 warmer worlds.However,implications of these global warming levels on locations,spatial scales,and emergence timings of hot spots to extremes are more relevant to policy-making but remain strikingly under-addressed.Based on a bivariate definitional framework,we show that compared to 2 ,the 1.5 target could avoid a transition of prevailing type of summertime hot extremes from daytime-/nighttime-only events to combined daytime-nighttime hot extremes in approximately 18% of global continents and protect 14%?26% of land areas from seeing over threefold-to-tenfold increases in occurrence of combined hot extremes.This half-a-degree reduction also matters for around 21% of global lands,mostly within the tropics,in constraining historically unprecedented combined hot extremes from becoming the new norm within just one to three decades ahead.By contrast,previous analyses based on univariate-defined hot days substantially underestimate the magnitude,areal extent,and emergence rate of 0.5 -caused aggravation of summertime hot extremes.These projected changes of bivariate-classified hot extremes,and therefore,underline not only the imperative but also the urgency of striving for the lower Paris target.Since the milestone Paris Agreement,policymakers are eager to know the extent to which and the time when their own regions will suffer from consequences associated with pertinent global warming levels (1.5 and 2 ).We show that even the aspirational 1.5 target would still be translated into huge threats from summertime hot extremes to the tropics,as manifested by a type transition toward health-damaging daytimenighttime combined heat and threefold-to-tenfold increases in its occurrence.Further rise to 2 would put an extra 20% of global continents at risk from similar transitions and increases.Unexpectedly,despite involving substantial reduction in carbon emissions,the 2 -compatible development pathway would bring about a rapidly emerging novel era of hot extremes for most tropical countries,where historically unprecedented daytime-nighttime combined heat will be registered every other year within the next one to three decades and thereafter.Our results highlight that the extra 0.5 of global warming,from 1.5 to 2 ,would impose the earliest and severest heat-related consequences on the least-developed regions,whose adaptive capacity is unfortunately very limited.(Chen Yang,Zhou Baiquan,Zhai Panmao)

6.11 A modeling study of the effects of vertical wind shear on the raindrop size distribution in Typhoon Nida (2016)

In this study,the effects of vertical wind shear (VWS) on the raindrop size distribution in tropical cyclone are investigated,based on the theoretical analyses that intense VWS,which commonly appears in the lower layers of tropical cyclones,can enhance the collisional breakup of raindrops.This is achieved by comparing the numerical sensitivity experiments of Typhoon Nida (2016) using Weather Research and Forecasting model against the polarimetric radar and disdrometer observations.In the control run with the default Morrison microphysics,unrealistic large raindrops are produced with excessively large differential reflectivity and heavier precipitation.An obvious decrease of raindrop size is present when the constant value of cloud droplet number concentration reduces from 250 to 30 (NC30),leading to more comparable microphysics characteristics with the observations due to the enhancement of autoconversion rate from cloud droplets to raindrops; however,some unrealistic large-sized raindrops still exist.A semiempirical raindrop collection/breakup parameterization is further proposed in NC30_WS run by modifying the threshold diameter of raindrops at which breakup occurs as a function of VWS.The certain improvements of simulating raindrop size distribution and precipitation in Typhoon Nida are present in NC30_WS run,owing to the efficient collisional breakup and the induced stronger raindrop evaporation cooling.Our results indicate that the combined effects of reasonable cloud droplet numbers as well as reliable raindrop breakup parameterization are pronounced and highlight the impacts of VWS on raindrop size distribution,which should be involved in current microphysical schemes to forecast the TCs more accurately.(Deng Lin,Gao Wenhua,Duan Yihong)

6.12 Using multisource satellite data to assess recent snow-cover variability and uncertainty in the Qinghai-Tibet Plateau

Snow cover in the Qinghai-Tibet Plateau (QTP) is a critical component in the water cycle and regional climate of East Asia.Fractional snow cover (FSC) derived from five satellite sources [the three satellites comprising the multisensor synergy of FengYun-3 (FY-3A/B/C),the Moderate Resolution Imaging Spectroradiometer (MODIS),and the Interactive Multisensor Snow and Ice Mapping System (IMS)] were intercompared over the QTP to examine uncertainties in mean snow cover and interannual variability over the last decade.A four-step cloud removal procedure was developed for MODIS and FY-3 data,which effectively reduced the cloud percentage from about 40% to 2%–3% with an error of about 2% estimated by a random sampling method.Compared to in situ snow-depth observations,the cloud-removed FY-3B data have an annual classification accuracy of about 94% for both 0.04 degrees and 0.01 degrees resolutions,which is higher than other datasets and is recommended for use in QTP studies.Among the five datasets analyzed,IMS has the largest snow extent (22% higher than MODIS) and the highest FSC (4.7% higher than MODIS),while the morning-overpass MODIS and FY-3A/C FSC are similar and are around 5% higher than the afternoonoverpass FY-3B FSC.Contrary to MODIS,IMS shows increasing variability in snow cover and snow duration over the last decade (2006–2017).Differences in variabilities of FSC and snow duration between products are greater at 5–6 km than lower elevations,with seasonal snow-cover change showing the largest uncertainty in snowmelt date.(Jiang Yingsha,Chen Fei,Gao Yanhong)

6.13 Pronounced extended duration of tropical cyclone quiescent periods over the western North Pacific in the super El Ni?o decaying years

This study investigated the relationship between the duration of the western North Pacific (WNP) tropical cyclone (TC) quiescent periods (no TC in the period) and the super El Ni?o events during 1951–2016.The results show that the average duration of the TC quiescent period (DTCQP) is shorter (90 days) during super El Ni?o developing (EN) years,compared with the 1951–2016 mean DTCQP (105 days).However,in the four super El Ni?o decaying (EN+1) years,the DTCQP is about 200 days,which is much longer than the 1951–2016 mean DTCQP.Further study suggests that the delayed super El Ni?o impacts on the DTCQP in the year following the El Ni?o peak is due to the persistence of the WNP anomalous anticyclone (WNPAC),which is enhanced during the mature phase of El Ni?o but maintained through the subsequent spring and summer.The anomalous development and persistence of the WNPAC significantly influences the monsoon trough activity,which leads to delayed and weak development of the monsoon trough in the summer of super EN+1 years.From April to June of the super EN+1 years,there is almost no monsoon trough activity over the WNP and the large-scale environmental conditions are unfavourable for TC genesis.In contrast,from April to June in the super EN years,the WNP is dominated by anomalous cyclonic circulation,which leads to early and strong development of the monsoon trough.The intensified and eastwards extended monsoon trough seems to coincide with favourable environmental conditions for TC genesis.(Wang Qian,Zhai Panmao)

6.14 Observational analyses of topographic effects on convective systems in an extreme rainfall event in North China

An extreme rainfall event occurred in North China between 18 and 21 July 2016,with the strongest precipitation of 783.4 mm occurring within the rainfall zone of Taihang Mountain.In this study,mesoscale convective systems (MCSs) resulting in heavy rainfall are studied using high-resolution surface observations,soundings and radar data.The topographic effect in addition to shear zone cyclonic circulation is mainly responsible for the heavy rainfall.The synoptic low-pressure environmental circulation promoted mesocyclone and convection development in North China,where a strong and moist low-level jet was observed.The interaction between mesocyclone and mesoscale topography produced two strong,separate precipitation centers,which were clearly the direct results of three MCSs.Orographic blocking played a crucial role in the development of MCSs.Diabatic cooling due to raindrop evaporation in association with MCS1 formed a cold pool on the plain east of the central Taihang Mountain area.Convective cell initiation and development in MCS2 was due to the impingement of southeasterly flow near the surface of the hills east of Linzhou basin.Convective cells that were successively generated and shifted along a mesoscale shear line comprised the MCS2 linear distribution and a northwestward rain belt.The northern extreme rainfall center was caused by MCS3 along the southern slopes of an eastward-opening valley.Convective cells were triggered along a shear line,which was affected by a combination of topography,a cold pool in the boundary layer and mesocyclone outer flow.Together,the orographic forcing and cold pool enhanced the Taihang Mountain precipitation event.(Kang Yanzhen,Peng Xindong,Wang Shigong)

6.15 Changes in concentrations of fine and coarse particles under the CO2-induced global warming

Using an aerosol-climate coupled model,we have investigated the climate response to increase in atmospheric carbon dioxide (CO2) levels and the resulting changes in the column concentrations of anthropogenic and natural particulate matters.Special attention has been paid on the fine particulate matters (PM2.5,particulate matters with aerodynamic diameters of 2.5 μm) and coarse particles of non-PM2.5(NPM,particulate matters with aerodynamic diameters of 2.5 μm).Rising CO2levels led to significant effects on surface air temperature,large scale circulation,surface water flux,precipitation,etc.,which considerably affect the column concentrations of anthropogenic and natural particulate matters,for both fine and coarse modes.Changes in burden of fine particles are major contributions to that of total anthropogenic particulate matters by CO2-induced global warming.The anthropogenic PM2.5burden was found to decrease in the regions with latitudes 30°N,whereas increase in the rest areas.The geographical distributions of changes in the column concentrations of fine and coarse natural particles were found in the same order of magnitude in most regions,and the particle size distribution shifted to the coarse mode.The physical mechanisms are analyzed to explain the changes in aerosol local column concentrations due to CO2-induced climate change.(Yang Dongdong,Zhang Hua,Li Jiangnan)

6.16 云微物理過程對(duì)臺(tái)風(fēng)數(shù)值模擬的影響

將中國(guó)氣象科學(xué)研究院（CAMS）混合雙參數(shù)云微物理方案用于中尺度天氣模式WRF，開展了對(duì)2013年超強(qiáng)臺(tái)風(fēng)“天兔”（1319）的模擬，通過與臺(tái)風(fēng)最佳路徑、強(qiáng)度及熱帶降雨測(cè)量衛(wèi)星（TRMM）資料對(duì)比，分析CAMS云微物理方案在模擬臺(tái)風(fēng)中的適用性及云微物理過程對(duì)模擬臺(tái)風(fēng)天兔的影響機(jī)制。設(shè)計(jì)了3組敏感性試驗(yàn)：修改雪粒子質(zhì)量和落速系數(shù)（EXP1），采用海洋性云滴參數(shù)（EXP2），同時(shí)修改雪粒子質(zhì)量和落速系數(shù)并采用海洋性云滴參數(shù)（EXP3）。結(jié)果表明：EXP1和EXP3由于霰碰并雪速率的增加及減小的雪下落通量，導(dǎo)致雪含量顯著降低，同時(shí)也減少了整體冰相物的含量；EXP2和EXP3模擬的臺(tái)風(fēng)眼區(qū)對(duì)流有效位能快速減小，再現(xiàn)了前期臺(tái)風(fēng)的快速增強(qiáng)過程，路徑偏差也最??；各試驗(yàn)?zāi)M的小時(shí)降水率總體偏強(qiáng)，EXP3的降水空間分布與實(shí)況更接近，明顯降低雪粒子含量，并一定程度上改善模擬的臺(tái)風(fēng)路徑、強(qiáng)度及降水分布等。該結(jié)果不但可為改進(jìn)適用于臺(tái)風(fēng)的云微物理參數(shù)化方案提供思路，也可加深云微物理過程對(duì)臺(tái)風(fēng)影響的認(rèn)識(shí)。（常婉婷，高文華，端義宏）

6.17 陰陽(yáng)網(wǎng)格上通量型非靜力模式動(dòng)力框架的理想試驗(yàn)

為改善球面經(jīng)緯度網(wǎng)格在高分辨率應(yīng)用的苛刻限制，提高全球大氣動(dòng)力模式的時(shí)間積分效率，選取以陰陽(yáng)網(wǎng)格為基礎(chǔ)構(gòu)建通量型非靜力大氣模式動(dòng)力框架，采用有限體積法和通量型平流顯式算法積分方案，保證模式的守恒計(jì)算性能。該動(dòng)力框架在標(biāo)準(zhǔn)三維大氣理想試驗(yàn)中進(jìn)行了中期積分試驗(yàn)，對(duì)動(dòng)力框架的計(jì)算效果、性能進(jìn)行檢驗(yàn)。在三維平衡流試驗(yàn)、羅斯貝-豪威茨波試驗(yàn)和山脈羅斯貝波試驗(yàn)中均表現(xiàn)出很好的穩(wěn)定性和三維計(jì)算效果，其中水平2.5°分辨率模式的平衡流垂直速度誤差為10-5量級(jí)，而經(jīng)向速度誤差在10-2量級(jí)，羅斯貝-豪威茨波保持基本波形穩(wěn)定傳播，而地形羅斯貝波試驗(yàn)則給出背風(fēng)坡激發(fā)低槽在發(fā)展過程中不斷向下游和南半球傳播。（黃超，彭新東，李曉涵）

6.18 ECMWF高分辨率模式降水預(yù)報(bào)能力評(píng)估與誤差分析

利用2015—2017年6—8月ECMWF高分辨率模式（ECMWF-Hi）的加工產(chǎn)品，結(jié)合我國(guó)2400多個(gè)國(guó)家氣象站逐小時(shí)降水觀測(cè)資料，對(duì)ECMWF-Hi產(chǎn)品24 h降水預(yù)報(bào)的準(zhǔn)確度、集中度和相關(guān)性進(jìn)行了評(píng)估，并與ECMWF集合預(yù)報(bào)模式（ECMWF-EPS）24 h降水預(yù)報(bào)產(chǎn)品進(jìn)行了比較。為更好地描述預(yù)報(bào)的集中度，避免單純用標(biāo)準(zhǔn)差比或平均值比刻畫預(yù)報(bào)集中度的缺陷，建立了一個(gè)綜合標(biāo)準(zhǔn)差和平均值的R指數(shù)，用之定量描述模式預(yù)報(bào)的集中度。結(jié)果表明：（1）ECMWF-Hi在均方根誤差的檢驗(yàn)方面并未表現(xiàn)出優(yōu)勢(shì)；而分辨率較低的ECMWF-EPS集合平均預(yù)報(bào)誤差最小。（2）ECMWF-Hi對(duì)研究區(qū)降水預(yù)報(bào)的集中度的整體描述較為準(zhǔn)確，離散度與觀測(cè)較為相似，預(yù)報(bào)期望也與觀測(cè)降水的期望最接近，ECMWF-Hi比ECMWF-EPS的集合控制預(yù)報(bào)與集合平均對(duì)觀測(cè)降水集中度的刻畫較為準(zhǔn)確。（3）研究區(qū)域內(nèi)各站點(diǎn)R指數(shù)分布表明，ECMWF-Hi與ECMWF-EPS控制預(yù)報(bào)、平均預(yù)報(bào)相比，對(duì)平均值預(yù)報(bào)不足的站點(diǎn)較多，且這些站點(diǎn)的預(yù)報(bào)集中度普遍大于觀測(cè)，ECMWF-Hi的降水預(yù)報(bào)更接近觀測(cè)降水。（4）評(píng)估應(yīng)用結(jié)果表明，R指數(shù)不僅能定性評(píng)估模式的集中度，也可定量描述集中度大小。（曹越，趙琳娜）

7 衛(wèi)星研究與應(yīng)用

7 Satellite research and application

7.1 快速輻射傳輸模式的研發(fā)及應(yīng)用

為了加速風(fēng)云衛(wèi)星數(shù)據(jù)在數(shù)值天氣預(yù)報(bào)模式中的應(yīng)用，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)室衛(wèi)星團(tuán)隊(duì)自主研發(fā)了先進(jìn)輻射傳輸模擬系統(tǒng)（ARMS：Advanced Radiative transfer Modeling Syste），作為新一代觀測(cè)算子。ARMS在美國(guó)快速輻射傳輸模式（CRTM：Community Radiative Transfer Model）和歐洲快速輻射傳輸模式（RTTOV：Radiative Transfer for the TIROS Operational Vertical Sounder TOVS）的基礎(chǔ)上優(yōu)化組合，融入了重要科學(xué)進(jìn)展。

經(jīng)過一年多的研發(fā)，ARMS已初步完成幾個(gè)關(guān)鍵模塊的研發(fā)，包括針對(duì)風(fēng)云衛(wèi)星傳感器的大氣透過率模塊、氣溶膠/云和降水的散射/吸收模塊、地表發(fā)射率模塊、矢量輻射傳輸方程求解模塊，以及切線性/伴隨模式。不同于CRTM和RTTOV，ARMS使用極化二流近似和矢量離散坐標(biāo)法作為輻射傳輸模式的核心求解方案，在散射和發(fā)射大氣下求解斯托克斯輻射分量。ARMS針對(duì)國(guó)產(chǎn)氣象衛(wèi)星儀器的光譜響應(yīng)函數(shù)，設(shè)計(jì)了精確的快速大氣透射率計(jì)算方案，建立了完整的大氣光譜學(xué)數(shù)據(jù)集以用于快速吸收系數(shù)的生成。此外，ARMS發(fā)展和建立了完整的氣溶膠、云粒子散射數(shù)據(jù)庫(kù)，實(shí)現(xiàn)在全天候條件下，紅外及微波大氣探測(cè)儀的快速高精度的輻射傳輸計(jì)算，并擴(kuò)展到可見光及紫外波段以實(shí)現(xiàn)更多儀器的應(yīng)用需求。同時(shí)，ARMS完善了海洋、陸面發(fā)射率理論模型和數(shù)據(jù)集，并著重發(fā)展紅外陸面及海冰紅外和微波發(fā)射率理論模型和數(shù)據(jù)集以增強(qiáng)“三極”地區(qū)復(fù)雜地表狀況下的應(yīng)用能力。

2019年4月29日至5月2日，由中國(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/衛(wèi)星研究與應(yīng)用聯(lián)合中心）、歐洲中期天氣預(yù)報(bào)中心（ECMWF）和美國(guó)衛(wèi)星數(shù)據(jù)同化中心（JCSDA）聯(lián)合發(fā)起的“2019衛(wèi)星數(shù)據(jù)同化快速輻射傳輸模式國(guó)際研討會(huì)”在天津順利召開，本次研討會(huì)有來自美國(guó)、英國(guó)、德國(guó)、日本等國(guó)家和地區(qū)以及國(guó)內(nèi)多家高校和科研院所的100余名專家出席。本次研討會(huì)通過回顧當(dāng)前國(guó)際前沿快速輻射傳輸模型的能力，了解衛(wèi)星數(shù)據(jù)同化輻射傳輸模型的新要求，并考慮優(yōu)先發(fā)展大氣和地表輻射傳輸過程中超快速計(jì)算能力，將進(jìn)一步為發(fā)展我國(guó)快速輻射傳輸模式提供參考。本次衛(wèi)星數(shù)據(jù)同化快速輻射傳輸模式國(guó)際研討會(huì)的順利召開，體現(xiàn)了中國(guó)氣象局在衛(wèi)星數(shù)據(jù)同化快速輻射傳輸模式研究中的主動(dòng)性，推進(jìn)了國(guó)際合作、提升了我國(guó)在輻射傳輸領(lǐng)域的國(guó)際影響力。中國(guó)快速輻射傳輸模式ARMS已與美國(guó)CRTM和歐洲RTTOV模式形成三足鼎立，共同成為支撐衛(wèi)星資料數(shù)據(jù)同化及產(chǎn)品研發(fā)和應(yīng)用的核心技術(shù)。

ARMS的研發(fā)和應(yīng)用，將為我國(guó)風(fēng)云衛(wèi)星發(fā)展提供關(guān)鍵理論技術(shù)，并為中國(guó)氣象局?jǐn)?shù)值預(yù)報(bào)系統(tǒng)提供重要技術(shù)支撐。在2019年GRAPES數(shù)值預(yù)報(bào)系統(tǒng)發(fā)展專項(xiàng)任務(wù)的支持下，衛(wèi)星團(tuán)隊(duì)已在GRAPESMESO框架下，實(shí)現(xiàn)快速輻射傳輸模式ARMS和RTTOV的可選調(diào)用并便捷比較。下一步，在對(duì)每種儀器類別的ARMS模擬不確定性進(jìn)行充分表征之后，將對(duì)偏差校正方案進(jìn)行完善，以期在四維變分全球/區(qū)域同化預(yù)報(bào)系統(tǒng)（GRAPES-4DVar）中集成同化更多的微波和紅外衛(wèi)星觀測(cè)數(shù)據(jù)。（翁富忠，楊俊，董佩明）

7.2 Verification of Fengyun-3D MWTS and MWHS calibration accuracy using GPS radio occultation data

The newly launched Fengyun-3D (FY-3D) satellite carries microwave temperature sounder (MWTS) and microwave humidity sounder (MWHS),providing the global atmospheric temperature and humidity measurements.It is important to assess the in orbit performance of MWTS and MWHS and understand their calibration accuracy before using them in numerical weather prediction and many other applications such as hurricane monitoring.This study aims at quantifying the biases of MWTS and MWHS observations relative to the simulations from the collocated Global Positioning System (GPS) radio occultation (RO) data.Using the collocated FY-3C Global Navigation Satellite System Occultation Sounder (GNOS) RO data under clearsky conditions as inputs to Community Radiative Transfer Model (CRTM),brightness temperatures and viewing angles are simulated for the upper level sounding channels of MWTS and MWHS.In order to obtain O-B statistics under clear sky conditions,a cloud detection algorithm is developed by using the two MWTS channels with frequencies at 50.3 and 51.76 GHz and the two MWHS channels with frequencies centered at 89 and 150 GHz.The analysis shows that for the upper air sounding channels,the mean biases of the MWTS observations relative to the GPS RO simulations are negative for channels 5?9,with absolute values＜1 K,and positive for channels 4 and 10,with values＜0.5 K.For the MWHS observations,the mean biases in brightness temperature are negative for channels 2?6,with absolute values ＜2.6 K and relatively small standard deviations.The mean biases are also negative for channels 11?13,with absolute values＜1.3 K,but with relatively large standard deviations.The biases of both MWTS and MWHS show scan-angle dependence and are asymmetrical across the scan line.The biases for the upper air MWTS and MWHS sounding channels are larger than those previously derived for the Advanced Technology Microwave Sounder.(Hou Xueyan,Han Yang,Hu Xiuqing)

7.3 Influences of physical processes and parameters on simulations of TOA radiance at UV wavelengths:Implications for satellite UV instrument validation

Numerous factors can influence the radiative transfer simulation of hyper-spectral ultraviolet satellite observation,including the radiative transfer scheme,gaseous absorption coefficients,Rayleigh scattering scheme,surface reflectance,aerosol scattering,band center wavelength shifts of sensor,and accuracy of input profiles.In this study,a Unified Linearized Vector Radiative Transfer Model (UNL-VRTM) is used to understand the influences of various factors on the top of atmosphere (TOA) normalized radiance in the ultraviolet (UV) region.A benchmark test for Rayleigh scattering is first performed to verify the UNL-VRTM accuracy,showing that the model performances agree well with earlier peer-reviewed results.Sensitivity experiments show that a scalar radiative transfer approximation considering only ozone and a constant surface reflectance within the UV region may cause significant errors to the TOA normalized radiance.A comparison of the Ozone Mapping and Profiler Suite (OMPS) radiances between simulations and observations shows that the surface reflectance strongly influences the accuracy for the wavelengths larger than 340 nm.Thus,using the surface reflectivity at 331 nm as a proxy for simulating the whole OMPS hyperspectral ultraviolet radiances is problematic.The impact of rotational Raman scattering on TOA radiance can be simulated through using SCIATRAN,which can also reduce the difference between measurements and simulations to some extent.Overall,the differences between OMPS simulations and observations can be less than 3% for the entire wavelengths.The bias is nearly constant across the cross-track direction.(Ding Shouguo,Weng Fuzhong)

7.4 Hourly PM2.5 estimates from a geostationary satellite based on an ensemble learning algorithm and their spatiotemporal patterns over central East China

Satellite-derived aerosol optical depths (AODs) have been widely used to estimate surface fine particulate matter (PM2.5) concentrations over areas that do not have PM2.5monitoring sites.To date,most studies have focused on estimating daily PM2.5concentrations using polar-orbiting satellite data (e.g.,from the Moderate Resolution Imaging Spectroradiometer),which are inadequate for understanding the evolution of PM2.5distributions.This study estimates hourly PM2.5concentrations from Himawari AOD and meteorological parameters using an ensemble learning model.We analyzed the spatial agglomeration patterns of the estimated PM2.5concentrations over central East China.The estimated PM2.5concentrations agree well with groundbased data with an overall cross-validated coefficient of determination of 0.86 and a root-mean-square error of 17.3 μg m?3.Satellite-estimated PM2.5concentrations over central East China display a north-to-south decreasing gradient with the highest concentration in winter and the lowest concentration in summer.Diurnally,concentrations are higher in the morning and lower in the afternoon.PM2.5concentrations exhibit a significant spatial agglomeration effect in central East China.The errors in AOD do not necessarily affect the retrieval accuracy of PM2.5proportionally,especially if the error is systematic.High-frequency spatiotemporal PM2.5variations can improve our understanding of the formation and transportation processes of regional pollution episodes.(Liu Jianjun,Weng Fuzhong,Li Zhanqing)

7.5 Satellite-based PM2.5 estimation directly from reflectance at the top of the atmosphere using a machine learning algorithm

Atmospheric particulate matter (PM) that have particle diameter less than 2.5 μm PM2.5are hazardous to public health whose concentration has been either measured on the ground or inferred from satellite-retrieved aerosol optical depth (AOD).The latter is subject to numerous sources of errors,making the satellite retrievals of PM2.5highly uncertain.This study developed an ensemble machine-learning (ML) algorithm for estimating PM2.5concentration directly from Advanced Himawari Imager satellite measured top-of-the-atmosphere (TOA) reflectances in 2016 integrated with meteorological parameters.The algorithm is demonstrated to perform well across China with high accuracies at different temporal scales.The model has an overall cross-validation coefficient of determination (R2) of 0.86 and a root-mean-square error (RMSE) of 17.3 μg m?3for hourly PM2.5concentration estimation.Such accuracies of the estimation on PM2.5concentration by using TOA reflectance directly are comparable with those of the common methods on estimating PM2.5concentration by using satellite-derived AODs,but the former has a relatively stronger predictive power relating to spatial-temporal coverages than the latter.Annual and seasonal variations of PM2.5concentration over the three major developed regions in China are estimated using the model and analyzed.The relatively stronger predictive ability of developed model in this study may help provide information about the diurnal cycle of PM2.5concentrations as well as aid in monitoring the processes of regional pollution episodes and the evolution of PM2.5concentration.(Liu Jianjun,Weng Fuzhong,Li Zhanqing)

7.6 基于多時(shí)相環(huán)境衛(wèi)星的冬前油菜種植面積估算

油菜是我國(guó)重要的油料作物之一，監(jiān)測(cè)油菜種植面積有助于了解油菜生長(zhǎng)狀況，為油菜病蟲害、濕漬害、凍害等災(zāi)害損失評(píng)估提供數(shù)據(jù)。文章以湖北省荊州市江陵縣為研究區(qū)，使用國(guó)產(chǎn)HJ-1A/B 30 m分辨率時(shí)序多光譜數(shù)據(jù)，通過地面調(diào)查及資料分析確定油菜與其他易混淆作物的主要NDVI時(shí)序特征，建立油菜識(shí)別決策樹，估算了2009—2015年（不包括2011—2012年生長(zhǎng)季）冬前油菜種植面積。將基于油菜開花期影像的最大似然法提取的油菜面積作為定性驗(yàn)證數(shù)據(jù)。以油菜籽面積統(tǒng)計(jì)數(shù)據(jù)和Google Earth高分辨率影像數(shù)據(jù)對(duì)冬前油菜提取的面積和空間位置結(jié)果進(jìn)行定量評(píng)價(jià)。定性評(píng)價(jià)結(jié)果：2009—2011年生長(zhǎng)季的決策樹方法提取冬前油菜面積結(jié)果與開花期影像最大似然法提取結(jié)果基本一致，2012—2015年生長(zhǎng)季的油菜提取面積空間分布差異較大。定量評(píng)價(jià)結(jié)果：決策樹方法提取冬前油菜面積的用戶精度達(dá)到80.40%～95.56%，生產(chǎn)者精度達(dá)到82.56%～91.43%，相對(duì)誤差低于15%。基于NDVI時(shí)間序列特征的決策樹算法估算冬前油菜面積具有可行性，但仍受到云和冬小麥的影響。（魏傳文，黃敬峰，楊玲波）

8 軟件及大氣科學(xué)試驗(yàn)與研究平臺(tái)

8 Software and atmospheric science experiment and research platform

8.1 An open source software suite for multi-dimensional meteorological data computation and visualisation

MeteoInfo Java software tools were developed for multi-dimensional meteorological data analysis and visualisation by integrating a Geographic Information System (GIS) and Scientific Computation Environment (SCE).Included are a Java class library for software developing,a GIS desktop application for spatial data operation and interactive multi-dimensional geoscientific data exploration,and a scientific computation and visualisation environment with Jython scripting.The popular geoscience data formats,such as NetCDF,HDF and GRIB,are supported based on a Unidata NetCDF Java library; also,its multi-dimensional array data model is used for scientific computation.In this paper,the software design framework and its implementation are presented.Furthermore,the software application capabilities are illustrated using several examples.(Wang Yaqiang)

8.2 大氣科學(xué)試驗(yàn)與研究平臺(tái)（ASERP2.0）

大氣科學(xué)試驗(yàn)與研究平臺(tái)是氣科院基本科研業(yè)務(wù)費(fèi)資助建立的，經(jīng)過3年的研發(fā)和建設(shè)，完成了預(yù)期工作目標(biāo)。

（1）研制了大氣科學(xué)試驗(yàn)數(shù)據(jù)管理規(guī)范“大氣科學(xué)試驗(yàn)多源數(shù)據(jù)分類與編碼”和“大氣科學(xué)試驗(yàn)數(shù)據(jù)集說明文檔格式規(guī)范”，開發(fā)了“科學(xué)試驗(yàn)數(shù)據(jù)文件名生成系統(tǒng)”和“科學(xué)試驗(yàn)數(shù)據(jù)說明文檔填報(bào)系統(tǒng)”，在大氣科學(xué)試驗(yàn)數(shù)據(jù)的規(guī)范化管理中實(shí)際應(yīng)用。

（2）大氣科學(xué)試驗(yàn)數(shù)據(jù)和數(shù)據(jù)產(chǎn)品的收集和規(guī)范化處理。包括3次青藏高原大氣科學(xué)試驗(yàn)、JICA青藏高原大氣科學(xué)試驗(yàn)、華南季風(fēng)/臺(tái)風(fēng)強(qiáng)降水觀測(cè)試驗(yàn)以及外場(chǎng)試驗(yàn)期間試驗(yàn)區(qū)相關(guān)業(yè)務(wù)數(shù)據(jù)等，整合生成大氣科學(xué)試驗(yàn)規(guī)范化數(shù)據(jù)集。

（3）開發(fā)了大氣科學(xué)試驗(yàn)場(chǎng)景展示系統(tǒng)。

（4）建立了大氣科學(xué)試驗(yàn)與研究綜合共享平臺(tái)。

（5）開展了華南暴雨試驗(yàn)強(qiáng)降水個(gè)例觀測(cè)數(shù)據(jù)的質(zhì)量控制及數(shù)值同化分析。

大氣科學(xué)試驗(yàn)與研究平臺(tái)提供了5個(gè)重大科學(xué)試驗(yàn)項(xiàng)目的規(guī)范化數(shù)據(jù)集、58個(gè)科研常用基礎(chǔ)數(shù)據(jù)集、多種實(shí)時(shí)數(shù)據(jù)及圖像產(chǎn)品的在線共享，以及數(shù)據(jù)下載服務(wù)。至2019年底平臺(tái)注冊(cè)用戶155人，全年數(shù)據(jù)下載量達(dá)37.8 TB，日均使用110 GB，用戶滿意率為93.76%。（高梅）