Comparison of Microphysical Characteristics of Warm-sector,Frontal and Shear-line Heavy Rainfall During the Pre-summer Rainy Season in South China

Warm-sector heavy rainfall(WR),shear-line heavy rainfall(SR),and frontal heavy rainfall(FR)are three types of rainfall that frequently occur during the pre-summer rainy season in south China.In this research,we investigated the differences in microphysical characteristics of heavy rainfall events during the period of 10-15 May 2022 based on the combined observations from 11 S-band polarimetric radars in south China.The conclusions are as follows:(1)WR has the highest radar echo top height,the strongest radar echo at all altitudes,the highest lightning density,and the most active ice-phase process,which suggests that the convection is the most vigorous in the WR,moderate in the FR,and the weakest in the SR.(2)Three types of rainfall are all marine-type precipitation,the massweighted mean diameter(Dm,mm)and the intercept parameter(Nw,mm^(-1) m^(-3))of the raindrops in the WR are the largest.(3)The WR possesses the highest proportion of graupel compared with the FR and SR,and stronger updrafts and more abundant water vapor supply may lead to larger raindrops during the melting and collision-coalescence processes.(4)Over all the heights,liquid and ice water content in the WR are higher than those in the SR and FR,the ratio of ice to liquid water content in the WR is as high as 27%when ZH exceeds 50 dBZ,definitely higher than that in the SR and FR,indicating that the active ice-phase process existing in the WR is conducive to the formation of heavy rainfall.

The Climate Characteristics of Heavy Rainfall in China from 1951 to 2000

This paper analyzed the temporal and spatial distribution of heavy rainfall in China from 1951 to 2000.The results showed that since 1980s,the occurrence frequency of rainfall and major storm disasters increased significantly in Sichuan Province.In 1990s,Hebei heavy rainfall frequency and major storm disasters had increased remarkably.Heavy rainfall occurred mainly from May to August.The heavy storm largely took place from April to September.Catastrophic rains occurred in October in 1990s.Liaoning and Hubei Provinces had undergone the most amounts of heavy storms in 1950s.Jiangxi Province had undergone the most amounts in 1960s and Shandong in 1970s,Sichuan in 1980s and Hebei in 1990s.

Characteristics of Heavy Rainfall at Changbei Airport

Based on the hourly observation data of heavy rainfall at Changbei Airport from 2011 to 2018,the main characteristics of heavy rainfall at the airport were analyzed. The results show that the heavy rainfall at Changbei Airport often occurred from April to August,most in June,mostly from the evening to midnight. Visibility and runway visual range( RVR) were often affected by the heavy rainfall,but the proportion of weather processes below the take-off and landing standards was relatively small. The main influencing factors of heavy rainfall were low vortex shear,front,high trough and subtropical high edge. The changing characteristics of meteorological elements in the high-centroid rainfall processes were more obvious,and they had greater impact on flight.

The Short-Duration Heavy Rainfall in Different Quadrants of Northeast China Cold Vortices

The Northeast China cold vortex(NCCV)is one of the main synoptic-scale systems causing short-duration heavy rainfall(SDHR)in Northeast China.Environmental conditions(e.g.,water vapor,instability,and vertical wind shear)are known to be distinctly different over the four quadrants of NCCVs,rendering prediction of the SDHR related to NCCVs(NCCV_SDHR)more challenging.Based on 5-yr hourly rainfall observations from 3196 automatic weather stations and ERA5 reanalysis data,10,232 NCCV_SDHR events were identified and divided into four quadrant groups according to their relative position to the center of the NCCV(CVC).The results show that the southeast quadrant features the highest frequency of SDHR,with stronger intensity,longer duration,and wider coverage;and the SDHR in different quadrants presents different formation mechanisms and varied temporal evolution.A new coordinate system is established relative to the CVC that uses the CVC as the origin and the radius of the NCCV(r CV)as the unit distance.In this new coordinate system,all of the NCCV_SDHR events in the 5-yr study period are synthesized.It is found that the occurrence frequency of NCCV_SDHR initially increases and then decreases with increasing distance from the CVC.The highest frequency occurs mainly between 0.8 and 2.5 times r CV from the CVC in the southeast quadrant.This can be attributed to the favorable conditions,such as convergence of the low-level shear line and abundant water vapor,which are concentrated in this region.Furthermore,high-frequency NCCV_SDHR larger than 50 mm(NCCV_SDHR50)is observed to be closer to the CVC.When NCCV_SDHR50occurs,the NCCV is in closer proximity to the subtropical high,resulting in stronger low-level convergence and more abundant water vapor.Additionally,there are lower lifting condensation levels and stronger 0-6-and 0-1-km vertical wind shears in these environments.These findings provide a valuable reference for more accurate prediction of NCCV_SDHR.

河南省近30年分级短时强降水时空分布特征分析

利用1992-2021年4-10月河南省101个台站逐时降水资料并结合地形,统计分析了河南省不同量级短时强降水的时空演变特征及其与地形的关系。结果表明:(1)R1h≥20 mm·h^(-1)的短时强降水和3个不同量级的短时强降水频次分布均呈东多西少的分布特征,短时强降水和[20 mm·h^(-1),50mm·h^(-1))量级的短时强水出现的频次均呈南多北少的分布特征,[50 mm·h^(-1),80 mm·h^(-1))量级的短时强水出现的频次表现为南北之间差别不大,而[80 mm·h^(-1),+∞)量级的短时强水出现的频次呈南少北多的分布特征。各月短时强降水频次的空间分布为东多西少,7月、8月和10月南北之间差别不大,其他月份呈南多北少的分布特征。(2)短时强降水年际变化差别大,月变化呈单峰型,6月下旬-8月上旬是各量级短时强降水多发时段。(3)短时强降水频次日变化分布呈双峰型,16-21时的发生频次最高,00-05时的次之,09-14时的最低。6-8月短时强降水频次的日变化特征呈双峰型,其他月份的双峰特征不明显。4-10月16-21时出现日峰值的站点最多,00-05时的次之,空间分布呈东大西小、南大北小的分布特征,各月00-05时出现日峰值的站数最多,16-21时的次之。(4)最大雨强和短时强降水量的占比均呈东高西低、北高南低的分布特征。(5)短时强降水的空间分布、日变化空间分布、最大雨强高值区和短时强降水量占比等均与河南省地形关系密切,地形对短时强降水有增(减)幅作用。

Statistical Characteristics of Environmental Parameters for Warm Season Short-Duration Heavy Rainfall over Central and Eastern China

Water vapor content, instability, and convergence conditions are the key to short-duration heavy rainfall forecasting. It is necessary to understand the large-scale atmospheric environment characteristics of short- duration heavy rainfall by investigating the distribution of physical parameters for different hourly rainfall intensities. The observed hourly rainfall data in China and the NCEP final analysis （FNL） data during 1 May and 30 September from 2002 to 2009 are used. NCEP FNL data are 6-hourly, resulting in sample sizes of 1573370, 355346, and 11401 for three categories of hourly rainfall （P） of no precipitation （P 〈 0.1 mm h-1）, ordinary precipitation （0.1≤ P 〈 20 mm h-1）, and short-duration heavy rainfall （P ≥ 20.0 mm h-1）, respectively, by adopting a temporal matching method. The results show that the total precipitable water （PWAT） is the best parameter indicating the hourly rainfall intensity. A PWAT of 28 mm is necessary for any short-duration heavy rainfall. The possibility of short-duration heavy rainfall occurrence increases with PWAT, and a PWAT of 59 mm is nearly sufficient. The specific humidity is a better indicator than relative humidity. Both 700- and 850-hPa relative humidity greater than 80% could be used to determine whether or not it is going to rain, but could not be used to estimate the rainfall intensity. Temperature and potential pseudo-equivalent temperature are also reasonable indicators of short-duration heavy rainfall. Among the atmospheric instability parameters, the best lifted index （BLI） performs best on the short- duration rainfall discrimination; the next best is the K index （KI）. The three rainfall categories are not well recognized by total totals （TT） or the temperature difference between 850 and 500 hPa （DT85）. Three- quarters of short-duration heavy rainfall occurred with BLI less than -0.9, while no short-duration heavy rainfall occurred when BLI was greater than 2.6. The minimum threshold of KI was 28.1 for short-duration heavy rainfall. The importance of dynamic conditions was well demonstrated by the 925- and 850-hPa divergence. The representativeness of 925-hPa divergence is stronger than that of 850 hPa. Three-quarters of short-duration heavy rainfall occurred under a negative divergence environment. However, both the best convective potential energy （BCAPE） and vertical wind shear were unable to discriminate the hourly rainfall intensities.

吉林省短时强降水时空特征分析

文章利用吉林省51个国家地面气象观测站1994—2023年4—10月逐小时降水资料,通过对短时强降水时间尺度、空间尺度进行分析,揭示吉林省短时强降水时空分布特征及变化规律。结果表明:1994—2023年短时强降水频次呈现先下降后上升的趋势;5—9月为吉林省短时强降水集中期,其中7—8月发生频次最多;短时强降水最早出现在5月15日前后,最晚出现在9月10日前后;降水日变化呈现双峰结构;降水空间分布不均匀。研究结果以期为短时强降水的预报提供气候背景,为预报预警服务提供参考依据。

一次大暴雨中尺度短时强降水回波特征分析

为了做好江西宜丰大暴雨天气的预警预报服务,使用常规天气图、宜丰自动站雨量、江西雷达拼图等资料,采用天气学、雷达气象学等原理,对2022年6月3日江西宜丰地区大暴雨过程进行分析。结果表明,通过对6月3日宜丰大暴雨年月日统计特征进行分析,1981—2022年宜丰每年大暴雨出现频次在0~2次,主要集中出现在6月份。宜丰此次大暴雨过程前期雨势不大,但由于云系发展和地形、环境等条件的影响,在6月3日08时小时雨强达到了65 mm,到了09时小时雨强达到最大的70 mm,造成了局地的超短时强降水。受低槽及低层切变东移影响,边界层及地面增温明显,动力抬升加强。850 hPa低涡东侧的切变线一直延伸至赣北北部,切变线南侧西南急流达到14 m/s,宜丰处在西南急流的左前方,同时地面辐合线稳定在宜丰附近并与低层切变耦合,导致辐合扰动加强,有利于强风暴在辐合线附近发生。回波形态为絮状回波带结构,絮状回波带包含着多个较强单体回波,影响宜丰的组合反射率CR回波最强达到50 dBZ,≥45 dBZ回波稳定在宜丰南部,为短时强降水的生成形成了非常有利的条件,随着回波顶高的升高,加强了该单体回波的降水效率,08时出现了小时雨强65 mm/h的超强降水。

Spatiotemporal characteristics of GNSS-derived precipitable water vapor during heavy rainfall events in Guilin,China

Precipitable Water Vapor(PWV),as an important indicator of atmospheric water vapor,can be derived from Global Navigation Satellite System(GNSS)observations with the advantages of high precision and all-weather capacity.GNSS-derived PWV with a high spatiotemporal resolution has become an important source of observations in mete-orology,particularly for severe weather conditions,for water vapor is not well sampled in the current meteorological observing systems.In this study,an empirical atmospheric weighted mean temperature(Tm)model for Guilin is estab-lished using the radiosonde data from 2012 to 2017.Then,the observations at 11 GNSS stations in Guilin are used to investigate the spatiotemporal features of GNSS-derived PWV under the heavy rainfalls from June to July 2017.The results show that the new Tm model in Guilin has better performance with the mean bias and Root Mean Square(RMS)of−0.51 and 2.12 K,respectively,compared with other widely used models.Moreover,the GNSS PWV estimates are validated with the data at Guilin radiosonde station.Good agreements are found between GNSS-derived PWV and radiosonde-derived PWV with the mean bias and RMS of−0.9 and 3.53 mm,respectively.Finally,an investigation on the spatiotemporal characteristics of GNSS PWV during heavy rainfalls in Guilin is performed.It is shown that variations of PWV retrieved from GNSS have a direct relationship with the in situ rainfall measurements,and the PWV increases sharply before the arrival of a heavy rainfall and decreases to a stable state after the cease of the rainfall.It also reveals the moisture variation in several regions of Guilin during a heavy rainfall,which is significant for the moni-toring of rainfalls and weather forecast.

滇中地区不同影响系统下3次短时强降水过程的大气环境特征和雷达特征分析

利用常规观测资料、NCEP 1°×1°再分析资料、逐时和逐5 min自动站降水资料以及昆明CINRAD/CC多普勒雷达资料,针对滇中地区2021年主汛期不同影响系统下的3次短时强降水过程,对比分析了降水特征、环流形势、大气环境特征以及雷达回波的结构、形状、演变的基本特征。结果表明:3次短时强降水过程影响系统差异主要在于500 hPa天气系统不同,700 hPa都有切变线影响,但是形成原因各异,地面均有辐合线或弱冷锋配合。3次过程的环境条件在不稳定层结、近地层水汽、垂直风切变方面与中国其他地区短时强降水发生的环境条件具有一致性,但是在大气整层可降水量、对流有效位能、SWEAT指数等方面存在明显差异。对流回波的形状有点状回波、块状回波、带状回波、絮状回波等。对流风暴分为高质心型、低质心型以及混合型;短时强降水有单独出现某种对流风暴类型的阶段,也有多种对流风暴类型同时出现的阶段;CAPE值和SWEAT指数与对流风暴类型具有一定的相关关系。强回波剖面呈柱状结构或者塔状结构,35 dBz强回波接地,而没有悬垂特征。短时强降水多产生于长时间停滞型或移动缓慢型的对流回波,还有部分短时强降水产生于“列车效应”中。短生命周期的单体生消形成的短时强降水持续时间绝大部分在1 h以内,但是单体合并组织和反复生消或者“列车效应”形成的短时强降水持续时间常在1~3 h。高质心型对流风暴产生的瞬时雨强可达10 mm·(5min)-1以上,低质心型和混合型对流风暴可产生的雨强范围较大,大多在3~10 mm·(5min)-1,少数也可达到10 mm·(5min)-1以上。

河北保定市“23·7”强降水过程的观测特征分析

利用常规、加密观测资料,风廓线、双偏振雷达探测数据等,对2023年7月29日至8月2日发生在河北省保定市的强致灾性极端强降水过程的阶段性演变、观测特征等进行了分析,结果表明:1)在大陆高压与副高形成“北方高压坝”、台风“杜苏芮”减弱低压北上受阻的环流背景下,“杜苏芮”倒槽、“杜苏芮”残涡东侧的暖式切变线以及副高外围南风气流先后造成保定3个阶段的降水,最长单站降水持续时间70 h,7月30日07:00(北京时间,下同)至8月1日03:00涿州上游、海拔高度介于0.1~1 km的浅山区内不断出现短时强降水、“列车效应”显著,导致该区域出现极端的洪灾。2)29日倒槽降水雨带呈东北—西南向并随时间西北移,最大降水强度39.4 mm/h;30日副高西移,倒槽东侧位势梯度加大,同时台风“卡努”北侧东南气流并入,冀鲁地区低空东南急流加强、北伸,雨带呈“人”字形,降水落区无变化但短时强降水频次增大、强降水范围集中,雨强增至82.2 mm/h。3)切变线降水阶段,对流不稳定层增厚,降水主要集中在西南风—东南风切变线与南风—东风切变线之间,多局地短时强降水,最大雨强为76.3 mm/h。4)“杜苏芮”影响结束后,副高外围的低层偏南气流有明显的风速辐合,引发暖区局地降水,雨带呈准南北向且分为多轮次,各轮次降水落区次第向东移动且强度不断减小,阶段内最大降水强度54.2 mm/h。5)双偏振雷达图像显示,在倒槽降水阶段,前期为低质心暖云降水,对流发展高度最低,暖云碰并机制明显,雨滴粒子直径最大;“卡努”东南急流并入时段,0°C层下降、-10°C层抬升,对流高度增加,霰粒子增长、冰相粒子聚合融化,雨滴粒子浓度增至最大。在切变线降水时0~-10°C层厚度减小而-10~-20°C层厚度增加,对流发展高度最高,霰粒子凇附增长更为明显。6)地形对降水有增幅作用,倒槽降水阶段东南气流加强、北伸时与偏东风在保定中、北部辐合抬升,保定浅山区开始有山洪出现;“卡努”北侧东南风气流并入时的倒槽降水阶段以及切变线降水阶段,东南风与太行山北段近乎正交,保定西南部山区30日08:00至31日08:00出现24 h降水量极值。

北京地区“23•7”特大暴雨型地质灾害特征及预警成效分析

极端降雨常伴随群发性地质灾害发生,严重危害易发区人民群众生命财产安全,影响经济社会健康发展。总结分析极端降水灾害时空分布特点及预警成效,对于提高地质灾害综合防御能力具有重要意义。以2023年“23•7”强降水引发的突发地质灾害为研究对象,以“北京市突发地质灾害监测预警系统”精细化降水数据为基础,分析了“23•7”强降水时空分布特性和地质灾害发育分布特征,剖析了地质灾害预警成效,结果表明:“23•7”强降水具有总量大、雨强大、历时长、范围广等特点,极端降水灾害具有群发性,地质灾害分级分类多维度预警成效显著,实现了极端天气条件下因地质灾害零伤亡的目标。研究成果可为积极防范和科学应对极端降水地质灾害提供参考。

丽江机场强降水天气特征分析

利用丽江机场自动观测站资料、NCEP再分析资料,引入HYSPLIT轨迹模式,对丽江机场2007—2019年出现的强降水天气特征进行分析。结果表明,丽江机场强降水日数年际差异较大,年平均强降水日数为7.8 d,最大日降水量为92.3 mm。强降水天气有明显的季节变化特征,雨季6—9月的强降水日数占比90%,暴雨主要分布在7—8月。根据500 hPa高度上主要的影响系统,总结出7种丽江机场强降水天气形势,其中切变冷锋型和两高合并型是丽江机场强降水的最主要天气形势,占比40%。强降水期间丽江机场上空整层为垂直上升速度大值区。水汽主要来自700 hPa高度,低层水汽辐合,高层辐散,有利于水汽向上垂直运动。通过HYSPLIT模式分析,丽江机场雨季水汽输送通道共有3条,其中西南路径占比最大,孟加拉湾地区的水汽输送是丽江机场雨季最主要的水汽来源;7—8月副热带高压强盛、台风活动频繁,因此有一定的南海方向水汽输送,即东南路径;8—9月受川滇切变线和西南涡影响,有少量来自川渝地区的水汽输送,即东北路径。

Failure process and monitoring data of an extra-large landslide at the Nanfen Open-pit Iron Mine

An extra-large landslide occurred on June 19,2021,on the footwall slope of the Nanfen Open-pit Iron Mine in Liaoning Province,China,with a volume of approximately 1.2×107 m3.To elucidate the causative factors,development process,and destructive mechanisms of this catastrophic landslide,comprehensive field tests,investigations,and laboratory experiments were conducted.Initially,the heavily weathered rock mass of the slope was intersected by faults and joint fissures,facilitating rainwater infiltration.Moreover,the landslide contained a substantial clay mineral with highly developed micro-cracks and micro-pores,exhibiting strong water-absorption properties.As moisture content increased,the rock mass underwent softening,resulting in reduced strength.Ultimately,continuous heavy rainfall infiltration amplified the slope's weight,diminishing the weak structural plane's strength,leading to fracture propagation,slip plane penetration,and extensive tensile-shear and uplift failure of the slope.The study highlights poor geological conditions as the decisive factor for this landslide,with continuous heavy rainfall as the triggering factor.Presently,adverse environmental factors persistently affect the landslide,and deformation and failure continue to escalate.Hence,it is imperative to urgently implement integrated measures encompassing slope reinforcement,monitoring,and early-warning to real-time monitor the landslide's deformation and deep mechanical evolution trends.

铜鼓及上游地区短时强降水回波特征分析

为了开展铜鼓县大暴雨过程中短时强降水的预报预警工作,文章利用铜鼓县、平江县和浏阳市雨量资料、流域地形资料、天气图、雷达回波等资料,对2013—2022年铜鼓、平江、浏阳在大暴雨事件中的短时强降水个例进行回波特征分析。结果表明:2013—2022年,铜鼓共出现大暴雨日10次,平江出现7次,浏阳出现4次;21次大暴雨中降水量≥30 mm/h的短时强降水有14次,几乎每次大暴雨都会出现降水量≥20 mm/h的短时强降水;500 hPa低槽、200 hPa出流区、850 hPa西南急流和地面辐合线有利于形成铜鼓及上游地区的大暴雨天气;铜鼓及上游地区短时强降水的雷达回波特征主要有絮状回波带(团)和絮状回波带中的短带回波两种;短时强降水回波的垂直结构主要特征为45 dBZ回波顶高为5 km~7 km,回波呈“直上直下”结构。研究结果为铜鼓短时强降水预报预警提供了分析依据。

鹰潭2023年7月短时强降水雷达回波特征分析

为了做好鹰潭短时强降水天气预报工作,文章从强降水实况、天气形势、雷达回波特征等方面分析了2023年7月鹰潭市4次短时强降水过程。结果得出:鹰潭强降水主要出现在午后到夜间,降水局地性强、时间长、强度大,往往造成一地或多地强降水;鹰潭处台风外围,低层辐合、高空辐散,水汽条件好,空气层结极不稳定并伴有强大的不稳定能量;强降水区垂直积分液态水含量达12 kg/m2以上,强反射率因子呈直上、直下的垂直结构,回波中心强度可达55 dBZ或以上,45 dBZ回波顶高在7 km~11 km,有辐合型速度;当有大范围45 dBZ以上强回波影响时,容易出现强降水;强降水区为气旋式环流并伴有显著的风向、风速辐合。研究结果为强降水的监测、预警服务提供了参考依据。

基于分钟数据的济南局地短时强降水演变特征

文章利用济南市2012-2020年123个地面观测站的逐分钟降水数据,采用个例统计方法分析了短时强降水过程的演变特征。统计得出济南市共发生113次局地短时强降水,降水日变化特征明显,降水量空间分布不均,短时强降水演变过程具有非对称性。研究结果可为短时强降水预警预报工作提供参考。

江西赣南一次短时强降水中尺度的特征及成因分析

2022年6月12日江西南部的强降水过程因对流性不强而在业务工作中漏报了短时强降水天气。对降水发生期间的环流背景以及12日20时前后的中尺度特征、雷达回波及降水成因进行了分析。结果表明,此次强降水发生于500 hPa低槽前、低空切变线南侧和急流轴前端,强降水期间副热带急流中心呈现波动状,高空分流辐散强盛,高低空耦合抽吸效应明显,造成此次降水偏强。短时强降水过程期间,尽管赣南北部环境参数显示对流条件偏弱,但受高空辐散低空辐合的抽吸作用与地形影响,造成水汽剧烈辐合和强烈上升运动,产生了明显的短时强降水。短时强降水发生时间和位置与雷达强回波位置吻合,雷达的演变与降水的演变关系对应较好,雨量较大时次45 dBZ以上强度回波的高度伸展至5 km以上,差分反射率(ZDR)≥1.5 dB。且雷达回波发生时间均超前于短时强降水过程中雨强的变化,其中反射率超前时间最多,约提前时间18—24 min,KDP超前时间稍短,但与降水的变化关系更为一致。

“2023-07-25”鹰潭短时强降水过程分析

为了做好短时强降水的预警预报工作,文章使用MICAPS天气资料、江西WebGIS雷达拼图、自动气象站等资料,采用中尺度天气分析方法和雷达气象学原理,对2023-07-25鹰潭短时强降水过程进行了分析。结果表明:“7.25”鹰潭短时强降水是由500 hPa高空槽、700 hPa切变线和地面偏东气流共同作用引起的。强对流回波在信江河谷地带产生,在地面偏东南气流的作用下,回波稳定少动,造成鹰潭城区出现短时强降水。此次降水过程提示预警预报工作要警惕突然发展、稳定少动的回波,研究结果为短时强降水天气的预报提供了分析依据。

极端持续性强降水过程雷达偏振量特征及演变

为研究极端持续性强降水过程的中尺度结构和云物理特征,利用龙岩S波段双偏振雷达、雨滴谱仪、二维闪电定位仪等多源资料结合雷达风场反演方法,分析2022年5月26—27日福建一次极端持续性强降水过程。结果表明:该过程水汽充沛,不稳定能量适中,有利于产生强降水。强降水期间不低于45 dBZ的强回波主要集中在西南向喇叭口地形收缩处的山脉迎风坡一侧。强回波在气流辐合处持续发展,前两个阶段暴雨区西侧回波持续移入形成后向传播的列车效应;第3阶段强回波在东北风引导下向东偏南移动。该过程以海洋性对流降水和暖云降水为主,强降水主要由高浓度小尺度的雨滴粒子造成。第2阶段强烈上升运动在0℃层以上形成霰粒子,并与冰晶碰撞,产生负闪,冰相过程使霰粒子下落融化与低层雨滴的碰并增长形成大雨滴,降水效率高。降水粒子集中在气流汇合处,中低层存在高浓度雨滴粒子。差分反射率大值区多分布在中层上升气流处,大雨滴在下落过程中破碎为小雨滴,进一步加大雨滴粒子数。