Microphysical Processes of a Stratiform Precipitation Event over Eastern China:Analysis Using Micro Rain Radar data

Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.

Comparison of the Bright Band Characteristics Measured by Micro Rain Radar (MRR) at a Mountain and a Coastal Site in South Korea

Data from a long term measurement of Micro Rain Radar （MRR） at a mountain site （Daegwallyeong, DG, one year period of 2005） and a coastal site （Haenam, HN, three years 2004-2006） in South Korea were analyzed to compare the MRR measured bright band characteristics of stratiform precipitation at the two sites. On average, the bright band was somewhat thicker and the sharpness （average gradient of reflectivity above and below the reflectivity peak） was slightly weaker at DG, compared to those values at HN. The peak reflectivity itself was twice as strong and the relative location of the peak reflectivity within the bright band was higher at HN than at DG. Importantly, the variability of these values was much larger at HN than at DG. The key parameter to cause these differences is suggested to be the difference of the snow particle densities at the two sites, which is related to the degree of riming. Therefore, it is speculated that the cloud microphysical processes at HN may have varied significantly from un-rimed snow growth, producing low density snow particles, to the riming of higher density particles, while snow particle growth at DG was more consistently affected by the riming process, and therefore high density snow particles. Forced uplifting of cloudy air over the mountain area around DG might have resulted in an orographic supercooling effect that led to the enhanced riming of supercooled cloud drops.

Rainfall Microphysical Properties of Landfalling Typhoon Yagi(201814)Based on the Observations of Micro Rain Radar and Cloud Radar in Shandong,China

The development and evolution of precipitation microphysical parameters and the vertical structure characteristics associated with Typhoon Yagi(201814)are analyzed in the city of Jinan,Shandong Province based primarily on the observations of a micro rain radar(MRR),a cloud radar,and a disdrometer.The precipitation process is further subdivided into four types:convective,stratiform,mixed,and light precipitation according to the ground disdrometer data,which is in agreement with the vertical profile of the radar reflectivity detected by the MRR.Vertical winds may be the main source of MRR retrieval error during convective precipitation.Convective precipitation has the shortest duration but makes the largest contribution to the cumulative precipitation.Collision-coalescence is the main microphysical process of stratiform precipitation and light precipitation below the bright band observed by the MRR.It is worth noting that as Typhoon Yagi(201814)transformed into an extratropical cyclone,its raindrop size distributions no longer had the characteristics of maritime precipitation,but become more typical of the characteristic of continental precipitation,which represents a very different raindrop size distribution from that which is normally observed in a landfalling typhoon.

Diurnal Variation in the Vertical Profile of the Raindrop Size Distribution for Stratiform Rain as Inferred from Micro Rain Radar Observations in Sumatra

The diurnal variation in the vertical structure of the raindrop size distribution(RSD)associated with stratiform rain at Kototabang,West Sumatra(0.20°S,100.32°E),was investigated using micro rain radar(MRR)observations from January 2012 to August 2016.Along with the MRR data,the RSD from an optical disdrometer and vertical profile of precipitation from the Tropical Rainfall Measuring Mission were used to establish the microphysical characteristics of diurnal rainfall.Rainfall during 0000–0600 LST and 1800–2400 LST had a lower concentration of small drops and a higher concentration of large drops when compared to rainfall during the daytime(0600–1800 LST).The RSD stratified on the basis of rain rate(R)showed a lower total concentration of drops and higher mass-weighted mean diameter in 0000–0600 LST and1800–2400 LST than in the daytime.During the daytime,the RSD is likely governed by a riming process that can be seen from a weak bright band(BB).On the other hand,during 0000–0600 LST and 1800–2400 LST,the BB was stronger and the rainfall was associated with a higher concentration of midsize and large drops,which could be attributed to more active aggregation right above the melting layer with minimal breakup.Diurnal variation in the vertical profile of RSD led to a different radar reflectivity(Z)–R relationship in the rain column,in which Z during the periods 0000–0600 LST and1800–2400 LST was larger than at the other times,for the same R.

Improving Radar Rainfall Estimation by Accounting for Microphysical Processes Using a Micro Rain Radar in West Africa

This study evaluates the improvement of the radar Quantitative Precipitation Estimation (QPE) by involving microphysical processes in the determination of Z-R algorithms. Within the framework of the AMMA campaign, measurements of an X-band radar (Xport), a vertical pointing Micro Rain Radar (MRR) to investigate microphysical processes and a dense network of rain gauges deployed in Northern Benin (West Africa) in 2006 and 2007 were used as support to establish such estimators and evaluate their performance compared to other estimators in the literature. By carefully considering and correcting MRR attenuation and calibration issues, the Z-R estimator developed with the contribution of microphysical processes and non-linear least-squares adjustment proves to be more efficient for quantitative rainfall estimation and produces the best statistic scores than other optimal Z-R algorithms in the literature. We also find that it gives results comparable to some polarimetric algorithms including microphysical information through DSD integrated parameter retrievals.

Analysis of Vertical Profiles of Precipitable Liquid Water Content in a Tropical Climate Using Micro Rain Radar

In this paper, some distinctive features of the vertical profile of precipitable liquid water content (LWC) with considerable respect to rain rates (R) and radar reflectivity (Z) obtained in a tropical location are presented. Assessment of LWC allows applications in the specific area of flight icing severity, aviation safety as well as signals traversing through the atmosphere. The parameters were typically measured using vertically-pointing Micro Rain Radar (MRR) over a period of 2 years (2011-2012) at Akure, a tropical location of Nigeria. The radar scanned at every 10 seconds and integrated over one minute samples to reduce event logging error associated with the instrument. The vertical profile of the LWC typically reveals a prominent seasonal variation. However, majority of the LWC profiles has low LWC, less than 0.1 gm?3 while the maximum observed LWC is about 3.18 gm?3. A strong like hood relation was observed between the melting layer height and the LWC, with the LWC reaches peak at the considerable height of about 4160 m which coincides precisely with the freezing height level (rain height of ~4520 m) of the study location. Good correlation was also observed between the LWC and R in most of the heights considered. The results obtained will assist system engineers to assess the level of absorption, reflection and attenuation of electromagnetic signals as a result of precipitable LWC along the transmitting paths. The novelty of the present work is in the area of linking LWC and Z as against usual relation between Z and R.

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。

三江源一次降水过程雨滴谱垂直演变特征

利用布设在泽库站内的微雨雷达(Micro Rain Radar,MRR)、OTT-PARSIVEL激光雨滴谱仪、雨量计(Rain Gauge,RG)观测资料,针对2021年9月17日一次降水天气过程,对比分析MRR在高原地区的适用性,研究了不同雨强MRR观测参量及雨滴谱的垂直变化特征。结果表明:在此次过程中MRR与雨滴谱仪及RG的累计雨量结果较为一致,MRR 200 m雨强与雨滴谱仪反演值相关性较好。不同雨强下降水参量在垂直分布上有所差异,雨强Ⅰ档,受蒸发作用影响反射率因子、液态水含量、雨强由高层至低层表现出波动变化的趋势;雨强Ⅱ档,蒸发作用减弱,各微物理量峰值高度有所降低;雨强Ⅲ档,粒子碰并作用增强直径增大,各微物理量随高度的降低而增大。此次降水过程以小粒子为主,在各个高度层小粒子对数浓度的贡献均最大。1000~4000 m小粒子对雨强贡献率均大于90%;1000 m以下中等粒子随着高度降低对雨强的贡献逐渐增大;大粒子在高层对雨强的贡献率大于低层。

An observational study on vertical raindrop size distributions during stratiform rain in a semiarid plateau climate zone

Vertical raindrop size distributions of two stratiform rain events were measured with a Micro Rain Radar during summer 2009 at a semiarid continental site located in Xilinhot, China （43°38′N, 116°42′E）. The sequential intensity filtering technique （SIFT） was used to minimize the effect of the spurious variability on disdrometric data to obtain the reflectivity-rain rate （Z-R） relationship （Z = αRb）. Compared with the least squares regression （LSR） method, SIFT led to a -5% to 4% change in the coefficient （a） and an 8%-1 5% increase in the exponent （b） of the Z-R relationship at 300 m. Rainfall estimation using the Z-R relationship with SIFT had lower standard deviation than that with LSR. The vertical variability of the mean rain rate, total raindrop numbers, and parameters （a and b） of the Z-R relationship was small below a melting layer, suggesting that using the radar reflectivity of weather radar to estimate stratiform rainfall is relatively accurate, at least in the Xilinhot area.

北京一次罕见1月初雪过程的复杂降水相态成因分析

2023年1月12日的降雪为北京近42年来首次出现在1月上中旬的初雪,期间降水相态经历了复杂的变化。应用多种常规观测资料和云雷达、微雨雷达等新型探测资料以及ERA5再分析资料,对此次过程进行分析,并重点探讨相态变化成因。结果表明:850 hPa以下偏南暖湿急流输送了丰富的水汽,但动力抬升较弱导致降水量不大,而近地层冷垫的缺失不利于全市范围转雪和降雪的维持;0℃层高度的东西差异是北京西部为雪、东部为雨的主要原因,融化和蒸发过程引起的冷却效应导致0℃层高度快速降至500 m以下使得平原地区转雪,>0℃暖层增厚和融化层以上雪花尺度与密度的减小导致平原相态由雪转为雨;针对复杂的降水相态转换,确定性模式无法准确刻画融雪过程,而短期时效内集合预报可弥补确定性模式的短板;综合应用云雷达、微雨雷达和微波辐射计等探测资料,可提高对云中成雪和边界层融雪的判断准确性,有助于提升临近时段降水相态的预报准确率。

Satellite estimates and subpixel variability of rainfall in a semi-arid grassland

Uncertainties in satellite rainfall estimation may derive from both the local rainfall characteristics and its subpixel variability.To study this issue,Micro Rain Radars and a rain gauge network were deployed within a 9-km satel-lite pixel in the semi-arid Xilingol grassland of China in summer 2009.The authors characterized the subpixel variability with the coefficient of variation(CV)and evaluated the satellite rainfall estimation for this semi-arid area.The results showed that rainfall events with a high CV were mostly convective with a small amount of rain-fall.Spatially inhomogeneous rainfall was most likely to occur at the edges of small clouds producing rain.The performance of the TRMM(Tropical Rainfall Measuring Mission)3B42V7 product for daily rainfall was better than that of the CMORPH(Climate Prediction Center morphing technique)and PERSIANN(Precipitation Estima-tion from Remotely Sensed Information Using Artificial Neural Networks)products,although the TRMM product tended to overestimate rainfall in a lake area of the semi-arid grassland.

基于微雨雷达的降水参数反演和粒子相态识别

本文基于微雨雷达原始的后向散射信号,采用一种新的功率谱处理算法(RaProM算法),在功率谱计算、噪声去除、退模糊等处理的基础上计算了雷达基本参量,并反演了液态降水参数,例如雷达反射率因子、雨强等,并对粒子相态进行识别。RaProM算法综合考虑粒子下落速度、等效雷达反射率因子、不同相态粒子的尺度特征以及是零度层亮带位置等信息,可识别的粒子相态包括雪、毛毛雨、雨、冰雹以及混合相态。选取了三个山东地区较为典型的个例对RaProM反演算法进行验证,即2021年7月2日典型层状云降水个例、2019年12月25日雨雪转换个例以及2018年3月4日零度层高度逐渐降低的降水个例。结果显示:粒子识别方法应用于典型层状云降水,垂直方向上不同相态粒子的分层较为明显,过冷层里的固态降水雪花、零度层附近冰水转换区的混合相态降水以及零度层以下的液态降水符合现有认识,验证了反演算法以及粒子识别算法的有效性。将结果进一步在雨雪转换降水相态识别中和零度层高度的检测,该反演算法均能得到较好应用,与同址同步观测的微波辐射计、云雷达、二维视频雨滴谱仪等观测结论一致。另外,与微雨雷达标准反演算法对比,RaProM算法的优势是没有粒子相态的原始假设,且考虑降水粒子向上的速度,反演结果与微波辐射计、云雷达在垂直结构上有较高的一致性。与地面激光雨滴谱仪观测数据对比显示,也有效提升了微雨雷达对雨滴谱和雨强的反演能力。

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。

河北冬季一次冷锋降雪云系微物理演变特征综合观测分析研究

利用河北省中南部地区皇寺国家观测站布设的毫米波云雷达、微雨雷达结合飞机等联合观测数据,对2019年2月14日河北中南部地区一次冷锋降雪云系微物理演变特征进行分析,探讨雷达回波与冰雪晶粒子微结构的关系,以便更好地认识该地区自然降雪的宏微观结构特征。研究结果表明:降雪初生阶段表现为双层云结构,中云云顶高约4100 m,云底高约3600 m,低云云顶高约3100 m,云底高约200 m,中间存在一干层,3000 m以下高度粒子增长以凇附过程为主。降雪发展阶段上下两层云相接,雷达回波强度较强的时段地面降水量也较大,该时段降雪过程主要以凝华-聚并增长为主。降雪后期回波强度最大值减小,云顶高降低,3000 m以下高度范围内回波强度、多普勒速度、谱宽随高度降低呈增大趋势;飞机观测结果显示,降雪消散阶段逆温层底部由于水云云层较薄,催化潜力较小,冰雪晶粒子主要位于云的中上部,随着高度降低,冰雪晶粒子在下落过程中增大,与雷达观测结果一致,毫米波云雷达和微雨雷达反射率因子随高度变化与降水粒子有效粒径之间相关系数分别为0.89和0.83,雷达反射率因子主要受冰雪晶等大尺度粒子主导。

毫米波云雷达数据衰减研究与应用

文章通过分析2021-08-19的1次持续时间长、雨量级小的层状云降水过程,以微雨雷达底层数据作为参考进行系统偏差订正,随后运用逐库法对毫米波云雷达回波进行订正,将订正后的结果与微雨雷达整层回波进行对比,验证订正效果,可为提高天气预报准确度及设计人工影响天气作业方案提供有效的数据支撑。

两次降水过程的微降雨雷达探测精度分析

垂直指向微降雨雷达(MRR)能够测量从近地面至高空的雷达反射率因子和雨滴谱分布特征,对认识降水微物理结构,改进雷达定量降水估计精度有重要作用。为评估MRR探测的雨滴谱分布、降水和雷达回波精度,利用南京地区夏季观测的两次降水过程,将MRR与业务S波段天气雷达、二维视频雨滴谱仪、常规雨量筒观测进行层状云降水和对流性降水下的定量对比分析。结果表明,MRR垂直探测的雷达反射率因子与S波段雷达观测在中低层(<4 km)平均差异<1 dB,但高层(>4 km)出现显著低估,且该现象随降水强度增强更明显,这主要是雷达回波衰减导致。MRR在回波强度<35 dBz时对降水率的探测精度较高,但在>35 dBz时低估降水。其中,层状云降水的降水率比对流性降水更接近雨量筒观测。常规雨量筒对0.1 mm以下的降水无探测能力,而MRR探测敏感度较高,对于微弱降水率的估计效果也很好。由于MRR最大探测范围的限制,相对于2DVD而言,MRR探测的最大粒子直径低估、最小粒子浓度高估,但在中间段的探测效果和2DVD雨滴谱观测一致性较高。总体而言,MRR是一个有效的降水探测仪器,其探测结果在层状云降水过程中优于对流性降水过程。

鄂西南一次早春强对流过程的多源资料分析

综合利用多普勒天气雷达、风廓线雷达、微雨雷达、二维视频雨滴谱仪、三维闪电监测网等多源探测资料对2020年2月14日发生在鄂西南一次伴有局地冰雹和雷雨大风的强对流过程进行了中小尺度特征分析,并探讨了分类强对流识别预警算法在强对流短临识别预警中的应用。结果表明:(1)由于鄂西南山地的阻挡作用,冷锋在宜昌北部南下缓慢,华北低槽、850 hPa低涡北部的暖式切变线和冷锋前侧不断渗入的冷空气在鄂西南交汇形成上干下湿的不稳定层结;中低层西南暖湿气流沿着低层锋区向鄂西南输送并发展,850 hPa切变线、地面冷锋和暖倒槽配合触发强对流发展加强,强冰雹发生在冷锋和暖倒槽交汇处。(2)风廓线雷达资料显示鄂西南处在地面冷锋前部暖倒槽中,持续增强的中高层西南急流和冷锋前侧不断渗入的冷空气有利于强对流的发生发展。(3)二维雨滴谱仪完整记录了降水过程的雨滴谱分布特征,粒子直径大多在1 mm以内,最大直径接近6 mm。(4)由微雨雷达探测的雨滴谱垂直分布特征可知,降水前期环境湿度低,蒸发作用明显;而在强降水时段,近地面雨滴碰并增长作用明显。(5)三维闪电观测网获得的闪电频次与雹暴单体的强度变化呈正相关,且两个雹暴单体的初次地闪分别提前于降雹30 min和33 min。(6)多普勒天气雷达探测到有界弱回波区、钩状回波等典型冰雹回波特征,而中气旋、中层径向辐合及高空辐散区的存在表明对流云内维持了较强的上升气流,有利于冰雹的生成生长。

微降水雷达测量精度分析

利用数值模拟的方法,讨论了利用微降水雷达MRR(Micro Rain Radar)雷达功率谱密度反演降水参数时,MIE散射(米散射)效应、垂直气流(包括上升气流、下沉气流)对数浓度N、雷达反射率Z、雨强I、液态含水量LWC等参数的影响。MIE散射主要影响直径为1.20~4.00 mm的粒子,MIE散射效应影响的N、Z、I、LWC偏差的平均值分别为2.74 m-3 mm-1、1.47 d BZ、0.0061 mm h^(-1)、0.0004 g m-3。下沉气流使反演液滴直径偏大,上升气流使得反演的液滴直径偏小,下沉气流的影响更大,尤其是对低层影响大于高层。例如,在300 m高度上,当液滴直径为2.67 mm时,下沉气流为2.00 m s-1时,理论上反演的直径为8.07 mm,超出了MRR探测的阈值,其相对误差值能接近200%。下沉气流使得反射率谱向大粒子方向平移,且谱型展宽;上升气流则相反。将MRR资料与同步观测的THIES雨滴谱仪数据进行比对,分析MRR资料的可靠性。选取2015年4月1日01~12时(协调世界时)山东济南的一次降水过程,将MRR在300 m高度上反演的雷达反射率因子、雨强、数浓度、中值体积直径与雨滴谱仪资料进行对比。结果表明:两种仪器探测的Z、I、N、中值体积直径D0在时间序列上都有较好的吻合度,变化趋势和幅度相近,Z、I、D0的平均偏差分别为1.19 d BZ、0.34 mm h^(-1)、0.36 mm。MRR反演的I值偏大,而粒子直径偏小,分析了产生偏差的主要原因,除了探测系统偏差、分析方法本身存在的偏差外,上升气流导致的偏差不容忽视。这些结果初步验证了微降水雷达观测的功率谱密度及其反演方法的可靠性。

一次东北冷涡云降水垂直结构特征分析

利用辽宁阜新国家站(121.7458°E,42.0672°N)的毫米波云雷达(8 mm)和微雨雷达(12.5 mm)对2020年8月12—13日东北冷涡影响下的一次降水过程进行了观测,分析了云降水的垂直结构特征并探讨了降水机制。结果表明:本次过程中,云水平方向发展不均匀,以层状云和层积混合云为主,云内有时还嵌有对流泡。云降水阶段性变化明显,先后出现了层状云降水、层积混合云降水和对流云降水。层状云降水和层积混合云降水均表现出明显的亮带特征,但层积混合云降水的雷达回波强度、回波顶高和降水强度明显大于层状云降水。对流云降水的雷达回波会因强降水而产生明显衰减,因此回波顶高不能表示出实际的云顶情况。层状云降水阶段,云雷达反射率随高度降低增长缓慢,雨滴在下落过程中受蒸发和碰并的共同作用,反射率降低。与层状云降水相比,层积混合云降水的碰并效应强,且由于前期降水对近地面的增湿作用,使云下蒸发弱。对流云降水阶段,反射率的增长主要发生在冰水混合层,有利于大滴的产生,拓宽了云滴谱,提高了碰并效率。

重庆地区一次雨转雪过程微物理特征分析

为了研究重庆地区雨转雪天气过程降水微物理特征,利用布设在重庆西部沙坪坝区气象站的一部MRR(Micro-rain Radar)微雨雷达及一台OTT Parsivel2雨滴谱仪探测到的2016年1月22-24日的雨转雪天气过程的垂直方向上的滴谱资料,对此次雨转雪天气过程的粒子下落速度、雷达反射率、粒子谱等微物理特征进行了分析.结果表明:雨滴谱仪及微雨雷达能较好地应用于云下垂直方向上的降水研究;此次过程,液(固)态降水中粒子平均直径、谱分布等特征具有明显差异,液态降水中表现为垂直下落方向上先减小后增大的特征,粒子以碰并增长为主,固态降水中垂直方向上各特征值则较为稳定;受仪器观测原理影响,雨转雪过程中粒子相态转变在微雨雷达观测特征量上表现为粒子下落速度均匀分布在1 m/s附近,粒子数浓度急剧增加1~2量级,回波反射率Z分布在10 dBZ附近.