Precipitation Microphysical Characteristics of Typhoon Ewiniar(2018) before and after Its Final Landfall over Southern China

In this paper, the evolution of the microphysical characteristics in different regions(eyewall, inner core, and outer rainbands) and different quadrants [downshear left(DL), downshear right(DR), upshear left(UL), and upshear right(UR)]during the final landfall of Typhoon Ewiniar(2018) is analyzed using two-dimensional video disdrometer and S-band polarimetric radar data collected in Guangdong, China. Due to the different types of underlying surfaces, the periods before landfall(mainly dominated by underlying sea surface) and after landfall(mainly dominated by underlying land surface) are also analyzed. Both before landfall and after landfall, the downshear quadrants had the dominate typhoon precipitation. The outer rainbands had more graupel than the inner core, resulting in a larger radar reflectivity, differential reflectivity, specific differential phase shift, and mass-weighted mean diameter below the melting layer. Compared with other regions, the eyewall region had the smallest mean logarithmic normalized intercept parameter before landfall and the smallest mean mass-weighted mean diameter and the largest mean logarithmic normalized intercept parameter after landfall. The hydrometeor size sorting was obvious in the eyewall and inner core(especially in the eyewall) after landfall. A high concentration of large raindrops fell in the DL quadrant, and more small raindrops fell in the UR quadrant. Although the icephase process and warm rain process were both important in the formation of tropical cyclone precipitation, the warm rain process(ice-phase process) contributed more liquid water before landfall(after landfall). This investigation provides a reference for improving the microphysical parameterization scheme in numerical models.

Microphysical Characteristics of Precipitation during Pre-monsoon,Monsoon, and Post-monsoon Periods over the South China Sea

Raindrop size distribution (RSD) characteristics over the South China Sea (SCS) are examined with onboard Parsivel disdrometer measurements collected during marine surveys from 2012 to 2016. The observed rainfall is divided into premonsoon, monsoon, and post-monsoon periods based on the different large-scale circumstances. In addition to disdrometer data, sounding observation, FY-2E satellite, SPRINTARS (Spectral Radiation-Transport Model for Aerosol Species), and NCEP reanalysis datasets are used to illustrate the dynamical and microphysical characteristics associated with the rainfall in different periods. Significant variations have been observed in respect of raindrops among the three periods. Intercomparison reveals that small drops (D < 1 mm) are prevalent during pre-monsoon precipitation, whereas medium drops (1?3 mm) are predominant in monsoon precipitation. Overall, the post-monsoon precipitation is characterized by the least concentration of raindrops among the three periods. But, several large raindrops could also occur due to severe convective precipitation events in this period. Classification of the precipitation into stratiform and convective regimes shows that the lg(Nw) value of convective rainfall is the largest (smallest) in the pre-monsoon (post-monsoon) period, whereas the Dm value is the smallest (largest) in the pre-monsoon (post-monsoon) period. An inversion relationship between the coefficient A and the exponential b of the Z?R relationships for precipitation during the three periods is found. Empirical relations between Dm and the radar reflectivity factors at Ku and Ka bands are also derived to improve the rainfall retrieval algorithms over the SCS. Furthermore, the possible causative mechanisms for the significant RSD variability in different periods are also discussed with respect to warm and cold rain processes, raindrop evaporation, convective activities, and other meteorological factors.

Statistical Characteristics of Raindrop Size Distribution in the South China Monsoon Region(Guangdong Province)

While heavy rainfall frequently takes place in southern China during summer monsoon seasons,quantitative precipitation forecast skills are relatively poor.Therefore,detailed knowledge about the raindrop size distribution(DSD)is useful in improving the quantitative precipitation estimation and forecast.Based on the data during 2018-2022 from 86stations in a ground-based optical disdrometer measurement network,the characteristics of the DSD in Guangdong province are investigated in terms of the particle size distribution(N(D)),mass-weighted mean diameter(Dm) and other integral DSD parameters such as radar reflectivity(Z),rainfall rate(R) and liquid water content(LWC).In addition,the effects of geographical locations,weather systems(tropical cyclones,frontal systems and the summer monsoon) and precipitation types on DSD characteristics are also considered.The results are shown as follows.1) Convective precipitation has a broader N(D) and larger mean particle diameter than the stratiform precipitation,and the DSD observations in Guangdong are consistent with the three-parameter gamma distribution.The relationships between the Z and R for stratiform and convective precipitation are also derived for the province,i.e.,Z=332.34 R1.32and Z=366.26R1.42which is distinctly different from that of the Next-generation Weather Radar(NEXRAD) Z-R relationship in United States.2) In the rainy season(April-September),the Dm, R and LWC are larger than those in the dry season(OctoberMarch).Moreover the above parameters are larger,especially in mid-May,which is the onset of the South China Sea summer monsoon.3) The spatial analysis of DSD shows that the coastal station observations indicate a smaller Dmand a larger normalized intercept parameter(log10Nw),suggestive of maritime-like rainfall.Dmis larger and log10Nwis smaller in the inland area,suggestive of continental-like rainfall.4) Affected by such weather systems as the tropical cyclone,frontal system and summer monsoon,the DSD shows characteristics with distinct differences.Furthermore,frontal system rainfall tends to present a continental-like rainfall,tropical cyclone rainfall tends to have a maritime-like rainfall,and summer monsoon rainfall characteristic are between maritime-and continental-like cluster(raindrop concentration and diameter are higher than continental cluster and maritime cluster,respectively.)

Seasonal Variations of Observed Raindrop Size Distribution in East China

Seasonal variations of rainfall microphysics in East China are investigated using data from the observations of a twodimensional video disdrometer and a vertically pointing micro rain radar. The precipitation and rain drop size distribution(DSD) characteristics are revealed for different rain types and seasons. Summer rainfall is dominated by convective rain,while during the other seasons the contribution of stratiform rain to rainfall amount is equal to or even larger than that of convective rain. The mean mass-weighted diameter versus the generalized intercept parameter pairs of convective rain are plotted roughly around the "maritime" cluster, indicating a maritime nature of convective precipitation throughout the year in East China. The localized rainfall estimators, i.e., rainfall kinetic energy–rain rate, shape–slope, and radar reflectivity–rain rate relations are further derived. DSD variability is believed to be a major source of diversity of the aforementioned derived estimators. These newly derived relations would certainly improve the accuracy of rainfall kinetic energy estimation, DSD retrieval, and quantitative precipitation estimation in this specific region.

Statistical Characteristics of Raindrop Size Distribution in the Tibetan Plateau and Southern China

The characteristics of raindrop size distribution （DSD） over the Tibetan Plateau and southern China are studied in this paper, using the DSD data from April to August 2014 collected by HSC-PS32 disdrometers in Nagqu and Yangjiang, com- prising a total of 9430 and 63661-rain raindrop spectra, respectively. The raindrop spectra, characteristics of parameter variations with rainfall rate, and the relationships between reflectivity factor （Z） and rainfall rate （R） are analyzed, as well as their DSD changes with precipitation type and rainfall rate. The results show that the average raindrop spectra appear to be one-peak curves, the number concentration for larger drops increase significantly with rainfall rate, and its value over southern China is much higher, especially in convective rain larger drops, especially for convective rain in southern China. Standardized Gamma distributions better describe DSD for All three Gamma parameters for stratiform precipitation over the Tibetan Plateau are much higher, while its shape parameter （,u） and mass-weighted mean diameter （Dm）, for convective precipitation, are less. In terms of parameter variation with rainfall rate, the normalized intercept parameter （Nw） over the Tibetan Plateau for stratiform rain increases with rainfall rate, which is opposite to the situation in convective rain. The/1 over the Tibetan Plateau for stratiform and convective precipitation types decreases with an increase in rainfall rate, which is opposite to the case for Dm variation. In Z-R relationships, like ＂Z = ARb＇＇, the coefficient A over the Tibetan Plateau is smaller, while its b is higher, when the rain type transfers from stratiform to convective ones. Furthermore, with an increase in rainfall rate, parameters A and b over southern China increase gradually, while A over the Tibetan Plateau decreases sub- stantially, which differs from the findings of previous studies. In terms of geographic location and climate over the Tibetan Plateau and southern China, the precipitation in the pre-flood seasons is dominated by strong convective rain, while weak convective rain occurs frequently in northern Tibet with lower humidity and higher altitude.

Raindrop Size Distribution Measurements at High Altitudes in the Northeastern Tibetan Plateau during Summer

Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern Tibetan Plateau.The analysis focuses on convective and stratiform precipitation at high altitudes from 2434 m to 4202 m.The results show that the contribution of stratiform and convective precipitation with rain rate between 1≤R<5 mm h^(-1) to the total precipitation increases with altitude,and the raindrop scale and number concentration of convective precipitation is larger than that for stratiform precipitation.The droplet size spectra of both stratiform and convective precipitation shows a single peak with a peak particle size between 0.31–0.50 mm,and they have essentially the same peak particle size and number concentration at the same altitude.The maximum spectral widths of stratiform clouds are between 4 mm and 5 mm,while those of convective clouds range from 4 mm to 8 mm.The Gamma distribution is more suitable than the Marshall-Palmer distribution in terms of the actual raindrop spectrum distribution.The stratiform precipitation particles are smaller with higher number concentration,while the opposite is true for the convective precipitation particles.The convective precipitation particles drop faster than stratiform precipitation particles when the particle size exceeds 2 mm,and the falling velocity of raindrops after standard curve fitting is underestimated during the observation period.Moreover,conventional radar estimation methods would underestimate the precipitation in the Northeastern Tibetan Plateau.

Observed Vertical Structure of Precipitation over the Southeastern Tibetan Plateau in Summer 2021

Mêdog County,with its mountains and valleys,is located in the southeastern Tibetan Plateau(TP)and at the lower reaches of the Yarlung Zangbo River.This area has the highest annual rainfall amount over the TP,and in situ measurements are very scarce due to frequent debris flows and transportation difficulties.A monitoring campaign focused on cloud and precipitation observations was established in Mêdog in 2019 as a part of the Second Tibetan Plateau Scientific Expedition and Research Program.This paper evaluates the accuracy of micro rain radar(MRR)measurements and investigates the variations in precipitation vertical structure in Mêdog using observations collected from the MRR,disdrometer,and rain gauges in summer 2021.The measurements from the three instruments show a strong consistency,with correlation coefficients exceeding 0.93.Although the profiles of integral rain parameters for different rain rate categories in Mêdog are similar to those in other regions,the vertical evolution of raindrop size distributions shows significant differences.For lightest rain,the evaporation of small raindrops and breakup of large raindrops are clear during their descent.For the rainfall rate category of 0.2–2.0 mm h−1(2.0–20.0 mm h−1),concentrations of small and medium(large)drops show almost uniform vertical structures,while the large(medium)drop number displays a positive(negative)gradient.A disturbance at height of 1.5–2.0 km above ground level(AGL)is observed in the heavy rainfall due to strong updrafts.In general,the MRR measurements in Mêdog are robust.The raindrop breakup process is more apparent in Mêdog than in other regions,resulting in high concentration of sizelimited raindrops.In addition,it is found that the interaction between steep terrain and Mêdog convective rain causes the strong updrafts between 1.5 and 2.0 km AGL.

Raindrop Size Distribution Parameters Retrieved from Xinfeng C-Band Polarimetric Radar Observations

The objective of this research was to acquire a raindrop size distribution(DSDs)retrieved from C-band polarimetric radar observations scheme for the first time in south China.An observation period of the precipitation process was selected,and the shape-slope(μ-Λ)relationship of this region was statistically analyzed using the raindrop sample observations from the two-dimensional video disdrometer(2DVD)at Xinfeng Station,Guangdong Province.Simulated data of the C-band polarimetric radar reflectivity ZHHand differential reflectivity ZDRwere obtained through scattering simulation.The simulation data were combined with DSD fitting to determine the ZDR-Λand log10(ZHH/N0)-Λrelationships.Using Xinfeng C-band polarimetric radar observations ZDRand ZHH,the raindrop Gamma size distribution parametersμ,Λ,and N0were retrieved.A scheme for using C-band polarimetric radar to retrieve the DSDs was developed.This research revealed that during precipitation process,the DSDs obtained using the C-band polarimetric radar retrieval scheme are similar to the 2DVD observations,the precipitation characteristics of rainfall intensity(R),mass-weighted mean diameter(Dm)and intercept parameter(Nw)with time obtained by radar retrieval are basically consistent with the observational results of the 2DVD.This scheme establishes the relationship between the observations of the C-band polarimetric radar and the physical quantities of the numerical model.This method not only can test the prediction of the model data assimilation system on the convective scale and determine error sources,but also can improve the microphysical precipitation processes analysis and radar quantitative precipitation estimation.The present research will facilitate radar data assimilation in the future.

Near Homogeneous Microphysics of the Record-Breaking 2020 Summer Monsoon Rainfall during the Northward Migration over East China

Knowledge of the raindrop size distribution(DSD)is crucial for disaster prevention and mitigation.The recordbreaking rainfall in the summer of 2020 caused some of the worst flooding ever experienced in China.This study uses 96 Parsivel disdrometers and eight-year Global Precipitation Measurement(GPM)satellite observations to reveal the microphysical aspects of the disastrous rainfall during its northward migration over East China.The results show that the nearly twice as heavy rainfall in Jiangsu Province compared to Fujian Province can be attributed to the earlier-than-average northward jump of the summer monsoon rainband to the Yangtze-Huaihe River valley.The persistent heavy monsoon rainfall showed similar near-maritime DSD characteristics,with a higher concentration of small raindrops than the surrounding climatic regimes.During the northward movement of the rainband,the DSD variables and composite spectra between the pre-summer rainfall in Fujian and mei-yu rainfall in Jiangsu exhibited inherent similarities with slight regional variations.These are associated with similar statistical vertical precipitation structures for both convective and stratiform rain in these regions/periods.The vertical profiles of radar reflectivity and DSD parameters are typical of monsoonal rainfall features,implying the competition between coalescence,breakup,and accretion of vital warm rain processes.This study attributes the anomalously long duration of the mei-yu season for the record-breaking rainfall and reveals inherent homogeneous rainfall microphysics during the northward movement of the summer monsoon rainband.The conclusion is statistically robust and would be helpful for accurate precipitation estimation and model parameterization of summer monsoon rainfall over East China.

Raindrop Size Distributions in the Zhengzhou Extreme Rainfall Event on 20 July 2021:Temporal-Spatial Variability and Implications for Radar QPE

In this study,a regional Parsivel OTT disdrometer network covering urban Zhengzhou and adjacent areas is employed to investigate the temporal-spatial variability of raindrop size distributions(DSDs)in the Zhengzhou extreme rainfall event on 20 July 2021.The rain rates observed by disdrometers and rain gauges from six operational sites are in good agreement,despite significant site-to-site variations of 24-h accumulated rainfall ranging from 198.3 to 624.1 mm.The Parsivel OTT observations show prominent temporal-spatial variations of DSDs,and the most drastic change was registered at Zhengzhou Station where the record-breaking hourly rainfall of 201.9 mm over 1500-1600 LST(local standard time)was reported.This hourly rainfall is characterized by fairly high concentrations of large raindrops,and the mass-weighted raindrop diameter generally increases with the rain rate before reaching the equilibrium state of DSDs with the rain rate of about 50 mm h^(−1).Besides,polarimetric radar observations show the highest differential phase shift(K_(dp))and differential reflectivity(Z_(dr))near surface over Zhengzhou Station from 1500 to 1600 LST.In light of the remarkable temporal-spatial variability of DSDs,a reflectivity-grouped fitting approach is proposed to optimize the reflectivity-rain rate(Z-R)parameterization for radar quantitative precipitation estimation(QPE),and the rain gauge measurements are used for validation.The results show an increase of mean bias ratio from 0.57 to 0.79 and a decrease of root-mean-square error from 23.69 to 18.36 for the rainfall intensity above 20.0 mm h^(−1),as compared with the fixed Z-R parameterization.This study reveals the drastic temporal-spatial variations of rain microphysics during the Zhengzhou extreme rainfall event and warrants the promise of using reflectivity-grouped fitting Z-R relationships for radar QPE of such events.

华南夏季沿岸与近海岛屿雨滴谱特征对比分析

充分理解降水微物理的局地变化特征有助于提升本地化降水的模拟和预报能力。利用我国华南地区夏季四个站点(广西北海涠洲岛、防城港,广东阳江、江门上川岛)的雨滴谱观测数据,研究对比近海岛屿与沿岸陆上的降水微物理特征差异。研究表明,对流性降水对华南地区夏季降水量的贡献最大,且对流性降水的微物理特征具有明显的局地差异,具体表现为东部站点(阳江、上川岛)大雨滴更多而小雨滴浓度偏低,而西部站点(涠洲岛、防城港)的小雨滴浓度更高。此外,沿岸站点(阳江、防城港)较岛屿站点(上川岛、涠洲岛)的大雨滴浓度更高。研究还讨论了降水微物理的局地差异与环境变量之间的关系,发现东部(沿岸)站较西部(岛屿)站具有更厚的暖云层,更长的雨滴下落路径增强了碰并过程,从而促进了雨滴粒径的增长。同时,还拟合了华南地区四站的μ-L关系和Z-R关系以应用于提高降水和雨滴谱的估计和反演精度。可为研究我国华南地区降水微物理的局地变化特征提供较全面的参考依据。

青藏高原中东部和四川盆地的夏季雨滴谱对比分析研究

为了进一步认识青藏高原中东部和下游四川盆地的降水微观特征和差异,本文利用2019年7-8月和2020年7-8月那曲、玉树、林芝、巴塘、泸定和成都6个地区的雨滴谱观测资料,研究了不同地区之间的雨滴谱特征和差异,并提出了各个地区降水的Gamma谱形状参数-斜率参数关系和反射率因子-雨强关系。结果表明:因更多强对流降水的贡献,盆地和邻近地区(成都和泸定)的雨滴谱整体比高原地区(那曲、玉树、林芝和巴塘)的更宽,中大雨滴(直径≥1.0 mm)数浓度更高;而高原地区的降水主要来自层云和弱对流,整体雨滴谱更窄,小雨滴(直径<1.0 mm)数浓度更高。6个地区的雨滴谱均随雨强增大而变宽,数浓度也逐渐升高。不同地区之间的雨滴谱差异也会随雨强变化而改变,当雨强超过0.1 mm·h-1后,那曲和林芝的小雨滴数浓度随雨强增大而增大的幅度明显比其他地区更大;当雨强达到5 mm·h-1后,成都和泸定的中大雨滴数浓度与其他高原地区的差异也逐渐变大。在谱形状参数相同情况下,成都和泸定的谱倾斜率更小,反映了这两个地区雨滴数浓度随粒径增大而减小的速率比高原地区的更慢。在相同雷达回波强度(反射率因子)情况下,那曲和林芝层云降水的雨强比其他地区大;林芝对流降水在雷达回波低于40 dBZ时,雨强也比其他地区的大,而那曲对流降水在雷达回波大于40 dBZ后,雨强比其他地区的小。

冷涡背景下积层混合云降水的雨滴谱垂直分布及演变

利用2021年8月24—25日吉林靖宇微雨雷达反演的垂直探测资料,结合雨滴谱仪、雨量计等地面资料,分析了长白山麓一次混合云降水过程的雨滴谱垂直分布及微物理特征参量演变特征。结果表明:雨量计、雨滴谱仪探测地面雨量与微雨雷达反演的150 m高度雨量变化趋势基本一致,但观测值与反演值存在一定偏差。Gamma函数对地面雨滴谱拟合优度达到0.99,拟合效果优于微雨雷达,对微雨雷达反演的大雨滴数浓度拟合值明显偏小。不同直径(D)雨滴对不同高度微物理参量贡献不同,小雨滴(D≤1.0 mm)对雨强、反射率因子、液态水含量、总数浓度贡献率一般随着高度降低而降低,中雨滴(1.0 mm<D≤3.0 mm)和大雨滴(D>3.0 mm)对参量贡献率基本随着高度降低而升高。不同降水阶段的雨滴蒸发、碰并作用不同,降水前期气温高且湿度低,雨滴下落过程中蒸发作用较强,而降水集中期相对湿度接近饱和,雨滴碰并增长作用明显。

3种新型探测资料在贵阳春季一次短时强降水天气过程中的分析应用

【目的】探讨新型探测资料在短时强降水天气监测预警中的应用。【方法】利用常规气象观测资料、ERA5再分析资料、风廓线雷达、地基微波辐射计以及雨滴谱资料对贵阳地区2023年3月16日1次短时强降水天气过程进行分析。【结果】(1)短时强降水发生前2 h,垂直运动较弱,垂直风切变强中心向下传播,降水前约0.5 h,0~7 km垂直速度明显增大,低层上升运动更为显著,正垂直风切变明显增强,低空急流指数迅速增大;(2)19—21时,大气液态水含量呈波动增长,受干侵入影响,1 km以下相对湿度减小,0~8 km形成相对湿度为“上下干中间湿”3层结构,降水前约0.5 h,大气液态水含量迅速增大,变为“上干下湿”2层结构,强降水发生时处于大气液态水总含量波峰;(3)强对流过程处于高能环境,K指数从午后开始超过35℃,在降水发生前约0.5 h,K指数和CAPE均有较大跃升,降水发生时,强烈的西南风低空急流带来了暖湿空气,在0.2~1 km出现逆温,有>25℃的极值中心;(4)该次短时强降水过程雨滴直径与下落速度的关系符合理论关系,降水强度贡献最多的为中等大小粒径的粒子,降水时段,雨滴尺度谱存在明显的双峰结构。【结论】新型探测资料可以更细微地捕捉到短时强降水天气发生前中小尺度特征;垂直速度、低空急流指数和大气液态水含量的显著增大,预示着降水即将开始,急流指数的脉动与雨强之间有很好的对应关系;此外,0~1 km垂直风切变的增大,对强降水的出现有较好的预示作用。

安宁河谷雨季层状云和对流云降水的雨滴谱特征

利用2017年8—10月安宁河谷的激光雨滴谱仪观测数据,对层状云和对流云降水粒子谱的微物理参量、Gamma函数拟合、Z-I拟合关系、降水粒子对数浓度和降水强度贡献率进行了分析。结果表明:层状云雨滴谱较对流云窄,对流云降水粒子总数浓度、降水强度、液态水含量和雷达反射率因子等均显著高于层状云。Gamma函数可以较好地拟合雨滴谱的分布情况,层状云的函数曲线较对流云更加平滑。层状云、对流云降水的Z-I拟合关系均较好,分别为Z=181.90I1.54和Z=175.59I1.54。层状云降水强度贡献率的80%集中在直径不超过2 mm的粒子,而对流云的90%集中在直径超过1 mm的粒子,表明降水粒子尺度较浓度对降水强度的影响更大,大尺度降水粒子对降水强度贡献更大。

昭苏夏季层状云和对流云降水的雨滴谱特征

利用2020—2021年昭苏地区夏季的雨滴谱数据,研究层状云和对流云降水的微物理参量及雨滴谱特征。结果表明:对流云降水的粒子数浓度和粒子直径明显偏大,较大的粒子直径和粒子数浓度使得其降水强度和液态含水量远大于层状云降水。两类降水云的雨滴谱均为单峰结构,峰值直径主要分布在0.5~0.625 mm,对流云降水的雨滴谱谱宽明显大于层状云降水。两类降水云的雨滴直径和粒子数浓度与青藏高原中部的观测值相近,且昭苏地区的对流云滴谱更倾向于大陆性对流簇。研究结果有助于加深对昭苏地区降水的微物理特征及其演变规律的理解。

藏东南墨脱地区季风期降水的垂直结构特征

以2021年6—9月(季风期)藏东南水汽输送通道入口关键区墨脱布设的微雨雷达、降水现象仪和雨量计的观测数据为基础,对比不同仪器测量结果的一致性。将降水划分为对流云降水、层状云降水、浅层云降水3种类型,研究不同类型降水的雨滴谱分布、下落速度、降水率、液态水含量和雷达反射率因子的平均垂直分布特征。结果表明:微雨雷达、降水现象仪和雨量计测量结果一致性较好,微雨雷达和雨量计日降水量相关系数最高达到0.96,各相关系数的显著性水平较高;对流云降水的各微物理量特征值较大,雨滴在下落过程中碰并增长过程显著,雨滴数浓度迅速增加,在1~2 km高度处存在明显的上升气流;层状云降水回波强度较弱,反射率因子、降水率和液态水含量随高度降低有所增加,雨滴下落速度在垂直方向基本保持均匀,中等大小的雨滴浓度随高度不变,蒸发、破碎和碰并过程处于相对平衡状态;浅层云降水各微物理量较小,但随高度变化明显,垂直方向上为明显的负梯度变化,以雨滴的碰并过程为主。

中国西天山两次短时强降水过程雨滴谱特征研究

2020年8月2日和18日(简称8∙2和8∙18过程)中国西天山新源站出现短时强降水,应用自动气象站、GPS/MET水汽探测仪、二维视频雨滴谱仪、风云2G静止卫星等高时空分辨率观测资料,研究降水过程的环流背景和雨滴谱特征。结果表明:(1)两次过程均是在中亚低涡有利的背景下产生短时强降水,8·2过程降水阶段性强,由低涡前部西风气流中生成的孤立β中尺度对流系统(Mesoscale convective system,MCS)造成,水汽源自低涡本身,水汽输送和辐合相对弱;8∙18过程持续100 min阶段性不明显,由低涡层云中β中尺度MCS造成,水汽不仅来自于低涡而且还有新疆以外充沛水汽输送。(2)两次短时强降水天气雨滴谱特征有明显差异。两次过程雨滴粒子直径(D_(m))<2 mm的粒子频数占比约为97%左右,即降水过程小粒子占绝大多数。8∙2过程D_(m)<2 mm粒子对降水量贡献达66.75%,D_(m)超过4 mm的大粒子对瞬时强雨强贡献大,对流降水粒子谱分散,既有粒子大、浓度小的雨滴,又有粒子小、浓度高的雨滴;而8∙18过程D_(m)<2 mm粒子对降水量贡献达86.34%,其中D_(m)为1~2 mm粒子对降水量贡献达71.99%,且无D_(m)>4 mm粒子,对流降水粒子谱相对集中,D_(m)>2 mm粒子远少于8∙2过程,水平极化雷达反射率(ZH)、差分反射率因子(ZDR)和差分相移率(KDP)平均值和最大值比8∙2过程均明显偏小。(3)应用2020~2021年夏季探测资料研究对流性降水雨滴谱,对流性降水雨滴谱特征年际差异大,呈雨滴粒子大、浓度低特征,表现出大陆性对流降水性质,ZDR和KDP比季风区对流降水明显偏小,加入偏振量的R(ZH,ZDR)、R(KDP,ZDR)拟合关系明显好于R(ZH)、R(KDP)关系。

山东省三个不同区域降水雨滴谱特征的对比分析

为了解山东黄河三角洲、内陆和沿海三个区域降水的微物理特征差异,以垦利、平阴和胶南3站为代表,利用2017—2020年降水雨滴谱资料,对3站不同雨强(R)、不同降水类型的雨滴谱特征进行对比分析。结果表明:(1)在6个R级别中,3站平均雨滴谱的谱型、谱宽和各级别降水量对总降水量的贡献均存在一定区别。(2)在层云降水中,平阴站、胶南站雨滴谱参数较接近,而在对流云降水中3站均存在差异。(3)比较3站标椎化截距参数(log10Nw)和质量加权平均直径(Dm)表明,层云降水中垦利站log10Nw数值最低;与国内外其他站点相比,平阴站log10Nw-Dm散点分布与在韩国首尔的观测结果较为接近。(4)Gamma分布斜率参数(λ)和形状因子(μ)的拟合曲线具有局地性特征。根据3站μ、λ随R变化趋势,可将R=10 mm·h^(-1)作为层云-对流云降水的分类指标,R增大至100 mm·h^(-1)以上,3站μ值均趋向于1~2 mm^(-1),λ值均趋向于2。(5)拟合雷达反射率因子(Z)与R关系(Z=ARb),气象业务雷达内置Z=300R1.4会高估垦利站、平阴站降水量,低估胶南站降水量,Z-R关系中系数A、指数b在对流云、层云降水中均有一定差异。

准全球6—8月雨粒子谱和降水反射率因子分布特征分析

获得准全球雨粒子谱(DSD)特征对研究降水具有重要科学意义,并在测雨雷达探测反演降水中具有重要应用价值。利用2014—2020年6—8月美国航空航天局(NASA)戈达德飞行中心(GFSC)提供的2ADPR数据以及欧洲天气预报中心再分析数据(ERA5),分析了准全球DSD参数(粒子中值直径D0、粒子浓度参数dBNw)和降水反射率因子(PRF)的三维结构特征,并对不同纬度带及青藏高原地区DSD参数和PRF三维结构特征的区域差异及海陆差异进行了对比和讨论。结果表明:DSD参数D0和dBNw的空间分布型不同,表现为dBNw大值区(>35)具有小D0(<1 mm),而dBNw低值区(<30)具有大D0(>1.2 mm)。近地面各纬度带上陆地平均D0均大于洋面,但平均dBNw均小于洋面,且热带及北半球地域的海陆差异很大。PRF的垂直分布主要由D0决定,dBNw为次要因子。D0平均垂直分布廓线表明大、中、小降水粒子的主要微物理过程存在差异,dBNw的廓线表明高层平均降水粒子浓度小于低层。和陆地其它区域相比,青藏高原DSD参数和PRF的概率密度分布最为集中,且降水粒子尺度最小、浓度偏低。