Supercells are the most severe and long-lasting type of highly organized convective storms, with the greatest potential for producing extreme weather events and causing significant disasters. This article provides a comprehensive overview and recent highlights of supercell research, including the unique structure, environmental characteristics, and the formation and maintenance mechanisms of the mesocyclone. Buoyancy instability is a necessary ingredient in the supercell’s environment, whereas dynamic factors such as vertical wind shear and low-level storm relative helicity are more sensitive parameters for distinguishing supercells from non-supercells. The near-storm environmental parameters derived from multi-sensor observations are expected to enhance high-resolution nowcasting of supercell storms. Different types of supercells, including those producing distinct hazardous weather, exhibit unique reflectivity morphology and dynamical/microphysical structures, e.g., tornadic supercells have a strong low-level mesocyclone while severe hail supercells feature a strong and deep mesocyclone. Mesocyclones associated with damaging winds are accompanied by significant mid-level radial convergence, while those responsible for heavy precipitation are typically located at low levels. The vertical vorticity of the mesocyclone is generated through the tilting of environmental horizontal vorticity by storm-related intense updrafts. The horizontal vorticity that tilts into the mid-level mesocyclone originates from the environmental vertical wind shear, which produces the horizontal vorticity along the inflow to the storms. In contrast, the horizontal vorticity contributing to the low-level mesocyclone derives from two distinct mechanisms, i.e., environmental vertical shear in the boundary layer and gust front-induced baroclinicity. It remains unclear which mechanism is more dominant. Moreover, the maintenance and enhancement mechanisms of mesocyclones are complex and vary across different scenarios, particularly when embedded within heavy precipitation, during storm mergers, or in proximity to surface mesoscale boundaries (e.g., fronts, drylines, gust fronts, and their associated convergence lines). In recent years, based on super high-resolution numerical experiment results, the physical conceptual models of the supercell tornadogenesis have been updated. The newly revealed microphysical and dynamic characteristics from polarimetric Doppler radar observations enable more accurate hail size detection. However, the refined physical conceptual model of severe hail growth still requires improvement, and our understanding of the formation mechanisms behind extreme wind gusts and flash floods associated with supercells remains limited.

The Pearl River Delta (PRD), a tornado hotspot, forms a distinct trumpet-shaped coastline that concaves toward the South China Sea. During the summer monsoon season, low-level southwesterlies over the PRD’s sea surface tend to be turned toward the west coast, constituting a convergent wind field along with the landward-side southwesterlies, which influences regional convective weather. This two-part study explores the roles of this unique land–sea contrast of the trumpet-shaped coastline in the formation of a tornadic mesovortex within monsoonal flows in this region. Part I primarily presents observational analyses of pre-storm environments and storm evolutions. The rotating storm developed in a low-shear environment (not ideal for a supercell) under the interactions of three air masses under the influence of the land–sea contrast, monsoon, and storm cold outflows. This intersection zone (or “triple point”) is typically characterized by local enhancements of ambient vertical vorticity and convergence. Based on a rapid-scan X-band phased-array radar, finger-like echoes were recognized shortly after the gust front intruded on the triple point. Developed over the triple point, they rapidly wrapped up with a well-defined low-level mesovortex. It is thus presumed that the triple point may have played roles in the mesovortex genesis, which will be demonstrated in Part II with multiple sensitivity numerical simulations. The findings also suggest that when storms pass over the boundary intersection zone in the PRD, the expected possibility of a rotating storm occurring is relatively high, even in a low-shear environment. Improved knowledge of such environments provides additional guidance to assess the regional tornado risk.

Based on the conventional meteorological observation data, the NCEP reanalysis data, the dual-polarization radar data, wind pro? filer radar data, and other datasets, the environmental conditions and dual-polarization radar characteristics of the phase transformation of precipitation in a rain and snow event in Hunan in late December 2021 is studied. The results are as follows: (1) The disappearing of dry lay? er, the thickening of wet layer, the whole-layer wet bulb temperature below 0 ℃, and the saturated stratification in the cold pad under the in? version layer before the snowfall favored the further cluster growth of falling snowflakes, resulting in the further enhancement of snowfall. (2) That the southwest jet exits at 700hPa and the strong water vapor convergences at 600-800 hPa, combined with the significant vertical up? draft at the middle and lower layers, provided sufficient moisture for the snowstorm. (3) The intermittent light rain (snow) in the evening of the 25th is closely related to the transit of short-wave trough frequently. In the morning of the 26th, the southwesterly wind turned to the westerly wind, which led to a short-term weakening of snowfall in Changsha. Furthermore, the warm-humid southwesterly flow strengthened over the cold pad, and the southeast wind in the cold pad turned to the northeast wind, which corresponded to the two peaks of snowfall in Changsha on the 26th. (4) There are certain differences in the correlation coefficient (CC), differential reflectance (Zdr), and horizontal reflectance factor (Zh) of different phases of precipitation. The dual-polarization products have a certain indication effect on the identification of rain and snow phases of this case. (5) The low-level"zero-velocity-level"is straight, and has the characteristics of wind-speed convergence, enhanced southwest jet core, and downward extension, etc., indicating that the dynamic climbing of warm-humid airflow over the cold pad would increase, and the snowfall could be maintained for a long time and would increase gradually. However, with the appearance of divergence of wind field, the snowfall gradually weakened. The findings of this study provide helpful criteria for the development, maintenance, and weak? ening of snow, which can be applied to the operational work of snowstorm nowcasting and forecasting.

Based on the Doppler weather radar and surface observations, the key mesoscale systems and features of the rainstorm structure during the period of the extreme precipitation in Henan province on 20 July 2021 are investigated. The results show that a nearly meso-α-scale West Henan Low Vortex (WHLV) near the Songshan Mountain, a surface mesoscale front, a horizontal shear convergence line in the lower troposphere and two strong low-level jets (LLJs) were the main mesoscale systems that triggered the extreme precipitation process. Many mesoscale vortices including meso-β-γ-scale vortices (i.e., meso-vortices) were found within the WHLV. Hourly precipitation over 50 mm was mostly caused by the storms with meso-vortices. In the heaviest precipitation stage of the Zhengzhou Storm (ZZS), a clear meso-vortex above 2 km AGL was identified with the diameter of 15–20 km and the vorticity of 1.0–2.0 × 10−3 s−1, while its lifetime was about 2 h. The low-level ambient airflows converged into the storm from the north, east and south, forming a strong low-level convergence that promoted the development of the storm. Strong convergence and uplift occurred along the east edge of the storm, while the strong easterly LLJ converged with the shallow outflow of the storm. The strongest updraft under 2 km AGL occurred at the northeast end of the storm when a short-lived meso-γ-scale vortex formed at that area. Both the strong low-level convergence and the merge of the convective cells from the east resulted in the eastward propagation of the ZZS.

影响北京和河北的对流风暴多半由太行山山区移来,为增加对从太行山东麓下山的对流风暴强度变化和维持时间等演变特征的了解,基于全国雷达组合反射率因子拼图,对2011-2020年10年期间暖季太行山东麓对流风暴下山演变的气候特征进行了统计分析.结果表明:下山对流风暴在石家庄北部、北京南部、保定中南部和沧州市西部存在≥45 dBz的强回波高频中心,且下山对流风暴常在石家庄北部近山平原和沧州西部显著增强;对于下山增强的对流风暴,17时前后在山区最为活跃,18时至次日02时主要影响平原地区;对流风暴来向越偏西,下山对流风暴数越多,下山增强的对流风暴比例越高,移速也越快;下山过程中,大多数对流风暴变得更强和更加具有组织性,下山初始时刻回波强度≥45 dBz的对流风暴86％能成功下山,其中水平尺度大于100 km、结构密实的强对流风暴超过90％能成功下山;下山增强的样本在下山过程中风暴的强回波面积急剧扩大,到达平原前一个时刻其面积约为初始面积的3倍,在平原地区继续发展后其平均面积可达到初始面积的4.6倍;下山增强的对流风暴大多下山用时仅为1～2 h,而影响平原的时长可持续4～8 h,影响平原时长4～8 h的对流风暴的风暴类型以线性MCS(47％)和非线性MCS(30％)为主.

In this paper, synoptic-scale analyses of frontogenesis, moisture budget, and tropospheric diabatic heating are performed to reveal the development and maintenance mechanisms for the extreme heavy rainfall in Henan Province of central China from 19 to 21 July 2021, based on station observations and the ECMWF Reanalysis version 5 (ERA5) data. The results demonstrate that owing to the blocking effect of local topography, low-level wind convergence in Henan appeared underneath high-level divergence, conducive to development and maintenance of a midtropospheric low-pressure system saddled by the Asian continental high and the western Pacific subtropical high (WPSH), during the extreme heavy rainfall. In the lower troposphere, frontogenesis occurred in the θse intensive region, as a result of the divergence and horizontal deformation (which play equally important roles), generating frontal secondary circulation with strong vertical motion favorable to heavy rainfall. Moisture budget analysis reveals that 1) with the continuous strengthening of the easterly wind from the north side of Typhoon In-Fa (2106), strong wind shear and orographic uplift led to abnormally strong convergence of water vapor flux in the boundary layer in Henan; 2) there occurred extremely strong net inflow of moisture in the boundary layer from the east. Horizontally, both the apparent heat source and the moisture sink coincided with the area of heavy rainfall; vertically, however, Q1 exhibited a single peak with the heating center in the middle and upper troposphere, while large Q2 values evenly resided over 850–400 hPa; and Q1 (Q2) was dominated by vertical (horizontal) transport of potential temperature (moisture). These indicate that the latent heat release from condensation of initial heavy rainfall provided a positive feedback, leading to increasingly heavy precipitation. All these synoptic settings sustained the extreme rainfall process.

In order to enhance the understanding of the environmental field characteristics of the convective regeneration triggered by thunderstorm gust fronts.Based on Beijing sounding observation， automatic stations， S-band Doppler radar and new detection data to analyse environmental field characteristics of two typical cases in which convection initiation triggered by thunderstorm gust fronts.The results show that： （1） One type is convection triggered by collision of multiple gust fronts or the encounter of gust fronts with other boundary layer convergence lines in the region with high Convective Available Potential Energy （CAPE） and sufficient water vapor （collision triggering）.In this type， the vertical velocity of two collision gust fronts is much larger than that of a single gust front.Strong upward movement is easy to provide good lifting conditions for the triggering of convection， and convection is easy to trigger.（2） The other type is the gust front triggers convection in the unstable region （non-collision trigger）.In this type， the low-level wind direction is perpendicular to the gust front， which is conducive to the strong convergence between the ambient wind near the ground and the gust front.Meanwhile， the updraft of the convection triggered by the gust front tends to be vertical， which is beneficial to convective initiation.（3） By comparing the environmental field of gust fronts trigger and non-trigger Convective Initiation （CI） cases， the results show that there are deep wet convection potential with high CAPE and low Convective Inhibition （CIN） of the environment field in these cases which CI are triggered by gust fronts.The wind profile and microwave radiometer observations indicate that there are cold dry advection at the upper level and warm wet advection at the lower level in most cases CI triggered by the gust fronts.In most cases which gust fronts trigger CI occur at the wind speed or wind direction convergence areas with high CAPE.（4） In cases which non-triggered CI， vertical distribution of environmental field is not conducive to the regeneration and development of convection， and gust fronts pass the area which are divergence or there are low CAPE and high CIN.These conditions are adverse to convection triggering.

From June 14 to the early morning of June 15,2005,affected by the northeast cold vortex,a hai weather process rarely seen in history occurred in Shandong,northwest Jiangsu and northeast Anhui.The maxi‐mum hail diameter was 15～18 cm.Based on the new generation doppler weather radar data of 08:00（Beijing time）from June 14 to 15,2005,this paper compares and analyzes the radar echo characteristics of extreme hai in Shuyang,Jiangsu,Siyang and Guzhen,Anhui.Results showed that:（1）The extreme hail process in the three regions is caused by different supercells,due to the strong environmental CAPE,deep vertical wind shear and low-level relative storm helicity,the three supercells formed successively and all had strong and mosocy‐clones.The interaction between strong and mosocyclones and the environment leads to an upward disturbance of the pressure gradient force,which greatly increases the updraft intensity of the supercell and strong developmen itself.（2）The radar echo shows that the supercell causing extreme hail in the three places has high echo starting height and strong echo intensity.The maximum reflectivity factor is more than 70 dBZ,and the strong echo last‐ed more than 3 hours.The maximum height of 60 dBZ is higher than 11 km.In comparison,Shuyang supercel has the longest duration;Siyang supercell has the largest echo intensity;The Guzhen supercell hailstorm has the highest vertical expansion height of reflectivity factor above 60 dBZ.Preliminary clues are obtained from the above three supercell hailstorm examples:when the maximum reflectivity factor exceeds 68 dBZ and the echo expansion height of 60 dBZ is above 10 km,it indicates that extreme hail appears.（3）The bounded weak echo area（BWER）or weak echo area（WER）and the overhangs of echoes above it are the typical hailstorm structure of a supercell storm.The Siyang hailstorm showed WER and broad echo overhang,while the Shuyang and Gu‐zhen hailstorms showed BWER and broad echo overhang.The continuous increase of mesocyclone shear value in Guzhen hailstorm is accompanied by the strong development of hailstorm.（4）The vertical integration of liquid water content（VIL）based on cells is abnormally high,reaching 88 kg·m -2 ,102 kg·m -2 and 89 kg·m -2 respec‐tively,far exceeding the VIL threshold of 65 kg·m -2 corresponding to large hail in June.The Guzhen hailstorm showed a strong storm top divergence,and the divergence velocity difference was as high as 80 m·s -1 （5）There are three-body scattering spike（TBSS）in guzhen hailstorm for nearly 1 hour,and there are obvious side-lobe echo characteristics in Shuyang and Guzhen hailstorms,all indicated the existence of large hails.

The downburst is the outburst of divergent flow on or near the ground induced by a strong convective downdraft.A single downburst affects a small area of several kilometers,and the downburst cluster can extend over several hundreds of kilometers resulting in many noncontinuous surface damaging gusts.Its enhancing mechanism may not be limited to the strong downdraft divergent outflow.This article reviews the definition of downburst,and dicusses downbursts under two different situations.One is the downburst induced by isolated storms and the other is the downbursts embedded in mesoscale convective systems,including the formation processes of downburst and warning technology of downburst based on Doppler weather radar.On the basis of the above review,the formation mechanism of downburst and the difficulties of warning are discussed,and the much-needed issues related to downburst are listed.

Boundary layer convergence lines (BLCLs), an important type of weather system that can trigger deep moist convection, correspond to quasi-linearly extending airflow confluence zones in the boundary layer. Multiple types of BLCLs exist, and mechanisms for their triggering of convection are complicated. This paper summarizes the existing studies on the climatological statistics of BLCLs (excluding cold fronts) and mechanisms for their triggering of convection, and the effects of local temperature and moisture disturbances on the convection triggering. These studies have presented that the triggering probability, the storm location and time correlation are all affected by different synoptic systems and BLCL types in different regions. Under certain favorable conditions, local temperature and moisture can not only affect BLCL intensity, but also affect the distribution of atmospheric stratification near BLCLs, and thus convection initiation can occur. Moreover, the dynamical and thermal interactions between local temperature and moisture disturbances and the environment make the convection triggering mechanisms more complicated. The paper also discusses some convection triggering issues that need to be further studied. Based on fine observations and numerical simulation, it is also suggested to carry out more systematic studies on the characteristics and mechanisms of convection triggering for different regions and different types of BLCLs in the future.

2021年7月31日16—22时冀豫交界区出现了由多个超级单体风暴造成的强对流天气过程,其中生命史最长的两个超级单体风暴(以下分别简称邯郸超级单体和濮阳超级单体)先后影响河北南部和河南北部,导致5次极端下击暴流事件.本文利用常规观测资料、区域自动站观测资料及多普勒天气雷达资料,并基于超级单体致灾下击暴流雷达回波预警指标,分析了上述5次极端下击暴流导致的冀豫交界区雷暴大风的雷达预警效果.结果表明:(1)5次极端下击暴流事件中,超级单体强回波伸展高度、中层径向辐合、低仰角径向速度大值区等雷达回波特征量化值均满足致灾下击暴流超级单体雷达回波预警指标,平均每次极端下击暴流前会出现12个与雷暴大风相关的回波特征,且最极端下击暴流出现前与雷暴大风相关的回波特征均最为显著或其特征量增至最强,其中与对流风暴下沉气流和地面大风直接相关的特征可提前10～37 min预警极端下击暴流.(2)两个超级单体风暴导致的首次极端下击暴流前均出现了反射率因子核、中气旋核和中气旋底高下降的特征,对极端下击暴流能提前19 min和22 min预警.(3)邯郸超级单体为典型的孤立超级单体风暴,濮阳超级单体为镶嵌在多单体中的超级单体风暴,前者比后者的回波结构清晰,更易判识,相关回波特征或特征量对其产生的下击暴流预警效果也更好.(4)超级单体风暴维持期间可导致多次极端下击暴流,其出现后(特别是在减弱阶段)仍需持续关注相关回波特征变化.

2018年5月7日冷锋前暖区暴雨和8月29日华南季风槽暴雨,这两次大暴雨都是由广东和闽南地区的沿岸线状中尺度对流系统产生,对其环境背景与对流系统特征进行对比分析,得到主要结论如下:两次过程均有明显850 hPa和925 hPa低空急流;5月7日过程,对流层中低层条件不稳定较大,大气斜压性较强,对流有效位能和0～6 km垂直风切变相对较大,对流层中部存在明显干层,有利于强降水和雷暴大风的产生;8月29日过程,对流层中下层为弱的条件不稳定,准正压大气,更高的融化层高度,对流有效位能和0～6 km垂直风切变相对较小,垂直整层相对湿度高,有利于强降水而不利于雷暴大风的产生.两次过程风暴承载层平均风均来自西南方向,前者的平流比后者要强很多;厦门及其周边闽南地区大暴雨是由于后向传播导致相继多个较强对流雨团移过同一区域形成的;5月7日后向传播形成是一个对流雨团的阵风锋与另一个对流雨团后侧的水平对流卷相遇触发新的对流导致的,新生对流来自陆地;8月29日后向传播形成则是低层暖湿气流遇到成熟对流雨团的后侧阵风锋触发新的对流,新生对流位于海上,持续移入陆地.5月7日导致大暴雨的对流系统中冰相过程和暖云过程对暴雨产生都很重要,8月29日导致极端暴雨的对流系统中暖云过程对强降水产生起主要作用.在两次过程中,对流系统冷池前沿阵风锋附近都有γ中尺度涡旋形成,与阵风锋辐合上升运动结合产生正的垂直螺旋度,有利于对流系统的维持.低空急流通过其对水汽和热量的输送以及与地形和对流系统冷池的相互作用,对沿岸线状中尺度对流系统的维持起到重要作用.

利用高空、加密地面、EC-ERA5(0.25o×0.25o)再分析和FY-2系列静止气象卫星云图(可见光星下点分辨率1.25 km,红外5 km)等资料,对黄河河套地区3次典型干线的形成及其在对流触发中的作用进行了详细分析.结果表明:(1)3次干线触发对流出现在中高纬度高空槽东移诱发蒙古气旋发展的背景下,高低空系统配置为前倾槽、高空西北气流及其携带的冷平流叠加在低层河套暖区之上,为大范围强对流天气提供了有利的环境条件;(2)3次干线均为蒙古气旋形势下黄土高原西高东低缓坡地形特有的现象,具有明显的地域特征,长600—800 km、宽80—100 km的显著干线呈北东北—南西南走向,与河套区域内海拔1300 m等高线走向基本吻合.受近于干绝热的下沉升温及高原西部下垫面非绝热加热快速升温降湿影响,在河套西部形成干热空气,其与东部暖湿气团在河套地区交汇是导致干线形成的主要原因之一;(3)干线具有明显的日变化特征,白天干线以西加热升温快,干线向东移动;夜间到凌晨干线西侧辐射降温快于东侧,干线向西后退.干线最强时段出现在14时(北京时,下同)前后,两侧露点梯度达10℃/(100 km)或以上,且伴有明显的偏西风和偏南风汇合(辐合)流场;(4)在干线及伴随的汇合(辐合)流场的作用下,13—14时初始对流在干线附近生成,随后在干线湿侧附近加强,形成明显的线状对流云带,在高空偏西气流引导下,对流云带东移发展并逐渐远离干线,在河套东部有利的环境条件下,线状对流云带继续东移并扩展至地面干线以东约500 km的范围内,导致陕西中北部和华北部分地区出现大范围雷暴大风、局地冰雹甚至龙卷等强对流天气.根据河套地区3次典型干线的共同特征,给出了河套地区干线形成和强对流易发区的天气学模型,为今后同类天气形势下干线触发对流天气分析和预报提供参考和借鉴.

Not many researches have been conducted on typical cases of convection triggered by dry lines in the Hetao region of China. The formation of three typical dry lines and their roles in triggering convection in the Hetao region of Yellow River are analyzed in detail based on upper air soundings, intensive surface observations, EC-ERA5 (0.25º×0.25º) reanalysis data and FY-2 meteorological satellite images (the resolution of subsatellite point in the visible images is 1.25 km while that in the infrared images is 5 km). The results are as follows. (1) The three cases occurred under the background of the development of the Mongolia cyclone, which was induced by the eastward movement of the upper trough in the middle and upper troposphere. The structure of the forward-tilting trough indicates that the upper-level northwesterly flows and cold advection were superimposed on the lower-level warm zone, providing a favorable environmental condition for the occurrence of severe convection over large areas. (2) All the three cases occurred along the gentle slope of the Loess Plateau, which is high in the west and low in the east, and under the condition of the Mongolia cyclone development, presenting significant regional characteristics. Besides, the dry lines with a length of about 600—800 km and a width of about 80—100 km were oriented along north-northeast to south-southwest direction and coincided with the orientation of the 1300 m contour line in the Hetao region. Furthermore, the main cause for dry lines generation is the effect of the dry-warm air produced by the near adiabatic descending warming and the rapid diabatic warming and dehumidification in the western Hetao area. (3) The dry lines show obvious diurnal characteristics. The western part of the dry line warmed up rapidly in the daytime and the dry line moved eastward, while it cooled off faster than the eastern part from the nighttime to early morning and the dry line retreated westward. The dry lines present their most marked features around 14:00 BT with the dew point temperature difference between wet and dry sides reaching 10℃/(100 km) or more with an obvious convergent flow field of the westerly and the southerly wind. (4) Due to impact of the dry line and its associated convergent flow field, the initial convection was generated near the dry line from 13:00 to 14:00 BT in the afternoon, which were then reinforced on both sides of the dry line and the linear convective band formed. The convective band moved eastward and gradually stayed away from the dry lines under the steering of upper-level westerly airflows and continued to move eastward, expanding to a range of about 500 km to the east of the ground drylines under favorable environmental conditions in the eastern Hetao region. Severe convections such as large-scale thunderstorms, strong winds, local hails and even tornadoes subsequently developed over central and northern Shannxi province and some areas in North China. Finally, the synoptic conceptual model of the generation of typical dry lines in Hetao and the areas prone to severe convection are summarized according to the common characteristics of the three typical dry lines in Hetao area. This study provides a reference for analysis and forecast of dry lines that could trigger convections in the similar situation.

边界层辐合线(BLCL)是指存在于边界层内的线状气流汇合带,被认为是深厚湿对流的主要触发系统,有多种类型,其触发对流作用非常复杂.文中就BLCL(不包括冷锋)触发对流事件的统计研究、其导致的局地温湿扰动对触发对流的影响、BLCL对流触发机制等方面的中外研究进行了系统回顾总结.已有研究结果表明,不同天气系统背景、不同地区BLCL的类型、表现形式不同,其触发深厚湿对流的概率、与对流风暴的位置、时间的相关也有所不同.BLCL能否触发对流还与大气环境条件、BLCL与其他动力学过程相互作用有关.在一定的对流环境条件下,局地温湿扰动不仅对BLCL的强度产生影响,而且还可以通过影响BLCL附近大气层结状态的分布影响到对流能否被触发.BLCL与环境动力和热力相互作用产生的局地变化使对流触发机制变得更加复杂.建议未来基于精细的观测资料和数值模拟试验针对不同区域、不同类型的BLCL的对流触发特征和机制开展系统研究.

Based on S-band Doppler weather radar data and damaging wind gust records, 56 damaging straight-line winds events from 2002 to 2020 above 25 m·s-1 caused by supercell storms are investigated. The relationship between Doppler weather radar echo characteristics and damaging straight-line winds caused by supercell storm is analyzed to obtain quantitative description of the structural characteristics. The results will be benefit for subjective and objective monitoring and warning of damaging straight-line winds produced by supercell storms. Superstorm is a highly organized strong convective storm with a long-life history, according to the statistical results, and it is possible to judge the potential of supercell storms that produce damaging gale by the Doppler weather radar echo structures. It shows that, in the supercell storm that produces damaging straight-line winds, the strong reflectivity echo above 60 dBZ is deep, and the average echo thickness of strong reflectivity is 5.5 km. The core height of the strong reflectivity of most supercell storms are above 6 km which indicate that the updraft in this kind of supercell storms can be very strong. The mid altitude radial convergence (MARC), the reflectivity core decline and rear inflow jet (RIJ) are important for warning of damaging straight-line winds features. The MARC is significant, the largest speed difference of the MARC is above 29 m·s-1 in most cases. The mesocyclone is mainly of medium intensity, the rotating speed of mesocyclone is 18.4 m·s-1 on average, which can extend up to the upper troposphere (7 km). The descending of supercell storm reflectivity core, the descending of mesocyclone core, the MARC which can exist for a long time with 29 m·s-1 largest radar radial speed difference and the decrease of vertically integrated liquid water content (VIL) value can be used as the warning indices of the damaging straight-line winds. Among them, the descending of supercell storm reflectivity core can give 15-minute precursor signal, the descending of mesocyclone core can give 8-minute precursor signal, the significant MARC can give 30-minute precursor signal, and the descending of VIL value can give 17-minute early warning signal of damaging winds. Based on narrow-band echo, the proportion that can be recognized as gust front of the supercell storm is low, and only a few damaging straight-line winds can be identified from the moving speed of storm or gust front characteristics. There are only 4 obvious low-level divergence velocity pairs identified in 56 cases, which indicate that most supercell storms produce asymmetric downburst because of horizontal movements.

利用常规观测资料、多普勒天气雷达和风廓线雷达资料,对一次罕见的鄂西南冬季强冰雹(直径1～3 cm)天气过程进行了分析,结果表明:强冰雹产生在上干冷、下暖湿,低空辐合、高空辐散的环流背景下,地面中尺度辐合和"喇叭口"的有利地形,给冷锋前暖区对流性天气提供了触发机制;地面冷锋南下伴随的垂直风切变增强有利于已经生成的对流风暴的维持和加强.强冰雹分别由孤立的超级单体和超级单体复合体(多单体结构中含有占支配地位的超级单体)产生.比较而言,孤立的超级单体发展更为高大,持续时间更长.风暴具有中气旋、高悬的强回波、低层入流、弱回波区与回波悬垂、中层径向辐合、风暴顶强辐散等超级单体风暴的典型特征;垂直累积液态含水量及其密度分别较长时间维持在35 kg·m-2和4 g·m-3以上的冬季高值;新一代天气雷达冰雹探测算法输出的冰雹指数产品预测到高概率的强冰雹.此次过程出现在冬末,虽然对流出现之后呈现出典型的风暴结构,可以提前10～30 min做出强冰雹的临近预警,但对于对流出现之前的提前数小时的强冰雹短时潜势预报而言,常用做判断强降雹潜势的探空特征(包括对流有效位能、0～6 km垂直风切变以及融化层高度)关键参数值非常不典型,会误导预报员忽视冰雹潜势的判断,预报员在这种环境背景下进行强对流天气潜势分析时,需要格外慎重和深入分析,才能得到正确预报结果.

为了研究高时空分辨率的相控阵阵列雷达可否精细探测强降水的演变,利用质量控制后的佛山X波段相控阵阵列天气雷达资料,分析了2020年9月4日广州省佛山市南海区发生的一次局地短时强降水天气过程.分析了16:00—17:30南海区出现的多单体风暴的强度场和三维风场结构,并探究强度场、三维风场与降水量之间的关系.结果表明:阵列天气雷达能够对强对流天气过程进行更精细的探测.合并阶段,观测到小尺度、短时间内多个对流单体的初生、分裂和合并过程.成熟阶段,分析γ中尺度气旋的形成过程以及气旋式辐合维持时强度场、三维风场、散度场和涡度场的结构.消亡阶段,分析γ中尺度反气旋的形成与增强过程.气旋与反气旋消失后,单体迅速消亡.基于高时空分辨率的强度场和三维风场获得的各统计量,发现在自动气象站降水出现前10～15 min以及最大5分钟降水出现前5～10 min,反射率因子与水平风速有明显变化.本研究结果对监测预警短时强降水有预示作用,为高时空分辨率的相控阵阵列雷达精细探测强降水的演变提供了参考依据.

基于2002—2019年高空、地面常规观测资料,卫星云图,部分新一代天气雷达单站资料以及2009年以后的中国雷达拼图资料,采用个例筛选与统计、动态合成分析、层次聚类和雷达图分析等方法,对发生在中国的大范围雷暴大风事件(Derechos)的时空分布、环境背景和对流系统形态特征进行了分析.结果表明:(1)Derechos事件主要发生在华北、华东、江南和华南地区,高频区有明显的季节变化,春季到夏季先向北移动后向南移动;Derechos事件主要发生在3—8月,6月频率最高,8月最低;造成Derechos的对流风暴多在正午前后生成,而Derechos事件多开始于午后到前半夜.(2)中国Derechos事件环境参数主要特征为:对流有效位能(CAPE)分布50％分位(中位数)为1420 J/kg,代表深层风垂直切变的0—6 km风矢量差50％分位数为18.0 m/s,对流下沉有效位能(DCAPE)的50％分位值为1090 J/kg.(3)Derechos事件环流背景的天气流型配置分为副高边缘型、弱槽型、高空干冷平流强迫型和强槽型,强槽型出现的频次最高,高空干冷平流强迫型出现的频次最低.(4)Derechos事件中最强对流大风产生时段的对流系统形态统计显示,出现频率由高到低分别为飑线、多单体风暴簇、超级单体或超级单体复合体.

Based on the 36 Derechos that occurred in China during 18 years from 2002 to 2019, a study on the spatiotemporal distribution and environmental characteristics of Derechos as well as the morphology of Derechos producing convective systems have been conducted using proximity soundings, surface observations, satellite images, single Doppler weather radar data, and weather radar mosaics data. The results are as follows. (1) Derechos mainly occur in the eastern half of China, including North China, East China, South China, and regions to the south of the Yangtze River. The regions of high occurrence frequency show remarkable seasonal variation, which is manifested as the northward movement during the first phase and the southward movement during the second phase from spring to summer. Derechos activity has significant seasonal changes. They mainly occur from March to August with the highest frequency in June and the lowest in August. The convective systems producing the Derechos tend to initiate around noon, while the Derechos themselves tend to occur between mid-afternoon and early midnight. (2) The main characteristics of environmental parameters of Derechos in China are as follows: The 50th percentile of CAPE is 1420 J/kg, the 50th percentile of the 0—6 km vertical shear is 18.0 m/s, the 50th percentile of DCAPE is 1090 J/kg. (3) The weather pattern of Derechos can be divided into the following four types: The subtropical high periphery type, the weak trough type, the high level dry-cold advection forced type and the strong trough type, among which the strong trough type has the highest frequency and the high level dry-cold advection forced type has the lowest frequency. (4) During the period when the maximum wind gust occurs, the most frequent convective storm type is squall line, the second frequent storm type is multi-cell cluster storm and the third frequent storm type is supercell storm.