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 A multiscale analysis of a nocturnal extreme rainfall event of 14 July 2017 in Northeast China

A multiscale observational analysis of a nocturnal extreme rainfall event that occurred at Changtu in Northeast China on 14 July 2017 is performed using global analysis, automated surface observations, Doppler radar, rawinsonde, and disdrometer data. Results show that the large-scale environment was characterized by high convective available potential energy and precipitable water, moderate convective inhibition, and a southwesterly low-level jet (LLJ) capped by an inversion layer. The first and subsequent convective cells developed along a quasi-stationary surface convergence zone in a convection-void region of a previously dissipated meso-a-scale convective line. Continuous convective initiation through backbuilding at the western end and the subsequent merging of eastward-moving convective cells led to the formation of a near-zonally oriented meso-β-scale rainband, with reflectivity exceeding 45 dBz (i.e., convective core intensity). This quasistationary rainband was maintained along the convergence zone by the LLJ of warm moist air, aided by local topographical lifting and convectively generated outflows. A maximum hourly rainfall amount of 96 mm occurred during 02:00?03:00 Beijing standard time as individual convective cores with a melting layer of > 55 dBz reflectivity moved across Changtu with little intermittency. The extreme-rain-producing stage was characterized with near-saturated vertical columns, and rapid number concentration increases of all raindrop sizes. It is concluded that the formation of the meso-β-scale rainband with continuous convective backbuilding, and the subsequent echo-training of convective cores with growing intensity and width as well as significant fallouts of frozen particles accounted for the generation of this extreme rainfall event. This extreme event was enhanced by local topography and the formation of a mesovortex of 20?30 km in diameter. (Wang Gaili, Zhang Da-Lin, Sun Jisong)

1.2 Analysis of the vertical air motions and raindrop size distribution retrievals of a squall line based on cloud radar Doppler spectral density data

A squall line is a type of strongly organized mesoscale convective system that can cause severe weather disasters. Thus, it is crucial to explore the dynamic structure and hydrometeor distributions in squall lines.This study analyzed a squall line over Guangdong Province on 6 May 2016 that was observed using a Kaband millimeter-wave cloud radar (CR) and an S-band dual-polarization radar (PR). Doppler spectral density data obtained by the CR were used to retrieve the vertical air motions and raindrop size distribution (DSD).The results showed the following: First, the CR detected detailed vertical profiles and their evolution before and during the squall line passage. In the convection time segment (segment B), heavy rain existed with a reflectivity factor exceeding 35 dBz and a velocity spectrum width exceeding 1.3 m s?1. In the PR detection,the differential reflectivity factor (Zdr) was 1?2 dB, and the large specific differential phase (Kdp) also represented large liquid water content. In the transition and stratiform cloud time segments (segments B and C), the rain stabilized gradually, with decreasing cloud tops, stable precipitation, and a 0 ℃ layer bright band.Smaller Kdpvalues (less than 0.9) were distributed around the 0 ℃ layer, which may have been caused by the melting of ice crystal particles. Second, from the CR-retrieved vertical air velocity, before squall line passage,downdrafts dominated in local convection and weak updrafts existed in higher-altitude altostratus clouds. In segment B, the updraft air velocity reached more than 8 m s?1below the 0 ℃ layer. From segments C to D, the updrafts changed gradually into weak and wide-ranging downdrafts. Third, in the comparison of DSD values retrieved at 1.5 km and DSD values on the ground, the retrieved DSD line was lower than the disdrometer, the overall magnitude of the DSD retrieved was smaller, and the difference decreased from segments C to D. The standardized intercept parameter (Nw) and shape parameter (μ) of the DSD retrieved at 1.8 km showed good agreement with the disdrometer results, and the mass-weighted mean diameter (Dm) was smaller than that on the ground, but very close to the PR-retrieved Dmresult at 2 km. Therefore, comparing with the DSD retrieved at around 2 km, the overall number concentration remained unchanged and Dmgot larger on the ground,possibly reflecting the process of raindrop coalescence. Lastly, the average vertical profiles of several quantities in all segments showed that, first of all, the decrease of Nwand Dmwith height in segments C and D was similar, reflecting the collision effect of falling raindrops. The trends were opposite in segment B, indicating that raindrops underwent intense mixing and rapid collision and growth in this segment. Then, PR-retrieved Dmprofiles can verify the rationality of the CR-retrieved Dm. Finally, a vertical velocity profile peak generated a larger Dmespecially in segments C and D. (Ma Ningkun, Liu Liping, Chen Yichen)

1.3 Cloud vertical structure measurements from a ground-based cloud radar over the southeastern Tibetan Plateau

The southeastern Tibetan Plateau (TP) is the critical region of water vapor transport over the TP. Groundbased Ka-band cloud radar (KaCR) measurements collected at the Motuo National Climate Observatory in 2019 were used to analyze the physical properties of clouds at the front of the water vapor channel over the TP. The cloud top heights (CTHs) measured by the KaCR were verified through a comparison with observations from the Fengyun-4A (FY-4A) satellite at the same location. The KaCR-obtained CTHs were generally consistent with the FY-4A-obtained CTHs, although the KaCR slightly overestimated the CTHs of nonprecipitation clouds and underestimated the CTHs of precipitation clouds. Negative deviations between the KaCR- and FY-4A-obtained CTHs increased with rainfall rate. Cloud cover frequently occurred over Motuo,with an annual mean occurrence frequency of 65.3%. Clouds tended to form frequently at night and dissipate gradually in the daytime. Two peaks in the cloud base height (CBH) distribution were observed in Motuo,located at 0?1 km and 2?3 km, corresponding to precipitation and nonprecipitation clouds, respectively.The CTHs reached a peak at 6?7 km, which might be related to precipitation clouds. Moreover, a maximum CTH probability was observed in the midnight-early morning hours during the rainy season, while the CTH frequency peaked in the evening during the dry season. In addition, low and middle clouds were prevalent in Motuo for the period of observation in 2019. Understanding the characteristics of clouds over the TP will provide key validations of satellite measurements and promote research on cloud forces over the TP. (Zhou Renran, Wang Gaili, Zhaxi Suolang)

1.4 Deep learning for polarimetric radar quantitative precipitation estimation during landfalling typhoons in South China

Heavy rain associated with landfalling typhoons often leads to disasters in South China, which can be reduced by improving the accuracy of radar quantitative precipitation estimation (QPE). At present, raindrop size distribution (DSD) -based nonlinear fitting (QPE of DSD) and traditional neural networks are the main radar QPE algorithms. The former is not sufficient to represent the spatiotemporal variability of DSDs through the generalized Z-R or polarimetric radar rainfall relations that are established using statistical methods since such parametric methods do not consider the spatial distribution of radar observables, and the latter is limited by the number of network layers and availability of data for training the model. In this paper, we propose an alternative approach to dual-polarization radar QPE based on deep learning (QPENet). Three datasets of dualpolarization radar observations-surface rainfall (DPO-SR) were constructed using radar observations and corresponding measurements from automatic weather stations (AWS) and used for QPENet (V1), QPENet (V2),and QPENet (V3). In particular, 13×13, 25×25, and 41×41 radar range bins surrounding each AWS location were used in constructing the datasets for QPENet (V1), QPENet (V2), and QPENet (V3), respectively. For training the QPENet models, the radar data and AWS measurements from eleven landfalling typhoons in South China during 2017?2019 were used. For demonstration, an independent typhoon event was randomly selected(i.e., Merbok) to implement the three trained models to produce rainfall estimates. The evaluation results and comparison with traditional QPE (DSD) algorithms show that the QPENet model has a better performance than the traditional parametric relations. Only when the hourly rainfall intensity is less than 5 mm (R < 5 mm h?1), the QPE (DSD) model shows a comparable performance to QPENet. Comparing the three versions of the QPENet model, QPENet (V2) has the best overall performance. Only when the hourly rainfall intensity is less than 5 mm (R < 5 mm h?1), QPENet (V3) performs the best. (Zhang Yonghua, Bi Shuoben, Liu Liping)

1.5 Estimating raindrop size distributions and vertical air motions with spectral difference using vertically pointing radar

Doppler spectra measured by vertically pointing radars are inherently linked to raindrop size distributions(DSDs). But accurate estimation of DSDs remains challenging because raindrop spectra are broadened by atmospheric turbulence and shifted by vertical air motions. This paper presents a novel method to estimate vertical air motions in which there is no need to assume a model for DSD at each range gate. The theory of the new method is that the spectral difference between the adjacent range gates is contributed by vertical air motions and the variability of DSDs. The contribution of the change of DSDs is estimated by looking up the prepared tables of raindrop velocity difference and shape function difference. Then the vertical air motions can be estimated by minimizing the cost function of the two spectra between the adjacent range gates. The retrieval algorithm is applied to three cases including a stratiform case and two convective cases observed by a C-band vertically pointing radar in Longmen, Guangdong Province, China, in June 2016. Before that, the spectrum broadening effect is removed by the traditional deconvolution method with a wind profiler. The vertical profiles of precipitation parameters are also retrieved to investigate the microphysical process. The precipitation parameters retrieved near the surface are compared with the ground data collected by a two-dimensional video disdrometer (2DVD), and the results show good agreement. (Pang Suzhou, Ruan Zheng, Yang Ling)

1.6 Raindrop size distribution measurements on the southeast Tibetan Plateau during the STEP project

As part of the Second Tibetan Plateau Scientific Expedition and Research (STEP) field campaign, raindrop size distribution (DSD) measurements were conducted with a laser optical particle size velocity disdrometer in Motuo on the Tibetan Plateau (TP). The DSD characteristics of five different rain rate classes and convective and stratiform precipitation types were studied using the DSD data from July to September 2019, comprising a total of 47774 1-min raindrop spectra. The average raindrop spectral width and number concentration of large drops increased with the rainfall intensity. Furthermore, the combination of smalland midsize drops dominated the precipitation in Motuo, and their contributions exceeded 99% of the number concentration. The convective precipitation in Motuo was identified as maritime-like precipitation and was characterized by a large normalized intercept parameter lgNw= 4.0 ? 4.4 and small mass-weighted mean diameter Dm= 1.1 ? 1.4 mm.Empirical relations among the three parameters (intercept N0, shape μ, and slope λ) of the gamma distribution model, Nwand Dmof the normalized gamma distribution were derived. We also obtained power-law relationships of Z = ARbfor the stratiform and convective precipitation in Motuo, and the empirical relation of Z = 300R1.4significantly underestimated the convective precipitation in Motuo. When the precipitation type transitioned from stratiform into convective precipitation, coefficient A decreased and exponent b increased.Finally, empirical relations between Dmand the radar equivalent reflectivity factor at the Ku and Ka bands were obtained to improve the rainfall retrieval algorithms of the dual-frequency precipitation radar on the southeast TP. (Wang Gaili, Zhou Renran, Zhaxi Suolang)

1.7 Study on radar echo-filling in an occlusion area by a deep learning algorithm

Radar beam blockage is an important error source that affects the quality of weather radar data. An echofilling network (EFnet) is proposed based on a deep learning algorithm to correct the echo intensity under the occlusion area in the Nanjing S-band new-generation weather radar (CINRAD/SA). The training dataset is constructed by the labels, which are the echo intensity at the 0.5° elevation in the unblocked area, and by the input features, which are the intensity in the cube including multiple elevations and gates corresponding to the location of bottom labels. Two loss functions are applied to compile the network: one is the common mean square error (MSE), and the other is a self-defined loss function that increases the weight of strong echoes.Considering that the radar beam broadens with distance and height, the 0.5° elevation scan is divided into six range bands every 25 km to train different models. The models are evaluated by three indicators: explained variance (EVar), mean absolute error (MAE), and correlation coefficient (CC). Two cases are demonstrated to compare the effect of the echo-filling model by different loss functions. The results suggest that EFnet can effectively correct the echo reflectivity and improve the data quality in the occlusion area, and there are better results for strong echoes when the self-defined loss function is used. (Yin Xiaoyan, Hu Zhiqun, Zheng Jiafeng)

1.8 Supercooled liquid water and secondary ice production in Kelvin-Helmholtz instability as revealed by radar Doppler spectra observations

Mixed-phase clouds are globally omnipresent and play a major role in the Earth’s radiation budget and precipitation formation. The existence of liquid droplets in the presence of ice particles is microphysically unstable and depends on a delicate balance of several competing processes. Understanding mechanisms that govern ice initiation and moisture supply are important to understand the life cycle of such clouds.This study presents observations that reveal the onset of drizzle inside a similar to 600 m deep mixed-phase layer embedded in a stratiform precipitation system. Using Doppler spectral analysis, we show how large supercooled liquid droplets are generated in Kelvin-Helmholtz (K-H) instability despite ice particles falling from upper cloud layers. The spectral width of the supercooled liquid water mode in the radar Doppler spectrum is used to identify a region of increased turbulence. The observations show that large liquid droplets,characterized by reflectivity values larger than 20 dBz, are generated in this region. In addition to cloud droplets, Doppler spectral analysis reveals the production of columnar ice crystals in the K-H billows. The modeling study estimates that the concentration of these ice crystals is 3?8 L?1, which is at least 1 order of magnitude higher than that of primary ice-nucleating particles. Given the detail of the observations, we show that multiple populations of secondary ice particles are generated in regions where larger cloud droplets are produced and not at some constant level within the cloud. It is, therefore, hypothesized that K-H in stability provides conditions favorable for enhanced droplet growth and formation of secondary ice particles. (Li Haoran, Korolev Alexei, Moisseev Dmitri)

1.9 Two-year statistics of columnar-ice production in stratiform clouds over Hyytiala, Finland:Environmental conditions and the relevance to secondary ice production

Formation of ice particles in clouds at temperatures of 10 or warmer was documented by using groundbased radar observations. At these temperatures, the number concentration of ice-nucleating particles (INPs)is not only expected to be small, but this number is also highly uncertain. In addition, there are a number of studies reporting that the observed number concentration of ice particles exceeds expected INP concentrations,indicating that other ice generation mechanisms, such as secondary ice production (SIP), may play an important role in such clouds. To identify formation of ice crystals and report conditions in which they are generated, W-band cloud radar Doppler spectra observations collected at the Hyytiala station for more than 2 years were used. Given that at these temperatures ice crystals grow mainly as columns, which have distinct linear depolarization ratio (LDR) values, the spectral LDR was utilized to identify newly formed ice particles.It is found that in 5% to 13% of clouds, where cloud top temperatures are 12 or warmer, production of columnar ice is detected. For colder clouds, this percentage can be as high as 33%, 40% to 50% of columnarice-producing events last less than 1 h, while 5% to 15% can persist for more than 6 h. By comparing clouds where columnar crystals are produced and to the ones where these crystals are absent, the columnar-iceproducing clouds tend to have larger values of liquid water path and precipitation intensity. The columnariceproducing clouds were subdivided into three categories, using the temperature difference, ΔT, between the altitudes where columns are first detected and cloud top. The cases where ΔT is less than 2 K are typically singlelayer shallow clouds where needles are produced at the cloud top. In multilayered clouds where ΔT is larger tahan 2 K, columns are produced in a layer that is seeded by ice particles falling from above. This classification allows us to study potential impacts of various SIP mechanisms, such as the Hallet-Mossop process or freezing breakup, on columnar-ice production. To answer the question whether the observed ice particles are generated by SIP in the observed single-layer shallow clouds, ice particle number concentrations were retrieved and compared to several INP parameterizations. It was found that the ice number concentrations tend to be 1?3 orders of magnitude higher than the expected INP concentrations. (Li Haoran, Mohler Ottmar, Petaja Tuukka)

1.10 Vertical during snow events in middle latitudes of China observed by a C-band vertically pointing radar

This study applied the C-band vertically pointing radar with frequency-modulation continuous-wave technology to obtain the continuous observation data of four shallow and two deep snow events during the winter of 2015?2016 in the midlatitudes of China. Generating cells (GCs) were found near the echo tops in every event. The ice particle number concentration (N), ice water content (IWC), and median mass diameter (Dm)retrieved from radar Doppler spectra were used to analyze the microphysical properties in the snow clouds.The clouds were divided into upper GC and lower stratiform (St) regions according to their vertical structure.The fall streaks (FSs) associated with GCs were embedded in the St regions. In the GC regions, the N values in shallow events were smaller compared with those in deep events, and Dmand IWC were larger. In the St regions, N decreased compared with that in the GC regions, and Dmand IWC increased, implying the existence of aggregation and deposition growth. The growth of particle size and mass mainly occurred in the St regions.The increases of N were usually observed near ?5 accompanied by bimodal Doppler spectra, which might be caused by ice multiplication. The average ratios of the median N, Dm, and IWC inside GCs to those outside GCs were 2, 1.3, and 2.5, respectively, for shallow events, with 1.7, 1.2, and 2.3, respectively, for deep events.These values were basically the same as those for the FSs, implying the importance of GCs to the enhanced ice growth subsequently found in FSs. The larger values of N, Dm, and IWC inside GCs could be related to the upward air motions inside GCs. The first Ze-IWC relationship suitable for snow clouds in the midlatitudes of China was also established. (Cui Ye, Ruan Zheng, Wei Ming)

1.11 Ka/Ku雙波段毫米波雷達(dá)功率譜數(shù)據(jù)反演液態(tài)水含量方法研究

單波段雷達(dá)用Z-LWC關(guān)系反演液態(tài)水因不同降水類型反演的液態(tài)水含量相差較大。利用雙波段雷達(dá)回波強(qiáng)度偏差反演液態(tài)水含量，直接將雙波段雷達(dá)基數(shù)據(jù)回波強(qiáng)度相減的差值不僅包括了衰減的偏差也包括散射不同帶來(lái)的偏差。因此，利用雙波段雷達(dá)功率譜數(shù)據(jù)經(jīng)過(guò)小粒子選擇計(jì)算受Mie散射影響小的粒子，用最小二乘法計(jì)算DWR（Dual Wavelength Ratio）的變化率反演液態(tài)水含量和液態(tài)水積分總量，將雙波段雷達(dá)基數(shù)據(jù)和功率譜數(shù)據(jù)反演結(jié)果與微波輻射計(jì)測(cè)量結(jié)果進(jìn)行對(duì)比。結(jié)果表明：（1）經(jīng)過(guò)小粒子選擇，去掉了雙波段雷達(dá)的回波強(qiáng)度因散射不同帶來(lái)的偏差。（2）在高度較低時(shí)雙波段雷達(dá)基數(shù)據(jù)和功率譜數(shù)據(jù)經(jīng)過(guò)小粒子選擇反演的液態(tài)水含量有著較大區(qū)別。隨著高度的增加，反演的液態(tài)水含量比較接近。（3）雙波段雷達(dá)基數(shù)據(jù)和功率譜數(shù)據(jù)反演的液態(tài)水含量與微波輻射計(jì)進(jìn)行定性分析，變化趨勢(shì)能夠達(dá)到較為一致，微波輻射計(jì)液態(tài)水含量較強(qiáng)的區(qū)域，兩者反演的液態(tài)水含量也相應(yīng)較大。（4）雙波段雷達(dá)基數(shù)據(jù)和功率譜數(shù)據(jù)反演的液態(tài)水積分總量和微波輻射計(jì)的液態(tài)水積分總量隨著時(shí)間的變化趨勢(shì)較為一致，但雙波段雷達(dá)功率譜數(shù)據(jù)總體程度小于基數(shù)據(jù)反演的液態(tài)水積分，雙波段雷達(dá)基數(shù)據(jù)與功率譜數(shù)據(jù)反演的液態(tài)水積分總量總體小于微波輻射計(jì)的液態(tài)水積分總量值。（鄒琳，劉黎平）

1.12 Ka/Ku雙波段云雷達(dá)反演空氣垂直運(yùn)動(dòng)速度和雨滴譜方法研究及初步應(yīng)用

在Ka波段云雷達(dá)上升級(jí)改造建成的Ka/Ku（Ka和Ku波段波長(zhǎng)分別為8.9 mm和2.2 cm）雙波段云雷達(dá)2019年用于華南云降水垂直結(jié)構(gòu)觀測(cè)，以改進(jìn)云內(nèi)動(dòng)力和微物理參數(shù)探測(cè)能力。為了利用該雙波段云雷達(dá)研究華南降水微物理和動(dòng)力結(jié)構(gòu)，本文提出了基于雙波段云雷達(dá)回波強(qiáng)度譜密度（SZ）數(shù)據(jù)和最優(yōu)估計(jì)技術(shù)的云內(nèi)空氣垂直運(yùn)動(dòng)速度（Vair）、雨滴譜（DSD）、液態(tài)水含量（LWC）、雨強(qiáng)（R）的反演方法（DWSZ），以及雨區(qū)衰減的訂正方法。利用2019年在廣東龍門觀測(cè)的一次降水過(guò)程數(shù)據(jù)，對(duì)比分析了云雷達(dá)反演的微物理參數(shù)與雨滴譜直接觀測(cè)量，并檢驗(yàn)了云雷達(dá)反演的低層空氣垂直運(yùn)動(dòng)速度，利用反演結(jié)果分析了一次混合云過(guò)程的Vair與這些微物理參數(shù)的垂直結(jié)構(gòu)和相互關(guān)系。結(jié)果表明：Ka/Ku雙波段云雷達(dá)合理反演了微降水微物理和動(dòng)力參數(shù)及其垂直分布，經(jīng)過(guò)衰減訂正的Ka和Ku波段回波強(qiáng)度偏差明顯減小。該雙波段云雷達(dá)數(shù)據(jù)可以用于分析0～30 dBz回波強(qiáng)度的云降水垂直結(jié)構(gòu)。本次過(guò)程為混合云降水，對(duì)流單體前部存在明顯的上升氣流，后部存在下沉氣流；從平均垂直結(jié)構(gòu)來(lái)看，Vair和粒子平均直徑（Dm）在2 km高度層到達(dá)最大，粒子數(shù)密度（Nw）、LWC和R在2 km以下明顯增強(qiáng)，粒子直徑卻減小，水汽凝結(jié)過(guò)程、雨滴碰并云滴是本次過(guò)程的主要機(jī)制。這一工作驗(yàn)證了Ka和Ku波段組合的雙波段云雷達(dá)的可行性，為Ka/Ku波段云雷達(dá)技術(shù)的推廣，單波段云雷達(dá)反演算法進(jìn)一步改進(jìn)，云降水精細(xì)結(jié)構(gòu)分析等提供了基礎(chǔ)。（劉黎平，張揚(yáng)，丁晗）

1.13 X波段雙偏振雷達(dá)相態(tài)識(shí)別與拼圖的關(guān)鍵技術(shù)

基于統(tǒng)計(jì)的隸屬函數(shù)參數(shù)改進(jìn)方法和基于衰減程度的拼圖融合方法，通過(guò)對(duì)比改進(jìn)后可有效提升水凝物相態(tài)識(shí)別結(jié)果的可靠性和多雷達(dá)拼圖結(jié)果的合理性。在2016年汛期北京典型個(gè)例中，融合后的X波段雷達(dá)網(wǎng)與當(dāng)?shù)豐波段業(yè)務(wù)雷達(dá)相比能夠提供更精細(xì)的回波結(jié)構(gòu)和水凝物相態(tài)分布，有效緩解S波段雷達(dá)在近處探測(cè)能力降低的問(wèn)題，識(shí)別的降雹區(qū)與地面觀測(cè)相符。（吳翀，劉黎平，仰美霖）

1.14 毫米波云雷達(dá)觀測(cè)和反演云降水微物理及動(dòng)力參數(shù)方法研究進(jìn)展

云雷達(dá)是探測(cè)和反演云降水微物理及動(dòng)力參數(shù)精細(xì)結(jié)構(gòu)的重要手段。回顧了世界和我國(guó)云雷達(dá)觀測(cè)模式、數(shù)據(jù)質(zhì)量控制和數(shù)據(jù)融合方法，特別是脈沖壓縮、相干積累和非相干積累技術(shù)在提高云雷達(dá)靈敏度的應(yīng)用，分析了基于回波強(qiáng)度與粒子下落速度關(guān)系、單波段云雷達(dá)小粒子跟蹤方法、雙波段云雷達(dá)回波強(qiáng)度譜密度比值方法等空氣垂直運(yùn)動(dòng)速度反演和雨滴譜反演方法，并討論了這些方法的特色，為今后云雷達(dá)觀測(cè)方法設(shè)定和數(shù)據(jù)分析提供參考。（劉黎平）

1.15 降水條件下的云雷達(dá)與微波輻射計(jì)反演液態(tài)水含量對(duì)比分析

為了發(fā)展云雷達(dá)與微波輻射計(jì)聯(lián)合反演液態(tài)水含量的方法，利用2019年4—9月中國(guó)氣象科學(xué)研究院在廣東龍門開展的綜合觀測(cè)試驗(yàn)中的雙波段云雷達(dá)和微波輻射計(jì)數(shù)據(jù)，首先檢驗(yàn)了在降水條件下微波輻射計(jì)天頂觀測(cè)和斜路徑觀測(cè)兩種探測(cè)模式反演溫度（T）、相對(duì)濕度（RH）、液態(tài)水含量（LWC）和液態(tài)水路徑（LWP）的合理性，然后分析了兩種探測(cè)設(shè)備反演LWC和LWP的差別。得到以下結(jié)論：（1）微波輻射計(jì)在斜路徑觀測(cè)模式下反演的產(chǎn)品受降水影響較小，其反演結(jié)果明顯優(yōu)于天頂觀測(cè)模式。（2）兩種探測(cè)設(shè)備反演的LWP相關(guān)性較好且隨時(shí)間變化較為一致，但云雷達(dá)反演LWP與平均回波強(qiáng)度有明顯相關(guān)，隨著雷達(dá)回波強(qiáng)度的增大，云雷達(dá)與微波輻射計(jì)反演的LWP之比越大。（3）兩種探測(cè)設(shè)備反演的LWC相關(guān)性較差且存在明顯偏差，在不考慮融化層的情況下單波段云雷達(dá)反演LWC與微波輻射計(jì)隨高度變化趨勢(shì)相近，雙波段云雷達(dá)反演LWC與微波輻射計(jì)反演結(jié)果在1 km及其以上區(qū)間存在明顯差異。（鄒明龍，劉黎平，鄭佳鋒）

1.16 利用貝葉斯方法改進(jìn)華南地區(qū)冰雹識(shí)別效果

使用2019年廣東S波段雙偏振雷達(dá)觀測(cè)的冰雹和非冰雹數(shù)據(jù)，統(tǒng)計(jì)得到冰雹和非冰雹的雷達(dá)反射率Z、差分反射率ZDR和相關(guān)系數(shù)CC先驗(yàn)概率密度分布，采用貝葉斯方法，根據(jù)雷達(dá)參量在冰雹和非冰雹條件下的概率以及冰雹和非冰雹的先驗(yàn)概率來(lái)確定某一距離庫(kù)上所測(cè)到的（Z、ZDR、CC）所代表冰雹和非冰雹的概率，并用兩個(gè)個(gè)例，比較分析了WSR-88D冰雹識(shí)別算法和貝葉斯方法對(duì)冰雹識(shí)別的效果，分析表明，兩種方法都能較準(zhǔn)確地識(shí)別出冰雹云，但是貝葉斯方法識(shí)別范圍較大，這可能與華南地區(qū)多為雨夾雹有關(guān)。（李博勇，胡志群，鄭佳鋒）

1.17 青藏高原墨脫地區(qū)云降水綜合觀測(cè)及初步統(tǒng)計(jì)特征分析

為加深對(duì)雅魯藏布大峽谷水汽通道入口處云和降水三維結(jié)構(gòu)及微物理特征的認(rèn)識(shí)，在第二次青藏高原綜合科學(xué)考察研究專題和國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目的支持下，中國(guó)氣象科學(xué)研究院于2019年在西藏墨脫地區(qū)建立了野外觀測(cè)試驗(yàn)基地，開展了水汽、云和降水的綜合觀測(cè)，先后布設(shè)了先進(jìn)的Ka波段云雷達(dá)、微波輻射計(jì)、X波段雙偏振相控陣?yán)走_(dá)、降水現(xiàn)象儀、K波段微雨雷達(dá)等設(shè)備，獲取了高時(shí)、空分辨率的云和降水的宏、微觀數(shù)據(jù)。文中簡(jiǎn)單介紹了此次觀測(cè)的情況，并利用云雷達(dá)2019年的觀測(cè)數(shù)據(jù)和降水現(xiàn)象儀2019年6月至2020年6月的觀測(cè)數(shù)據(jù)對(duì)云的宏觀特征及雨滴譜特征進(jìn)行了統(tǒng)計(jì)分析。從云的宏觀特征來(lái)看，該地區(qū)云的發(fā)生率較高，云廓線占2019年云雷達(dá)觀測(cè)廓線的67%，降水云廓線占總云廓線的45%。旱季和雨季云底高度的頻率分布在垂直方向均有兩個(gè)高值區(qū)，分別為0～1 km和2～3 km，且超過(guò)40%的云底高度低于1 km，這可能是墨脫降水云較多造成的。接近60%的云頂高度在4～7 km?？偟膩?lái)說(shuō)，墨脫地區(qū)以中云和低云為主，云通常在下午到晚上形成，早上到中午慢慢消散；從雨滴譜分布特征來(lái)看，該地區(qū)平均的雨滴譜譜寬和大雨滴的濃度隨雨強(qiáng)的增大而增大，降水以中、小粒子為主，中、小粒子濃度超過(guò)粒子數(shù)濃度的99%。對(duì)流云降水的特點(diǎn)是粒子直徑較小，而數(shù)濃度較高。粒子質(zhì)量加權(quán)平均直徑（Dm）的范圍在1.0～1.6 mm（平均1.38 mm），標(biāo)準(zhǔn)化截距參數(shù)（lgNw）的范圍在3.6～4.5（平均4.01），表現(xiàn)出海洋性對(duì)流降水的特征。此外，該地區(qū)降水的lgNw呈現(xiàn)雙峰特征，分別對(duì)應(yīng)于對(duì)流云和層狀云降水。（王改利，周任然，扎西索郎）

1.18 雙偏振相控陣?yán)走_(dá)與業(yè)務(wù)雷達(dá)的定量對(duì)比及觀測(cè)精度研究

相控陣天氣雷達(dá)突破了全機(jī)械驅(qū)動(dòng)天線天氣雷達(dá)的時(shí)空分辨率瓶頸，能夠提供更加快速、精細(xì)的觀測(cè)資料。但陣列天線存在性能參數(shù)隨掃描角偏離法向而惡化的情況，使相控陣?yán)走_(dá)定量測(cè)量存在困難。本文針對(duì)中國(guó)華南地區(qū)最新布網(wǎng)的雙偏振相控陣天氣雷達(dá)，通過(guò)與當(dāng)?shù)豐波段業(yè)務(wù)雷達(dá)在相同區(qū)域內(nèi)的定量對(duì)比，評(píng)估了反射率因子差分反射率因子的誤差量級(jí)及其隨掃描角、觀測(cè)時(shí)間的變化趨勢(shì)。研究結(jié)果表明，相控陣?yán)走_(dá)反射率因子的誤差不大，約0.82 dB，而差分反射率因子的誤差則高達(dá)1.04 dB，并且不同仰角、不同時(shí)刻之間也存在一定的波動(dòng)。為此本文提出了基于S波段雷達(dá)實(shí)時(shí)數(shù)據(jù)的訂正方案，能夠較好地解決雙偏振相控陣天氣雷達(dá)的定標(biāo)問(wèn)題，為相控陣?yán)走_(dá)的業(yè)務(wù)應(yīng)用提供了保障。（張蔚然，吳翀，劉黎平）

1.19 星載雷達(dá)DPR與地基雷達(dá)CR的匹配對(duì)比及系統(tǒng)偏差初探

將GPM衛(wèi)星搭載的雙頻降水雷達(dá)DPR和廣東龍門觀測(cè)站的地基Ka/Ku雙波段雷達(dá)CR在2019年4—9月的觀測(cè)數(shù)據(jù)進(jìn)行時(shí)空匹配，結(jié)合微雨雷達(dá)MRR 的雨滴譜數(shù)據(jù)對(duì)CR衰減訂正處理，比較DPR與CR探測(cè)回波強(qiáng)度差異，最后對(duì)兩者的系統(tǒng)偏差進(jìn)行分析。結(jié)果表明：（1） DPR和CR探測(cè)到的回波強(qiáng)度隨高度變化的趨勢(shì)大體一致，零度層亮帶高度基本一致，同樣高度下DPR探測(cè)到的回波強(qiáng)度明顯大于CR。（2）統(tǒng)計(jì)弱的非降水云算得CR雙頻系統(tǒng)偏差約為3.1 dBz。（3）雨強(qiáng)越強(qiáng)，CR天線罩水膜厚度越大，回波衰減越大。（4）逐庫(kù)訂正過(guò)程中利用雨滴譜數(shù)據(jù)計(jì)算衰減系數(shù)，CR在Ka與Ku波段的反射率因子訂正量不超過(guò)4 dBz。（5）綜合所有適配數(shù)據(jù)，CR與DPR的反射率因子在Ka波段內(nèi)訂正后平均系統(tǒng)偏差為15.7 dBz，在Ku波段內(nèi)訂正后平均系統(tǒng)偏差為14.4 dBz。雖然經(jīng)訂正處理后兩部雷達(dá)間的系統(tǒng)偏差偏大，但對(duì)改善地基Ka/Ku雙波段雷達(dá)的數(shù)據(jù)質(zhì)量有明顯的改善。（曾震瑜，劉黎平，鄭佳鋒）

1.20 一次強(qiáng)雹云過(guò)程冰雹增長(zhǎng)機(jī)制分析及防雹探討

2018年9月29日大連市出現(xiàn)了強(qiáng)雹云天氣過(guò)程。初始雹云在渤海上空生成，經(jīng)3 h東移和發(fā)展演變，在大連北部沿海登陸并發(fā)展為成熟的強(qiáng)雹云。當(dāng)?shù)刈鳂I(yè)點(diǎn)及時(shí)開展人工防雹與聯(lián)防作業(yè)，并對(duì)作業(yè)前后雹云雷達(dá)特征參數(shù)變化及成熟強(qiáng)雹云空間結(jié)構(gòu)特征等進(jìn)行分析，深入研究和探討了成熟強(qiáng)雹云有效人工防雹兩道防線技術(shù)方法，即在重要作物保護(hù)區(qū)上游空曠地帶，或低值作物區(qū)增設(shè)人工防雹高炮，當(dāng)成熟強(qiáng)雹云進(jìn)入該高炮射程，立即實(shí)施高炮作業(yè)（且仰角≥55°，即打在雹云強(qiáng)回波區(qū)），促使冰雹提前和充分降落，從而保護(hù)下游的重要作物，將雹災(zāi)損失降到最低，達(dá)到人工防雹的目的。（李紅斌，胡志群，張靖萱）

1.21 風(fēng)廓線雷達(dá)組網(wǎng)觀測(cè)新型應(yīng)用研究進(jìn)展

風(fēng)廓線雷達(dá)具有高的時(shí)間和空間分辨率，已經(jīng)被廣泛應(yīng)用于大氣探測(cè)、環(huán)境氣象以及災(zāi)害性雷暴天氣監(jiān)測(cè)預(yù)警等領(lǐng)域。但風(fēng)廓線雷達(dá)組網(wǎng)二次開發(fā)產(chǎn)品缺乏，一定程度限制了其在天氣氣候領(lǐng)域的深度應(yīng)用。簡(jiǎn)要介紹中國(guó)風(fēng)廓線雷達(dá)網(wǎng)站點(diǎn)分布及其水平風(fēng)廓線和譜寬等數(shù)據(jù)產(chǎn)品；闡述基于風(fēng)廓線雷達(dá)觀測(cè)產(chǎn)生的高時(shí)間分辨率邊界層高度、垂直風(fēng)切變、湍流強(qiáng)度和散度等新產(chǎn)品特點(diǎn)，并給出了相應(yīng)的應(yīng)用場(chǎng)景或案例。最后，展望了風(fēng)廓線雷達(dá)組網(wǎng)觀測(cè)的不足及其未來(lái)應(yīng)用前景。（郭建平，劉博銘，郭曉冉）

2 青藏高原天氣研究

2 Research on weather over the Tibetan Plateau

2.1 2021年度第二次青藏高原綜合科學(xué)考察研究進(jìn)展

中國(guó)工程院院士徐祥德承擔(dān)“第二次青藏高原綜合科學(xué)考察研究”十大科考任務(wù)的第一任務(wù)，并負(fù)責(zé)第5專題。項(xiàng)目科考及研究重點(diǎn)目標(biāo)是針對(duì)亞洲水塔水資源、生態(tài)變化的影響因素，研究氣候變化及其西風(fēng)與季風(fēng)協(xié)同作用，拓展青藏高原科考計(jì)劃實(shí)施的多圈層綜合觀測(cè)系統(tǒng)的應(yīng)用領(lǐng)域；提升科考團(tuán)隊(duì)研究成果在青藏高原地球系統(tǒng)前沿領(lǐng)域中的重要地位，著力解決氣候變化對(duì)青藏高原亞洲水塔水資源與生態(tài)環(huán)境的影響理論及其應(yīng)用問(wèn)題，并提出有助于西藏社會(huì)經(jīng)濟(jì)高質(zhì)量發(fā)展的科學(xué)合理氣候應(yīng)對(duì)戰(zhàn)略決策；助力深入理解氣候變化對(duì)青藏高原水資源和生態(tài)環(huán)境的影響機(jī)理，筑牢氣象防災(zāi)減災(zāi)第一道防線。青藏高原科學(xué)考察面向國(guó)家戰(zhàn)略需求，在復(fù)雜地形和水循環(huán)條件下，構(gòu)建青藏高原天—地—空一體化的綜合觀測(cè)體系，揭示青藏高原氣候和生態(tài)變化機(jī)理，著力解決青藏高原生態(tài)環(huán)境、災(zāi)害風(fēng)險(xiǎn)、國(guó)家重大工程建設(shè)安全等方面的問(wèn)題，推動(dòng)青藏高原可持續(xù)發(fā)展，推進(jìn)國(guó)家生態(tài)文明建設(shè)。

項(xiàng)目除在雅魯藏布沿江建立微波輻射計(jì)、自動(dòng)氣象站與邊界層站外，還在水汽輸送關(guān)鍵入口區(qū)墨脫、珠峰北側(cè)等設(shè)立雷達(dá)超級(jí)站，在墨脫及雅魯藏布江沿岸實(shí)施天—地—空一體化綜合觀測(cè)試驗(yàn)，填補(bǔ)了復(fù)雜河谷地形多尺度水汽輸送及云降水結(jié)構(gòu)特征綜合探測(cè)的空白；開展了云、降水粒子微物理特征分析研究，拓展了青藏高原天—地—空一體化的綜合觀測(cè)體系。為獲取中國(guó)東部地區(qū)災(zāi)害天氣上游“強(qiáng)信號(hào)”區(qū)青藏高原高時(shí)空分辨率的大氣溫度、濕度和水汽的垂直結(jié)構(gòu)信息。項(xiàng)目還設(shè)計(jì)和研制了基于車載平臺(tái)的氣象與環(huán)境三維結(jié)構(gòu)動(dòng)態(tài)探測(cè)系統(tǒng)，首次實(shí)施了青藏高原東南部氣象與環(huán)境三維結(jié)構(gòu)動(dòng)態(tài)探測(cè)試驗(yàn)，獲取了可靠的高時(shí)空分辨率溫濕度、水汽、氣溶膠等三維結(jié)構(gòu)動(dòng)態(tài)探測(cè)數(shù)據(jù)集。在歷史與現(xiàn)今氣象觀測(cè)站網(wǎng)數(shù)據(jù)、多類再分析與衛(wèi)星遙感產(chǎn)品大數(shù)據(jù)助力下，項(xiàng)目提出了亞洲水塔核心區(qū)熱力驅(qū)動(dòng)下高原區(qū)域與全球能量、水分循環(huán)“窗口效應(yīng)”綜合相關(guān)模型，揭示了青藏高原低云活動(dòng)、深對(duì)流對(duì)全球，尤其是南北極水汽輸送的重要作用；通過(guò)地面觀測(cè)站與和高分辨率衛(wèi)星（TRMM）觀測(cè)相結(jié)合的方式，得到高原地區(qū)高分辨率降水資料，揭示了青藏高原大氣降水“補(bǔ)給”差異對(duì)高原南、北冰川消融速率影響。項(xiàng)目研究高原氣候變暖背景下凍土退化對(duì)生態(tài)及國(guó)家重大工程建設(shè)帶來(lái)的影響及其風(fēng)險(xiǎn)，并提交氣候變暖對(duì)青藏高原鐵路、公路路基穩(wěn)定性風(fēng)險(xiǎn)研究成果。此次科學(xué)考察拓展了多圈層多元信息觀測(cè)分析數(shù)據(jù)集，構(gòu)建了雅魯藏布江水循環(huán)三維結(jié)構(gòu)數(shù)據(jù)集、衛(wèi)星遙感冰川面積數(shù)據(jù)集、墨脫雷達(dá)綜合觀測(cè)數(shù)據(jù)集、珠峰雷達(dá)綜合觀測(cè)數(shù)據(jù)集、高原湖泊數(shù)據(jù)集等9個(gè)數(shù)據(jù)集。數(shù)據(jù)及研究結(jié)果應(yīng)用到數(shù)值天氣預(yù)領(lǐng)域，發(fā)展了川藏鐵路敏感區(qū)數(shù)值模式追蹤技術(shù)，建立了川藏鐵路工程區(qū)天氣雷達(dá)資料同化預(yù)報(bào)系統(tǒng)；搭建了夾卷混合機(jī)制的參數(shù)化方案，改進(jìn)了中尺度天氣預(yù)報(bào)模式（WRF）中Mirrison微物理方案，為有效解決模式預(yù)報(bào)高原降水高估問(wèn)題提供技術(shù)支撐；開展了高原地區(qū)衛(wèi)星協(xié)同多元觀測(cè)的融合技術(shù)研究，并實(shí)施了我國(guó)風(fēng)云4號(hào)氣象衛(wèi)星AGRI和LMI資料協(xié)同地面、雷達(dá)數(shù)據(jù)的三維大氣和三維云融合技術(shù)研究。（徐祥德，張勝軍）

2.2 A new inverse modeling approach for emission sources based on the DDM-3D and 3DVAR techniques: An application to air quality forecasts in the Beijing-Tianjin-Hebei region

We develop a new inversion method which is suitable for linear and nonlinear emission source (ES)modeling, based on the three-dimensional decoupled direct (DDM-3D) sensitivity analysis module in the community multiscale air quality (CMAQ) model and the three-dimensional variational (3DVAR) data assimilation technique. We established the explicit observation operator matrix between the ES and receptor concentrations and the background error covariance (BEC) matrix of the ES, which can reflect the impacts of uncertainties of the ES on assimilation. Then we constructed the inversion model of the ES by combining the sensitivity analysis with 3DVAR techniques. We performed the simulation experiment using the inversion model for a heavy haze case study in the Beijing-Tianjin-Hebei (BTH) region during 27?30 December 2016.Results show that the spatial distribution of sensitivities of SO2and NOxESs to their concentrations, as well as the BEC matrix of ES, is reasonable. Using a posteriori inversed ES, underestimations of SO2and NO2during the heavy haze period are remarkably improved, especially for NO2. Spatial distributions of SO2and NO2concentrations simulated by the constrained ES were more accurate compared with an apriori ES in the BTH region. The temporal variations in regionally averaged SO2, NO2, and O3modeled concentrations using a posteriori inversed ES are consistent with in situ observations at 45 stations over the BTH region, and simulation errors decrease significantly. These results are of great significance for studies on the formation mechanism of heavy haze, the reduction of uncertainties of the ES and its dynamic updating, and the provision of accurate virtual emission inventories for airquality forecasts and decision-making services for optimization control of air pollution. (Cheng Xinghong, Hao Zilong, Zang Zengliang)

2.3 Development of three-dimensional variational data assimilation method of aerosol for the CMAQ model: An application for PM2.5 and PM10 forecasts in the Sichuan Basin

A three-dimensional variational (3DVAR) data assimilation method for the aerosol variables of the community multiscale air quality (CMAQ) model was developed. This 3DVAR system uses PM2.5and PM2.5-10(the difference between PM10and PM2.5) as control variables and uses the AERO6 aerosol chemical mechanism in the CMAQ model. Two parallel experiments, one with and one without data assimilation (DA), were performed to evaluate the assimilating effects of surface PM2.5and PM10during a heavy haze episode from 13 to 16 January, 2018 in the Sichuan Basin (SCB) region. The results show that simulations without DA clearly underestimated PM2.5and PM10concentrations, and the analysis field with aerosol DA is skillful at fitting the observations and effectively improving subsequent forecasts of PM2.5and PM10. For the analysis fields of PM2.5and PM10after DA comparing with those without DA, the correlation coefficient (CORR) of PM2.5and PM10increased by 0.59 and 0.65, the bias (BIAS) increased by 82.29 and 125.41 μg m?3, and the root mean square error (RMSE) declined by 73.69 and 116.30 μg m?3, respectively. Improvement of subsequent 24-h forecasts of PM2.5and PM10with DA is also significant. Statistical results of forecasting improvement with DA indicated that the CORR, BIAS, and RMSE for PM2.5and PM10at 78% and 89% of stations in the SCB region are improved, respectively. From the perspective of assimilation duration time, the improvement of PM2.5and PM10can be maintained for similar to 24 h. (Zhang Zhendong, Zang Zengliang, Cheng Xinghong)

2.4 How were the eastward-moving heavy rainfall events from the Tibetan Plateau to the lower reaches of the Yangtze River enhanced?

This study investigates eastward-moving summer heavy rainfall events in the lower reaches of the Yangtze River (LRYR), which are associated with the Tibetan Plateau (TP) vortices. On the basis of rainfall data from gauges and additional atmospheric data from ERA-Interim, the dynamic and thermodynamic effects of moisture transport and diabatic heating are estimated to determine the physical mechanisms that support the eastward-moving heavy rainfall events. As the rainband moves eastward, it is accompanied by anomalous cyclonic circulation in the upper and middle troposphere and enhanced vertical motion throughout the troposphere. In particular, the rainfall region is located in the fore of the upper-level trough, which is ideal for baroclinic organization of the convective system and further development of the eastward-moving vortex. The large atmospheric apparent heat source also contributes to lifting the lower-level air into the upper atmosphere and to enhancing the low-level convective motion and convergence during the heavy rainfall process. Piecewise potential vorticity inversion further verifies the crucial role that the diabatic heating played in developing the anomalous geopotential height favorable for the enhanced rainfall. The combined action of the dynamic and thermodynamic processes, as well as the rich moisture supply from the seas, synergistically sustained and enhanced the eastward-moving rainfall. (Zhao Yang, Chen Deliang, Deng Yi)

2.5 Intensified moisture sources of heavy precipitation events contributed to interannual trend in precipitation over the Three-Rivers-Headwater region in China

Evidence has indicated an overall wetting trend over the Three-Rivers Headwater region (TRHR) in the recent decades, whereas the possible mechanisms for this change remain unclear. Detecting the main moisture source regions of the water vapor and its increasing trend over this region could help understand the longterm precipitation change. Based on the gauge-based precipitation observation analysis, we find that the heavy precipitation events act as the main contributor to the interannual increasing trend of summer precipitation over the TRHR. A Lagrangian moisture tracking methodology is then utilized to identify the main moisture source of water vapor over the target region for the boreal summer period of 1980?2017, with focus particularly on exploring its change associated with the interannual trend of precipitation. On an average, the moisture sources for the target regions cover vast regions, including the west and northwest of the Tibetan Plateau by the westerlies, the southwest by the Indian summer monsoon, and the adjacent regions associated with the local recycling. However, the increased interannual precipitation trend over the TRHR could be largely attributed to the enhanced moisture sources from the neighboring northeastern areas of the targeted region, particularly associated with the heavy precipitation events. The increased water vapor transport from the neighboring areas of the TRHR potentially related to the enhanced local hydrological recycling over these regions plays a first leading role in the recent precipitation increase over the TRHR. (Zhao Ruiyu, Chen Bin, Xu Xiangde)

2.6 The key supply source of long-distance moisture transport for the extreme rainfall event on July 21, 2012 in Beijing

In this study, the weather research and forecasting (WRF) model and meteorological observation data were used to research the long-distance moisture transport supply source of the extreme rainfall event that occurred on July 21, 2012 in Beijing. Recording a maximum rainfall amount of 460 mm in 24 h, this rainstorm event had two dominant moisture transport channels. In the early stage of the rainstorm, the first channel comprised southwesterly monsoonal moisture from the Bay of Bengal (BOB) that was directly transported to North China along the eastern edge of Tibetan Plateau (TP) by orographic uplift. During the rainstorm,the southwesterly moisture transport was weakened by the transfer of Typhoon Vicente. Moreover, the southeasterly moisture transport between the typhoon and the western Pacific subtropical high (WPSH) became another dominant moisture transport channel. The moisture in the lower troposphere was mainly associated with the southeasterly moisture transport from the South China Sea and the East China Sea, and the moisture in the middle troposphere was mainly transported from the BOB and Indian Ocean. The control experiment well reproduced the distribution and intensity of rainfall and moisture transport. By comparing the control and three sensitivity experiments, we found that the moisture transported from Typhoon Vicente and a tropical cyclone in the BOB both significantly affected this extreme rainfall event. After Typhoon Vicente was removed in a sensitivity experiment, the maximum 24-h accumulated rainfall in North China was reduced by approximately 50% compared with that of the control experiment, while the rainfall after removing the tropical cyclone was reduced by 30%. When both the typhoon and tropical cyclone were removed, the southwesterly moisture transport was enhanced. Moreover, the sensitivity experiment of removing Typhoon Vicente also weakened the tropical cyclone in the BOB. Thus, the moisture pump driven by Typhoon Vicente played an important role in maintaining and strengthening the tropical cyclone in the BOB through its westerly airflow. Typhoon Vicente was not only the moisture transfer source for the southwesterly monsoonal moisture but also affected the tropical cyclone in the BOB, which was a key supply source of long-distance moisture transport for the extreme rainfall event on July 21, 2012 in Beijing. (Li Juan, Xu Xiang de, Li Yue qing)

2.7 Warm cover: Precursory strong signals for haze pollution hidden in the middle troposphere

Eastern China (EC), located in the downstream region of the Tibetan Plateau (TP), is a large area with frequent haze pollution. In addition to air pollutant emissions, meteorological conditions are a key inducement for air pollution episodes. Based on the study of the Great Smog of London in 1952 and haze pollution in EC over recent decades, it is found that the abnormal warm cover (air-temperature anomalies) in the middle troposphere, as a precursory strong signal, could be connected to severe air pollution events. The convection and vertical diffusion in the atmospheric boundary layer (ABL) were suppressed by a relatively stable structure of warm cover in the middle troposphere leading to ABL height decreases, which were favorable for the accumulation of air pollutants in the ambient atmosphere. The anomalous structure of the troposphere’s warm cover not only exists in heavy haze pollution on the daily scale, but also provides seasonal, interannual and interdecadal strong signals for frequently occurring regional haze pollution. It is revealed that a close relationship existed between interannual variations of the TP’s heat source and the warm cover strong signal in the middle troposphere over EC. The warming TP could lead to anomalous warm cover in the middle troposphere from the plateau to the downstream EC region and even the entire East Asian region, thus causing frequent winter haze pollution in EC region. (Xu Xiangde, Cai Wenyue, Zhao Tianliang)

2.8 南海臺(tái)風(fēng)生成前48 h環(huán)流特征及熱力與動(dòng)力條件

利用1979—2019年4—11月中國(guó)氣象局上海臺(tái)風(fēng)研究所熱帶氣旋最佳路徑資料和靜止衛(wèi)星紅外云圖資料，篩選出189例南海臺(tái)風(fēng)，結(jié)合歐洲中期天氣預(yù)報(bào)中心1°×1°再分析資料，分析南海臺(tái)風(fēng)生成前48 h至生成時(shí)刻的天氣環(huán)流和動(dòng)力、熱力條件。結(jié)果表明：南海臺(tái)風(fēng)生成于熱帶洋面大范圍的高海表溫度、高水汽含量和高不穩(wěn)定層結(jié)區(qū)，其生成前的主要環(huán)境背景環(huán)流是赤道輻合帶、西南季風(fēng)或東風(fēng)波等；臺(tái)風(fēng)生成前擾動(dòng)中心常常處于其北側(cè)風(fēng)切變小而南側(cè)風(fēng)切變大的過(guò)渡帶中，少數(shù)擾動(dòng)中心傾向于風(fēng)切變小值中心附近，風(fēng)切變與擾動(dòng)的發(fā)展之間無(wú)顯著相關(guān)；擾動(dòng)中心一般與垂直渦度中心重合，垂直渦度中心是表征擾動(dòng)自身強(qiáng)弱的物理量，但垂直渦度自身的大小與未來(lái)擾動(dòng)發(fā)展趨勢(shì)關(guān)系不明顯，而Okubo-Weiss（OW）指數(shù)則對(duì)于擾動(dòng)的發(fā)展以及擾動(dòng)位置確定有較好的指示意義；在擾動(dòng)發(fā)展過(guò)程中，擾動(dòng)中心附近存在一個(gè)貫穿整個(gè)對(duì)流層的位渦柱，低層擾動(dòng)部分與位渦柱中的中低層位渦相互作用，有利于擾動(dòng)發(fā)展。（高拴柱，張勝軍，呂心艷）

3 暴雨和強(qiáng)對(duì)流研究

3 Research on heavy rainfall and strong convection

3.1 A double-moment SBU-YLIN cloud microphysics scheme and its impact on a squall line simulation

A double-moment version of the SBU-YLIN cloud microphysical scheme in WRF is introduced. It predicts the mass and number mixing ratios of cloud droplets, rains, cloud ice, and precipitating ice. In addition, a number of physical processes, like rain evaporation, collection between rain and snow are also optimized in the new scheme. The scheme is evaluated and compared with the original one-moment scheme for a squall line case. We found that the double-moment approach gives a better representation of rain evaporation,which is critical for the development, morphology, and evolution of the simulated squall line, especially for the enhanced trailing stratiform cloud and leading convective line. The relationship between key microphysical processes and squall line dynamics is investigated to identify the driving mechanisms of the descending rear inflow, cold pool, and slantwise updraft. Furthermore, formation of the transition zone in the simulated squall line strongly depends on the flexible description of ice particle properties, such as size, degree of riming and fall speed. (Zhao Xi, Lin Yanluan, Luo Yali)

3.2 A study of the fraction of warm rainfall in a pre-summer rain event over South China

The precipitation is divided into the warm-rain and cold-rain processes according to the microphysical mechanism, but which processes are more important in a heavy precipitation even? An approach that quantitatively separates the warm-rain from total-rain processes is proposed by adding a set of new variables in microphysics schemes of the Weather Research and Forecasting model. The fraction of rainfall that formed by warm-rain processes and the related microphysical characteristic are investigated by a heavy precipitation event in South China on 9 May 2016. The simulation using the Thompson microphysics reasonably reproduces the spatial distribution of precipitation and temporal evolution of rain bands. It is found that when the composite reflectivity is between 25 and 35 dBz, the lowest percentage of warm-rain fraction occurs (median of 20%?30%). While in the strong precipitation area, the contribution of warm-rain steadily increases with the median of ?50% due to the continuous moisture supply. The similar characteristics by two other microphysics schemes (Morrison and CAMS) further verify the results. In addition, abundant supercooled water exists above the 0 level due to the high condensation rate. The strong updrafts in lower-middle layers are closely associated with the areas of water vapor condensation, implying that the phase-change processes should be responsible for the small-scale buoyancy production. The budget of rain water shows that the warmrain processes play a leading role in the initiating stage of convection, and the weak advection of rain water indicates that the transport of cloud body from surroundings to the precipitation area is quite limited. (Gao Wenhua, Xue Lulin, Liu Liping)

3.3 Analysis of a record-breaking rainfall event associated with a monsoon coastal megacity of South China using multisource data

Monsoon coastal cities often suffer from extreme rain-induced flooding and severe hazard. However, the associated physical mechanisms and detailed storm structures are poorly understood due to the lack of highresolution data. This study presents an analysis of a thunderstorm that produces extreme hourly rainfall (EXHR)of 219 mm over the Guangzhou megacity on the southern coast of China using integrated multiplatform observations and a four-dimensional variational Doppler radar analysis system. Results indicate that weak environmental flows and convectively generated weak cold pool facilitate the formation of a quasi-stationary storm, while onshore warm and moist flows in the boundary layer (BL) provide the needed moisture supply.The 219-mm EXHR is attendant by a shallow meso-gamma-scale vortex due to stretching of intense latent heating-induced convergence, which, in turn, helps organize convective updrafts into its core region. Lightning and dual-polarization radar observations reveal active warm-rain (but weak mixed-phase) microphysical processes, with raindrop size distribution (RSD) closer to marine convection. In contrast, another storm develops about 4 h earlier and only 35 km to the northwest, but with more lightning, higher cloud tops, more graupels, higher supercooled liquid water content and continental RSD, little evidence of rotation, and much less rainfall. They are attributable to the presence of larger convective available potential energy resulting from the urban heat island effects and less moisture supply in the BL. These results highlight the importance of using multisource remote sensing data sets in understanding the microphysical and kinematic structures of EXHRproducing storms. (Li Mingxin, Luo Yali, Zhang Da-Lin)

3.4 Atmospheric-boundary-layer-height variation over mountainous and urban sites in Beijing as derived from radar wind-profiler measurements

The evolution of the atmospheric boundary layer (ABL) varies greatly with terrain, so that the spatial and temporal variabilities of the ABL height remain poorly understood over complex terrain. Using radar wind-profiler measurements obtained from rural mountainous (Yanqing) and adjoining urban-plain (Haidian)landscapes of Beijing, China in 2019, ABL heights are calculated based on a normalized signal-to-noise-ratio threshold. The seasonally contrasting features of ABL height variation and growth rate over the two sites are revealed for clear-sky conditions. Interestingly, the ABL in spring remains suppressed during the morning and evolves rapidly in the afternoon over Haidian; however, a usual diurnal ABL evolution is observed over Yanqing. During the winter, more rapid evolution of the ABL is observed over Haidian, although on average the daytime ABL height remains less than 800 m above ground level. The growth rate of ABL height is found to undergo a more pronounced seasonal variation over Haidian while being relatively less variable over Yanqing. As expected, the lowest (highest) growth rate of 90 m h?1(188 m h?1) occurs in winter (summer) over Haidian. The analysis of the seasonal variations in wind profiles reveals deeper insights into the development of the local plain-to-mountain flow circulation over the region and possible implications on the contrasting seasonal ABL variations, particularly during the spring and summer. Additionally, the slower ABL evolution over Haidian in autumn and winter could be associated with an aerosol-induced stable ABL as well as stronger urban heat accumulation. The findings have implications for the better understanding of air pollution meteorology in regions with mountainous terrain. (Solanki Raman, Guo Jianping, Li Jian)

3.5 On the anomalous development of a series of heavy rainfall events from central to northern China during 19?21 July 2016

This study examines the development of a series of heavy rainfall events over four different geographical regions from the central to northern China on 19?21 July 2016, with the maximum 48-h-accumulated and hourly rainfall amounts of 875 and 139 mm, respectively. Results show that the heavy rainfall events occurred in an environment with an anomalous deep trough associated with unusual extratropical cyclogenesis during this warm month and a pronounced moisture anomaly compared to a 30-year climatology. The cyclogenesis coincided with dry-air intrusion from the lower stratosphere, and its merging with a northwest and a southwest vortex in the lower troposphere. After its formation, the cyclone moved northward on the east side of Mt.Taihang and then northeastward across Mt. Yanshan. The presence of the southwest vortex and an abnormally strong western Pacific subtropical high contributed to the maintenance and intensification of a southwesterly low-level jet (LLJ) carrying ample moisture, leading to the heavy rainfall in central China. The further enhanced southwesterly LLJ through the cyclogenesis and its accompanying southeasterly LLJ provided much needed precipitable water for the heavy rainfall events over North China. It was the quasi-geostrophic forcing of the extratropical cyclone, together with its cold/warm frontal systems, and especially its northward movement with the approaching airflows near-perpendicular to the general mountain orientations that provided optimized settings for the generation of a series of heavy rainfall events along the windward foothills of the major mountains in the northern China. (Xia Rudi, Zhang Da-Lin, Fu Shenming)

3.6 On the diurnal cycle of heavy rainfall over the Sichuan Basin during 10?18 August 2020

A sustained heavy rainfall event occurred over the Sichuan Basin in Southwest China during 10?18 August 2020, showing pronounced diurnal rainfall variations with nighttime peak and afternoon minimum values, except on the first day. Results show that the westward extension of the anomalously strong western Pacific subtropical high was conducive to the maintenance of a southerly low-level jet (LLJ) in and to the southeast of the basin, which favored continuous water vapor transport and abnormally high precipitable water in the basin. The diurnal cycle of rainfall over the basin was closely related to the periodic oscillation of the LLJ in both wind speed and direction that was caused by the combination of inertial oscillation and terrain thermal forcing. The nocturnally enhanced rainfall was produced by moist convection mostly initiated during the evening hours over the southwest part of the basin where high convective available potential energy with moister near-surface moist air was present. The convective initiation took place as cold air from either previous precipitating clouds from the western Sichuan Plateau or a larger-scale northerly flow met a warm and humid current from the south. It was the slantwise lifting of the warm, moist airflow above the cold air,often facilitated by southwest vortices and quasi-geostrophic ascent, that released the convective instability and produced heavy rainfall. (Xia Rudi, Luo Yali, Zhang Da-Lin)

3.7 On the localized extreme rainfall over the Great Bay Area in South China with complex topography and strong UHI effects

In this study, high-resolution surface and radar observations are used to analyze 24 localized extreme hourly rainfall (EXHR; > 60 mm h?1) events with strong urban heat island (UHI) effects over the Great Bay Area (GBA) in South China during the 2011?2016 warm seasons. Quasi-idealized, convection-permitting ensemble simulations driven by diurnally varying lateral boundary conditions, which are extracted from the composite global analysis of 3?5 June 2013, are then conducted with a multilayer urban canopy model to unravel the influences of the UHI and various surface properties nearby on the EXHR generation in a complex geographical environment with sea-land contrast, topography, and vegetation variation. Results show that EXHR is mostly distributed over the urban agglomeration and within about 40 km on its downwind side, and produced during the afternoon-to-evening hours by short-lived meso-γ- to meso-β-scale storms. On the EXHR days, the GBA is featured by a weak gradient environment with abundant moisture, and a weak southwesterly flow prevailing in the boundary layer (BL). The UHI effects lead to the development of a deep mixed layer with warm bubbles over the urban agglomeration, in which the lower-BL convergence and BL-top divergence is developed, assisting in convective initiation. Such urban BL processes and associated convective development with moisture supply by the synoptic low-level southwesterly flow are enhanced by orographically increased horizontal winds and sea breezes under the influence of the herringbone coastline, thereby increasing the inhomogeneity and intensity of rainfall production over the pi-shaped urban clusters. Vegetation variations are not found to be an important factor in determining the EXHR production over the region. (Sun Xiaoyan, Luo Yali, Gao Xiaoyu)

3.8 Spatiotemporal characteristics of atmospheric turbulence over China estimated using operational high-resolution soundings

Large-scale in situ observations are sorely lacking, leading to poor understanding of nationwide atmospheric turbulence over China. Nevertheless, high-resolution soundings have become available starting in 2011, providing a unique opportunity to investigate turbulence across China. Here, we calculated the mean turbulence dissipation rate from radiosonde measurements across China for the period 2011?2018 using the Thorpe analysis. The atmospheric layers that had stronger turbulence indicated by larger epsilon generally came with larger Thorpe length but with smaller Brunt-Vaisala frequency. Overall, the clear-air epsilon in the free atmosphere exhibited large spatial variability with a “south-high north-low” pattern. Large clear-air epsilon values were observed in both the lower stratosphere (LS) and upper troposphere (UT), especially over the Tibetan Plateau (TP) and its neighboring regions with complex terrain likely due to large-amplitude mountain waves. Particularly, less frequent but more intense clear-air turbulence was observed in both lower troposphere(LT) and UT over the TP, while more frequent, less intense clear-air turbulence was found in the northern China. The all-sky turbulence considering the moist-saturation effects was much stronger in the troposphere,notably in the southern China where convective clouds and precipitation of tentimes dominated. In the vertical direction, the altitude of peak clear-air epsilon in the troposphere was found to decrease poleward, broadly consistent with the meridional gradient of tropopause height in the Northern Hemisphere. A double-peak mode stood out for the profiles of clear-air epsilon at midlatitudes to the north of 30°N in winter: one peak was at altitudes of 15?18 km, and another at altitudes of 5?8 km. The strong shear instabilities around the westerly jet stream could account for the vertical bimodal structures. The seasonality of epsilon was also pronounced,reaching maxima in summer and minima in winter. Our results may help understand and avoid clear-air turbulence, as related to aviation safety among other issues. (Lyu Yanmin, Guo Jianping, Li Jian)

3.9 Technical note: First comparison of wind observations from ESA’s satellite mission Aeolus and ground-based radar wind profiler network of China

Aeolus is the first satellite mission to directly observe wind profile information on a global scale. After implementing a set of bias corrections, the Aeolus data products went public on 12 May 2020. However,Aeolus wind products over China have thus far not been evaluated extensively by ground-based remote sensing measurements. In this study, the Mie-cloudy and Rayleigh-clear wind products from Aeolus measurements are validated against wind observations from the radar wind profiler (RWP) network in China. Based on the position of each RWP site relative to the closest Aeolus ground tracks, three matchup categories are proposed,and comparisons between Aeolus wind products and RWP wind observations are performed for each category separately. The performance of Mie-cloudy wind products does not change much between the three matchup categories. On the other hand, for Rayleigh-clear and RWP wind products, categories 1 and 2 are found to have much smaller differences compared with category 3. This could be due to the RWP site being sufficiently approximate to the Aeolus ground track for categories 1 and 2. In the vertical, the Aeolus wind products are similar to the RWP wind observations, except for the Rayleigh-clear winds in the height range of 0?1 km.The mean absolute normalized differences between the Mie-cloudy (Rayleigh-clear) and the RWP wind components are 3.06 (5.45), 2.79 (4.81), and 3.32 (5.72) m/s at all orbit times and ascending and descending Aeolus orbit times, respectively. This indicates that the wind products for ascending orbits are slightly superior to those for descending orbits, and the observation time has a minor effect on the comparison. From the perspective of spatial differences, the Aeolus Mie-cloudy winds are consistent with RWP winds in most of East China, except in coastal areas where the Aeolus Rayleigh-clear winds are more reliable. Overall, the correlation coefficient R between the Mie-cloudy (Rayleigh-clear) wind and RWP wind component observation is 0.94(0.81), suggesting that Aeolus wind products are in good agreement with wind observations from the RWP network in China. The findings give us sufficient confidence in assimilating the newly released Aeolus wind products in operational weather forecasting in China. (Guo Jianping, Liu Boming, Gong Wei)

3.10 The impact of the observation data assimilation on atmospheric reanalyses over Tibetan Plateau and western Yunnan-Guizhou Plateau

Three modern atmospheric reanalyses with different input observation data (NOAA-CIRES 20th century reanalysis (20CR), Japanese 55-year reanalysis (JRA-55) and (JRA-55C) were compared against the independent radiosonde observations over the Tibetan Plateau (TP) and the western Yunnan-Guizhou Plateau(YGP) from the China-Japan Meteorological Disaster Reduction Cooperation (JICA/Tibet) Center Project in the summer of 2018 to investigate the effects of the assimilation of the observation data on the quality and accuracy of the reanalyses in the troposphere. The results indicate that the mean biases and mean root-meansquare errors of horizontal wind, temperature, and specific humidity significantly decreased when comparing the 20CR reanalysis (assimilating only surface pressure) to the JRA-55C (assimilating conventional surface and upper-air observations) and the JRA-55 (assimilating conventional and satellite observations), and the bias spreads of these aboveground variables in JRA-55C and JRA-55 were cut to almost half of those observed in 20CR. However, the mean biases and uncertainties varied little from JRA-55C to JRA-55. This means that the assimilation of conventional observation data plays a vital role in the quality of reanalyses for the troposphere over these data-sparse plateaus. It was also found that the temperature and specific humidity near the ground over TP showed larger mean biases and bias spans than those over YGP, likely due to the sparser surface observation over TP. (Bao Xinghua, Zhang Fuqing, Zhao Yang)

3.11 The significant role of radiosonde-measured cloud-base height in the estimation of cloud radiative forcing

The satellite-based quantification of cloud radiative forcing remains poorly understood, due largely to the limitation or uncertainties in characterizing cloud-base height (CBH). Here, we use the CBH data from radiosonde measurements over China in combination with the collocated cloud-top height (CTH) and cloud properties from MODIS/Aqua to quantify the impact of CBH on shortwave cloud radiative forcing (SWCRF).The climatological mean SWCRF at the surface (SWCRFSUR), at the top of the atmosphere (SWCRFTOA),and in the atmosphere (SWCRFATM) are estimated to be ?97.14, ?84.35, and 12.79 W m?2, respectively for the summers spanning 2010 to 2018 over China. To illustrate the role of the cloud base, we assume four scenarios according to vertical profile patterns of cloud optical depth (COD). Using the CTH and cloud properties from MODIS alone results in large uncertainties for the estimation of SWCRFATM, compared with those under scenarios that consider the CBH. Furthermore, the biases of the CERES estimation of SWCRFATM tend to increase in the presence of thick clouds with low CBH. Additionally, the discrepancy of SWCRFATM relative to that calculated without consideration of CBH varies according to the vertical profile of COD. When a uniform COD vertical profile is assumed, the largest SWCRF discrepancies occur during the early morning or late afternoon. By comparison, the two-point COD vertical distribution assumption has the largest uncertainties occurring at noon when the solar irradiation peaks. These findings justify the urgent need to consider the cloud vertical structures when calculating the SWCRF which is otherwise neglected. (Xu Hui, Guo Jianping, Li Jian)

3.12 The synoptic impacts on the convection initiation of a warm-sector heavy rainfall event over coastal South China prior to the monsoon onset: A numerical modeling study

A series of convection-permitting numerical experiments using the weather research and forecasting model with different model configurations are performed to investigate physical mechanisms governing convection initiation (CI) at the coast of South China (SC) during a warm-sector heavy rainfall event occurred before the South China Sea (SCS) monsoon onset. The simulation results are more sensitive to initial state from the different reanalysis products than the microphysics schemes, horizontal resolutions, initialization time, and lateral boundary conditions with the variation examined. It is found that the speeds of easterly to southeasterly winds in the boundary layer (BL) over the northern SCS determine the strength of horizontal convergence of the warm and moist airflows arriving at the coast. The midtropospheric divergence over the west coastal areas of SC and its southwest upstream impact vertical motion of the mid-to-lower tropospheric southwesterly airflows when approaching the coast. Differences in such features of upstream airflows in the experiments lead to distinct temporal evolutions of BL dynamic lifting and temperature stratification in the mid-to-lower levels at the CI location, and thus the level of free convection and convective available potential energy. The modeling evidence presented shows that the synoptic dynamic and thermodynamic characteristics of the upstream airflows in BL and mid-to-lower troposphere, with local modulation by the coastal mountains,play important roles in determining the time and location of CI, and the distribution and amount of rainfall.Studies on more cases are needed to gain more general and robust conclusions about physical mechanism governing the warm-sector coastal CI. (Bao Xinghua, Luo Yali, Gao Xiaoyu)

3.13 Typhoon disaster risk zoning for China’s coastal area

Previous studies on typhoon disaster risk zoning in China have focused on individual provinces or smallscale areas and lack county-level results. In this study, typhoon disaster risk zoning is conducted for China’s coastal area, based on data at the county level. Using precipitation and wind data for China and typhoon disaster and social data at the county level for China’s coastal area from 2004 to 2013, first we analyze the characteristics of typhoon disasters in China’s coastal area and then develop an intensity index of factors causing typhoon disasters and a comprehensive social vulnerability index. Finally, by combining the two indices, we obtain a comprehensive risk index for typhoon disasters and conduct risk zoning. The results show that the maximum intensity areas are mainly the most coastal areas of both Zhejiang and Guangdong,and parts of Hainan Island, which are similar to the distribution of typhoon disasters. The maximum values of vulnerability are in the northwest of Guangxi, parts of Fujian coastal areas and parts of the Shandong Peninsula. The comprehensive risk index generally decreases from coastal areas to inland areas. The high-risk areas are mainly distributed over Hainan Island, south-western Guangdong, most coastal Zhejiang, the coastal areas between Zhejiang and Fujian and parts of the Shandong Peninsula. (Zhu Jing, Lu Yi, Ren Fumin)

3.14 Vertical structures of temperature inversions and clouds derived from high-resolution radiosonde measurements at Ny-?lesund, Svalbard

The knowledge of the vertical atmospheric structures in the Arctic region remains elusive, due largely to sparse long-term continuous profiling observations. Based on the temporally high-resolution (1 s) radiosonde measurements from April 2017 to September 2019 collected at the Ny-?lesund (11.92°E, 78.92°N) station in the Arctic, we analyzed the characteristics of temperature inversion (TI) and clouds, including the diurnal and seasonal variabilities under different atmospheric circulations. Clouds mainly appear in the lower troposphere,with the largest contribution by double-layer clouds. The seasonal variation of vertical cloud distribution above 7 km seems closely linked to the seasonal variability of tropopause height. Besides, the diurnal variation of TI frequency exhibits significant seasonality, with a bimodal distribution in the vertical, with stronger TI intensity in summer. The lowest temperatures at the top of bottom of the elevated inversion are observed in winter,whereas the lowest temperature of the surface-based inversion top is observed in spring, which may be related to the seasonal variation of sea surface temperature. The characteristics of cloud and TI are further analyzed under the five typical circulation patterns. It is found that the low-pressure system and southerly wind in front of the trough are favorable for cloud formation in the lower troposphere, while the impact of synoptic pattern on clouds in the upper troposphere seems negligible, likely due to the cold environment. The TI associated with cyclone systems tends to be much thinner and weaker, owning to the conditionally unstable conditions.These findings provide key reference for the vertical structure of the inversion and cloud in the Arctic, which is expected to help improve cloud parameterization in numeric models. (Wang Ding, Guo Jianping, Xu Hui)

3.15 Vorticity and moisture budget analyses on a plateau vortex that cause an intense rainfall event within the Qaidam Basin

As one of the most seriously arid areas in China, the Qaidam Basin (QB) features a notable growing probability of intense rainfall under global warming. Compared to a normal/humid region, intense rainfall usually results in more severe disasters in an arid area. Considering that few studies focused on intense rainfall within the QB, there is an urgent need to understand the mechanisms governing intense rainfall in this region. A type of Tibetan Plateau vortex (TPV) associated intense rainfall within the QB was investigated in this study, which partly fills the existing research gaps in the field. The main findings are as follows: (a) The intense-rainfall-producing TPV formed and maintained in a favorable background environment which was characterized by a notable upper-level divergence north of a strong upper-level jet and a strong middle-level warm advection ahead of a shortwave trough over the Tibetan Plateau. (b) Vorticity budget indicates that two factors affected the vortex’s formation notably, one was the convergence-related vertical stretching, which dominated the vortex’s formation and the other was the import of the horizontal transport of anticyclonic vorticity which was the most detrimental factor for the formation of the TPV. Tilting and vertical transport only exerted weak effects on the TPV’s formation, since convective activities were relatively weak in this event.(c) Moisture budget shows that the southwestern and southern moisture transport channels, which were mainly driven by the wind field associated with the shortwave trough over the Tibetan Plateau, contributed similar to 70% to the total moisture income of the intense rainfall within the QB. The transport was accomplished primarily through the southern boundary of the QB, with the moisture mainly coming from the Indian Peninsula and Indochina Peninsula. (Li Wanli, Xia Rudi, Zhong Qi)

3.16 Warm-season mesoscale convective systems over eastern China: Convection-permitting climate model simulation and observation

Mesoscale convective systems (MCSs) are important warm-season precipitation systems in the eastern China. However, our knowledge of their climatology and capability in their simulation is still insufficient. This paper examines their characteristics over the 2008?2017 warm seasons using convection-permitting climate simulations (CPCSs) with a 3-km grid spacing that explicitly resolves MCSs, as well as a high-resolution gauge-satellite merged precipitation product. An object-based tracking algorithm is applied to identify MCSs.Results indicate that the MCS genesis and occurrence are closely related to the progression of the East Asian monsoon and are modulated by the underlying topography. On average, about 243 MCSs are observed each season and contribute 19% and 47% to total and extreme warm-season precipitation. The climatological attributes and variabilities are reasonably reproduced in the CPCS. The major model deficiencies are excessive small MCS occurrence and overmuch MCS rainfall, consequently overestimating the precipitation contributions, whereas observational uncertainties may play a role too. Both the observed and simulated MCS precipitation feature a nocturnal or morning maximum and an eastward delayed diurnal peak east of the Tibetan Plateau, in contrast to the dominant afternoon peak of non-MCS precipitation. The favorable comparison with observations demonstrates the capability of CPCSs in simulating MCSs in the Asian monsoon climate, and its usefulness in projecting the future changes of MCSs under global warming. The finding that non-MCS precipitation is responsible for the high biased afternoon precipitation provides helpful guidance for further model improvement. (Yun Yuxing, Liu Changhai, Luo Yali)

3.17 Contrasting effect of soil moisture on the daytime boundary layer under different thermodynamic conditions in summer over China

The investigation is still lacking concerning the effect of soil moisture (SM) on the evolution of planetary boundary layer (PBL) under different land conditions in a huge domain as large as China. We perform an explicit correlation analysis between daytime PBL height (PBLH) and SM for convective, neutral and stable boundary layer regimes (i.e., CBL, NBL, and SBL), respectively. A negative correlation exists between SM and daytime PBLH for CBL and NBL, exhibiting a spatial pattern of east strong west weak, albeit a positive correlation for SBL. The standard deviation of PBLH for CBL and NBL exhibits a spatial pattern of northwest high southeast low. Cloudy, humid, and stable atmosphere result in CBL shoaling. PBLH more correlates with the sensible heat flux (CBL: r=0.25; NBL: r=0.33) over dry areas, but over Northwest China the PBL depends more on meteorology likely owing to the extremely dry soil. The effect of SM on the evolution of PBL throughout China remains elusive. This study explores the correlation between PBLH and SM under different PBL regimes, using the 5-year record of high-resolution summertime soundings across China. The CBL and NBL heights during daytime are found to negatively correlate with SM. In contrast, the SBL height anticorrelates with SM, likely due to more fluid and moisture intermittent turbulence caused by enhanced SM in SBL. The spatial pattern of the standard deviation of CBL and NBL height exhibits a pronounced northwest high southeast low pattern. Our study also reveals more significant impact of sensible heat flux on CBL and NBL regimes over dry areas, compared to over wet areas, indicating that land surface processes are more coupled to the PBL evolution over dry areas. Besides, less cloud, dry and unstable atmosphere favor the development of CBL in wet areas, and PBLH is more dependent on meteorological quantities, but less on SM in dry areas, likely owing to extremely dry soil and bare land over Northwest China. (Xu Zhiqi, Chen Haishan,Guo Jianping)

3.18 Increased turbulence in the Eurasian upper-level jet stream in winter: Past and future

Anthropogenic activities have been increasingly strengthening the meridional temperature gradient in the upper atmosphere, which has a profound impact on the wind shear and turbulence in mid-latitudes. Here we examined the trends of the wintertime jet stream and clear-air turbulence at 250 hPa over the Eurasian.The zonal wind speed showed a significantly increasing trend in the region between 40°N and 60°N where the meridional temperature gradient between the equator and the pole was increasing sharply in the past 4 decades (1980?2019). In addition, there existed a clear trend toward stronger vertical shear at 250 hPa in the latitudinal zone between 30°N and 40°N where the zonal wind increased, while a declining trend was shown to the south of 30°N, according to three different reanalysis datasets, including ERA5, JRA55, and NCAR/NCEP,which may be related to the poleward shift of the subtropical jet stream. The turbulence, closely related to the occurrence of vertical wind shear, was found to become stronger in the latitudinal zone between 30°N and 40°N consequently. The projections based on phase 6 of Coupled Model Intercomparison Project models show that the zonal wind speed in the mid-latitudes will increase significantly for the period 2015?2100, especially between the latitudinal zone between 40°N and 60°N, and the corresponding vertical wind shear in this area tends to dramatically increase. The findings not only help us better understanding of turbulence occurrence in the past 40 years, but also have profound implications for the projection of turbulence occurrence under global warming over mid-latitude regions of the Northern Hemisphere. (Lyu Yanmin, Guo Jianping, Li Jian)

3.19 Investigation of near-global daytime boundary layer height using high-resolution radiosondes:First results and comparison with ERA5, MERRA-2, JRA-55, and NCEP-2 reanalyses

The planetary boundary layer (PBL) governs the vertical transport of mass, momentum, and moisture between the surface and the free atmosphere, and thus the determination of PBL height (BLH) is recognized as crucial for air quality, weather, and climate analysis. Although reanalysis products can provide important insight into the global view of BLH in a seamless way, the BLH observed in situ on a global scale remains poorly understood due to the lack of high-resolution (1 or 2 s) radiosonde measurements. The present study attempts to establish a near-global BLH climatology at synoptic times (00:00 and 12:00 UTC) and in the daytime using high-resolution radiosonde measurements over 300 radiosonde sites worldwide for the period from 2012 to 2019, which is then compared against the BLHs obtained from four reanalysis datasets, including ERA5, MERRA-2, JRA-55, and NCEP-2. The variations in daytime BLH exhibit large spatial and temporal dependence, and as a result the BLH maxima are generally discerned over the regions such as the western United States and western China, in which the balloon launch times mostly correspond to the afternoon.The diurnal variations in BLH are revealed with a peak at 17:00 local solar time (LST). The most promising reanalysis product is ERA5, which underestimates BLH by around 130 m as compared to radiosondes released during daytime. In addition, MERRA-2 is a well-established product and has an underestimation of around 160 m. JRA-55 and NCEP-2 might produce considerable additional uncertainties, with a much larger underestimation of up to 400 m. The largest bias in the reanalysis data appears over the western United States and western China, and it might be attributed to the maximal BLH in the afternoon when the PBL has risen. Statistical analyses further indicate that the biases of reanalysis BLH products are positively associated with orographic complexity, as well as the occurrence of static instability. To our best knowledge, this study presents the first near-global view of high-resolution radiosonde-derived boundary layer height and provides a quantitative assessment of the four frequently used reanalysis products. (Guo Jianping, Zhang Jian, Yang Kun)

3.20 Large-scale pattern of the wintertime diurnal temperature range variations over North America during 1979?2018

The atmospheric circulation and remote forcing of SST anomalies play an imporant role in the formation of largescale cloud cover and precipitation anomalies as well as the patterns of diurnal temperature range (DTR)variability. In this study, the dominant patterns of the wintertime DTR variations over North America (NA) and the underlying mechnisms are investigated based on observational and reanalysis datasets during 1979?2018.The first leading mode is characterized by a widespread same-sign loading in the majority of NA. The corresponding principal component (PC) shows an obvious interannual time-scale variations. The second mode displays a north-south dipole-like pattern in the NA and the corresponding PC exhibits a decline trend during 1979?2018. Both patterns of DTR variations are closely associated with the changes in local cloud cover and precipitation. Furthermore, clear effects are identified of El Ni?o-southern oscillation (ENSO) and Tropical/Northern Hemisphere (TNH) teleconnection on the formation of the two dominant patterns of wintertime DTR variabilty over NA through changing the atmospheric circulation and associated transportation of temperature and moisture. Our findings provide a new insight into understanding the DTR changes during recent decades.(Liu Lin, Chen Wen, Guo Jianping)

3.21 Regional variability of summertime raindrop size distribution from a network of disdrometers in Beijing

Regional raindrop size distribution (DSD) features are poorly understood due to the lack of observations.Here we investigate the regional variability of summertime DSD in Beijing, using the DSD observations from ten disdrometer sites from April to September 2017. The characteristics of DSD are analyzed for both convective and stratiform precipitation, mainly classified by rain rate (R). The shape (μ) and slope (λ)parameters follow a second-degree polynomial regression relationship for both stratiform and convective precipitation. On average, stratiform precipitation is found to have larger values of μ and λ than convective precipitation, whereas convective precipitation has a larger mass-weighted mean diameter (Dm) and a generalized intercept parameter (Nw). Interestingly, the north of Beijing has larger values of μ and λ, as opposed to Dmand Nwthat exhibit greater values in the south, which could probably be attributed to terrain differences.The rain rate dependence on DSD is analyzed as well. In general, the Dm-R and Nw-R relationships follow a power-law distribution, and both Dmand Nwincrease significantly with R. As the rain rate increases, Dmkeeps increasing to around 1.5 mm until an equilibrium state is reached. The findings obtained here could provide useful reference for better estimations of rainfall using the remote sensing techniques. (Han Yi, Guo Jianping,Yun Yuxing)

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

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

3.23 Assessing the surface-layer stability over China using long-term wind-tower network observations

Surface-layer stability is important in many processes, such as in the surface energy budget, atmospheric pollution, and boundary-layer parametrizations. Most previous studies on stability, however, conducted either theoretical or observational investigations at specific sites, thus leaving a gap with regard to the large-scale pattern. Here, wind-speed and temperature observations at multiple heights from the wind-tower network of China are used to estimate low-level stability during the 2009?2016 period. A series of data-quality-control procedures are conducted and data from 170 wind towers with more than 2 years of valid observations are selected. The degree of stability is classified by the Obukhov length, which is derived from the wind speed and temperature at 10 m and 70 m above ground level, combined with information regarding the roughness length. Overall, the occurrence frequency of surface-layer instability exhibits significant temporal and spatial variability, being particularly larger in spring and summer than in autumn and winter. The maximum frequency of summertime instability occurs in the time period 1000?1200 local solar time, approximately 2 h earlier than in autumn. Geographically, the peak instability frequency occurs much earlier in the day in Northwest China than in other regions, likely owing to the arid and semi-arid land cover. Also noteworthy is the steady increase in instability frequency observed during the period analyzed here, likely resulting from the reduction in the vertical gradient of wind speed. Our findings call for explicit consideration of stability variability in the windenergy industry and in fundamental boundary-layer investigations in China. (Li Jian, Guo Jianping, Xu Hui)

3.24 Study of the formation of the Arctic cell associated with the two-wave middle-high latitude circulation

The formation of the Arctic cell associated with the two-wave middle-high latitude circulation, which is a major atmospheric circulation common to the three-cell and four-cell mean meridional circulations in the Northern Hemisphere, is analyzed using a long period of reanalysis data. In the context of the two-wave middle-high latitude circulation, when the high near the Arctic region from 120°E to 80°W (AH120E80W)weakens and withdraws eastward and the low near the Arctic region from 80°W to 120°E (AL80W120E)strengthens and expands northeastward, the Arctic tends to be controlled by obvious low pressure and associated upward motion, leading to the formation of the Arctic cell. The eastward withdrawal of the AH120E80W is attributed to an eastward retreat of the North Pacific Low, because it promotes the strong anticyclonic wind shear associated with the maintenance of the AH120E80W to migrate eastward. The eastward retreat of the North Pacific Low is induced by the decrease in the width of the East Asian Trough,which results from the response of the high terrain in Central Asia to the weakening of middle-latitude westerly winds caused by a northward shift of the Azores high. On the other hand, the eastward withdrawal of the AH120E80W results in the decay of the Arctic high, causing the winds near the Arctic to change from easterly to westerly. At the same time, the northward shift of the Azores high promotes the strong Icelandic Low to expand poleward. The combination of the Arctic westerly winds and the poleward expansion of the strong Icelandic Low leads to the northeastward expansion of the AL80W120E. (Liang Zhaoming, Gao Shouting)

3.25 A dynamical and numerical study of the effects of the topography of the Tibetan Plateau and westerly wind speed on the East Asian Trough

The effects of the topography of the Tibetan Plateau (TP) and westerly wind speed on the East Asian Trough (EAT) are discussed with analysis using a dynamical model, and verified with numerical experiments based on real cases. The dynamical model utilizes a complex terrain function to approximate the TP topography, and derives a stream function generated by the TP terrain. The numerical experiments used for the verification consider the influence of different TP terrain heights and westerly wind speeds. The results show that the topography of the TP has a prominent contribution to the intensity of the EAT, but little effect on its position. The topography of the TP in the westerly winds causes a low-pressure trough to its east, which promotes a deepening of the EAT to the east side of the TP. In contrast, in the context of the TP, westerly wind speed has an important influence on the position of the EAT, but a minor impact on the deepening of the EAT. A larger westerly wind speed causes a more eastern position of the EAT. These findings indicate that the combination of large-scale topography and westerly wind speed plays a key role in the evolution of the EAT, in the terms of intensity and position. (Liang Zhaoming, Xu Pengcheng, Gao Shouting, Zuo Qunjie)

3.26 Organized warm-sector rainfall in the coastal region of South China in an anticyclone synoptic situation: Observational analysis

Organized warm-sector rainfall (OWSR) near the coast of South China tends to occur in certain synoptic situations characterized with either a low-level jet or an anticyclone, with the latter being less investigated.This paper fills the gap by analyzing 15 OWSR events that occurred in an anticyclone synoptic situation during the pre-summer rainy season of 2011–2016, based on high-resolution observational and reanalysis data. The results show that the anticyclone synoptic situation produces marked northerly boundary-layer winds inland and obvious northeasterly, easterly/southwesterly, and southeasterly boundary-layer winds near the coasts of the eastern Guangdong, western Guangdong, and Guangxi, respectively. The coastal boundary-layer winds promote favorable environmental conditions and strong convergence for convection initiation; consequently,OWSR is prone to occur near the coasts of the western Guangdong and Guangxi, but exhibits different formation and propagation features in the following two subareas. (1) The southeasterly boundary-layer winds tend to converge near the border area between Guangxi and Guangdong (BGG), promoting the formation of a stable convective line along the mountains. The convective line persists with support of upper-level southwesterly winds that facilitate convective cells to propagate along the convective line, producing heavy OWSR along the mountains near BGG. (2) In contrast, a west-east convective line tends to form and maintain near the coast of Yangjiang (YJ) area, about 200 km east of BGG, owing to stable convergence between the easterly (or southwesterly) and the northerly boundary-layer winds reinforced by the mountains near YJ.Moreover, the coupling of upper-level westerly winds with the easterly (southwesterly) boundary-layer winds facilitates expansion (eastward propagation) of the convective line, causing west–east-oriented heavy OWSR near the coast of YJ. In a word, this study reveals refined properties of OWSR initiation and development in the anticyclone synoptic situation, which may help improve the forecast skill of OWSR during the pre-summer rainy season in South China. (Liang Zhaoming, Gao Shouting)

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

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

3.28 北京地區(qū)一次颮線的組織化過(guò)程及熱動(dòng)力結(jié)構(gòu)特征

2015年8月7日華北西北部的一次斷線狀對(duì)流系統(tǒng)向東南方向移動(dòng)，并與平原地區(qū)多單體雷暴合并、組織，最終形成強(qiáng)颮線，造成北京地區(qū)出現(xiàn)較大范圍的風(fēng)雹和局地短時(shí)強(qiáng)降水天氣?；诙嘣促Y料的研究結(jié)果表明：（1）颮線形成有上游線狀對(duì)流發(fā)展移動(dòng)、平原多個(gè)單體雷暴的新生和合并、線狀對(duì)流并入本地多單體后組織成颮線3個(gè)階段。第2階段中，城區(qū)北部邊緣地面熱力分布不均，配合局地風(fēng)場(chǎng)輻合，觸發(fā)了雷暴。雷暴冷池范圍不斷擴(kuò)大，溫度梯度區(qū)向南擴(kuò)展，造成新生對(duì)流向南傳播。（2）颮線的組織化過(guò)程，呈現(xiàn)出兩支強(qiáng)入流為典型特征的動(dòng)力結(jié)構(gòu)：一支位于雷暴冷池后側(cè)中層（4500～5000 m），另一支位于低層颮線前側(cè)，由強(qiáng)輻合區(qū)垂直于颮線指向云內(nèi)。這兩支強(qiáng)入流分別構(gòu)成颮線前側(cè)和后側(cè)兩個(gè)獨(dú)立的順時(shí)針垂直環(huán)流圈。后側(cè)入流和前側(cè)入流在同時(shí)加強(qiáng)，造成颮線前側(cè)垂直環(huán)流不斷加強(qiáng)，與之對(duì)應(yīng)的環(huán)境垂直風(fēng)切變也同步增強(qiáng)。這一動(dòng)力過(guò)程形成了有利于颮線組織化的中尺度垂直切變環(huán)境，垂直風(fēng)切變?cè)龃蟮谋举|(zhì)實(shí)際上是颮線發(fā)展反饋的結(jié)果，同時(shí)也是驅(qū)動(dòng)颮線快速向前移動(dòng)和發(fā)展的重要因素。當(dāng)后側(cè)中層入流消失，前側(cè)垂直環(huán)流也隨之逐漸減弱，預(yù)示著颮線從成熟開始減弱消亡。（3）從熱力結(jié)構(gòu)看，下山的線狀對(duì)流冷池與平原地區(qū)多單體雷暴的冷池合并，形成了擾動(dòng)溫度低于-8 、厚度加深到1.5 km的強(qiáng)冷池，其前沿的β中尺度鋒面附近的輻合上升運(yùn)動(dòng)加強(qiáng)，進(jìn)一步促進(jìn)了颮線在平原地區(qū)發(fā)展加強(qiáng)，并出現(xiàn)陣風(fēng)鋒。（雷蕾，孫繼松，陳明軒）

3.29 強(qiáng)臺(tái)風(fēng)“菲特”（1323）極端降水研究進(jìn)展

臺(tái)風(fēng)暴雨災(zāi)害是臺(tái)風(fēng)三類災(zāi)害（暴雨、大風(fēng)、風(fēng)暴潮）之首，而臺(tái)風(fēng)極端降水是暴雨災(zāi)害的直接原因，對(duì)臺(tái)風(fēng)極端降水的研究有利于增強(qiáng)對(duì)臺(tái)風(fēng)極端降水機(jī)理的認(rèn)識(shí)和提高極端降水的預(yù)報(bào)水平。強(qiáng)臺(tái)風(fēng)“菲特”（1323）具有登陸強(qiáng)度歷史罕見、降雨強(qiáng)度大、影響范圍廣、引發(fā)災(zāi)害重等特點(diǎn)，本文對(duì)“菲特”極端降水特征及其形成機(jī)理研究進(jìn)行了回顧和總結(jié)。“菲特”的強(qiáng)降水過(guò)程主要分為兩個(gè)階段，造成了杭州灣一帶和浙閩交界處兩個(gè)強(qiáng)降水中心?！胺铺亍睒O端降水的產(chǎn)生主要源于環(huán)境因子、地形和內(nèi)部條件多尺度相互作用：環(huán)境因子涉及雙臺(tái)風(fēng)作用、弱冷空氣侵入、臺(tái)風(fēng)倒槽、垂直風(fēng)切變和高空急流等，其中“丹娜絲”臺(tái)風(fēng)外圍偏東氣流源源不斷的水汽輸送是“菲特”極端降水形成的關(guān)鍵物理因子；山脈等地形增幅作用是浙江余姚等地出現(xiàn)歷史性強(qiáng)降水的重要原因；水汽輻合和凝結(jié)與霰的融化和對(duì)流區(qū)雨滴的遷移是暴雨增幅重要的內(nèi)部因素。（秦思，姚美，任福民）

3.30 山東半島海風(fēng)鋒在一次颮線系統(tǒng)演變過(guò)程中的作用

2016年6月30日生成于華北南部的一次長(zhǎng)生命期的強(qiáng)颮線過(guò)程，造成了山東地區(qū)大范圍風(fēng)雹天氣。文中利用常規(guī)觀測(cè)資料、區(qū)域自動(dòng)氣象站觀測(cè)數(shù)據(jù)及雷達(dá)監(jiān)測(cè)產(chǎn)品，分析了山東半島復(fù)雜的海風(fēng)鋒特征在這次颮線系統(tǒng)的斷裂、再組織化以及極端大風(fēng)、冰雹災(zāi)害形成過(guò)程中的重要作用。結(jié)果表明：（1）初始對(duì)流是在地面冷鋒輻合線上觸發(fā)的弱對(duì)流，在對(duì)流系統(tǒng)向更不穩(wěn)定區(qū)域移動(dòng)時(shí)與水平對(duì)流卷相交，對(duì)流迅速發(fā)展，并組織成東西走向的直線型颮線。（2）颮線系統(tǒng)在平原地區(qū)繼續(xù)向前移動(dòng)的過(guò)程中發(fā)生斷裂，這一過(guò)程與渤海灣在黃河三角洲形成的兩條移動(dòng)方向不同的海風(fēng)鋒以及颮線系統(tǒng)的陣風(fēng)鋒有關(guān)：向內(nèi)陸推進(jìn)的兩條海風(fēng)鋒與陣風(fēng)鋒在颮線系統(tǒng)中段的前部相交，誘發(fā)新生單體，造成該處對(duì)流系統(tǒng)更快地向前傳播，最終導(dǎo)致颮線系統(tǒng)斷裂;與此同時(shí)，斷裂后的西段風(fēng)暴因低層暖濕入流被切斷而逐漸減弱。（3）斷裂后西段殘留風(fēng)暴系統(tǒng)出流陣風(fēng)產(chǎn)生的新生風(fēng)暴向東北方向發(fā)展，與斷裂后的東段風(fēng)暴的后向傳播（向西南方向發(fā)展）機(jī)制相互作用，完成了颮線的再次組織化，形成了具有典型弓狀特征、水平尺度更大、近似于東北—西南走向的颮線系統(tǒng)。（4）長(zhǎng)生命期颮線系統(tǒng)造成的極端雷暴大風(fēng)和最大冰雹出現(xiàn)在颮線再組織化初期，位于颮線系統(tǒng)“弓部”位置，地面極端雷暴大風(fēng)是冷池密度流、后側(cè)入流急流和水成物對(duì)應(yīng)的前側(cè)下沉氣流共同作用的結(jié)果，其中與后側(cè)入流急流幾乎完全分離的、與水成物對(duì)應(yīng)的前側(cè)下沉氣流在這次極端地面大風(fēng)發(fā)生時(shí)可能起到了重要作用。（5）山東半島東側(cè)的黃海海風(fēng)鋒向內(nèi)陸推進(jìn)（東南向西北）過(guò)程中與自西北向東南移動(dòng)的颮線相遇，加強(qiáng)了風(fēng)暴前側(cè)的抬升、水汽供給和組織化程度，為颮線的長(zhǎng)時(shí)間維持提供了有利條件。（萬(wàn)夫敬，孫繼松，孫敏）

3.31 中小尺度對(duì)流系統(tǒng)的高分辨率數(shù)值模擬近況和未來(lái)挑戰(zhàn)

隨著高速、大容量、并行計(jì)算能力的迅速增長(zhǎng)和中尺度數(shù)值模式的不斷完善，近年來(lái)不斷涌現(xiàn)使用1 km乃至次千米網(wǎng)格距開展中、小尺度對(duì)流系統(tǒng)的數(shù)值模擬研究。這些數(shù)值模擬工作展現(xiàn)出目前觀測(cè)手段還無(wú)法得到的動(dòng)力學(xué)一致的高分辨率氣象信息，大大提高了對(duì)一些中、小尺度對(duì)流系統(tǒng)內(nèi)部結(jié)構(gòu)和演變的理解。但高分辨率數(shù)值模擬的未來(lái)發(fā)展也面臨著不少問(wèn)題和挑戰(zhàn)。本研究回顧了提高模式分辨率至1 km乃至次千米模擬中、小尺度對(duì)流系統(tǒng)的進(jìn)展，并綜述目前在高分辨率數(shù)值模擬中的資料同化和物理過(guò)程處理方法，同時(shí)指出中尺度模式中處理積云對(duì)流、大氣邊界層和輻射過(guò)程時(shí)值得注意的分辨率“灰色區(qū)”，介紹使用1 km和次千米分辨率模擬中、小尺度對(duì)流系統(tǒng)的幾篇有代表性的工作，最后討論了高分辨率數(shù)值模擬的未來(lái)發(fā)展和挑戰(zhàn)。（黎慧琦，張大林）

4 臺(tái)風(fēng)研究

4 Typhoon research

4.1 臺(tái)風(fēng)快速更新短臨預(yù)報(bào)系統(tǒng)TRANS v1.0業(yè)務(wù)運(yùn)行

聚焦影響我國(guó)臺(tái)風(fēng)的風(fēng)雨短臨預(yù)報(bào)，集成 “隨流型而變”的集合卡爾曼濾波同化方案、空間均勻雷達(dá)資料稀疏化算法（ESTM）等臺(tái)風(fēng)“973”項(xiàng)目關(guān)鍵技術(shù)，氣科院牽頭發(fā)展的臺(tái)風(fēng)快速更新短臨預(yù)報(bào)系統(tǒng)（TRANS）于2021年1月實(shí)現(xiàn)業(yè)務(wù)化運(yùn)行，實(shí)現(xiàn)沿海雷達(dá)資料同化，逐小時(shí)更新強(qiáng)風(fēng)雨短臨預(yù)報(bào)。TRANS成為臺(tái)風(fēng)逐小時(shí)定位、定強(qiáng)的重要依據(jù)，強(qiáng)風(fēng)雨臨近預(yù)報(bào)的重要參考。2020年TRANS系統(tǒng)相比歐洲中心ECMWF模式暴雨以上量級(jí)降水和10級(jí)大風(fēng)預(yù)報(bào)準(zhǔn)確率提高16%。該系統(tǒng)的持續(xù)升級(jí)優(yōu)化將服務(wù)于我國(guó)臺(tái)風(fēng)業(yè)務(wù)預(yù)報(bào)和防災(zāi)減災(zāi)。（端義宏，馮佳寧，趙大軍）

4.2 臺(tái)風(fēng)登陸前后強(qiáng)度結(jié)構(gòu)變化機(jī)理研究

基于非定常的卡諾熱機(jī)原理，建立了基于非定?？ㄖZ熱機(jī)和邊界層動(dòng)力過(guò)程的熱帶氣旋（TC）增強(qiáng)的動(dòng)力系統(tǒng)模型，能定量估計(jì)理想數(shù)值模擬和實(shí)際TC的增強(qiáng)率（即強(qiáng)度變化）。同時(shí)，為了彌補(bǔ)TC增強(qiáng)的動(dòng)力系統(tǒng)模型動(dòng)力過(guò)程缺失的不足，基于TC邊界層內(nèi)切向風(fēng)的收支方程和熱力學(xué)熵的準(zhǔn)平衡假定，通過(guò)引入一個(gè)表征等熵面與等角動(dòng)量面匯合的程度的因子，推導(dǎo)出另外一個(gè)時(shí)間依賴的TC增強(qiáng)理論模型。雖然基于不同假設(shè)，兩個(gè)模型描述臺(tái)風(fēng)加強(qiáng)率的公式形式極為相似，這說(shuō)明從能量學(xué)和動(dòng)力學(xué)考慮，TC增強(qiáng)的基本動(dòng)力過(guò)程具有一致性。這兩個(gè)協(xié)調(diào)一致的TC增強(qiáng)率方程可以再現(xiàn)模擬TC生命史中的強(qiáng)度時(shí)間演變。將在后續(xù)的工作中考慮環(huán)境場(chǎng)的影響并試驗(yàn)用于實(shí)際TC的強(qiáng)度變率預(yù)報(bào)。為建立TC登陸后的強(qiáng)度衰減預(yù)報(bào)模型，系統(tǒng)評(píng)估了三個(gè)經(jīng)典的登陸TC強(qiáng)度衰減模型，為后續(xù)建立更優(yōu)化的適用于我國(guó)的登陸TC強(qiáng)度衰減模型奠定基礎(chǔ)。（王玉清，徐晶，劉璐）

4.3 臺(tái)風(fēng)眼墻小尺度精細(xì)結(jié)構(gòu)對(duì)模式水平分辨率的敏感性研究

利用超高分辨率大渦模擬結(jié)果分析，發(fā)現(xiàn)次公里級(jí)分辨對(duì)熱帶氣旋（TC）風(fēng)圈、垂直上升運(yùn)動(dòng)，強(qiáng)度的描述優(yōu)于中尺度數(shù)值模擬。166 m能夠開始部分分辨邊界層滾渦，55 m分辨率可分辨不同尺度滾渦以及龍卷尺度的相互作用。邊界層方案比如YSU方案能夠在500 m分辨率上部分分辨滾渦，但是其結(jié)構(gòu)以及波長(zhǎng)尺度與大渦模擬結(jié)果相差較遠(yuǎn)。具有尺度依賴的邊界層算法能夠提高邊界層方案對(duì)滾渦等小尺度系統(tǒng)的分辨能力，但是對(duì)其尺度依賴函數(shù)具有較強(qiáng)的敏感性。（王玉清，徐洪雄，趙大軍）

4.4 基于臺(tái)風(fēng)事件隨機(jī)模擬新技術(shù)的風(fēng)險(xiǎn)評(píng)估模型

面向臺(tái)風(fēng)防災(zāi)減災(zāi)需求，建立了基于統(tǒng)計(jì)學(xué)習(xí)方法的熱帶氣旋（TC）風(fēng)險(xiǎn)評(píng)估模型，研究提出了一種多變量函數(shù)型數(shù)據(jù)分析方法，用于TC隨機(jī)事件的全路徑模擬，將貫穿TC生命史的各種屬性，如中心坐標(biāo)、最大風(fēng)速等聯(lián)合起來(lái)視作多元函數(shù)型隨機(jī)變量，構(gòu)建協(xié)同統(tǒng)一的一體化模型，據(jù)此進(jìn)行TC全路徑多要素的同步模擬。該方法在TC年發(fā)生概率模型、隨機(jī)模擬模型優(yōu)化等方面均有創(chuàng)新性的應(yīng)用。綜合評(píng)價(jià)表明，該方法可與風(fēng)場(chǎng)模型和工程風(fēng)險(xiǎn)性模型結(jié)合使用，為政府和保險(xiǎn)/再保險(xiǎn)行業(yè)估計(jì)經(jīng)濟(jì)和保險(xiǎn)損失提供科學(xué)依據(jù)。（徐晶）

4.5 呂宋島地形影響下的臺(tái)風(fēng)結(jié)構(gòu)變化及新眼墻形成機(jī)制

利用高分辨率模式研究典型臺(tái)風(fēng)穿過(guò)呂宋島過(guò)程中的眼墻破壞和重組，發(fā)現(xiàn)臺(tái)風(fēng)登陸呂宋島后由于摩擦和海面熵通量減小，原始眼墻收縮并且減弱消失，與此同時(shí)，在島外海洋上的外雨帶持續(xù)增強(qiáng)并且軸對(duì)稱化，引起島嶼外圍大眼墻生成。當(dāng)臺(tái)風(fēng)中心過(guò)島重新進(jìn)入中國(guó)南海后，原始眼墻又重新產(chǎn)生。這種重新產(chǎn)生的眼墻結(jié)構(gòu)是由渦旋內(nèi)部殘余對(duì)流和海洋熵通量增加所導(dǎo)致。（王玉清，王慧）

4.6 臺(tái)風(fēng)極端降水（TCER）的氣候特征及季風(fēng)涌對(duì)登陸臺(tái)風(fēng)極端降水的影響

研究發(fā)現(xiàn)影響我國(guó)的臺(tái)風(fēng)極端降水（TCER）頻次（強(qiáng)度）有波動(dòng)增多趨勢(shì)。造成TCER的臺(tái)風(fēng)有兩類路徑，一是以西北行路徑影響（登陸）臺(tái)灣之后進(jìn)而登陸我國(guó)東南沿海，二是以西北行或西行路徑影響（登陸）海南島及兩廣地區(qū)。研究季風(fēng)涌對(duì)登陸臺(tái)風(fēng)極端降水影響發(fā)現(xiàn)整層水汽通量積分在極端暴雨發(fā)生前1～2天達(dá)到峰值；極端暴雨熱帶氣旋（TC）整層水汽通量明顯高于非極端暴雨TC，極端暴雨類TC比非極端暴雨類TC水汽通量輻合更強(qiáng)。極端暴雨類TC風(fēng)場(chǎng)輻合主要是由西南低空急流疊加TC本體環(huán)流引起。動(dòng)態(tài)季風(fēng)涌指數(shù)對(duì)ERLTC有較好指示意義，有潛力成為一個(gè)業(yè)務(wù)預(yù)報(bào)新指標(biāo)。（李英，趙大軍）

4.7 A numerical study of typhoon Megi (2010). Part II: Eyewall evolution crossing the Luzon Island

Typhoon Megi (2010) experienced drastic eyewall structure changes when it crossed the Luzon Island and entered the South China Sea (SCS), including the contraction and breakdown of the eyewall after landfall over the Luzon Island, the formation of a new large outer eyewall accompanied by reintensification of the storm after it entered the SCS, and the appearance of a short-lived small inner eyewall. These features were reproduced reasonably well in a control simulation using the advanced weather research and forecasting(ARW-WRF) model. In this study, the eyewall processes of the simulated Megi during and after landfall have been analyzed. Results show that the presence of the landmass of the Luzon Island increased surface friction and reduced surface enthalpy flux, causing the original eyewall to contract and break down and the storm to weaken. The formation of the new large eyewall results mainly from the axisymmetrization of outer spiral rainbands after the storm core moved across the Luzon Island and entered the SCS. The appearance of the small inner eyewall over the SCS was due to the increased surface enthalpy flux and the revival of convection in the central region of the storm core. In a sensitivity experiment with the mesoscale mountain replaced by flat surface over the Luzon Island, a new large outer eyewall formed over the western Luzon Island with its size about one-third smaller after the storm entered the SCS than that in the control experiment with the terrain over the Luzon Island unchanged. (Wang Hui, Wang Yuqing)

4.8 An investigation of the impact of different turbulence schemes on the tropical cyclone boundary layer at turbulent gray-zone resolution

Accurately resolving turbulence in the tropical-cyclone boundary layer (TCBL) is crucial for realistic simulations of tropical cyclones (TCs), but how well the fine-scale structure of the simulated TCBL can be reproduced at gray-zone resolutions by state-of-the-art planetary boundary layer (PBL) parameterization schemes, and why the simulated fine-scale structure is so sensitive to the PBL scheme, are yet to be evaluated and understood. To address these issues, a series of numerical experiments under idealized conditions were conducted using the advanced research weather research and forecasting (WRF-ARW) model at 500 and 166 m grid spacing. An 18 h WRF-ARW large-eddy simulation (LES) with a 55 m grid spacing based on the nonlinear backscatter and anisotropy subfilter-scale (NBA-SFS) stress scheme was used as reference (RLES).Results from experiments using five different PBL schemes, that is, two conventional schemes-the Yonsei University (YSU) and the original MYNN (termed MYNN1)-two scale-aware schemes-the Shin-Hong (SH) and the revised MYNN (termed MYNN2)-and the coarse-resolution LES (CLES), were subsequently compared with the RLES. The YSU and S-H not only produced better simulations of TC intensity and structure than the other three PBL schemes, but also produced a fine-scale turbulent structure reasonably well compared with the RLES. Discrepancies in the simulated fine-scale structure among the PBL schemes result primarily from the different strength of vertical mixing, which could be reduced by the scale-aware option. Results from a series of sensitivity experiments with a 166-m grid spacing demonstrate that the scale-aware S-H can significantly improve the finer resolution simulations than the conventional YSU at relatively finer grid spacing at gray zone. (Xu Hongxiong, Wang Hui, Duan Yihong)

4.9 Associations between strong earthquakes and local rainfall in China

Strong earthquakes are a major cause of natural disasters and may also be related to heavy rainfall events. Both phenomena have received considerable attention in seismology and meteorology, two relatively independent disciplines, but we do not yet know whether there is a connection between them. We investigated the characteristics of daily rainfall over seismic areas in China. Our statistical analyses showed that there was a strong correlation between strong earthquakes (Ms≥6.0) and rainfall over the seismic area, with 74.9%of earthquakes in China accompanied by seismic epicenter rainfall and 86.6% by seismic area rainfall. The statistics also showed that the daily precipitation over the seismic area, including the epicenter, was mainly light rain, with only a few instances of torrential or storm rain, with 80% of the rainfall events lasting two or more days. The maximum cumulative precipitation corresponded well with the strong earthquakes occurring over steep terrain, such as the Taiwan central mountains and the eastern Tibetan Plateau. The earthquake area rainfall had a higher frequency than the 30-year climatological average and was dominated by earthquake events in the wet season. The WRF-ARW numerical simulation of seismic local rainfall during the devastating Ms 8.0 Wenchuan earthquake in May 2008 showed that the geothermal heat from the earthquake strengthened the local convergence of moisture and vertical motion near the epicenter and the upward transport of the sensible heat flux, which favored seismic rainfall. The results of this study show that rainfall in the seismic area is closely related to strong earthquakes and can be triggered and enhanced by geothermal heat. (Zhao Dajun,Chen Lianshou, Yu Yubin)

4.10 Contribution of the intensity of intraseasonal oscillation to the interannual variation of tropical cyclogenesis over the western North Pacific

The present study compares the contributions of seasonal, intraseasonal, and synoptic variations of environmental factors, i.e., mid-level moisture, vertical instability, and lower-level relative vorticity, to the interannual variation of tropical cyclone (TC) genesis over the western North Pacific (WNP) during July-August-September-October (JASO) of 1979?2015. It is found that the TC genesis frequency has a significant positive correlation with the intensity of intraseasonal oscillation, but a weak correlation with the intensity of synoptic variation of environmental factors during JASO in the WNP. In addition, the intraseasonal components of convection and lower-level vorticity at the location of TC genesis have a larger contribution than the interannual and synoptic components to the differences between more and less TC years over the WNP. The present results indicate that the intensity of intraseasonal oscillation of environmental factors has an important effect on the interannual variation of the TC genesis frequency over the WNP. This study enhances our understanding of the impacts of intraseasonal oscillation on the interannual variation of the WNP TC activity and indicates that the intensity of intraseasonal oscillation has the potential to be used in the seasonal prediction of the WNP TC genesis. (Cao Xi, Wu Renguang, Xu Jing)

4.11 Contribution of vertical advection to supergradient wind in tropical cyclone boundary layer: A numerical study

The existence of supergradient wind in the interior of the boundary layer is a distinct feature of a tropical cyclone (TC). Although the vertical advection is shown to enhance supergradient wind in the TC boundary layer (TCBL), how and to what extent the strength and structure of supergradient wind are modulated by vertical advection are not well understood. In this study, both a TCBL model and an axisymmetric full-physics model are used to quantify the contribution of the vertical advection process to the strength and vertical structure of supergradient wind in TCBL. Results from the TCBL model show that the removal of vertical advection of radial wind reduces both the strength and height of supergradient wind by slightly more than 50%. The removal of vertical advection of agradient wind reduces the height of the supergradient wind core by similar to 30% but increases the strength of supergradient wind by similar to 10%. Results from the fullphysics model show that the removal of vertical advection of radial wind or agradient wind reduces both the strength and height of supergradient wind but the removal of that of radial wind produces a more substantial reduction (52%) than the removal of that of agradient wind (35%). However, both the intensification rate and final intensity of the simulated TCs in terms of maximum 10-m wind speed show little differences in experiments with and without the vertical advection of radial or agradient wind, suggesting that supergradient wind contributes little to either the intensification rate or the steady-state intensity of the simulated TC. (Fei Rong, Wang Yuqing, Li Yuanlong)

4.12 Effect of the vertical diffusion of moisture in the planetary boundary layer on an idealized tropical cyclone

Previous numerical studies have focused on the combined effect of momentum and scalar eddy diffusivity on the intensity and structure of tropical cyclones. The separate impact of eddy diffusivity estimated by planetary boundary layer (PBL) parameterization on the tropical cyclones has not yet been systematically examined. We have examined the impacts of eddy diffusion of moisture on idealized tropical cyclones using the Advanced Research Weather Research and Forecasting model with the Yonsei University PBL scheme. Our results show nonlinear effects of moisture eddy diffusivity on the simulation of idealized tropical cyclones.Increasing the eddy diffusion of moisture increases the moisture content of the PBL, with three different effects on tropical cyclones: (1) a decrease in the depth of the PBL; (2) an increase in convection in the inner rain band and eyewall; and (3) drying of the lowest region of the PBL and then increasing the surface latent heat flux. These three processes have different effects on the intensity and structure of the tropical cyclone through various physical mechanisms. The increased surface latent heat flux is mainly responsible for the decrease in pressure. Results show that moisture eddy diffusivity has clear effects on the pressure in tropical cyclones,but contributes little to the intensity of wind. This largely influences the wind-pressure relationship, which is crucial in tropical cyclones simulation. These results improve our understanding of moisture eddy diffusivity in the PBL and its influence on tropical cyclones, and provide guidance for interpreting the variation of moisture in the PBL for tropical cyclone simulations. (Xu Hongxiong, Zhao Dajun)

4.13 Impact of the monsoonal surge on extreme rainfall of landfalling tropical cyclones

A comparative analysis and quantitative diagnosis has been conducted of extreme rainfall associated with landfalling tropical cyclones (ERLTC) and non-extreme rainfall (NERLTC) using the dynamic composite analysis method. Reanalysis data and the tropical cyclone precipitation dataset derived from the objective synoptic analysis technique were used. Results show that the vertically integrated water vapor transport (Qvt)during the ERLTC is significantly higher than that during the NERLTC. The Qvtreaches a peak 1?2 days before the occurrence of the ERLTC and then decreases rapidly. There is a stronger convergence for both the Qvtand the horizontal wind field during the ERLTC. The Qvtconvergence and the wind field convergence are mainly confined to the lower troposphere. The water vapor budget on the four boundaries of the tropical cyclone indicates that water vapor is input through all four boundaries before the occurrence of the ERLTC,whereas water vapor is output continuously from the northern boundary before the occurrence of the NERLTC. The water vapor inflow on both the western and southern boundaries of the ERLTC exceeds that during the NERLTC, mainly as a result of the different intensities of the southwest monsoonal surge in the surrounding environmental field. Within the background of the East Asian summer monsoon, the low-level jet accompanying the southwest monsoonal surge can increase the inflow of water vapor at both the western and southern boundaries during the ERLTC and therefore could enhance the convergence of the horizontal wind field and the water vapor flux, thereby resulting in the ERLTC. On the other hand, the southwest monsoonal surge decreases the zonal mean steering flow, which leads to a slower translation speed for the tropical cyclone associated with the ERLTC. Furthermore, a dynamic monsoon surge index (DMSI) defined here can be simply linked with the ERLTC and could be used as a new predictor for future operational forecasting of ERLTC. (Zhao Dajun, Yu Yubin, Chen Lianshou)

4.14 Increasing lifetime maximum intensity of rapidly intensifying tropical cyclones over the western North Pacific

The long-term trend in the annual mean lifetime maximum intensity (LMI) of rapidly intensifying tropical cyclones (RI-TCs) over the western North Pacific (WNP) is investigated in this study. During 1970?2019, a notable upward trend is observed in the average RI-TC LMI, which is primarily linked to a significant increase in the mean intensification rate prior to LMI. This intensification rate increase is caused by an increase in the mean magnitude of RI cases. By contrast there is no significant change in the RI ratio, which is calculated as the proportion of 24 h RI records to all 24 h records before a RI-TC reaches its LMI. Furthermore, there is a significantly greater RI magnitude at the west of 155°E, where the vast majority of RI cases occur on average.Over this region, there are significant increases in sea surface temperatures, TC heat potential, 700?500 hPa relative humidity and 200 hPa divergence during 1970?2019. Only a small region of significantly reduced 850?200 hPa vertical wind shear is observed to the northeast of the Philippines during 1970?2019. These results imply that both thermodynamic and dynamic variables play an important role in modulating RI magnitude over the WNP. (Song Jinjie, Klotzbach Philip J., Duan Yihong)

4.15 Modulation of tropical cyclone formation over the western North Pacific by the ENSO combination mode

Previous studies have shown that a combination mode (C-mode) is formed by nonlinear interactions between the western Pacific warm pool annual cycle and El Ni?o-southern oscillation variability. We find a significant inverse relationship between the western North Pacific (WNP) tropical cyclone (TC) frequency and the C-mode index on monthly timescales from 1970 to 2019. During positive C-mode phases, TC formation is significantly suppressed over a region spanning 5°?20°N and 140°?175°E, primarily due to reduced 850 hPa relative vorticity and increased 850-200-hPa vertical wind shear. By contrast, there is significantly enhanced TC genesis over the region spanning 25°?30°N and 125°?135°E, mainly due to increased 850 hPa relative vorticity and 600 hPa relative humidity. All of these changes in atmospheric conditions are further linked to an anomalous large-scale anticyclone over the WNP generated by the C-mode. Our results suggest that C-mode variability can serve as a potential predictor for forecasting monthly WNP TC activity. (Song Jinjie, Klotzbach Philip J., Duan Yihong)

4.16 Monsoon surges enhance extreme rainfall by maintaining the circulation of landfalling tropical cyclones and slowing down their movement

Extreme rainfall induced by landfalling tropical cyclones (ERLTCs) in China can cause flash floods and other disastrous impacts, so investigating their genesis and mechanism of enhancement has been attracting considerable attention. This study demonstrates that the extreme rainfall of landfalling tropical cyclones(LTCs) possesses two key properties, namely, maintenance of the LTC circulation and a lagging (slowing down or looping) of its movement, and the monsoon surge can provide a positive contribution to these properties. Specifically, diagnostics show that the low-level cyclonic vorticity and upper-level divergence of ERLTCs are significantly stronger than those of NERLTCs (non-extreme-rainfall-producing LTCs). The continuous intensification of the cyclonic rotation in the lower troposphere before the occurrence of extreme rainfall is a significant feature that distinguishes ERLTCs from NERLTCs. Vorticity budget analysis further shows that the relative vorticity advection term contributes the most to the local increase and maintenance of vorticity in the middle and lower troposphere of ERLTCs under the influence of the southwest monsoonal surge, thus demonstrating that the monsoonal surge favors the maintenance of LTC circulation. On the other hand, the activity of the southwest monsoonal surge is mainly manifested in the zonal wind anomaly, and the corresponding strong westerly transport can significantly reduce the zonal component of the steering flow.As a result, the total steering flow can be weakened, which decreases the northwestward translation speed of ERLTCs, and thus the monsoonal surge favors a lagging (slowing down or looping) of LTC movement.These results reveal the mechanism of influence through which the monsoonal surge affects ERLTCs via its direct impacts on the maintenance of their circulation and lagging of their movement-two distinct evolutionary characteristics. (Zhao Dajun, Chen Lianshou, Yu Yubin)

4.17 Recent weakening of the interannual relationship between ENSO Modoki and boreal summer tropical cyclone frequency over the western North Pacific

This study shows that the impact of El Ni?o-southern oscillation (ENSO) Modoki on boreal summer tropical cyclone (TC) formation over the western North Pacific (WNP) has experienced decadal changes during the past few decades. The correlation between the ENSO Modoki index and TC frequency over the WNP was weak during 1975?1989, becomed strong and significant during 1990?2004, and becomed weak again during 2005?2019. Over the eastern part of the WNP, ENSO Modoki enhanced TC formation during 1990?2004 but did not significantly impact on the TC formation during 1975?1989 and 2005?2019. The difference in correlation strength primarily results from changes in large-scale features related to ENSO Modoki among the three subperiods (1975?1989, 1990?2004, and 2005?2019). El Ni?o Modoki during 1990?2004 was characterized by a tripole sea surface temperature (SST) pattern with maximum SST anomalies in the equatorial central Pacific, while during 1975?1989 and 2005?2019, the maximum SST anomalies were located over the subtropical northeastern Pacific. The two primary environmental variables likely leading to these observed relationships between ENSO Modoki and TCs were mid-level moisture (RH600) and low-level vorticity (VOR850). During 1990?2004, TC formation was enhanced both at the south of 20°N and north of 20°N. The increase in TC activity during El Ni?o Modoki at the south of 20°N was likely tied to greater RH600 and north of 20°N to larger cyclonic VOR850. In contrast, ENSO Modoki’s impacts on both VOR850 and RH600 were weak during 1975?1989 and 2005?2019. (Song Jinjie, Klotzbach Philip J., Duan Yihong)

4.18 Sensitivity of fine-scale structure in tropical cyclone boundary layer to model horizontal resolution at sub-kilometer grid spacing

In view of the increasing interest in the explicit simulation of fine-scale features in the tropical cyclone(TC) boundary layer (TCBL), the effects of horizontal grid spacing on a 7?10 h simulation of an idealized TC are examined using the weather research and forecasting (ARW-WRF) mesoscale model with one-way moving nests and the nonlinear backscatter with anisotropy (NBA) sub-grid-scale (SGS) scheme. In general, reducing the horizontal grid spacing from 2 km to 500 m tends to produce a stronger TC with lower minimum sea level pressure (MSLP), stronger surface winds, and smaller TC inner core size. However, large eddies cannot be resolved at these grid spacings. In contrast, reducing the horizontal grid spacing from 500 to 166 m and further to 55 m leads to a decrease in TC intensity and an increase in the inner-core TC size. Moreover, although the 166-m grid spacing starts to resolve large eddies in terms of TCBL horizontal rolls and tornado-scale vortex,the use of the finest grid spacing of 55 m tends to produce shorter wavelengths in the turbulent motion and stronger multi-scale turbulence interaction. It is concluded that a grid spacing of sub-100-meters is desirable to produce more detailed and fine-scale structure of TCBL horizontal rolls and tornado-scale vortices, while the relatively coarse sub-kilometer grid spacing (e.g., 500 m) is more cost-effective and feasible for research that is not interested in the turbulence processes and for real-time operational TC forecasting in the near future. (Xu Hongxiong, Wang Yuqing)

4.19 Statistical linkage between coastal El Ni?o-southern oscillation and tropical cyclone formation over the western North Pacific

This study investigates the modulation of tropical cyclone (TC) formation over the western North Pacific (WNP) by coastal El Ni?o-southern oscillation (ENSO). There is a significant inverse relationship between WNP TC frequency during July?October from 1961 to 2019 and simultaneous Nino 1+2 sea surface temperature anomalies. TC formation is significantly suppressed and enhanced over the subtropical and equatorial WNP during coastal El Ni?o, respectively, while TC formation exhibits opposite-signed anomalies during La Ni?a. This north-south dipolar pattern during coastal ENSO is distinct from the pattern observed in basin-wide ENSO events. Additional analyses show that coastal ENSO influences WNP TC formation through modulation of the large-scale environment. Changes in mid-level moisture and low-level vorticity appear to be the primary large-scale influences on TC formation during both coastal ENSO phases. These changes can be further linked to the anomalous large-scale circulation over the WNP during coastal ENSO. (Song Jinjie,Klotzbach Philip J., Duan Yihong)

4.20 Stochastic simulation of tropical cyclones for risk assessment at one go: A multivariate functional PCA approach

A multivariate functional principal component analysis approach to the full-track simulation of tropical cyclones (TCs) is developed for risk assessment. Elemental variables of TC along the track necessary for risk assessment, such as center coordinates, maximum wind speed, minimum central pressure and ordinal dates, can be simulated simultaneously at one go, using solely the best-track data with no data supplemented from any other sources. The simulation model is optimally determined by means of the ladle estimator. A TC occurrence model using the Conway-Maxwell-Poisson distribution is proposed as well, by which different dispersion features of annual occurrence can be represented in a unified manner. With the occurrence model,TCs can be simulated on an annual basis. The modeling and simulation process is programmed and fully automated such that little manual intervention is required, which greatly improves the modeling efficiency and reduces the turnaround time, especially when newly available TC data are incorporated periodically into the model. Comprehensive evaluation shows that this approach is capable of generating high-performance synthetic TCs in terms of distributional and extreme value features, which can be used in conjunction with wind field and engineering vulnerability models to estimate economic and insurance losses for governments and insurance/reinsurance industry. Tropical cyclones (TCs) are one of the biggest threats to life and property around the world. However, the infrequent nature of catastrophic TCs invalidates the standard actuarial loss estimation approaches. TC risk assessment requires estimation of catastrophic TCs having a very low occurrence probability, or equivalently a very long return period spanning up to thousands of years. Since reliable TC data are available only for recently decades, stochastic modeling and simulation turned out to be an effective approach to achieve more stable TC risk estimates for regions where little or no historical TC records exist. Here we present a novel model for the full-track simulation of TCs for risk assessment, via a machine learning approach called multivariate functional principal component analysis. Using this model, highperformance synthetic TCs can be generated in a fully automated manner such that little manual intervention is required, which greatly improves the modeling efficiency and reduces the turnaround time, especially when newly available TC data are incorporated periodically into the model. These synthetic TCs can be used in conjunction with wind field and engineering vulnerability models to estimate economic and insurance losses for governments and insurance/reinsurance industry. (Yang Chi, Xu Jing, Yin Jianming)

4.21 The cold avoidance of typhoons in their north turning over the South China Sea

Based on the typhoon best tracks of the China Meteorological Administration (CMA), ERA5 reanalysis data of ECMWF at 0.25° horizontal resolution, and NOAA optimal interpolated sea surface temperature (OISST V2) data, the dynamical compositing analysis is used to study the north turning at nearly 90° of 4 westward typhoons over the South China Sea (SCS). The composite analysis results show that: (1) As the typhoon goes westward into the SCS, the upper-level westerly trough moves eastward to the vicinity of 110°E in the mainland of China, and the western North Pacific subtropical high (SH) retreats eastward at the same time,which weakens the steering flow of typhoon and slowes down its movement. (2) The cold air guided by the westerly trough invades southwardly into the western part of SCS from the mainland leading to a descending and divergent airflow in the lower-to-middle atmospheric layers and enhancing the eastward pressure gradient force (PGF) in the west quadrant of the typhoon, which blocks and repesls the typhoon from moving any further westward. (3) Due to the cold air intrusion, the vertical atmospheric stratification in the west quadrant of the typhoon becomes static and stable, which may suppress the convection, impeding a typhoon’s westward motion. (4) With the cold air involving to the south of the typhoon, the direction of the PGF on the typhoon switches from eastward to northward, and the SH falling southward enhances the southwesterly airflow on the south of the typhoon at the same time. The remarkable increase of the northward steering airflows of the typhoon results in an abrupt northward turn. (5) In addition, the sea surface temperature (SST) and the ocean heat content (OHC) on the western part of the SCS are also reduced, attributed to the cold air cooling, and the typhoon is likely to avoid the cold ocean and approachs a relatively warmer region. This study suggests that cold avoidance during the westward movement of typhoons is worthy of consideration in the operational forecast of typhoon tracks. (Lai Shaojun, Li Ying, He Fen, Wang Yufei)

4.22 The intensity dependence of tropical cyclone intensification rate in a simplified energetically based dynamical system model

In this study, a simple energetically based dynamical system model of tropical cyclone (TC) intensification is modified to account for the observed dependence of the intensification rate (IR) on the storm intensity.According to the modified dynamical system model, the TC IR is controlled by the intensification potential(IP) and the weakening rate due to surface friction beneath the eyewall. The IP is determined primarily by the rate of change in the potential energy available for a TC to develop, which is a function of the thermodynamic conditions of the atmosphere and the underlying ocean, and the dynamical efficiency of the TC system.The latter depends strongly on the degree of convective organization within the eyewall and the inner-core inertial stability of the storm. At a relatively low TC intensity, the IP of the intensifying storm is larger than the frictional weakening rate, leading to an increase in the TC IR with TC intensity in this stage. As the storm reaches an intermediate intensity of 30?40 m s?1, the difference between IP and frictional weakening rate reaches its maximum, concurrent with the maximum IR. Later on, the IR decreases as the TC intensifies further because the frictional dissipation increases with TC intensity at a faster rate than the IP. Finally, the storm approaches its maximum potential intensity (MPI) and the IR becomes zero. The modified dynamical system model is validated with results from idealized simulations with an axisymmetric nonhydrostatic, cloudresolving model. (Wang Yuqing, Li Yuanlong, Xu Jing)

4.23 The performance of three exponential decay models in estimating tropical cyclone intensity change after landfall over China

In this study, the performance of three exponential decay models in estimating intensity change of tropical cyclones (TCs) after landfall over China is evaluated based on the besttrack TC data during 1980–2018.Results indicate that the three models evaluated can reproduce the weakening trend of TCs after landfall, but two of them (M1 and M2) tend to overestimate TC intensity and one (M3) tends to overestimate TC intensity in the first 12 h and underestimate TC intensity afterwards. M2 has the best performance with the smallest errors among the three models within 24 h after landfall. M3 has better performance than M1 in the first 20 h after landfall, but its errors increase largely afterwards. M1 and M2 show systematic positive biases in the southeastern China likely due to the fact that they have not explicitly included any topographic effect. M3 has better performance in the southeastern China, where it was originally attempted, but shows negative biases in the eastern China. The relative contributions of different factors, including landfall intensity, translational speed, 850-hPa moist static energy, and topography, to model errors are examined based on classification analyses. Results indicate that the landfall intensity contributes about 18%, translational speed, moist static energy and topography contribute equally about 15% to the model errors. It is strongly suggested that the TC characteristics and the time-dependent decay constant determined by environmental conditions, topography and land cover properties, should be considered in a good exponential decay model of TC weakening after landfall. (Liu Lu,Wang Yuqing,Wang Hui)

4.24 The role of boundary layer dynamics in tropical cyclone intensification. Part I: Sensitivity to surface drag coefficient

This study examines the role of boundary layer dynamics in tropical cyclone (TC) intensification using numerical simulations. The hypothesis is that although surface friction has a negative effect on TC intensification due to frictional dissipation (direct effect), it contributes positively to TC intensification by determining the amplitude and radial location of eyewall updrafts/convection (indirect effect). Results from a boundary layer model indicate that TCs with a larger surface drag coefficient (CD) can induce stronger and more inwardly penetrated boundary layer inflow and upward motion at the top of the boundary layer. This can lead to stronger and more inwardly located condensational heating inside the radius of maximum wind with higher inertial stability and is favorable for more rapid intensification. Results from full-physics model simulations using TC Model version 4 (TCM4) demonstrate that the intensification rate of a TC during the primary intensification stage is insensitive to CD if CD is changed over a reasonable range. This is because the increased/reduced positive contribution by the indirect effect of surface friction to TC intensification due to increased/reduced CD is roughly offset by the increased/reduced negative (direct) dissipation effect due to surface friction. However, greater surface friction can significantly shorten the initial spinup period through stronger frictional moisture convergence and Ekman pumping and thus expedite moistening of the inner-core column of the TC vortex but is likely to lead to a weaker storm in the mature stage. (Li Tsung-Han, Wang Yuqing)

4.25 The role of boundary layer dynamics in tropical cyclone intensification. Part II: Sensitivity to initial vortex structure

In Part I of this series of studies, we demonstrated that the intensification rate of a numerically simulated tropical cyclone (TC) during the primary intensification stage is insensitive to the surface drag coefficient. This leads to the question of what is the role of the boundary layer in determining the TC intensification rate given sea surface temperature and favorable environmental conditions. This part attempts to answer this question based on a boundary layer model and a full-physics model as used in Part I. Results from a boundary layer model suggest that TCs with a smaller radius of maximum wind (RMW) or of lower strength (i.e., more rapid radial decay of tangential wind outside the RMW) can induce stronger boundary layer inflow and stronger upward motion at the top of the boundary layer. This leads to stronger condensational heating inside the RMW with higher inertial stability and is thus favorable for a higher intensification rate. Results from full-physics model simulations indicate that the TC vortex initially with a smaller RMW or of lower strength has a shorter initial spinup stage due to faster moistening of the inner core and intensifies more rapidly during the primary intensification stage. This is because the positive indirect effect of boundary layer dynamics depends strongly on vortex structure, but the dissipation effect of surface friction depends little on the vortex structure. As a result, the intensification rate of the simulated TC is very sensitive to the initial TC structure. (Li Tsung-Han,Wang Yuqing)

4.26 The simulation of five tropical cyclones by sample optimization of ensemble forecasting based on the observed track and intensity

The quality of ensemble forecasting is seriously affected by sample quality. In this study, the distributions of ensemble members based on the observed track and intensity of tropical cyclones (TCs) were optimized and their influence on the simulation results was analyzed. Simulated and observed tracks and intensities of TCs were compared and these two indicators were combined and weighted to score the sample. Samples with higher scores were retained and samples with lower scores were eliminated to improve the overall quality of the ensemble forecast. For each sample, the track score and intensity score were added as the final score of the sample with weight proportions of 10 to 0, 9 to 1, 8 to 2, 7 to 3, 6 to 4, 5 to 5. These were named as tr, 91, 82,73, 64, and 55, respectively. The WRF model was used to simulate five tropical cyclones in the northwestern Pacific to test the ability of this scheme to improve the forecast track and intensity of these cyclones. The results show that the sample optimization effectively reduced the track and intensity error, 55 usually had better performance on the short-term intensity prediction, and tr had better performance in short-term track prediction. From the overall performance of the track and intensity simulation, 91 was the best and most stable among all sample optimization schemes. These results may provide some guidance for optimizing operational ensemble forecasting of TCs. (Li Jihang, Zhang Zhiyan, Liu Lu)

4.27 川藏高原一次混合型強(qiáng)對(duì)流天氣的觀測(cè)特征

利用中國(guó)氣象局地面自動(dòng)氣象站、探空、天氣雷達(dá)等觀測(cè)資料和ERA-Interim再分析資料，分析2016年9月8日川藏高原一次強(qiáng)對(duì)流天氣過(guò)程。結(jié)果表明:該過(guò)程多站出現(xiàn)8級(jí)雷暴大風(fēng)、10 mm以上小時(shí)強(qiáng)降水且伴有最大直徑為18 mm的冰雹，是川藏高原一次混合型強(qiáng)對(duì)流過(guò)程。對(duì)流系統(tǒng)發(fā)生在500 hPa弱冷平流和低層切變線影響下，中低層深厚濕層、環(huán)境中等強(qiáng)度對(duì)流有效位能和垂直風(fēng)切變?yōu)槌?jí)單體的形成和維持提供有利條件。初始北側(cè)多單體和南側(cè)弱對(duì)流在地面輻合線上生成，向東南移入適宜環(huán)境后，北側(cè)多單體發(fā)展成線狀對(duì)流系統(tǒng)，與南側(cè)單體合并且促使其迅速發(fā)展成超級(jí)單體。成熟超級(jí)單體低層具有清晰的前側(cè)入流缺口、鉤狀回波和中氣旋特征。強(qiáng)回波區(qū)隨高度前傾，呈顯著的上沖云頂突起、回波懸垂和有界弱回波區(qū)。風(fēng)暴內(nèi)中層徑向輻合、上升氣流減弱和反射率因子核心快速下降預(yù)示下?lián)舯┝鞯漠a(chǎn)生。中層干空氣的夾卷和水凝物快速下落的拖曳作用加強(qiáng)下沉氣流，結(jié)合峽谷地形的狹管效應(yīng)，引起地面大風(fēng)。（王黌，李英，文永仁）

4.28 臺(tái)風(fēng)“山竹”（2018）遠(yuǎn)距離暴雨的成因分析

熱帶氣旋遠(yuǎn)距離暴雨（TRP）往往成為高影響天氣，是業(yè)務(wù)預(yù)報(bào)難點(diǎn)。本文用地面、探空觀測(cè)資料、雷達(dá)遙感資料以及NCEP一日四次0.5°×0.5°再分析資料，對(duì)2018年第22號(hào)臺(tái)風(fēng)“山竹”登陸廣東期間在長(zhǎng)江三角洲（簡(jiǎn)稱長(zhǎng)三角）地區(qū)引起的遠(yuǎn)距離暴雨過(guò)程進(jìn)行分析。結(jié)果表明：（1）這是一次發(fā)生在副熱帶高壓（簡(jiǎn)稱副高）控制范圍內(nèi)的熱帶氣旋遠(yuǎn)距離暴雨，低層受臺(tái)風(fēng)倒槽影響。（2）這次過(guò)程第一階段暴雨主要是在強(qiáng)的對(duì)流不穩(wěn)定條件下，由對(duì)流層低層“山竹”倒槽中的輻合線觸發(fā)對(duì)流產(chǎn)生，同時(shí)對(duì)流層高層“山竹”的極向流出匯入加大了中緯度西風(fēng)風(fēng)速，在長(zhǎng)三角地區(qū)上空產(chǎn)生輻散，有利于上升運(yùn)動(dòng)的維持。第二階段，對(duì)流不穩(wěn)定條件有所減弱，但前一階段強(qiáng)回波產(chǎn)生的低層偏北外出氣流與東南風(fēng)形成輻合線，輻合線上還有中γ尺度的渦旋產(chǎn)生，又促進(jìn)了對(duì)流發(fā)展。850 hPa臺(tái)風(fēng)倒槽北端形成一個(gè)低渦，500 hPa副高邊緣發(fā)展出一個(gè)短波槽，暴雨的動(dòng)力條件更為有利。（3）長(zhǎng)三角的3個(gè)強(qiáng)降水中心分別在長(zhǎng)江口、杭州灣北岸的嘉興沿海及寧波沿海，都是在水陸邊界附近。（4）遠(yuǎn)距離暴雨區(qū)的渦度收支診斷發(fā)現(xiàn)：暴雨的初始擾動(dòng)主要由近地層水平輻合輻散項(xiàng)提供，850 hPa的水平輻合輻散項(xiàng)和扭曲項(xiàng)共同作用形成和加強(qiáng)低渦，并通過(guò)垂直運(yùn)動(dòng)上傳使中層700～500 hPa附近渦度增長(zhǎng)，進(jìn)而發(fā)展出500 hPa短波槽。850 hPa渦度來(lái)自于臺(tái)風(fēng)倒槽和副高邊緣的偏南急流。（5）在這次遠(yuǎn)距離暴雨過(guò)程中，臺(tái)風(fēng)“山竹”與海上西太平洋副高之間形成偏南低空急流，向長(zhǎng)三角輸送水汽，這與典型TRP事件相似。不同之處在于：典型TRP中暴雨的初始擾動(dòng)一般由西風(fēng)槽提供，而這次過(guò)程主要由低空臺(tái)風(fēng)倒槽和偏南急流提供，渦度上傳形成高空短波槽，是不同于典型TRP事件的一個(gè)物理過(guò)程。（陳淑琴，李英，范悅敏）

4.29 臺(tái)風(fēng)“利奇馬”（1909）雙眼墻特征及長(zhǎng)時(shí)間維持機(jī)制

利用CIMSS微波衛(wèi)星產(chǎn)品和多普勒天氣雷達(dá)資料，分析超強(qiáng)臺(tái)風(fēng)“利奇馬”（1909）的長(zhǎng)時(shí)間雙眼墻特征，并采用集合卡爾曼濾波方法同化雷達(dá)徑向風(fēng)資料，診斷臺(tái)風(fēng)“利奇馬”雙眼墻的三維結(jié)構(gòu)演變特征。結(jié)果表明：在雙眼墻演變過(guò)程初期，受強(qiáng)垂直風(fēng)切變和中高層干空氣入侵的影響，外眼墻對(duì)流減弱，呈非對(duì)稱特征。Sawyer-Eliassen方程診斷結(jié)果顯示：臺(tái)風(fēng)“利奇馬”（1909）內(nèi)、外眼墻次級(jí)環(huán)流之間的相互作用不明顯，不同于發(fā)生眼墻替換過(guò)程的臺(tái)風(fēng)，其外眼墻處非絕熱加熱引起的下沉運(yùn)動(dòng)發(fā)生在內(nèi)眼的眼心，內(nèi)眼墻的上升運(yùn)動(dòng)并未受到外眼墻次級(jí)環(huán)流抑制。另外，在強(qiáng)垂直風(fēng)切變條件下，非對(duì)稱的外眼墻不能持續(xù)增強(qiáng)收縮并取代內(nèi)眼墻，因此雙眼墻結(jié)構(gòu)得以長(zhǎng)時(shí)間維持?？梢?，臺(tái)風(fēng)“利奇馬”（1909）外眼墻的非對(duì)稱結(jié)構(gòu)和特殊的次級(jí)環(huán)流分布是其雙眼墻能夠長(zhǎng)期維持的重要原因。（劉濤，端義宏，馮佳寧）

5 雷電研究

5 Lighting research

5.1 雷電野外科學(xué)試驗(yàn)

雷電團(tuán)隊(duì)克服新冠疫情影響，于5—8月在廣州從化開展了第16年度的人工觸發(fā)閃電試驗(yàn)。期間建設(shè)了新型人工引雷平臺(tái)，成功觸發(fā)閃電8次，改進(jìn)了弱電流測(cè)試方案；圍繞引雷試驗(yàn)場(chǎng)建設(shè)了低功耗太陽(yáng)能供電的閃電中低頻電場(chǎng)探測(cè)陣列；完成了針對(duì)廣州塔雷電流直接測(cè)量的方案設(shè)計(jì)和工程建設(shè)；升級(jí)實(shí)時(shí)低頻電場(chǎng)探測(cè)陣列，引入混合基線GPU三維定位算法實(shí)現(xiàn)快速全閃定位；在海南和西藏那曲新建了新一代三維全閃探測(cè)網(wǎng)絡(luò)，關(guān)注海陸雷暴和高原雷暴的閃電活動(dòng)探測(cè)。通過(guò)上述技術(shù)發(fā)展和試驗(yàn)開展，顯著提升了雷電團(tuán)隊(duì)對(duì)閃電過(guò)程的綜合數(shù)據(jù)獲取能力和數(shù)據(jù)質(zhì)量。（呂偉濤，鄭棟，張陽(yáng)，樊艷峰，馬穎）

5.2 雷電探測(cè)技術(shù)研發(fā)

在VHF閃電探測(cè)和定位方面，提出了利用DBM_EEMD方法對(duì)寬帶干涉儀VHF信號(hào)進(jìn)行帶通截?cái)嗟荣|(zhì)量控制，通過(guò)廣義互相關(guān)、信號(hào)閾值和相似度約束等方法實(shí)現(xiàn)不同天線信號(hào)的精準(zhǔn)匹配的方法，對(duì)閃電通道解析能力獲得顯著提升。在低頻閃電探測(cè)和定位方面，引入深度學(xué)習(xí)技術(shù)，提出了基于編碼特征的脈沖匹配新方法，大大提高了匹配效率和定位速度。評(píng)估了粵港澳閃電定位系統(tǒng)和廣東電網(wǎng)地閃定位系統(tǒng)在粵港澳大灣區(qū)范圍內(nèi)的地閃探測(cè)性能。提出了一種考慮輻射源密度和通道重復(fù)放電的輻射源連接方法，能夠獲得體現(xiàn)時(shí)間和空間信息的閃電放電尺度參量，更好地描述閃電放電過(guò)程和受影響區(qū)域。（張陽(yáng)，范祥鵬，劉恒毅）

5.3 雷電物理研究

發(fā)現(xiàn)廣州塔觸發(fā)式上行閃電的正極性連續(xù)先導(dǎo)產(chǎn)生之前，普遍存在先導(dǎo)企圖發(fā)展過(guò)程，并指出觸發(fā)式上行正先導(dǎo)在初始速度上比人工觸發(fā)閃電高一個(gè)量級(jí)；發(fā)現(xiàn)有14%的高建筑物負(fù)地閃回?fù)羰录淅^后回?fù)艄饷}沖峰值大于首次回?fù)?。提出了一種閃擊距離估算方法，發(fā)現(xiàn)雷擊建筑物的高度和頂部幾何形狀是影響閃擊距離的關(guān)鍵因素；在正地閃回?fù)艉蟮乃酵ǖ郎习l(fā)現(xiàn)了類“針”狀結(jié)構(gòu)，指出其是正地閃回?fù)艉笃诤瓦B續(xù)電流期間大量負(fù)電荷被輸送至水平通道上的結(jié)果。提出了以集合經(jīng)驗(yàn)?zāi)B(tài)分解方法為基礎(chǔ)的高能云內(nèi)脈沖（EIP）放電事件電場(chǎng)波形分解方法，指出EIP的發(fā)生機(jī)制是逃逸電子雪崩產(chǎn)生的大電流過(guò)程；發(fā)現(xiàn)EIP與地源伽馬射線閃（TGF）之間的密切關(guān)系，將任一EIP亦是TGF的可能性由原來(lái)的超過(guò)37%提到了74%～100%。（樊艷峰，武斌，齊奇，呂凡超）

5.4 雷暴電學(xué)研究

給出了高原、中國(guó)中東部和喜馬拉雅山南麓雷暴結(jié)構(gòu)、電荷區(qū)大小以及起電效率概念圖，提出閃電頻次隨著雷暴對(duì)流增強(qiáng)持續(xù)增大而閃電尺度則先增大再減小的觀點(diǎn)，指出閃電頻次和尺度的反向關(guān)系出現(xiàn)在當(dāng)對(duì)流強(qiáng)度超過(guò)一定閾值時(shí)，發(fā)現(xiàn)冬季雷暴正地閃主要發(fā)生在正常極性和反極性電荷結(jié)構(gòu)中，不支持先前的傾斜偶極子假說(shuō)和雷暴消亡階段的單層正電荷區(qū)假說(shuō)。利用閃電數(shù)據(jù)以及衛(wèi)星云頂亮溫和云分類數(shù)據(jù)建立了亞太區(qū)域雷暴特征數(shù)據(jù)集，揭示我國(guó)陸地和毗鄰海域以及西太平洋地區(qū)的雷暴活動(dòng)和雷暴云結(jié)構(gòu)特征。發(fā)現(xiàn)全球閃電探測(cè)網(wǎng)（WWLLN）和星基光學(xué)成像儀（LIS）探測(cè)的高原閃電活動(dòng)時(shí)空分布存在差異，指出高原雷暴云電屬性存在區(qū)域差異和季節(jié)性變化。發(fā)現(xiàn)一類只發(fā)生在高原山地雷暴環(huán)境中的山頂與其上部雷暴主負(fù)電荷區(qū)之間的一種特殊放電過(guò)程，它可以產(chǎn)生上百kA的瞬態(tài)電流；揭示中尺度對(duì)流系統(tǒng)層云區(qū)閃電分布位置、尺度以及相互之間的關(guān)系。（鄭棟，張文娟，王飛）

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

發(fā)現(xiàn)湍流耗散率是指示閃電初生以及區(qū)分雷暴和非雷暴的有效參量；針對(duì)閃電活動(dòng)短時(shí)預(yù)報(bào)，發(fā)展了基于自動(dòng)氣象站、歷史閃電觀測(cè)和WRF模式模擬的多源時(shí)空數(shù)據(jù)深度神經(jīng)網(wǎng)絡(luò)閃電預(yù)報(bào)框架（LightNet+）。針對(duì)閃電活動(dòng)臨近預(yù)警，利用閃電監(jiān)測(cè)數(shù)據(jù)以及雷達(dá)數(shù)據(jù)，構(gòu)建了一個(gè)基于主從時(shí)空預(yù)測(cè)網(wǎng)絡(luò)模型（MSTNet）的雷電臨近預(yù)警方法；對(duì)比Gatlin算法和σ算法，指出2σ閃電躍增算法更適于基于閃電資料預(yù)警北京冰雹天氣；實(shí)現(xiàn)基于CMA-meso的中國(guó)南海區(qū)域閃電活動(dòng)預(yù)報(bào)，30 km鄰域半徑下，6～24 h預(yù)報(bào)時(shí)效下的CSI評(píng)分超過(guò)0.2。初步完成基于人工智能的雷電短時(shí)預(yù)報(bào)系統(tǒng)的研制，找到適合不同評(píng)估標(biāo)準(zhǔn)的預(yù)報(bào)概率閾值，并于2021年5月起在廣東省氣象安全技術(shù)支持中心開展運(yùn)行試驗(yàn)，取得較好效果。（姚雯，孟青，徐良韜）

5.6 A comprehensive study on the improved radio-frequency magnetic field measurement for the initial upward leader of a negative rocket-triggered lightning flash

The spectrum analysis of the lightning current in the experiment campaign of 2019 reveals that the lightning current waveform contains rich medium-frequency (MF) radiation signals in the initial stage.However, there is a lack of resolution for MF signals by using conventional magnetic sensors. The bandwidth of radio-frequency magnetic field measurement is improved by extending to 20 kHz to 1.2 MHz in the Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD). During the previously noticed quiet period that can only maintain the upward propagation with relatively small-scale breakdown, magnetic pulses of quiet period (MPQPs) are discerned more clearly than the previous experiment in GCOELD. Aided by the improvement of a magnetic sensor, this paper captures richer magnetic field signals radiated from the weak discharge of the precursory phase than previous experiments in GCOELD. The analysis shows that both aborted UPLs and UPLs are caused by weak discharge pulses called initial precursor pulses (IPPs), which are very similar to the amplitude of the streamer discharge obtained in the laboratory.In summary, the signals detected by an improved magnetic sensor will provide an important reference for exploring the pulse characteristics of the whole discharge process and formation mechanism of the UPL in the initial stage of triggered lightning. (Shi Tao, Lu Gaopeng, Fan Yanfeng)

5.7 A new method for connecting the radiation sources of lightning discharge extension channels

The connections of lightning radiation sources along channels are greatly affected by the radiation source density, and the channel length is geometrically scaled when neglecting repeated discharges in the same channel. Based on lightning mapping array (LMA) three-dimensional radiation source location data of two lightning flashes, this study presents a radiation source connection method considering the source density and repeated discharges in channels that includes two steps: the connection of radiation sources and the connection of segments. After increasing the spatial connection threshold determined by the source density, the stability of the channel scale under different detection capabilities (source densities) is improved compared with that of the traditional fixed spatial threshold method. The channel growth rate of the low-density case reaches 120.99%, which is close to the real situation, and the connection shape is consistent with the real situation.For repeated discharge paths, by limiting the time interval of the radiation source connection, the optimized threshold obtained in this paper can distinguish between discharges occurring in the same channel at different times. Compared with the geometric scale, the discharge scale is significantly larger (similar to 2.8 times the geometric scale in one case) and can better characterize both the lightning discharge process and the affected area. These comprehensive results show that the proposed method can reduce the number of incorrect connections, increase the channel length, and obtain a more realistic discharge scale. (Li Yurui, Zhang Yang,Zhang Yijun)

5.8 A positive cloud-to-ground flash caused by a sequence of bidirectional leaders that served to form a ground-reaching branch of a pre-existing horizontal channel

High-speed video and electric field change data were used to analyze the initiation and propagation of four predominantly vertical bidirectional leaders making connection to a predominantly horizontal channel previously formed aloft. The four bidirectional leaders sequentially developed along the same path and served to form a positive branch of the horizontal in-cloud channel, which became a downward positive leader producing a 135-kA positive cloud-to-ground (+CG) return stroke. The positive (lower) end of each bidirectional leader elongated abruptly at the time of connection of the negative (upper) end to the pre-existing channel aloft. Thirty-six negative streamer-like filaments (resembling recently reported needles) extended sideways over similar to 110 to 740 m from the pre-existing horizontal channel at speeds of similar to(0.5?1.9)×107m s?1, in response to the injection of negative charge associated with the +CG. (Wu Bin,Lyu Weitao, Qi Qi)

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

The application of empirical mode decomposition (EMD) in the analysis and processing of lightning electric field waveforms acquired by the low-frequency e-field detection array (LFEDA) in China has significantly improved the capabilities of the low-frequency/very-low-frequency (LF/VLF) time-of-arrival technique for studying the lightning discharge processes. However, the inherent mode mixing and the endpoint effect of EMD lead to certain problems, such as an inadequate noise reduction capability, the incorrect matching of multistation waveforms, and the inaccurate extraction of pulse information, which limit the further development of the LFEDAs positioning ability. To solve these problems, the advanced ensemble EMD (EEMD)technique is introduced into the analysis of LF/VLF lightning measurements, and a double-sided bidirectional mirror (DBM) extension method is proposed to overcome the endpoint effect of EMD. EEMD can effectively suppress mode mixing, and the DBM extension method proposed in this article can effectively suppress the endpoint effect, thus greatly improving the accuracy of a simulated signal after a 25500-kHz bandpass filter.The resulting DBMEEMD algorithm can be used in the LFEDA system to process and analyze the detected electric field signals to improve the systems lightning location capabilities, especially in terms of accurate extraction and location of weak signals from lightning discharges. In this article, a 3-D image of artificially triggered lightning obtained from an LF/VLF location system is reported for the first time, and methods for further improving the location capabilities of the LF/VLF lightning detection systems are discussed. (Fan Xiangpeng, Zhang Yijun, Krehbiel Paul R.)

5.10 Characteristics of negative leader propagation area of lightning flashes initiated in the stratiform regions of mesoscale convective systems

To investigate the characteristics of extension areas (mainly the propagation areas of negative leaders in this study), the lightning location data of 254 lightning flashes initiated in the stratiform regions (stratiform lightning flashes) of 14 mesoscale convective systems (MCSs) are analyzed. The results show that most of the flashes have a relatively small lightning area (LA) (≤100 km2), although they are initiated in the stratiform regions. In small or developing MCSs, most negative leaders of stratiform lightning flashes concentrate within the 9?12 km altitude range. In other MCSs with a large-sized and developed stratiform region, besides being in this high-altitude range, the negative leaders are also found to propagate more frequently in a low-altitude range of 5?7 km. Further analysis indicates that most of the stratiform lightning flashes with a large LA (＞100 km2)propagate their negative leaders within the high-altitude range, no matter where they are initiated. Moreover,the stratiform lightning flashes with or near the largest LA tend to be initiated 4?6 km below their negative leaders, while most of the stratiform lightning flashes usually propagate their negative leaders horizontally within ± 1 km of the first detected very-high-frequency (VHF) radiation source. It is inferred that some insitu electrifications occurring before and during the formation of the high reflectivity layers in the low-altitude range contribute to these flashes, although the influence of the advection charges from the convective regions still cannot be totally ruled out. (Wang Fei, Zhang Yijun, Dong Wansheng)

5.11 Electromagnetic characteristics of upward leader initiated from the Canton Tower: A comparison with rocket-triggered lightning

By using the synchronous observation data obtained at the Tall-Object Lightning Observatory in Guangzhou (TOLOG) of 2019, the electromagnetic characteristics of upward positive leader (UPL) ascending from the 600 m high Canton Tower are examined, and are compared with the magnetic field (B-field) radiation of UPL in rocket-triggered lightning. Before the inception of sustained UPL, small electric field (E-field) pulses are superposed on the fast E-field changes. The timescale of B-field pulses corresponding to the E-field pulses ranges from 5 to 9 μs, and the inter-pulse interval is about 30 μs, which are both similar to the B-field pulses associated with the precursors of rocket-triggered lightning. Measurements show that the precursor-like stage is likely common for upward lightning initiated from the Canton Tower. Moreover, the UPL channel of towerinitiated upward lightning extends significantly in the first several ms with the initial average two-dimensional(2-D) velocity of 8.77×105m s?1(3-D velocity of 11.0×105m s?1), which is one order of magnitude faster than the UPL initiated from the wire tip of rocket-triggered lightning, indicating that initiation of UPL from Canton Tower benefits from a substantial E-field enhancement of nearby lightning discharges. However, this favorable condition is rapidly consumed during the UPL development, causing the average 2-D velocity of UPL to decrease rapidly and maintain at about 0.5×105m s?1. It is noted that the variation in the 2-D speed of sustained UPL differs from tower-initiated upward lightning reported in the literature, which is possibly associated with the physical and geometric properties of the tower. (Fan Yanfeng, Lyu Weitao, Lu Gaopeng)

5.12 Fast and fine location of total lightning from low frequency signals based on deep-learning encoding features

Lightning location provides an important means for the study of lightning discharge process and thunderstorms activity. The fine positioning capability of total lightning based on low-frequency signals has been improved in many aspects, but most of them are based on post waveform processing, and the positioning speed is slow. In this study, artificial intelligence technology is introduced for the first time to lightning positioning, based on the low-frequency electric-field detection array (LFEDA). A new method based on deep-learning encoding features matching is also proposed, which provides a means for fast and fine location of total lightning. Compared to other LFEDA positioning methods, the new method greatly improves the matching efficiency, up to more than 50%, thereby considerably improving the positioning speed. Moreover,the new algorithm has greater fine-positioning and anti-interference abilities, and maintains high-quality positioning under low signal-to-noise ratio conditions. The positioning efficiency for return strokes of triggered lightning was 99.17%, and the standard deviation of the positioning accuracy in the X and Y directions was approximately 70 m. (Wang Jingxuan, Zhang Yang, Tan Yadan)

5.13 First documented downward positive cloud-to-ground lightning initiated by an upward negative lightning

An interesting downward positive cloud-to-ground lightning (DPCG) initiated by an upward negative cloud-to-ground lightning (UNCG) was recorded by the instruments installed at the Tall-Object Lightning Observatory in Guangzhou. The characteristics of the discharges before and after the DPCG return stroke were investigated in detail using both optical and electric field change data. The UNCG was triggered from the tip of the Canton Tower (600 m high) by a distant +CG lightning. A sequence of intracloud (IC) discharges developed toward and connected to several pre-existing channels of the UNCG. As a result, some positive charge was pumped from remote thundercloud regions to the region around the intersection of the pre-existing and new channels. A branch of one IC channel developed from the intersection point toward the ground, transformed into a downward positive leader, terminated on the ground, and resulted in a positive return stroke. After that,the discharge processes in the cloud continued to neutralize the remaining positive charge. The UNCG served to facilitate the IC discharges that supplied positive charges for the DPCG. Most of the charge involved in the UNCG-initiated DPCG originated from remote positively charged regions in the cloud. These observations constitute evidence for a new scenario of the initiation of +CG lightning. Key Points A downward +CG initiated by an upward tall-object -CG was recorded for the first time. The characteristics of the discharges before and after the +CG were investigated using optical and electric field change data. The observed sequence of events constitutes evidence for a new scenario of the initiation of downward +CG (Jiang Ruijiao, Lyu Weitao, Wu Bin)

5.14 Lightning fatalities in China, 2009?2018

The statistical characteristics of 1789 deaths, 1552 injuries and 1904 disasters caused by lightning based on the 2009 to 2018 National Lightning Disaster Compilation of Mainland China were analyzed. The results showed that males accounted for 53% of casualties. Lightning disasters were more common in the east and south than in the west and north. The number of lightning disasters and casualties in the south accounted for 82.98% and 82.94% of the totals, respectively. May to August of each year is the intensive period of lightning disasters in China, and the number of deaths, injuries and disasters caused by lightning during these four months accounted for 84.80%, 79.45% and 82.77% of the total numbers per year, respectively. From 2009 to 2018, the annual injury and death rates per million people in China were 0.13 and 0.12, respectively. After population weighting, the high death rate of lightning disaster shows a certain trend of transferring from the concentrated area to the sparsely populated area, and after area weighting, the casualty density was higher in small provinces and lower in large provinces. The analysis of the environments in which lightning disaster casualties occurred found that environments closely related to agriculture, such as farmland (35%) and paddy fields or ponds (4%), accounted for nearly 40% of the casualties; accordingly, rural farmers were the main victims, accounting for 80.96% of the total casualties. Lightning protection and disaster reduction measures in rural agricultural areas should be the focus of future work. (Yin Qiyuan, Liu Hengyi, Fan Xiangpeng)

5.15 New insights into the correlation between lightning flash rate and size in thunderstorms

Thunderstorms over the Tibetan Plateau (TP), Central and Eastern China (CEC), and southern foothills of the Himalayas (SHF), have the correlations between lightning flash rate and size disagreeing with the previously published negative correlation in thunderstorms with different dynamics. There is a positive correlation when comparing TP and CEC thunderstorms. Compared with SHF thunderstorms, TP thunderstorms have much lower flash rate and similar flash size. It is explored that the TP and SHF thunderstorms have the weakest and strongest convection, respectively, and both have small effective charge regions (ECRs). The CEC and SHF thunderstorms contain more ECRs than TP thunderstorms. The weak convection in TP thunderstorm should be responsible for the common occurrence of small flash rate and size. The results suggest that the negative correlation between flash rate and size may require the dynamic intensity of compared thunderstorms to exceed a certain threshold. (Zheng Dong, Zhang Yijun)

5.16 Spatiotemporal lightning activity detected by WWLLN over the Tibetan Plateau and its comparison with LIS lightning

Herein, we compared data on the spatiotemporal distribution of lightning activity obtained from the World Wide Lightning Location Network (WWLLN) with that from the lightning imaging sensor (LIS). The WWLLN and LIS both suggest intense lightning activity over the central and southeastern Tibetan Plateau (TP) during May—September. Meanwhile, the WWLLN indicates relatively weak lightning activity over the northeastern TP, where the LIS suggests very intense lightning activity, and it also indicates a high-density lightning center over the southwestern TP that is not suggested by the LIS. Furthermore, the WWLLN lightning peaks in August in terms of monthly variation and in late August in terms of 10-day variation, unlike the corresponding LIS lightning peaks of July and late June, respectively. Other observation data were also introduced into the comparison. The blackbody temperature (TBB) data from the Fengyun-2E geostationary satellite (as a proxy of deep convection) and thunderstorm-day data support the spatial distribution of the WWLLN lightning more.Meanwhile, for seasonal variation, the TBB data are more analogous to the LIS data, whereas the cloud-toground (CG) lightning data from a local CG lightning location system are closer to the WWLLN data. It is speculated that the different WWLLN and LIS observation modes may cause their data to represent different dominant types of lightning, thereby leading to differences in the spatiotemporal distributions of their data. The results may further imply that there exist regional differences and seasonal variations in the electrical properties of thunderstorms over the TP. (Ma Ruiyang, Zheng Dong, Zhang Yijun)

5.17 Turbulence characteristics of thunderstorms before the first flash in comparison to nonthunderstorms

This study evaluates how clouds evolve into thunderstorms in terms of the turbulence characteristics producing the first flash. Observations of 57 (39) isolated thunderstorm (non-thunderstorm) cells during 2016?2017 in South China are provided by an S-band polarimetric radar and three independent lightning location systems. The vertical turbulence characteristics of clouds associated with thunderstorms are obviously different from non-thunderstorms. For thunderstorms, the maximum of the eddy dissipation rate (mean value in each height layer) in the entire height is 0.19 m2s?3, which occurs at the first flash stage, and the achievable height of turbulence exceeds the ?30 layer. For non-thunderstorms, however, the maximum is 0.12 m2s?3,and the achievable turbulence height hardly exceeds the ?10 layer. Additionally, the turbulence intensities of the locations where the initial discharge pulse events of the first flashes occur are weak. These turbulence characteristics are useful for lightning nowcasting. (Zhao Chuanhong, Zheng Dong, Zhang Yijun)

5.18 Two-dimensional striking distance of lightning flashes to a cluster of tall buildings in Guangzhou

Based on the high-speed video records of 54 lightning flashes striking on a cluster of tall buildings in Guangzhou and the return stroke peak currents provided by lightning location systems, this paper analyzed the two-dimensional (2D) first-return-stroke striking distances (SD) of lightning flashes to buildings with a height ranging from 100 to 600 m. Three methods, including one proposed in this study, have been used to estimate the 2D SD. The results with different methods basically agree with each other and show that the height and the top geometry of the structure on which lightning terminates are key factors that affect the SD. The correlation between the SD and the peak return stroke current appeared very scattered, particularly in the cases when each building was considered separately. Besides, we found that: (a) the estimated 2D average initiation speed of upward connecting leader (UCL) on different buildings are similar, ranging from 4.9 to 23×104m s?1, with an average of 13.4×104m s?1; (b) about 87% (27/31) flashes that struck on buildings with simple top shape only have one upward leader observed, while for buildings with complicated top shape, only 26% (6/23) flash cases have one upward leader observed; (c) for the 36 flashes to four tall buildings with heights higher than 300 m,the 2D average speed ratio of the downward leader and the UCL is 0.74 during the last 0.1 ms before the first return stroke. (Qi Qi, Lyu Weitao, Wang Daohong.)

5.19 Winter positive cloud-to-ground lightning flashes observed by LMA in Japan

Using a lightning mapping array (LMA), we have observed 24 positive cloud-to-ground (CG) flashes occurred in three thunderstorm days. These flashes can be apparently grouped into 5 clusters according to their occurrence times. We have obtained the charge structures for both the individual flashes and clusters.It was found that 4 out of 5 clusters of positive CG flashes exhibited either inverter dipolar or tri-polar charge structures. This result indicates that the high percentage of positive CG flashes in Hokuriku winter thunderstorms originated from the inverted charge structure rather than the various deformations of normal charge structures widely accepted in literatures. The flash positive charge appeared to distribute usually in a layer with its thickness of around 1 km, its horizontal area of more than 100 km2and its bottom altitude of around 1?2 km above the ground. For each of the flash, we have also obtained its duration, length, duration before the first stroke and convex area. It was found that all flashes with a large peak return stroke current had short durations before their first return strokes. (Wang Daohong, Zheng Dong, Wu Ting)

5.20 CMA＿FEBLS低頻三維全閃探測(cè)技術(shù)研究及觀測(cè)10年進(jìn)展

三維全閃探測(cè)已經(jīng)成為了深入認(rèn)識(shí)閃電物理機(jī)制和雷暴電活動(dòng)規(guī)律的重要手段。中國(guó)氣象局雷電野外科學(xué)試驗(yàn)基地（CMA_FEBLS）自主研發(fā)了低頻電場(chǎng)探測(cè)陣列（LFEDA），并持續(xù)開展了針對(duì)廣東地區(qū)雷暴全閃電活動(dòng)的綜合觀測(cè)試驗(yàn)，在精細(xì)化三維定位算法和基于三維全閃數(shù)據(jù)的閃電放電過(guò)程研究方面取得了若干研究結(jié)果。（1） LFEDA具備雷暴電活動(dòng)的無(wú)死時(shí)間捕獲能力以及優(yōu)于百米的定位精度和一定的通道定位能力。（2）發(fā)展了基于簡(jiǎn)單脈沖特征的三維全閃定位算法，并進(jìn)一步將經(jīng)驗(yàn)?zāi)B(tài)分解及衍生方法引入到閃電信號(hào)處理中，提高了定位的精細(xì)化水平；發(fā)展了融合到達(dá)時(shí)差和時(shí)間反轉(zhuǎn)技術(shù)的定位方法，提升了抗干擾能力、降低了對(duì)站網(wǎng)的要求。（3）實(shí)現(xiàn)了典型放電事件的電流波形反演，獲得了窄偶極性放電事件（NBE）、初始擊穿脈沖（IBP）和爆發(fā)式脈沖簇（RBPs）的放電特征；研究發(fā)現(xiàn)絕大多數(shù)閃電始發(fā)于IBP，而作為始發(fā)的NBE則具有更大的孤立性、更大的相對(duì)幅度和更快的發(fā)展速度。（4）發(fā)現(xiàn)隨著起始放電高度增加，初始階段持續(xù)時(shí)間和步長(zhǎng)增加，發(fā)展速度和脈沖豐度下降；始發(fā)于強(qiáng)對(duì)流區(qū)時(shí)始發(fā)階段通常有更大的速度和脈沖豐度。（張陽(yáng)，王敬軒，鄭棟）

5.21 FY-4A LMI觀測(cè)的“利奇馬”（2019）臺(tái)前颮線閃電活動(dòng)及其與對(duì)流演變的關(guān)系

為研究風(fēng)云四號(hào)A星閃電成像儀（FY-4A LMI）閃電資料在強(qiáng)對(duì)流天氣的監(jiān)測(cè)預(yù)警能力，以2019年臺(tái)風(fēng)“利奇馬”臺(tái)前颮線為例，利用FY-4A LMI閃電資料、FY-4A云頂亮溫資料（TBB）、地基閃電定位資料（ADTD）、組網(wǎng)雷達(dá)組合反射率因子資料和東南沿海自動(dòng)站風(fēng)雨資料，研究“利奇馬”臺(tái)前颮線全閃電活動(dòng)的時(shí)空分布特征及其與颮線內(nèi)對(duì)流演變的關(guān)系。結(jié)果表明：FY-4A LMI閃電頻次的時(shí)空變化與臺(tái)前颮線的演變過(guò)程相一致，LMI閃電爆發(fā)對(duì)臺(tái)前颮線強(qiáng)度增強(qiáng)具有提早約1 h的指示作用。在閃電活動(dòng)與臺(tái)前颮線對(duì)流的演變關(guān)系上，LMI閃電與衛(wèi)星TBB深對(duì)流及雷達(dá)強(qiáng)回波的時(shí)空演變存在較好的相關(guān)性。LMI觀測(cè)的閃電頻數(shù)與強(qiáng)回波（35～55 dBz）頂高具有對(duì)應(yīng)關(guān)系，與-72 ℃冷云區(qū)面積及35 dBz以上雷達(dá)組合反射率因子面積的變化特征相同。閃電活動(dòng)集中位于TBB低值區(qū)的左側(cè)和前部的亮溫梯度大值區(qū)，對(duì)地面雷暴大風(fēng)和強(qiáng)降水的可能發(fā)生位置具有判識(shí)作用。LMI與ADTD的比較發(fā)現(xiàn)二者所揭示的“利奇馬”臺(tái)前颮線閃電活動(dòng)特征基本一致。（林小紅，張文娟，范能柱）

5.22 不同閃電躍增算法在北京地區(qū)應(yīng)用效果對(duì)比

基于S波段多普勒天氣雷達(dá)基數(shù)據(jù)、北京閃電定位網(wǎng)全閃定位數(shù)據(jù)和北京地區(qū)降雹的人工觀測(cè)結(jié)果，對(duì)比分析Gatlin和σ兩種閃電躍增算法在不同配置下對(duì)北京地區(qū)2015—2018年共177次冰雹天氣過(guò)程的預(yù)警效果。結(jié)果表明：不同倍數(shù)的σ算法預(yù)警結(jié)果差別很大，2σ（要求當(dāng)前閃電頻數(shù)變化率超過(guò)之前平均閃電頻數(shù)變化率兩倍標(biāo)準(zhǔn)差）在σ算法中的預(yù)警效果最佳;不同N（總閃頻數(shù)變化率的數(shù)量）配置下的Gatlin算法的預(yù)警結(jié)果差別不大，其中當(dāng)N = 6時(shí)的預(yù)警效果最佳。2σ算法的命中率、虛警率和臨界成功指數(shù)分別為80.2%，41.6%和51.1%，N = 6的Gatlin算法的相應(yīng)結(jié)果分別為82.5%，62.0%和35.2%。另外，詳細(xì)分析了一次多單體雷暴過(guò)程和一次颮線過(guò)程中兩種算法的應(yīng)用情況，結(jié)果也表明Gatlin算法比2σ算法的命中率略高，但虛警率偏高很多，臨界成功指數(shù)偏低。綜合Gatlin算法和σ算法對(duì)冰雹預(yù)報(bào)結(jié)果評(píng)估情況，發(fā)現(xiàn)2σ閃電躍增算法更適于對(duì)北京冰雹天氣的預(yù)警，對(duì)提升閃電數(shù)據(jù)在北京地區(qū)冰雹預(yù)報(bào)業(yè)務(wù)的可用度有一定參考價(jià)值。（田野，姚雯，尹佳莉）

5.23 廣州高建筑物雷電回?fù)艄饷}沖特征分析

為了深入認(rèn)識(shí)負(fù)地閃放電過(guò)程中光輻射信號(hào)的特性，對(duì)廣州高建筑物雷電觀測(cè)站所獲得的回?fù)艄饷}沖波形進(jìn)行了分析。對(duì)觀測(cè)到的88例負(fù)地閃事件中的184次回?fù)簦ò?0次下行閃電首次回?fù)簟?8次下行閃電繼后回?fù)簟?6次上行閃電繼后回?fù)簦┑墓饷}沖特征進(jìn)行了統(tǒng)計(jì)分析。結(jié)果表明：下行閃電首次回?fù)艄饷}沖10%～90%上升時(shí)間T1的算術(shù)平均值/中值為32.5/31.4 μs，20%～80%上升時(shí)間T2的算術(shù)平均值/中值為22.6/22.4 μs，半峰寬度T3的算術(shù)平均值/中值為131.1/117.0 μs。下行閃電繼后回?fù)艄饷}沖T1的算術(shù)平均值/中值為30.4/27.7 μs，T2的算術(shù)平均值/中值為19.5/17.6 μs，T3的算術(shù)平均值/中值為153.6/142.6 μs。在21例下行多回?fù)糌?fù)地閃事件中，光脈沖回?fù)糸g隔時(shí)間在12.6～368.6 ms范圍之間，算術(shù)平均值為78.7 ms，有14%閃電事件存在繼后回?fù)艄饷}沖峰值大于首次回?fù)舻那闆r。上行閃電繼后回?fù)艄饷}沖T1的算術(shù)平均值/中值為27.5/24.3 μs，T2的算術(shù)平均值/中值為17.0/15.7 μs，T3的算術(shù)平均值/中值為132.2/124.5 μs?？傮w上，下行閃電首次回?fù)舻墓饷}沖上升時(shí)間最長(zhǎng)、下行閃電繼后回?fù)舸沃?、上行閃電繼后回?fù)糇钚?下行閃電繼后回?fù)裘}沖半峰寬度比下行閃電首次回?fù)艏吧闲虚W電繼后回?fù)舻母蟆＃S曉磊，呂偉濤，武斌）

5.24 華南颮線系統(tǒng)對(duì)流與層云區(qū)閃電起始和通道位置處的云微物理特征

利用廣州S波段雙偏振雷達(dá)觀測(cè)數(shù)據(jù)和低頻電場(chǎng)探測(cè)陣列三維閃電定位數(shù)據(jù)，分析了2017年5月4日和5月8日華南地區(qū)兩次颮線過(guò)程中閃電起始和通道位置處的雷達(dá)偏振參量和降水粒子特征。兩次颮線中約80%的閃電起始和通道（統(tǒng)稱閃電放電）定位于對(duì)流區(qū)。對(duì)流區(qū)閃電放電位置處的雷達(dá)反射率（ZH）要比層云區(qū)平均大4～5 dBz，其它偏振參量的平均值較為接近。閃電放電位置處的ZH中值隨高度增加而減小，但差分反射率（ZDR）、差分傳播相移率（KDP）和共極化相關(guān)系數(shù)（CC）在-10 ℃層以上隨高度變化不大；-10 ℃層以下，對(duì)流區(qū)閃電放電位置對(duì)應(yīng)ZDR和KDP隨高度下降明顯增大。閃電起始位置的平均ZH比閃電通道位置處的平均ZH大1～2 dBz，但前者在對(duì)流區(qū)內(nèi)對(duì)應(yīng)ZH分布峰值區(qū)間為25～30 dBz，弱于后者的30～35 dBz；同時(shí)，它們的對(duì)比關(guān)系在-20 ℃層上下不同。對(duì)流區(qū)內(nèi)閃電放電位置處的主導(dǎo)性粒子是霰和冰晶，它們的區(qū)域占比接近。在層云區(qū)內(nèi)，閃電放電位置主要是干雪和冰晶，干雪區(qū)域的占比顯著大于冰晶。（趙川鴻，鄭棟，張義軍）

5.25 基于閃電聚類方法的西北太平洋區(qū)域雷暴活動(dòng)特征

利用2010—2018年全球閃電探測(cè)網(wǎng)（WWLLN）觀測(cè)資料，采用基于閃電密度的空間聚類算法（DBSCAN）建立了西北太平洋地區(qū)雷暴數(shù)據(jù)集，研究了該區(qū)域雷暴的時(shí)空分布特征，并進(jìn)行海陸差異對(duì)比。研究結(jié)果表明，在合理設(shè)定DBSCAN參數(shù)閾值的條件下，基于WWLLN閃電聚類的雷暴與天氣雷達(dá)觀測(cè)在時(shí)空分布和過(guò)程演變上具有一致性。西北太平洋區(qū)域的日均雷暴數(shù)為3869，雷暴的閃電密集區(qū)平均面積為557.91 km2，平均延展尺度為31.99 km，平均每小時(shí)每個(gè)雷暴閃電頻次為33次。在空間分布上，東南亞沿海地區(qū)與熱帶島嶼的雷暴活動(dòng)最強(qiáng)，南海的雷暴活動(dòng)強(qiáng)于深海。距離海岸線越近的海域其雷暴面積越大。在季節(jié)分布上，整個(gè)區(qū)域雷暴活動(dòng)在夏季（6—8月）達(dá)到全年最強(qiáng)，南海雷暴活動(dòng)6月達(dá)到峰值，而日本東部近海海域的雷暴活動(dòng)則在冬季達(dá)到最強(qiáng)。我國(guó)內(nèi)陸南方地區(qū)雷暴3月開始顯著增多，雷暴平均面積達(dá)到最大，但雷暴平均閃電頻次5月才達(dá)到峰值。在日變化方面，陸地雷暴活動(dòng)呈現(xiàn)典型的單峰型特征，大部分雷暴發(fā)生在午后及傍晚。海洋雷暴日變化則較為平緩，南海具有其獨(dú)特的雷暴日變化特征。（周鑫，張文娟，張義軍）

5.26 雷暴閃電活動(dòng)特征研究進(jìn)展

從一般雷暴、災(zāi)害性雷暴和臺(tái)風(fēng)的閃電活動(dòng)特征以及雷暴閃電尺度特征四個(gè)方面對(duì)相關(guān)研究進(jìn)行梳理。一般雷暴通常具有正常極性電荷結(jié)構(gòu)，云/地閃比例在3左右（中緯度地區(qū)），地閃中正地閃占比為10%左右，負(fù)地閃位置往往更集中于對(duì)流區(qū)。災(zāi)害性雷暴傾向具有活躍的云閃，低比例的地閃，易出現(xiàn)反極性電荷結(jié)構(gòu)，正地閃比例偏高。閃電活動(dòng)與災(zāi)害性天氣現(xiàn)象之間存在關(guān)聯(lián)性，部分雹暴過(guò)程具有兩次閃電活躍階段。臺(tái)風(fēng)中大部分閃電發(fā)生在外雨帶，眼壁/外雨帶閃電爆發(fā)很可能預(yù)示氣旋強(qiáng)度的增強(qiáng)以及路徑的改變。由閃電持續(xù)時(shí)間、通道空間擴(kuò)展所表征的閃電尺度與雷暴對(duì)流強(qiáng)度相關(guān)。弱對(duì)流雷暴或雷暴的弱對(duì)流區(qū)域可能由水平擴(kuò)展、垂直分層的電荷分布形態(tài)主導(dǎo)，閃電頻次低，閃電空間尺度大；強(qiáng)對(duì)流雷暴或雷暴的強(qiáng)對(duì)流區(qū)域可能由交錯(cuò)分布的小電荷區(qū)主導(dǎo)，閃電頻次高，閃電尺度小。（鄭棟，張文娟，姚雯）

5.27 雷暴云特征數(shù)據(jù)集及我國(guó)雷暴活動(dòng)特征

基于FY-2E氣象衛(wèi)星相當(dāng)黑體亮度溫度（TBB）和云分類數(shù)據(jù)（CLC）及全球閃電探測(cè)網(wǎng)（WWLLN）閃電數(shù)據(jù)，通過(guò)對(duì)TBB不超過(guò)-32 ℃的云區(qū)進(jìn)行橢圓擬合，定義1 h內(nèi)上述云區(qū)或橢圓區(qū)域有WWLLN閃電發(fā)生的個(gè)例為雷暴云，獲得雷暴云時(shí)間、位置、形態(tài)、結(jié)構(gòu)、閃電活動(dòng)等特征參量，構(gòu)建雷暴云特征數(shù)據(jù)集，并基于該數(shù)據(jù)集初步分析了我國(guó)陸地和毗鄰海域的雷暴活動(dòng)特征。研究表明：我國(guó)華南、西南、青藏高原東、中部和南海雷暴最為活躍，華北和東北地區(qū)是北方雷暴活動(dòng)較強(qiáng)的區(qū)域。雷暴活動(dòng)時(shí)間變化海陸差異明顯，陸地雷暴活動(dòng)峰值出現(xiàn)在6—8月，南海雷暴活動(dòng)一個(gè)峰值出現(xiàn)在5月左右，另一峰值出現(xiàn)在8月后，且緯度越低出現(xiàn)越晚。陸地大部分地區(qū)雷暴活動(dòng)在14:00—20:00（北京時(shí)）達(dá)到峰值，毗鄰海域雷暴活動(dòng)峰值主要出現(xiàn)在早上。雷暴云TBB不超過(guò)-32 ℃面積符合對(duì)數(shù)正態(tài)分布，峰值區(qū)間位于1×103～1×104km2，平均值為3.0×104km2。南海雷暴云面積最大，陸地上大于雷暴云面積平均值1.2×105km2的區(qū)域主要分布于我國(guó)地形的第一階梯和柴達(dá)木盆地。（馬瑞陽(yáng)，鄭棟，姚雯）

5.28 熱帶氣旋閃電活動(dòng)特征研究綜述

針對(duì)熱帶氣旋（TC）閃電已有研究，首先從閃電活動(dòng)分布特征、眼壁閃電爆發(fā)對(duì)TC強(qiáng)度和路徑的指示、外雨帶閃電活動(dòng)與雨帶對(duì)流結(jié)構(gòu)的關(guān)系3個(gè)方面進(jìn)行了總結(jié)；其次從動(dòng)力—微物理方面對(duì)TC閃電的形成原因和特征機(jī)理進(jìn)行了梳理；最后提出當(dāng)前研究中存在的兩個(gè)關(guān)鍵問(wèn)題，并對(duì)后續(xù)研究?jī)?nèi)容進(jìn)行了展望?；诘鼗涂栈嘟Y(jié)合的綜合閃電探測(cè)得到的閃電屬性特征參量，有望建立一個(gè)明確的、具有代表性的閃電活動(dòng)-TC強(qiáng)度變化關(guān)系。利用沿海地區(qū)架設(shè)的三維閃電定位系統(tǒng)結(jié)合地基雙偏振雷達(dá)，針對(duì)登陸臺(tái)風(fēng)強(qiáng)對(duì)流過(guò)程開展的綜合觀測(cè)研究，將有助于推進(jìn)閃電觀測(cè)資料在臺(tái)風(fēng)中小尺度強(qiáng)對(duì)流監(jiān)測(cè)、預(yù)警和資料同化中的應(yīng)用。（張文娟，張義軍，鄭棟）

5.29 銣原子簇自發(fā)磁矩的試驗(yàn)觀測(cè)及理論分析

在堿金屬原子簇磁性的研究中，存在自由原子簇含有的原子個(gè)數(shù)及其磁矩難以準(zhǔn)確確定的問(wèn)題，本文采用光磁共振光譜檢測(cè)手段，對(duì)工作溫度約為328 K的飽和銣蒸汽樣品中單原子分子87Rb1和14種簇粒子（87Rb）n'（n' = 2，3，…，15）的磁矩進(jìn)行了深入研究。試驗(yàn)結(jié)果表明：在同一外磁場(chǎng)下，14種簇粒子（87Rb）n'的共振頻率fn'與87Rb1的共振頻率f*之間存在fn'= f*/n'的數(shù)值關(guān)系，并且各簇粒子的磁矩值與振幅值均隨n'的大小和奇、偶性呈現(xiàn)不同性質(zhì)的變化規(guī)律。運(yùn)用分子軌態(tài)理論通過(guò)87Rbn= 87Rbn-1+87Rb聯(lián)合原子簇構(gòu)造模式，給出14種簇粒子87Rbn（n = 2，3，…，15）的基態(tài)和最低激發(fā)態(tài)的電子組態(tài)和分子態(tài)項(xiàng)型，分析了各分子態(tài)的穩(wěn)定性和發(fā)生可見塞曼效應(yīng)的可能性。進(jìn)一步基于雙原子分子磁矩公式計(jì)算，發(fā)現(xiàn)當(dāng)n = n'時(shí)87Rbn的磁矩值與（87Rb）n'的磁矩值嚴(yán)格吻合（平均相對(duì)誤差僅為0.6765%），證實(shí)了（87Rb）n'和87Rbn的對(duì)應(yīng)關(guān)系。（邸淑紅，張陽(yáng)，楊會(huì)靜）

5.30 粵港澳大灣區(qū)兩套閃電定位系統(tǒng)地閃探測(cè)性能的對(duì)比分析

根據(jù)2014—2018年粵港澳閃電定位系統(tǒng)（GHMLLS）和廣東電網(wǎng)地閃定位系統(tǒng)（GDLLS）兩套閃電定位系統(tǒng)的觀測(cè)資料，對(duì)粵港澳大灣區(qū)范圍內(nèi)二者的地閃探測(cè)性能進(jìn)行評(píng)估和對(duì)比。結(jié)果表明：在粵港澳大灣區(qū)，對(duì)于地閃回?fù)粲涗洠瑥母髟路萦涗浐涂臻g密度的分布上來(lái)看，GDLLS的探測(cè)數(shù)都多于GHMLLS，二者的比值為1.24；兩套系統(tǒng)總回?fù)?、?fù)回?fù)?、正回?fù)舻脑路植己腿兆兓卣骰疽恢?；兩系統(tǒng)地閃回?fù)舻钠ヅ溆涗浽诖鬄硡^(qū)大部分區(qū)域內(nèi)的偏差量都在1.5 km內(nèi)；對(duì)于匹配后的負(fù)、正回?fù)綦娏鞣逯担哂休^強(qiáng)的相關(guān)性，相關(guān)系數(shù)分別為0.99和0.98，GDLLS的負(fù)、正回?fù)綦娏鞣逯捣謩e為GHMLLS的1.47倍和1.45倍。（張悅，呂偉濤，陳綠文）

6 模式和再分析資料

6 Model and reanalysis data

6.1 A large-eddy simulation study on the diurnally evolving nonlinear trapped lee waves over a twodimensional steep mountain

The diurnally evolving trapped lee wave over a small-scale two-dimensional steep mountain is investigated in large-eddy simulations based on a fully compressible and nonhydrostatic model (Icosahedral Nonhydrostatic, ICON) with triangular grids of 50-m-edge length. An idealized atmospheric profile derived from a realistic case is designed to account for influences from the stagnant layer near the surface, the stability of the atmospheric boundary layer (ABL) and the upper-level jet. First, simulations were done to bridge from the linear regime to the nonlinear regime by increasing the mountain height, which showed that largeramplitude lee waves with longer wavelength can be produced in the nonlinear regime than in the linear regime.Second, the effects of the stagnant layer near the surface and the ABL stability were explored, which showed that the stagnant layer or the stable ABL can play a similar wave-absorbing role in the nonlinear regime as in linear theories or simulations. Third, the role of the upper-level jet was explored, indicating that a stronger(weaker) upper-level jet can help to produce longer (shorter) lee waves. The stable ABL with a stagnant layer can more (less) efficiently absorb the longer (shorter) lee waves due to the stronger (weaker) jet, so that the wave response is more sensitive to the wave-absorption layer when an upper-level jet is present. Finally,the momentum budget was analyzed to explore the interaction between the upper and lower levels of the troposphere, which showed that the momentum flux due to the upward-propagating waves and trapped waves varies with the upper-level jet strength and low-level stagnancy and ABL stability. (Xue Haile, Giorgetta Marco A.)

6.2 A new perspective on evaluating high-resolution urban climate simulation with urban canopy parameters

The “state-of-the-art” urban climate models have not been evaluated against dense meteorological networks under various weather conditions. In this study, we conducted high-resolution urban climate simulations in Beijing and investigated the relationship between their performances and urban canopy parameters (UCPs). The latest version of single-layer (UCM) and multi-layer (BEP) urban canopy models were tested separately. Results show that model performances are insensitive to rainfall events in summer, but change significantly with wind conditions in winter. Inclusion of UCPs has a limited impact on air temperature simulations. In terms of wind speed simulations, consistent overestimations by UCM and BEP are found in both summer and winter. The overestimation by BEP reduces significantly when UCPs are available, especially on windy days in winter. On the other hand, performance of UCM can degrade over urban areas with canopy parameters. Wind speed biases are found to correlate significantly with UCPs. The accuracy of wind speed simulations by UCM and BEP increases with urban fraction and building surface ratio. This indicates poor model performances over low-density urban areas, which requires enhanced aerodynamic parameterizations to better account for UCPs. This study reveals the limitation of current urban climate simulations and provides guidance for future model developments. (Yu Miao, Chen Xuan, Yang Jiachuan)

6.3 A study of extrapolation nowcasting based on IVAP-retrieved wind

In this study, we propose a new way to obtain motion vectors using the integrating velocity-azimuth process (IVAP) method for extrapolation nowcasting. Traditional tracking methods rely on tracking radar echoes of a few time slices. In contrast, the IVAP method does not depend on the past variation of radar echoes; it only needs the radar echo and radial velocity observations at the latest time. To demonstrate it is practical to use IVAP-retrieved winds to extrapolate radar echoes, we carried out nowcasting experiments using the IVAP method, and compared these results with the results using a traditional method, namely, the tracking radar echoes by correlation (TREC) method. Comparison based on a series of large-scale mature rainfall cases showed that the IVAP method has similar accuracy to that of the TREC method. In addition, the IVAP method provides the vertical wind profile that can be used to anticipate storm type and motion deviations. (Luo Yi,Liang Xudong, Wang Gang)

6.4 Advances in research on the ITCZ: Mean position, model bias, and anthropogenic aerosol influences

The zonal-mean position of the intertropical convergence zone (ITCZ) and its shift in the meridional direction significantly influence both the tropical and even global climate. This work reviews three aspects of the progress in ITCZ-relevant research: 1) the mechanism behind the asymmetry of the ITCZ annual- and zonal-mean positions relative to the equator; 2) causes of the double-ITCZ problem (pervasive in climate models) and the efforts to solve it; and 3) the physical mechanisms by which anthropogenic aerosols affect the location of the zonal-mean ITCZ. According to recent studies, the north-of-the-equator location of the annualand zonal-mean ITCZ is mainly driven by the cross-equatorial energy transports in the ocean, induced by the Atlantic overturning circulation. A quantitative relationship between the ITCZ shift and the anomalous crossequatorial energy transport in the atmosphere has been found. Presently, the double-ITCZ problem is still the most common and pronounced bias in tropical precipitation simulations with climate models. Recently,some studies have found that simply correcting the biases in hemispheric energy contrast does not improve the simulation of the ITCZ with climate models; whereas others have found that improving model resolutions and convective parameterizations in climate models, such as entrainment rate, rain-droplet re-evaporation, and convection triggering function, can alleviate the double-ITCZ bias. Therefore, it seems that the double-ITCZ problem in climate models is rooted in the complex physics of the models, which is not yet well-understood. In addition, anthropogenic aerosols are suggested to be able to induce meridional shifts of the ITCZ, but through various physical mechanisms. Absorbing aerosols like black carbon influence the ITCZ position basically via instantaneous absorption of shortwave radiation in the atmosphere, whereas scattering aerosols like sulfate affect the location of the ITCZ through the cloud lifetime effect and the subsequent response of surface evaporation. (Zhang Hua, Ma Xinyu, Zhao Shuyun)

6.5 An investigation into the vertical structures of low-altitude atmosphere over the Central Taklimakan Desert in summer

In this study, 1-month continuous radiosonde observational data were applied to present the low-altitude vertical structures and their evolutions over the Central Taklimakan Desert (CTD). The primary focus is to highlight the vertical structures near the ground with the high-resolution (10 m in height and 6 h in time)radiosonde data. One of the unique features evident in our results is an obvious diurnal transition in lower layers near the ground due to strong surface heating or cooling. Unlike a traditional vertical structure in the boundary layer observed over a nondesert surface, both superadiabatic and inversion layers are distinct during the day. More specifically, the superadiabatic layer is obvious in the daytime because of strong solar radiation over the desert, and the superadiabatic can reach up to 0.2 km. In contrast, an apparent inversion layer forms in the nighttime due to the surface cooling. It is found that the surface forcing mainly dominates the structures in the boundary layer. At last, the vertical structures from the observations are compared with those from the ERA-Interim and MERRA2 reanalysis data sets. The results indicate that both reanalysis products can provide similar vertical profile patterns and diurnal variations. However, the diurnal transitions of temperature and wind profiles over the CTD are underestimated severely by both reanalysis data. Besides, the reanalysis data sets completely miss the superadiabatic near the ground in the daytime. (Yin Jinfang, Gu Haodong, Huang Jie)

6.6 Challenges in developing finite-volume global weather and climate models with focus on numerical accuracy

High-resolution global non-hydrostatic gridded dynamic models have drawn significant attention in recent years in conjunction with the rising demand for improving weather forecasting and climate predictions. By far it is still challenging to build a high-resolution gridded global model, which is required to meet numerical accuracy, dispersion relation, conservation, and computation requirements. Among these requirements, this review focuses on one significant topic—the numerical accuracy over the entire non-uniform spherical grids.The paper discusses all the topic-related challenges by comparing the schemes adopted in well-known finitevolume-based operational or research dynamical cores. It provides an overview of how these challenges are met in a summary table. The analysis and validation in this review are based on the shallow-water equation system. The conclusions can be applied to more complicated models. These challenges should be critical research topics in the future development of finite-volume global models. (Xie Yuanfu, Qin Zilong)

6.7 Changes in anthropogenic particulate matters and resulting global climate effects since the Industrial Revolution

In order to quantify air pollution effects on climate change, we investigated the climate response associated with anthropogenic particulate matters (PMs) by dividing fine PM (PM2.5, particle size ≤2.5 μm)and coarse particulate matter (CPM, particle size >2.5 μm) in great detail in this work, with an aerosol-climate coupled model. We find that the changes in PM2.5and CPM are very different and thus result in different, even opposite effects on climate, especially on a regional scale. The column burden of PM2.5increases globally from 1850 to the present, especially over Asia’s southern and eastern parts, whereas the column concentration of CPM increases over high-latitude regions and decreases over South Asia. The resulted global annual mean effective radiative forcing (ERF) values due to PM2.5and CPM changes are -1.21 W m?2and -0.24 W m?2,respectively. Increases in PM2.5result in significant cooling effects on the climate, whereas changes in CPM produce small and even opposite effects. The global annual mean surface air temperature (SAT) decreases by 0.94 K due to PM2.5increase. Coolings caused by increased PM2.5are more apparent over the Northern Hemisphere (NH) terrain and ocean at mid- and high- latitudes. Increases in SATs caused by increased CPM are identified over high latitudes in the NH, whereas decreases are identified over mid-latitude regions. Strong cooling due to increased PM2.5causes a southward shift of the Intertropical Convergence Zone (ITCZ),whereas the Hadley circulation associated with CPM is enhanced slightly over both hemispheres, along with the weak movement of corresponding ITCZ. The global annual mean precipitation decreases by approximately 0.11 mm day?1due to the increased PM2.5. Generally, PM2.5concentration changes contribute more than 80%of the variation caused by all anthropogenic aerosols in ERF, SAT, cloud fraction, and precipitation. (Yang Dongdong, Zhang Hua, Wang Zhili)

6.8 Discontinuous Galerkin isogeometric analysis of convection problem on surface

The objective of this work is to study finite element methods for approximating the solution of convection equations on surfaces embedded in R-3. We propose the discontinuous Galerkin (DG) isogeometric analysis(IgA) formulation to solve convection problems on implicitly defined surfaces. Three numerical experiments shows that the numerical scheme converges with the optimal convergence order. (Wang Liang, Xiong Chunguang, Yuan Xinpeng)

6.9 Effects of mosaic representation of land use/land cover on skin temperature and energy fluxes in Noah-MP land surface model over China

The representations of land use/land cover (LULC) play an important role in land surface models (LSMs)for the simulation of the energy flux partition, soil moisture redistribution, and runoff generation. This study was designed to investigate the regional effects of mosaic LULC representations on skin temperature (Ts) and energy fluxes over China at three horizontal resolutions and how these effects changed with climate regimes,using Noah with multiparameterization (Noah-MP) LSM. The current officially released Noah-MP only considered the most abundant LULC type within one model grid. In this study, the mosaic method considering all the LULC types existing in one model grid was implemented into Noah-MP. Against the reference data(including MODIS land surface temperature products, FLUXCOM energy flux data and Numerical Terra dynamic Simulation Group evapotranspiration data), the mosaic method generally performed better than the default method and reduced the root-mean-squared-error of Tsand energy fluxes significantly over urban region. The mosaic method affected the Tsand energy fluxes by changing leaf area index and soil moisture,mainly by the former. The warm (monthly mean air temperature larger than 10 ) and relatively humid climate(annual total precipitation larger than 200 mm) could enlarge the effect of mosaic method on Tsand energy fluxes. The mosaic method reduced discrepancies of Tsand energy fluxes among three horizontal resolutions(0.0625°, 0.25°, and 0.50°), especially over the heterogeneous vegetated and urban region. Key Points Mosaic representation of land use/land cover was implemented in Noah-MP to obtain more accurate land surface information Noah-MP incorporated with the mosaic method improved the skin temperature and energy fluxes.Warm climate regimes enlarged the effect of mosaic method on skin temperature and energy fluxes through LAI changes. (Zhang Guo, Li Jianduo, Zhou Guangsheng)

6.10 Effects of organic soil in the Noah-MP land-surface model on simulated skin and soil temperature profiles and surface energy exchanges for China

Inclusion of the thermal and hydraulic effect of soil organic matter plays an important role in land-surface models (LSMs) for simulating soil temperature and surface energy exchanges. The current officially released Noah with multiparameterization (Noah-MP) LSM, implemented in the community weather research and forecasting (WRF) model, does not include a parameterization for soil organic matter. In this study, the thermal and hydraulic effect of soil organic matter was parameterized into Noah-MP LSM. Based on the profiled soil organic matter data for China and the observations of skin temperature and soil temperature profiles from more than 2000 surface meteorological stations, we investigated the effects of organic soil using the Noah-MP LSM with and without the profiled soil organic matter at the regional scales. Compared with the simulation without the inclusion of organic soil parameterization, the Noah-MP LSM simulation with the profiled soil organic matter improved the skin temperature and soil temperature profiles, especially soil temperature in deep soils under cold and arid regions. The realistic representation of snow depth and the snow insulation dependency on snow depth were confirmed to be a pre-requisite in Noah-MP in the high latitudes. By incorporating the profiled soil organic matter, the Noah-MP LSM enlarged the regional mean sensible heat flux (SH) and lower the regional mean latent heat flux (LH). In the warm and humid regions, a relatively smaller effect of organic soil on soil temperature could lead to a larger effect on SH and LH, especially LH. (Zhang Guo, Chen Yueli, Li Jianduo)

6.11 Evaluating the impacts of cloud microphysical and overlap parameters on simulated clouds in global climate models

The improvement of the accuracy of simulated cloud-related variables, such as the cloud fraction, in global climate models (GCMs) is still a challenging problem in climate modeling. In this study, the influence of cloud microphysics schemes (one-moment versus two-moment schemes) and cloud overlap methods(observation-based versus a fixed vertical decorrelation length) on the simulated cloud fraction was assessed in the BCC_AGCM2.0_CUACE/Aero. Compared with the fixed decorrelation length method, the observationbased approach produced a significantly improved cloud fraction both globally and for four representative regions. The utilization of a two-moment cloud microphysics scheme, on the other hand, notably improved the simulated cloud fraction compared with the one-moment scheme; specifically, the relative bias in the global mean total cloud fraction decreased by 42.9%?84.8%. Furthermore, the total cloud fraction bias decreased by 6.6% in the boreal winter (DJF) and 1.64% in the boreal summer (JJA). Cloud radiative forcing globally and in the four regions was improved by 0.3%?1.2% and 0.2%?2.0%, respectively. Thus, our results showed that the interaction between clouds and climate through microphysical and radiation processes is a key contributor to simulation uncertainty. (Wang Haibo, Zhang Hua, Xie Bing)

6.12 Evaluation of a flexible single ice microphysics and a Gaussian probability-density-function macrophysics scheme in a single column model

Scale-aware parameterizations of subgrid scale physics are essentials for multiscale atmospheric modeling.A single-ice (SI) microphysics scheme and Gaussian probability-density-function (Gauss-PDF) macrophysics scheme were implemented in the single-column global-to-regional integrated forecast system model (SGRIST)and they were tested using the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) and the Atmospheric Radiation Measurement Southern Great Plains Experiment in 1997 (ARM97). Their performance was evaluated against observations and other reference schemes. The new schemes simulated reasonable precipitation with proper fluctuations and peaks, ice, and liquid water contents, especially in lower levels below 650 hPa during the wet period in the TWP-ICE. The root mean square error (RMSE) of the simulated cloud fraction below 200 hPa was 0.10/0.08 in the wet/dry period, which showed an obvious improvement when compared to that, i.e., 0.11/0.11 of the original scheme. Accumulated ice water content below the melting level decreased by 21.57% in the SI. The well-matched average liquid water content displayed between the new scheme and observations, which was two times larger than those with the referencing scheme. In the ARM97 simulations, the SI scheme produced considerable ice water content, especially when convection was active.Low-level cloud fraction and precipitation extremes were improved using the Gauss-PDF scheme, which displayed the RMSE of cloud fraction of 0.02, being only half of the original schemes. The study indicates that the SI and Gauss-PDF schemes are promising approaches to simplify the microphysics process and improve the low-level cloud modeling. (Li Jiabo, Peng Xindong, Li Xiaohan)

6.13 Evaluation of CMIP6 global climate models for simulating land surface energy and water fluxes during 1979?2014

This study examined the overall performance of the climate models in the Coupled Model Intercomparison Project phase 6 (CMIP6) in simulating the key energy and water fluxes over land. For this purpose, this study selected multiple land flux products as reference data sets and assessed the global spatial means, patterns, trends, seasonal cycles, and regional mean estimates of the sensible heat (SH), latent heat (LH),net radiation (RN), runoff (RF), and precipitation (PR) simulated by 32 CMIP6 models in recent decades. The global (Antarctica, Greenland, and hot deserts are not included) mean SH, LH, RN, RF, and PR simulated by the CMIP6 models are 37.55 ± 4.81 W m?2, 49.88 ± 5.31 W m?2, 89.10 ± 4.45 W m?2, 351.31 ± 95.28 mm yr?1,and 948.35 ± 88.77 mm yr?1, respectively. The ensemble median of CMIP6 simulations (CMIP6-MED) can provide robust estimates of global and regional land fluxes, which are within the ranges given by the reference data sets, and highly consistent spatiotemporal patterns of these fluxes. The comparison of CMIP6-MED with the first preferred reference data sets shows that CMIP6-MED generally overestimates the water and energy fluxes over land, except for the simulated RF and PR in the Amazon region. The most disagreements between CMIP6-MED and the reference data sets occur in South America (particularly the Amazon region) and the Tibetan Plateau. Finally, the sources of model biases are discussed. It is suggested that current land flux products should be widely used to optimize the structures and parameters of climate models in future work. (Li Jianduo, Miao Chiyuan, Wei Wei)

6.14 Evaluation of five reanalysis products with radiosonde observations over the Central Taklimakan Desert during summer

To provide guidance for the use of reanalysis data in the Central Taklimakan Desert (CTD), five reanalysis products are evaluated based on the radiosonde data obtained from two field experiments during summer for the first time in the CTD, including the European Center for Medium-Range Weather Forecasts (ECMWF)reanalysis version 5 (ERA5), ECMWF reanalysis-interim (ERA-Interim), Japanese 55-years reanalysis(JRA55), modern-era retrospective analysis for research and applications version 2 (MERRA2), and the National Centers for Environmental Prediction-Department of Energy reanalysis version 2 (NCEP2). The results show that reanalysis temperature (T), specific humidity (Q), geopotential height (GPH), and wind field(U and V components) are consistent with the radiosonde observations in terms of the vertical distribution. In general, ERA5 has the best performance in the CTD during the study period, followed closely by ERA-Interim.However, NCEP2 produces the largest error. The errors of all the reanalysis data show significant diurnal variations, and the diurnal variations differ from each other. Moreover, the results indicate that the reanalysis datasets have the largest deviation at 850 hPa (near the ground), which means that in the desert region complex interactions may exist between the land surface and the atmosphere. Therefore, more attention should be paid to the description of complex interactions between land and atmosphere over the moving-sand desert region in the numerical models. (Huang Jie, Yin Jinfang, Wang Minzhong)

6.15 High-order conservative and oscillation-suppressing transport on irregular hexagonal grids

A third-order numerical scheme was developed for 2D irregular hexagonal meshes for the advection problems in this study. The scheme is based on a multi-moment constrained finite-volume method (MCV) in Cartesian coordinates and entails the introduction of a general integration method over a hexagonal cell. Unlike in the conventional finite-volume method, various discrete moments, that is, point value and volume-integrated average, are adopted as computational constraints to achieve high-order computation. The high-order spatial reconstruction can therefore be built in a local space, which considerably reduces the stencil length. The numerical scheme is tested using various idealized experiments. Compared with the existing schemes, this scheme is demonstrated to be flexible for application in irregular hexagonal meshes without increasing cost or compromising on accuracy. The general integration formulation based on a third-order polynomial helps to expand the application to arbitrary hexagons that does not require the use of centroids as computational points or Voronoi tessellation. It is also convenient to define the orthogonal wind components in the Cartesian system to directly drive the atmospheric transport. (Jiao Han, Peng Xindong, Che Yuzhang)

6.16 Impact of parameterizing the turbulent orographic form drag on convection-permitting simulations of winds and precipitation over South China during the 2019 pre-summer rainy season

A turbulent orographic form drag (TOFD) parameterization, which accounts for the unresolved drag induced by the subgrid orographic variance, is implemented in the Weather Research and Forecasting (WRF)model with a horizontal grid spacing of 3 km. Its impact on the surface wind and precipitation forecasts over South China during a pre-summer rainy season (April?June 2019) is evaluated based on 3-hour observations from more than 2500 stations, by comparing the results from two series of parallel simulation with the TOFD parameterization turned on or off, respectively. Results show that the seasonal mean root mean square error(RMSE) and bias of the surface wind have been significantly reduced by more than 7% and 5%, respectively.The low-level wind is also shown improved by comparing the two series of simulations with 12-hour observations from 26 sounding stations. Consequently, the equitable threat score (ETS) is increased by the TOFD parameterization for most rainfall-intensity categories, and the six-category mean ETS shows an improvement of more than 3%. The mechanism of the TOFD impact on low-level wind and precipitation is investigated as well. The low-level southwesterlies from the South China Sea flow over the rough land in South China are found to be weakened, which leads to the low-level wind convergence and more precipitation over those regions. Moreover, this effect is more apparent during the daytime. (Xue Haile, Zhou Xu, Luo Yali)

6.17 Modulation of snow on the daily evolution of surface heating over the Tibetan Plateau during winter: Observational analyses

Studying the daily evolution of turbulent fluxes modulated by snowfall over the Tibetan Plateau (TP) is of great importance to understand the features of the change in the TP heat source/sink and its contribution to Asian atmospheric circulation and weather processes. However, the lack of data over the TP restricts the detailed studies. Based on observations from four sites of the Third TP Atmospheric Scientific Experiment,the process of surface energy balance impacted by snow is investigated. The results show that the surface albedo largely increases on the first day of snow and then slowly decreases. Correspondingly, the sensible heat(H) flux sharply decreases after snow and then gradually recovers to the original level during the following approximately 10 days. The latent heat (LE) flux becomes more active and stronger after snowfall and persists for a longer period than H, since the soil moisture may still contribute to a high LE after snowmelt.As the synergistic result of H and LE modulated by snow, the surface turbulent heating (i.e., the sum H and LE) of the TP decreases at the early period of snow events and then even enhances to a higher level after the snowmelt than before snow. Comparison analyses reveal that the impact of snow on the H and LE over the TP is much stronger than over similar latitude low-altitude regions in North America and Europe, which may be partly attributed to the larger and more drastic change of the surface net solar radiation associated with snow processes in the TP. The ERA5 and CFS reanalysis data sets fail to reproduce the modulation of snow on the heat fluxes, which suggests that the physical schemes of the models should be further improved based on the observational analyses over TP. This study may help further understand the detailed physical processes of modulation of snow events on Asian weather processes during winter and is also conducive to the improvement of surface parameterization schemes of models. (Xin Yufei, Liu Ge, Chen Yueli)

6.18 Potential driving factors on surface solar radiation trends over China in recent years

The annual mean surface solar radiation (SSR) trends under all-sky, clear-sky, all-sky-no-aerosol, and clear-sky-no-aerosol conditions as well as their possible causes are analyzed during 2005?2018 across China based on different satellite-retrieved datasets to determine the major drivers of the trends. The results confirm clouds and aerosols as the major contributors to such all-sky SSR trends over China but play differing roles over sub-regions. Aerosol variations during this period result in a widespread brightening, while cloud effects show opposite trends from south to north. Moreover, aerosols contribute more to the increasing all-sky SSR trends over the northern China, while clouds dominate the SSR decline over the southern China. A radiative transfer model is used to explore the relative contributions of cloud cover from different cloud types to the alltypes-of-cloud-cover-induced (ACC-induced) SSR trends during this period in four typical sub-regions over China. The simulations point out that the decreases in low-cloud-cover (LCC) over the North China Plain are the largest positive contributor of all cloud types to the marked annual and seasonal ACC-induced SSR increases, and the positive contributions from both high-cloud-cover (HCC) and LCC declines in summer and winter greatly contribute to the ACC-induced SSR increases over East China. The contributions from mediumlow-cloud-cover (mid-LCC) and LCC variations dominate the ACC-caused SSR trends over the southwestern and South China all year round, except for the larger HCC contribution in summer. (Wang Qiuyan, Zhang Hua,Yang Su)

6.19 Reconstruction of missing data in weather radar image sequences using deep neuron networks

Missing data in weather radar image sequences may cause bias in quantitative precipitation estimation(QPE) and quantitative precipitation forecast (QPF) studies, and also the obtainment of corresponding highquality QPE and QPF products. The traditional approaches that are used to reconstruct missing weather radar images replace missing frames with the nearest image or with interpolated images. However, the performance of these approaches is defective, and their accuracy is quite limited due to neglecting the intensification and disappearance of radar echoes. In this study, we propose a deep neuron network (DNN), which combines convolutional neural networks (CNNs) and bi-directional convolutional long short-term memory networks(CNN-BiConvLSTMs), to address this problem and establish a deep-learning benchmark. The model is trained to be capable of dealing with arbitrary missing patterns by using the proposed training schedule. Then the performances of the model are evaluated and compared with baseline models for different missing patterns.These baseline models include the nearest neighbor approach, linear interpolation, optical flow methods,and two DNN models three-dimensional CNN (3DCNN) and CNN-ConvLSTM. Experimental results show that the CNN-BiConvLSTM model outperforms all other baseline models. The influence of data quality on interpolation methods is further investigated, and the CNN-BiConvLSTM model is found to be basically uninfluenced by less qualified input weather radar images, which reflects the robustness of the model. Our results suggest good prospects for applying the CNN-BiConvLSTM model to improve the quality of weather radar datasets. (Gao Lihao, Zheng Yu, Wang Yaqiang, Xia Jiangjiang, Chen Xunla, Li Bin, Luo Ming, Guo Yuchen)

6.20 Classification of the circulation patterns related to strong dust weather in China using a combination of the Lamb-Jenkinson and K-means clustering methods

Sand and dust storms (SDSs) cause major disasters in the northern China. They have serious impacts on human health, daily life, and industrial and agricultural production, in addition to threatening the regional ecological environment and social economy. Based on meteorological observational data and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 dataset for spring 2000–2021, we used the Lamb-Jenkinson circulation classification method to classify the three major areas influencing SDSs in the northern China. We also used the K-means clustering method to classify the overall circulation pattern in the northern China. Our results show that the circulation types favoring SDSs in the southern basin of Xinjiang are southwesterly winds (SW), cyclones (C), and anticyclones (A). The circulation types favoring SDSs in the western Inner Mongolia and southern Mongolia are northwesterly winds (NW), northerly winds (N), cyclones(C), and anticyclones (A). The circulation types favoring SDSs in the central Inner Mongolia are northwesterly winds (NW), northerly winds (N), southwesterly winds (SW), and anticyclones (A). The 500 hPa and surface circulation patterns in China can be divided into nine types. Among them, five dominant circulation patterns favor strong SDSs: a cold high-pressure region and cold front (T1), a Mongolian cyclone (T2), a mixed type of Mongolian cyclone and cold front (T3), a thermal depression and cold front (T5), and a cold front (T8). During 2000?2004, the T8 circulation pattern occurred most frequently as the main influencing circulation. From 2005 to 2010, the T3 and T8 circulation patterns dominated. Circulation patterns T1 and T3 dominated during 2011–2015 and 2016–2020, respectively. We analyzed the main circulation patterns for four SDS events occurring in 2021 by combining the Lamb-Jenkinson and k-means methods. The SDS events in 2021 were closest to the T3 circulation pattern and were mainly influenced by Mongolian cyclones and surface cold fronts. The main propagation paths were westerly and northwesterly. (Yi Ziwei, Wang Yaqiang, Chen Wencong, Guo Bin, Zhang Bihui, Che Huizheng, Zhang Xiaoye)

6.21 IPCC AR6對(duì)地球氣候系統(tǒng)中反饋機(jī)制的新認(rèn)識(shí)

氣候反饋反映了氣候系統(tǒng)內(nèi)部對(duì)外界干擾的適應(yīng)過(guò)程，在很大程度上影響對(duì)未來(lái)氣候變化的預(yù)估。本文對(duì)政府間氣候變化專門委員會(huì)（IPCC）第六次評(píng)估報(bào)告（AR6）中有關(guān)氣候反饋的內(nèi)容進(jìn)行了梳理。相比第五次評(píng)估報(bào)告（AR5），AR6對(duì)云反饋的認(rèn)識(shí)有了較大的提高，尤其是副熱帶海洋上空低云的反饋。AR6認(rèn)為在高信度上云反饋參數(shù)為正值，即對(duì)氣候變化起到一種放大效應(yīng)。不過(guò)，云反饋的不確定范圍在所有反饋機(jī)制中依然是最大的。除了普朗克反饋外，其他反饋機(jī)制（包括水汽、溫度直減率、地表反照率、云、生物地球物理和非CO2生物地球化學(xué)反饋）均在正值區(qū)間或零附近，總體上對(duì)氣候變化起到放大效應(yīng)。AR6對(duì)總的氣候反饋的估計(jì)值為-1.16 W/（m2.℃），5%～95%的置信區(qū)間為（-1.81～-0.51） W/（m2.℃）。隨著氣候平均態(tài)的增暖，氣候反饋參數(shù)很可能會(huì)更靠近正值。（趙樹云，孔鈴涵，張華）

6.22 IPCC AR6報(bào)告解讀：地球能量收支、氣候反饋和氣候敏感度

文中對(duì)IPCC第六次評(píng)估報(bào)告（AR6）第一工作組（WGI）報(bào)告的第七章關(guān)于地球能量收支、氣候反饋和氣候敏感度中的重要內(nèi)容進(jìn)行了凝練，并簡(jiǎn)要總結(jié)該方面的最新研究成果和結(jié)論。評(píng)估顯示，自工業(yè)革命以來(lái)，人類活動(dòng)造成的有效輻射強(qiáng)迫（ERF）為2.72（1.96～3.48）W/m2，其中，均勻混合溫室氣體的貢獻(xiàn)為3.32（3.03～3.61）W/m2，氣溶膠的貢獻(xiàn)為-1.1（-1.7～-0.4）W/m2。凈的氣候反饋參數(shù)為-1.16（-1.81～-0.51）W/（m2.℃），云仍然是氣候反饋整體不確定性的最大來(lái)源。平衡態(tài)氣候敏感度（ECS）和瞬態(tài)氣候響應(yīng)（TCR）可用于評(píng)估全球平均地表溫度對(duì)強(qiáng)迫的響應(yīng)，是衡量全球氣候響應(yīng)的有效手段。ECS和TCR的最佳估計(jì)分別為3.0（2.0～5.0）℃和1.8（1.2～2.4）℃。（張華，王菲，趙樹云）

6.23 尺度自適應(yīng)大氣邊界層參數(shù)化改進(jìn)及其對(duì)一次海霧的數(shù)值模擬研究

大氣邊界層湍流運(yùn)動(dòng)是地球大氣運(yùn)動(dòng)最重要的能量輸送過(guò)程之一。當(dāng)數(shù)值模式分辨率接近活躍含能湍渦長(zhǎng)度尺度時(shí)，湍流運(yùn)動(dòng)被部分解析，被稱為“灰色區(qū)域”，傳統(tǒng)的邊界層方案不適合此時(shí)模式湍流問(wèn)題的描述。為了提高模式邊界層方案在包括“灰色區(qū)域”的不同網(wǎng)格尺度上的描述能力，適應(yīng)不同分辨率模式的需要，在雷諾平均湍流理論基礎(chǔ)上，修正Mellor-Yamada-Nakanishi-Niino （MYNN）方案湍流長(zhǎng)度尺度參數(shù)和非局地湍流的參數(shù)表達(dá)，改進(jìn)濕度和溫度在“灰色區(qū)域”的湍流輸送參數(shù)化及對(duì)網(wǎng)格尺度的自適應(yīng)能力。利用改進(jìn)的MYNN尺度自適應(yīng)方案，分別采用3 km和1 km、1.5 km和0.5 km分辨率單向嵌套網(wǎng)格WRF中尺度模式，對(duì)2014年2月26日的一次黃海海霧過(guò)程進(jìn)行模擬試驗(yàn)，檢驗(yàn)不同分辨率下改進(jìn)后的MYNN大氣邊界層參數(shù)化方案的合理性和對(duì)海霧的模擬效果。尺度自適應(yīng)MYNN大氣邊界層參數(shù)化方案在千米級(jí)網(wǎng)格尺度上獲得穩(wěn)定、合理的湍流垂直輸送計(jì)算結(jié)果。參照霧區(qū)衛(wèi)星云圖，不同分辨率模式低層云水混合比模擬結(jié)果具有穩(wěn)定表現(xiàn)，模擬的霧區(qū)分布和溫度、濕度等物理量結(jié)構(gòu)都較好地再現(xiàn)了再分析“觀測(cè)事實(shí)”，初步表明該參數(shù)化方案有較高的網(wǎng)格尺度自適應(yīng)能力。（盧緒蘭，彭新東）

6.24 次季節(jié)波動(dòng)對(duì)青藏高原及其下游東亞季風(fēng)區(qū)降水的影響

影響青藏高原及其下游季風(fēng)區(qū)的次季節(jié)波動(dòng)對(duì)我國(guó)乃至亞洲地區(qū)的洪澇災(zāi)害起著不容忽視的作用。本文回顧了近40年來(lái)在青藏高原及下游東亞季風(fēng)區(qū)的次季節(jié)降水方面取得的進(jìn)展，主要從影響降水的次季節(jié)尺度波動(dòng)的特征、來(lái)源和傳播機(jī)制對(duì)研究成果進(jìn)行了歸納?；仡櫛砻?，青藏高原及下游東亞季風(fēng)區(qū)的降水主要受到來(lái)自歐亞大陸及孟加拉灣——南海地區(qū)30～60天及準(zhǔn)雙周次季節(jié)波動(dòng)的強(qiáng)烈影響，同時(shí)高原次季節(jié)波動(dòng)能夠直接與間接地影響下游季風(fēng)區(qū)降水。本文有助于系統(tǒng)理解高原及下游東亞季風(fēng)區(qū)次季節(jié)大氣振蕩及降水，并基于現(xiàn)有研究提出了該領(lǐng)域值得進(jìn)一步研究的重點(diǎn)和方向，具有一定的科學(xué)意義和參考價(jià)值。（楊琳韻，王淑瑜，符淙斌）

6.25 復(fù)雜地形對(duì)大理地區(qū)風(fēng)場(chǎng)的影響研究——兼論觀測(cè)、理論和數(shù)值模擬配合解答科學(xué)問(wèn)題

引用了一次基于真實(shí)地形和大氣背景的大渦模擬，闡述了大理大風(fēng)成因并就如何配合使用觀測(cè)資料、理論研究和模式模擬來(lái)研究小尺度高影響天氣現(xiàn)象進(jìn)行了討論。通過(guò)大渦模擬的方式補(bǔ)充了觀測(cè)的稀疏和理論的缺失，解答了大理三處地方大風(fēng)形成的機(jī)制。同時(shí)又反過(guò)來(lái)分別對(duì)觀測(cè)、理論和模式發(fā)展提出了新要求。（1）背風(fēng)波是否真實(shí)存在，具有何種日變化和季節(jié)變化特征，如要提供更加堅(jiān)實(shí)的證據(jù)，就必須要有長(zhǎng)期的三維流場(chǎng)觀測(cè)。（2） 背風(fēng)波為什么會(huì)有周期性增強(qiáng)伸展和減弱縮短的現(xiàn)象，這要求對(duì)這種特殊的大振幅背風(fēng)波的機(jī)理進(jìn)行研究，而機(jī)理研究要求進(jìn)行理論研究和理想模擬研究，因此本次大渦模擬對(duì)模式和理論也提出了新要求。（3）背風(fēng)波的這種周期性變化會(huì)對(duì)動(dòng)量在垂直和水平方向上的分布造成何種影響，其導(dǎo)致的背風(fēng)波轉(zhuǎn)子會(huì)對(duì)水汽和熱量通量造成何種影響，這要求建立這種大振幅背風(fēng)波的參數(shù)化方案或者使用超高分辨率大范圍模擬，這對(duì)模式研發(fā)也提出了新要求。（薜海樂(lè)）

6.26 基于功率譜的風(fēng)廓線雷達(dá)回波強(qiáng)度定標(biāo)方法

風(fēng)廓線雷達(dá)已在我國(guó)得到大范圍的業(yè)務(wù)布網(wǎng)應(yīng)用，現(xiàn)有業(yè)務(wù)產(chǎn)品主要為風(fēng)場(chǎng)信息。為了充分發(fā)揮風(fēng)廓線雷達(dá)的作用，獲取更多的天氣過(guò)程信息，該文提出僅使用風(fēng)廓線雷達(dá)返回信號(hào)功率譜進(jìn)行數(shù)據(jù)定標(biāo)（DCNP）的方法。使用雷達(dá)系統(tǒng)噪聲功率對(duì)返回信號(hào)功率譜單位幅度進(jìn)行標(biāo)校計(jì)算，基于標(biāo)校后的雷達(dá)探測(cè)功率譜分布數(shù)據(jù)計(jì)算回波強(qiáng)度功率譜密度分布、回波強(qiáng)度、大氣折射率結(jié)構(gòu)常數(shù)。利用2017年北京風(fēng)廓線雷達(dá)、2016年南京風(fēng)廓線雷達(dá)和2018年梅州風(fēng)廓線雷達(dá)觀測(cè)數(shù)據(jù)，對(duì)我國(guó)業(yè)務(wù)運(yùn)行的3種主要型號(hào)風(fēng)廓線雷達(dá)進(jìn)行算法評(píng)估試驗(yàn)。定標(biāo)方法的計(jì)算結(jié)果穩(wěn)定，風(fēng)廓線雷達(dá)不同探測(cè)模式之間的一致性較好。使用每個(gè)測(cè)站定標(biāo)結(jié)果與相鄰天氣雷達(dá)數(shù)據(jù)進(jìn)行比較，風(fēng)廓線雷達(dá)回波強(qiáng)度定標(biāo)結(jié)果與天氣雷達(dá)也有較好的一致性。DCNP方法與基于信噪比（SNR）的強(qiáng)度計(jì)算方法進(jìn)行比較，與SNR方法相比，DCNP方法定標(biāo)結(jié)果更加穩(wěn)定可靠。（李豐，阮征，王紅艷）

6.27 冬季穩(wěn)定性降水相態(tài)預(yù)報(bào)研究進(jìn)展

冬季降水無(wú)論對(duì)地面的人類生產(chǎn)生活還是對(duì)高空飛機(jī)航行都可能造成嚴(yán)重災(zāi)害，降水相態(tài)預(yù)報(bào)的準(zhǔn)確性決定了冬季降水預(yù)報(bào)的成功。該文較系統(tǒng)地回顧了近幾十年來(lái)降水相態(tài)的預(yù)報(bào)方法與技術(shù)的研究成果。降水相態(tài)預(yù)報(bào)的方法大致分為3類：第1類是基于觀測(cè)或者數(shù)值預(yù)報(bào)建立的指標(biāo)或回歸方程，其中某些方法高度依賴于數(shù)值預(yù)報(bào)模式的準(zhǔn)確率；第2類是數(shù)值模式預(yù)報(bào)微物理方案法和集合預(yù)報(bào)法；第3類是基于觀測(cè)和數(shù)值預(yù)報(bào)資料的人工智能預(yù)報(bào)法。近年來(lái)降水相態(tài)模式預(yù)報(bào)產(chǎn)品的預(yù)報(bào)準(zhǔn)確率不斷提高，成為降水相態(tài)預(yù)報(bào)中一個(gè)重要的產(chǎn)品支撐。但如何將降水相態(tài)形成機(jī)制的微物理研究成果用于改善數(shù)值預(yù)報(bào)模式降水相態(tài)預(yù)報(bào)的技巧以及利用人工智能等技術(shù)提高降水相態(tài)預(yù)報(bào)的準(zhǔn)確率等方面還需不斷努力。（趙琳娜，慕秀香，馬翠平，王秀娟，李締華）

6.28 中國(guó)氣象局野外科學(xué)試驗(yàn)基地管理服務(wù)平臺(tái)

中國(guó)氣象局野外科學(xué)試驗(yàn)基地管理服務(wù)平臺(tái)是中國(guó)氣象局氣象科學(xué)決策支撐應(yīng)用集約化建設(shè)項(xiàng)目的一個(gè)子系統(tǒng)，由中國(guó)氣象科學(xué)研究院承擔(dān)建設(shè)。平臺(tái)開發(fā)采用前后端分離技術(shù)，通過(guò)nginx+tomcat方式有效解耦。前端開發(fā)采用vue+ElementUI框架，使用異步調(diào)用后端接口方式實(shí)現(xiàn)前后端數(shù)據(jù)交互和呈現(xiàn)。后端采用快速、敏捷的Springboot開發(fā)框架，應(yīng)用tomcat服務(wù)實(shí)現(xiàn)接口發(fā)布，與前端實(shí)現(xiàn)數(shù)據(jù)交互。平臺(tái)提供了兩類管理服務(wù)：（1）面向基地工作人員和各級(jí)管理人員等內(nèi)部注冊(cè)用戶，平臺(tái)提供了基地管理信息、設(shè)備信息和數(shù)據(jù)信息的填報(bào)、審核與共享服務(wù)。通過(guò)預(yù)置的數(shù)據(jù)分析模型，生成分類或綜合數(shù)據(jù)分析圖、表，也可按需生成數(shù)據(jù)查詢結(jié)果。（2）面向普通用戶，平臺(tái)網(wǎng)站提供了基地綜合信息展示、基地短視頻宣傳和基地全景科普服務(wù)。通過(guò)瀏覽器呈現(xiàn)野外試驗(yàn)基地全景的視覺效果。用戶使用鼠標(biāo)控制環(huán)視方向，猶如置身現(xiàn)場(chǎng)環(huán)境中，在三維窗口中瀏覽外場(chǎng)試驗(yàn)基地的環(huán)境、場(chǎng)景、儀器設(shè)備、觀測(cè)數(shù)據(jù)和集成的研究成果。2021年該平臺(tái)完成了與氣政通平臺(tái)的集成，實(shí)現(xiàn)了31個(gè)基地在線信息填報(bào)，多個(gè)基地全景虛擬現(xiàn)實(shí)展示和短視頻制作。（高梅）

7 衛(wèi)星研究與應(yīng)用

7 Satellite research and application

7.1 An observational study on the local climate effect of the Shangyi Wind Farm in Hebei Province

Zhangjiakou is an important wind power base in Hebei Province, China. The impact of its wind farms on the local climate is controversial. Based on long-term meteorological data from 1981 to 2018, we investigated the effects of the Shangyi Wind Farm (SWF) in Zhangjiakou on air temperature, wind speed, relative humidity,and precipitation using the anomaly or ratio method between the impacted weather station and the nonimpacted background weather station. The influence of the SWF on land surface temperature (LST) and evapotranspiration (ET) using MODIS satellite data from 2003 to 2018 was also explored. The results showed that the SWF had an atmospheric warming effect at night especially in summer and autumn (up to 0.95 ). The daytime air temperature changes were marginal, and their signs were varying depending on the season. The annual mean wind speed decreased by 6%, mainly noted in spring and winter (up to 14%). The precipitation and relative humidity were not affected by the SWF. There was no increase in LST in the SWF perhaps due to the increased vegetation coverage unrelated to the wind farms, which canceled out the wind farm-induced land surface warming and also resulted in an increase in ET. The results showed that the impact of wind farms on the local climate was significant, while their impact on the regional climate was slight. (Liu Yonghong, Dang Bing, Xu Yongming)

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

Accurate information on the thermal structures of tropical cyclones (TCs) is essential for monitoring and forecasting their intensity and location. In this study, a scene-dependent 1-D variation (SD1DVAR)algorithm is developed to retrieve atmospheric temperature and moisture profiles under all-weather conditions.In SD1DVAR, the background and observation error matrix varies according to the scattering intensity.Especially, the observation error matrix increases in precipitating atmospheres due to a larger uncertainty in the forward operator. With the data from the advanced technology microwave sounder (ATMS) onboard the Suomi National Polar-orbiting Partnership (NPP) satellite, SD1DVAR can retrieve better thermal structures in the storm life cycle than the NOAA Microwave Integrated Retrieval System (MIRS). Comparing with the aircraft dropsonde observations, the temperature and humidity errors from SD1DVAR are about 3 K and 20%,respectively, whereas those from MIRS are around 4?5 K and 30%, respectively. SD1DVAR is also applied for microwave temperature sounder (MWTS) and microwave humidity sounder (MWHS) onboard the FengYun3D(FY-3D) satellite. The MWTS and MWHS data sets are first combined into a single comprehensive microwave suite (CMWS) data stream and then used to retrieve the hurricane thermal structures. It is shown that the hurricane structure from CMWS is very similar to that from ATMS. However, due to the availability of 118-GHz measurements from the CMWS, the hurricane temperature vertical structure is better resolved, and the humidity error is also reduced by about 5%. (Hu Hao, Han Yang)

7.3 Discrete ordinate adding method (DOAM), a new solver for advanced radiative transfer modeling system (ARMS)

Satellite data assimilation requires a computationally fast and accurate radiative transfer model. Currently,three fast models are commonly used in the numerical weather prediction (NWP) models for satellite data assimilation, including the Radiative Transfer for TIROS operational vertical sounder (RTTOV), community radiative transfer model (CRTM), and advanced radiative transfer modeling system (ARMS). ARMS was initiated in 2018 and is now becoming the third pillar supporting many users in NWP and remote sensing fields. Its radiative transfer solvers (e.g. doubling adding method) are inherited from CRTM. In this study,we propose a discrete ordinate adding method (DOAM) to solve the radiative transfer equation including both solar and thermal source terms. In order to accelerate the DOAM computation, the single scattering approximation is used in the layer with an optical depth less than 10?8or a single scattering albedo less than 10?10. From principles of invariance, the adding method is then applied to link the radiances between the layers. The accuracy of DOAM is evaluated through four benchmark cases. It is shown that the difference between DOAM and the DIScrete ordinate radiative transfer (DISORT) decreases with an increase of stream number. The relative bias of the 4-stream DOAM ranges from -5.03% to 5.92% in the triple layers of a visible wavelength case, while the maximum bias of the 8-stream DOAM is only about 1%. The biases can be significantly reduced by the single scattering correction. Comparing to the visible case, the accuracy of the 4-stream DOAM is much higher in the thermal case with a maximum bias -1.69%. Similar results are also shown in two multiple-layer cases. In the MacBook Pro (15-inch, 2018) laptop, the 2-stream DOAM only takes 1.68 seconds for calculating azimuthally independent radiance of 3000 profiles in the hyper-spectral oxygen A-band (wavelength ranges from 0.757 μm to 0.775 μm), while the 4-stream DOAM takes 4.06 seconds and the 16-stream DOAM takes 45.93 seconds. The time of the 2-, 4- and 16-stream DOAM are 0.86 seconds,1.09 seconds and 4.34 seconds for calculating azimuthally averaged radiance. DISORT with 16 streams takes 1521.56 seconds and 127.64 seconds under the same condition. As a new solver, DOAM has been integrated into ARMS and is used to simulate the brightness temperatures at the microwave humidity sounder (MWHS)as well as the microwave radiation imager (MWRI) frequencies. The simulations by the DOAM are compared to those by the Doubling Adding method and the accuracy of both solvers shows a general agreement. All the results show that the DOAM is accurate and computational efficient for applications in NWP data assimilation and satellite remote sensing. (Shi Yining, Yang Jun, Weng Fuzhong)

7.4 Impact of hematite on dust absorption at wavelengths ranging from 0.2 to 1.0 μm: An evaluation of literature data using the T-matrix method

Hematite is the absorbing mineral component of dust aerosols in the shortwave spectral region. However,dust shortwave absorption related to hematite suffers from significant uncertainties. In this study, we evaluated available hematite complex refractive index data in the literature on determining the dust effective refractive index at wavelengths ranging from 0.2 to 1.0 μm using rigorous T-matrix methods. Both spherical and superspheroidal dust with hematite inclusions were examined to compute the dust optical properties and associated effective refractive indices. We found that the imaginary part of the effective refractive index retrieved from all available hematite complex refractive index data is larger than the measured effective values from Di Biagio et al. The result obtained using the hematite refractive index from Hsu and Matijevic is closest to but approximately two times larger than Di Biagio et al. Our results emphasize the importance of accurate measurements of mineral refractive indices to clarify the dust absorption enigma. (Zong Ruirui, Weng Fuzhong, Bi Lei)

7.5 Impacts of urban spatial layout and scale on local climate: A case study in Beijing

Based on the meteorological data (2009?2018) acquired by high-density automatic meteorological stations (AMSs) in Beijing, the influences of urbanization on urban heat island (UHI), wind, and humidity were described by UHI, wind speed ratio (Wsr), and specific humidity ratio (qr), respectively. For the 37 AMSs in central Beijing, the relationships between UHI, Wsr, and qrand six spatial morphological parameters (building height (BH), building density (BD), floor area ratio, sky view factor, frontal area index, and roughness length(RL)) and two land surface parameters (vegetation coverage and impervious cover) in the range of 200?3000 m from the station were studied. The scale effect of each parameter on local climate was also studied. The results showed that individually, these parameters account for 46.8%?79.6% of the change in UHI, 25.6%?52.8% of the change in Wsr, and 25.7%?29.3% of the change in qr. The impact of spatial morphological parameters on local climate has surpassed that of land surface parameters. The parameters that make the largest contributions to the annual average UHI, Wsr, and qrare RL, BH, and BD, respectively. The optimal influencing ranges of the spatial morphological parameters on UHI, Wsr, and qrare 800?1000 m, 1600?2600 m, and 1200?1400 m,respectively. (Liu Yonghong, Xu Yongming, Weng Fuzhong)

7.6 Influence of the urban spatial layout of central Beijing on the atmospheric humidity field

Based on the meteorological data (2009?2018) acquired by high-density automatic meteorological stations in the central urban area (CUA) of Beijing, this study adopted an urban-rural ratio method to construct a qrto quantify the impact of urbanization on the spatial and temporal distribution of specific humidity (q). And the urban morphological parameters such as building height (BH), building density (BD), floor area ratio (FAR),sky view factor (SVF), and land surface parameters including vegetation coverage (VC) and impervious coverage (IC) with 500-m spatial resolution in CUA were calculated, and furthermore, the relationships between the six spatial layout parameters and another indicator, urban heat island (UHI) intensity, and qrwere studied. The results show that q of CUA is 81% to 114% of that of the suburbs, and the urban dry island(UDI) effect and urban wet island (UWI) effect coexist throughout the year. The maximum UDI occurs during autumn daytime and the maximum UWI appears at night in winter. The UDI effect is prone to occur in areas with VC < 11%, IC >85%, BH > 15 m, and BD > 24%, while the UWI effect is more likely to appear in areas with VC > 35% and FAR < 0.3. The contributions of the six urbanization parameters to the spatial change of qrin different time periods are 6.2% to 33.5%, and VC is the largest (33.5%), followed by BD (31.9%) and SVF(29.9%), and the main factor affecting the annual average qris BD with the contribution of 18.9%. Compared with the urbanization parameters, the UHI is more important and the contribution to the change of q can be up to 35.7%. The results show that these spatial layout parameters are not sufficient to explain the main change in q,and more other parameters need to be considered. (Liu Yonghong, Xu Yongming, Han Xiuzhen)

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

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

7.8 The potential of satellite sounding observations for deriving atmospheric wind in all-weather conditions

Atmospheric wind is an essential parameter in the global observing system. In this study, the water vapor field in Typhoon Lekima and its surrounding areas simulated by the weather research and forecasting (WRF)model is utilized to track the atmospheric motion wind through the Farneback Optical Flow (OF) algorithm.A series of experiments are conducted to investigate the influence of temporal and spatial resolutions on the errors of tracked winds. It is shown that the wind accuracy from tracking the specific humidity is higher than that from tracking the relative humidity. For fast-evolving weather systems such as typhoons, the shorter time step allows for more accurate wind retrievals, whereas for slow to moderate evolving weather conditions, the longer time step is needed for smaller retrieval errors. Compared to the traditional atmospheric motion vectors(AMVs) algorithm, the Farneback OF wind algorithm achieves a pixel-wise feature tracking and obtains a higher spatial resolution of wind field. It also works well under some special circumstances such as very low water vapor content or the region where the wind direction is parallel to the moisture gradient direction. This study has some significant implications for the configuration of satellite microwave sounding missions through their derived water vapor fields. The required temporal and spatial resolutions in the OF algorithm critically determine the satellite revisiting time and the field of view size. The brightness temperature (BT) simulated through community radiative transfer model (CRTM) is also used to track winds. It is shown that the error of tracking BT is generally larger than that of tracking water vapor. This increased error may result from the uncertainty in simulations of brightness temperatures at 183 GHz. (Zhang Yijia, Hu Hao, Weng Fuzhong)

7.9 北京城市空間形態(tài)對(duì)熱島分布影響研究

在城市尺度上探究城市空間形態(tài)布局對(duì)城市熱島（UHI）影響研究，對(duì)于城市規(guī)劃中通風(fēng)環(huán)境改善、生態(tài)宜居城市建設(shè)具有重要意義。以北京為例，利用2009—2018年高密度自動(dòng)氣象站逐小時(shí)氣溫資料和2018年NPP/VIIRS夜光衛(wèi)星資料，分析了UHI時(shí)空分布特征；利用2017年1∶2000基礎(chǔ)地理信息和Landsat8衛(wèi)星資料，開展了北京主城區(qū)建筑高度（BH）、建筑密度（BD）、建筑高度標(biāo)準(zhǔn)差（BSD）、容積率（FAR）、迎風(fēng)截面積指數(shù)（FAI）、粗糙度長(zhǎng)度（RL）、天空開闊度（SVF）、城市分?jǐn)?shù)維（FD）等8個(gè)空間形態(tài)參數(shù)和植被覆蓋度（VC）、不透水蓋度（IC）、反照率（AB）等3個(gè)陸表參數(shù)的提取，并在城市尺度上開展了這些參數(shù)與UHI之間空間相關(guān)性及對(duì)UHI變化影響研究。結(jié)果顯示：2009—2018年北京主城區(qū)年均、四季以及夜晚02:00 UHI均存在一個(gè)較為固定的形態(tài)，年均、春、夏、秋、冬、白天14:00和夜晚02:00UHI分別為1.81 ℃、1.50 ℃、1.43 ℃、2.16 ℃、2.17 ℃、0.48 ℃和2.77 ℃；8個(gè)空間形態(tài)參數(shù)在一年中大部分時(shí)段與UHI存在明顯空間相關(guān)性，這種相關(guān)性在冬季強(qiáng)于其他季節(jié)，在夜晚02:00強(qiáng)于白天14:00，排名前三的分別為SVF、FAR和BD?？臻g形態(tài)參數(shù)已超越陸表參數(shù)成為UHI變化的重要驅(qū)動(dòng)因子，11種參數(shù)對(duì)UHI變化的單獨(dú)貢獻(xiàn)為13.7%～63.7%，其中夏季、冬季和全年時(shí)段貢獻(xiàn)最大的空間形態(tài)參數(shù)分別是BD（43.7%）、SVF（63.7%）和SVF（45.4%），貢獻(xiàn)最大的陸表參數(shù)分別是VC（42.6%）、AB（57.1%）和VC（45.3%）；夏季、冬季和全年時(shí)段多個(gè)參數(shù)對(duì)UHI變化的綜合貢獻(xiàn)分別為51.4%、69.1%和55.3%，主導(dǎo)要素分別為BD、SVF和BD。（劉勇洪，徐永明，張方敏）

7.10 衛(wèi)星微波大氣遙感溫濕廓線及應(yīng)用進(jìn)展

簡(jiǎn)要回顧了星載微波探測(cè)儀對(duì)大氣溫濕廓線遙感應(yīng)用技術(shù)進(jìn)展，對(duì)統(tǒng)計(jì)回歸反演方法、一維變分反演方法以及最新的場(chǎng)景自適應(yīng)反演方法的發(fā)展進(jìn)行了介紹。最后通過(guò)介紹新型微波探測(cè)儀搭載平臺(tái)，對(duì)可能的新反演產(chǎn)品和技術(shù)進(jìn)行展望。（胡皓，翁富忠）