利用Ka波段毫米波雷达功率谱反演云降水大气垂直速度和雨滴谱分布研究

利用中国气象科学研究院2016年华南云降水试验中Ka波段毫米波雷达探测一次层状云降水过程,开展了云内大气垂直速度和雨滴谱的反演研究,并与地面激光雨滴谱仪和微降水雷达的测量雨滴谱结果进行对比分析。首先,采用小粒子示踪法从功率谱密度中反演大气垂直速度以得到静止空气条件下的功率谱密度,进而利用粒子下落末速度-粒子直径关系反演出雨滴谱,最后进行标准化的Gamma分布拟合。研究表明:(1)云降水从零度层到地面1 km,主要由下沉气流主导,近地面大气浮游粒子和直流干扰造成的晴空杂波会影响雷达的功率谱分布;受动态范围限制,回波强度过饱和现象会影响近地面大气垂直速度的反演结果;(2)毫米波雷达CR、微雨雷达MRR和地面雨滴谱仪测量回波强度存在一定差异,MRR相较于CR与地面雨滴谱仪测量偏差较小;在稳定降水时CR和MRR功率谱密度对比较为一致;(3) CR和MRR反演雨滴谱对比实验中,雨滴谱反演对大气垂直速度十分敏感,大气垂直速度的变化,会使CR反演雨滴谱随着高度增加数浓度量级变大、粒子平均半径变小。CR反演的雨滴谱与M RR反演结果基本一致,验证了CR功率谱反演雨滴谱方法的可靠性;(4) CR与地面雨滴谱仪雨滴谱拟合参数的对比表明,CR大气垂直反演的雨滴谱与地面雨滴谱相比粒子平均直径Dm较小,数浓度则较为一致。     

山西汾阳地区层状云和对流云降水雨滴谱特征

基于多普勒天气雷达和OTT Parsivel激光雨滴谱仪资料对山西汾阳地区2次降水进行分析,对比对流云和层状云降水的雨滴谱特征。结果表明:层状云降水雨滴平均数浓度和雨强分别为286.20个·m~(-3)和1.33 mm·h~(-1),对流云降水雨滴平均数浓度和雨强分别为516.13个·m~(-3)和10.17 mm·h~(-1);对流云降水雨强主要由降水粒子数浓度决定,直径为1—2 mm的粒子对2种云系雨强贡献最大;2种云系不同雨强下雨滴谱分布和雨滴平均谱分布均呈单峰型,对流云降水雨滴平均谱宽大于层状云降水雨滴平均谱宽,Gamma分布对2种云系降水平均谱拟合均存在一定偏差;通过雨滴谱计算的雷达反射率因子估算降水会造成对降水的低估。     

地面激光雨滴谱仪反演降水参量的特性探究

采用河南省2016—2017年100个日降水资料,对比分析雨滴谱反演回波与雷达回波的差异、雨滴谱反演降水强度与雨量计观测降水强度的差异;进行雨滴谱Gamma拟合,以探究河南省雨滴谱分布及降水云系类型;进行Z-I关系拟合,以探究河南省降水回波与降水强度的关系。结果表明:(1)雨滴谱反演回波、雷达观测回波的变化趋势具有较好一致性。而前者普遍小于后者,其可能原因:一是雷达通过最低仰角观测到的地面雨滴谱仪上方回波与地面雨滴谱仪之间存在一定高度差,二是雨滴下落时的蒸发、破碎过程,使到达地面的雨滴直径减小。(2)雨滴谱反演的降水强度与雨量计观测的降水强度相比,存在一定差异,但无显著偏大或偏小规律性特征。(3)对流云及层积混合云的雨滴谱宽大于层状云,中等尺度雨滴数密度较大。层状云的小水滴数密度较大。河南省大部分降水过程为雨滴谱较窄的层状云降水。(4)河南省降水回波与降水强度的拟合公式:Z=262I~(1.34),层状云拟合公式:Z=219I~(1.30),对流云拟合公式:Z=307I~(1.38)。(5)雨滴数浓度较高月份为6—7月(1500个·m~(-3)左右),降水强度较高月份为8—10月(60 mm·h~(-1)),雨滴最大直径较高月份为4—8月(4.3～4.8 mm),雨滴平均直径较高月份为3—4月(3 mm左右)。雨滴数浓度、降水强度、最大直径、平均直径的月份特征变化无一致性。     

C-FMCW雷达反演飑线大气垂直速度和雨滴谱

垂直指向探测的C波段调频连续波雷达具有高灵敏度和高时空分辨率等特点,以2016年5月广东两次飑线降水为例,结合同址K波段微雨雷达和地面激光雨滴谱仪,探究C波段调频连续波雷达两种反演大气垂直速度(V_a)和雨滴谱的方法:粒子平均下落末速度(V_t)-反射率因子(Z_e)关系法(简称经验关系法)和小粒子示踪法(简称示踪法)。结果表明:经验关系法和示踪法反演的上升和下沉气流的时空分布基本一致;当地面雨强R≤1 mm·h^-1,经验关系法反演的雨滴谱与雨滴谱仪观测结果更接近;当1-1时,两种方法反演的雨滴谱均与雨滴谱仪观测及微雨雷达产品较吻合;当R>10 mm·h^-1时,两种方法反演的中雨滴数浓度与雨滴谱仪观测结果接近,但大雨滴数浓度较低;从各物理量时序变化看,经验关系法反演结果更接近雨滴谱仪观测结果。     

利用微雨雷达研究一次冷锋云系降水的垂直结构分布及演变特征

本文利用河北邢台测站Ka波段微雨雷达（MRR）观测到的一次冷锋云系降水过程分析降水的垂直分布及演变特征。将MRR观测结果与天气雷达、地面雨滴谱仪、雨量计观测结果进行对比以检验MRR数据的可靠性。同时将MRR与雨滴谱仪和激光云高仪结合,研究了不同相对湿度阶段特征量、雨滴谱的平均垂直分布特征和降水特征量随时间、高度的演变特征。结果表明:MRR与雨量计及雨滴谱仪累计雨量结果较为接近,趋势一致。MRR 200 m雨强值与地面雨滴谱仪雨强值偏差最小,平均偏差为0.05 mm h?1,相关系数为0.93。相比雨滴谱仪,MRR观测到的小滴数浓度出现高估,大滴数浓度出现低估,中滴数浓度较为一致。降水在云内和云外受不同微物理过程影响,垂直变化特征不同。降水初期平均反射率和雨强在云底以下明显减小,小滴和中滴平均数浓度明显减小,蒸发作用影响较强。而在其余时间段在云内随高度降低平均反射率和雨强略有增加,小滴平均数浓度变化较小,中滴大滴平均数浓度增加,表明云内有云滴与雨滴间的碰并发生。而在云外低层,随高度降低平均有效直径明显增加,平均雨滴总数浓度明显减小,小滴平均数浓度显著减小,大滴平均数浓度显著增加,表明在云外低层雨滴间的碰并作用较强。     

雨滴谱垂直演变特征的微雨雷达观测研究

雨滴谱的垂直变化特征对于认识降水过程、改进模式和雷达定量估计降水等具有重要意义。利用2016年6月1日-9月30日雨量筒、微雨雷达（micro rain radar,简称MRR）和PARSIVEL雨滴谱仪连续4个月的观测数据,在对比3种仪器观测结果的基础上,研究了层状云降水不同降水强度下微物理特征量和雨滴谱垂直演变特征。结果表明:MRR与PARSIVEL雨滴谱仪观测降水强度相关性较好,且两种仪器观测的雨滴谱在中等粒子段（0.5~2.5 mm）表现出较好的一致性,而对于小粒子段（雨滴直径小于0.5 mm）PARSIVEL雨滴谱仪观测的数浓度明显低于MRR。对于弱降水（降水强度R ≤ 0.2 mm·h-1）,液水含量和降水强度随高度降低减小,雨滴在下落过程中蒸发明显。对于较强降水（R>2 mm·h-1）,随高度降低,雷达反射率因子增大,小滴数浓度减小的同时大滴数浓度增加明显,雨滴下落过程碰并作用明显。所有高度直径不超过0.5 mm的小滴对数浓度贡献均为最大。高层雨滴直径不小于1 mm的小粒子对降水强度的贡献可达50%,小粒子对降水强度贡献随高度降低减小。     

北京对流性降水的雨滴尺寸分布瞬时特征与雷达降水的关系

采用HSC-Parsivel雨滴谱仪对北京的2007年8月1日低涡类中尺度降水采样,得到了雨滴分布的瞬时特征。研究表明,雨滴分布的瞬时特征有系统性分布特点,利用其瞬时特征可以将中小尺度对流性降水分为对流性降水阶段、层化阶段和层状云降水3个阶段。对应这3个阶段,降水有着不同的Z-R关系;中值直径D0、雷达反射率因子Z、瞬时降水R三者有阶段性的变化趋势,上升运动对雨滴谱分布影响显著。3个阶段有明显不同的垂直结构:对流阶段对应着较强的垂直上升运动;层化阶段的下沉气流则与融化等有很大的关系,是造成地面雨滴中值直径与瞬时雨强较小的主要原因;层状云的较强降水与对流泡和微弱上升气流等有关。这些因素导致了雨滴分布呈现阶段性变化。     

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。     

基于雷达反射率因子的降水性层状云中雨滴谱参数的反演方法与检验研究

对基于雷达反射率因子观测数据的层状云降水粒子谱参数反演算法进行研究。（1）给出层状云降水粒子谱参数的反演理论和反演算法流程;（2）选取吉林省伊通县的一次降水层状云过程进行反演试验和验证分析,利用雷达反射率因子观测数据反演得到雨滴平均直径和数浓度参数,并用放置在伊通县气象局观测场中的Parsivel激光雨滴谱仪的实测数据与近地层反演结果进行对比。结果发现,通过反演算法计算得到的滴谱与实测滴谱的变化趋势基本相同,而且反演的雨滴平均直径和数浓度在量级和数值上的大小与实测数据具有良好的一致性,说明该反演方法用于从现有天气雷达回波强度数据中挖掘出降水性层状云的微物理参数是可行的。      

山东不同云系降水微物理参数特征

研究不同云系降水的微物理参数特征,对研究降水机制、人工影响天气、雷达定量测量降水、数值预报模式中微物理参数化方案的选择等都有一定意义。本文针对2015年济南地区的液态降水过程,基于微降水雷达(Micro Rain Radar,简称MRR)资料,研究不同云系降水的微物理参数。在400 m高度上,层状云降水0.02~0.2 mm h-1雨强样本数很大,但对累计降水量的贡献很小。混合云和对流云降水在大粒子端数浓度较高。在垂直方向上,层状云降水中的粒子的尺度较集中,中值体积直径D0平均在1 mm左右,随高度的变化不大。对流云降水在雨强大于20 mm h-1时,强垂直气流(包括上升气流和下沉气流)对粒子直径的影响较大,进而影响空中微降水雷达反演降水参数的数据质量。而垂直气流的影响对层状云降水影响较小,在层状云降水时,微降水雷达可以用来分析零度层亮带以下雨滴谱在垂直方向上的演变。     

Kinematic features of a bow echo in southern China observed with doppler radar

A bow echo is a type of mesoscale convective phenomenon that often induces extreme weather and appears with strong reflectivity on radar images. A strong bow echo that developed from a supercell was observed over Foshan City in southern China on 17 April 2011. The intense gusty winds and showers caused huge losses of property and severely affected human lives. This paper presents an analysis of this strong meso- n-scale convective system based on Doppler radar observations. The isolated bow echo exhibited a horizontal scale of about 80 km in terms of reflectivity above 40 dBZ, and a life span of 8 hours. The system originated from the merging of a couple of weakly organized cells in a shear line, and developed into an arch shape as it moved through the shear zone. Sufficient surface moisture supply ensured the convective instability and development of the bow echo. The low-altitude winds retrieved from single Doppler radar observations showed an obvious rear-inflow jet along the notch area. Different from the conventional definition, no book- end anticyclone was observed throughout the life cycle. Very strong slantwise updrafts and downdrafts were recognizable from the retrieved winds, even though the spatial scale of the bow echo was small. Strong winds and induced damage on the surface are considered to have been caused by the mid-level rear-inflow jet and intense convective downdrafts.     

Kinematics and Microphysical Characteristics of the First Intense Rainfall Convective Storm Observed by Jiangsu Polarimetric Radar Network

The polarimetric radar network in Jiangsu Province has just been operationalized since 2020. The first intense precipitation event observed by this polarimetric radar network and disdrometer occurred during August 28-29, 2020 and caused severe flooding and serious damage in eastern Jiangsu Province. The microphysics and kinetics for this heavy precipitation convective storm is diagnosed in this study, in order to promote the application of this polarimetric radar network. Drop size distribution(...     

Characteristics of vertical turbulent velocities in the urban convective boundary layer

Turbulence measurements of the vertical velocity component were obtained by an instrumented aircraft under fair weather conditions in the St. Louis, Missouri, metropolitan area. Time series of vertical velocity fluctuations from horizontal flight segments made in the lower part of and near the middle of the convective boundary layer (CBL) over the urban area and surrounding region were subjected to various statistical and objective analyses. Higher order vertical velocity moments, and positive and negative velocity statistics, were computed. The horizontal dimensions of updrafts and downdrafts, and related properties of these turbulent eddies were derived by conditional sampling analysis. Emphasis is on a comparison of the results from urban and selected rural measurements from the lower part of the CBL.The vertical velocity probability density distribution for each segment was positively skewed and the mode was negative. The means and standard deviations of positive and negative velocity fluctuations were greater over the urban area. The urban vertical velocity variance was 50% greater than rural values, and power spectra revealed greater production of vertical turbulent energy in the urban area over a wide frequency range.The mean and maximum widths of downdrafts were generally larger than the corresponding values for updrafts. Differences between urban and rural eddy sizes were not statistically significant. The widths of the largest updraft and downdraft are comparable to the boundary-layer depth, Z _i, and the mean value of the ratio of spectral peak wavelength to Z _iwas about 1.3 and 1.1 for urban and rural areas, respectively. Convective similarity scaling parameters appeared to order both the urban and rural measurements.On assignment from the National Oceanic and Atmospheric Administration, U.S. Dept. of Commerce.     

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 Z_(HH)and differential reflectivity Z_(DR)were obtained through scattering simulation.The simulation data were combined with DSD fitting to determine the Z_(DR)-Λand log_(10)(Z_(HH)/N_0)-Λrelationships.Using Xinfeng C-band polarimetric radar observations Z_(DR)and Z_(HH),the raindrop Gamma size distribution parametersμ,Λ,and N_0were 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 (D_m) and intercept parameter (N_w) 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.     

A study of microphysical properties within a precipitation system using wind profiler spectra

This study investigates microphysical properties from wind profiler Doppler spectra observed within a precipitation system that produced high rainfall rates up to 40 mm hr^?1 near the southern coast of the Korean Peninsula on 25～26 June 2010. A 1290-MHz wind profiler located in the National Center for Intensive Observation of Severe Weather at Boseong, Korea, observed a widespread stratiform region and short-lived convective cells from 1850 UTC 25 to 0200 UTC 26 June 2010. By using a spectral model applied to observed profiler spectra, rainfall parameters and raindrop size distributions were retrieved below a melting layer during this period. Three representative periods during precipitation were selected based on intensities of bright band and characteristics in vertical profiles of radar reflectivity and Doppler velocity. During a brief convective period (～30 min), radar reflectivity tended to be proportional to vertical air motion (positive upward), suggesting that updrafts up to ～3 m s^?1 over a large vertical extent through the melting layer probably contributed to increasing rainfall rates at the surface. In reflectivityrainfall rate distributions, large drop spectra (high reflectivity) were analyzed within downdrafts and small drop spectra (low reflectivity) within updrafts, similar to the large and small drop spectra but found in stratiform and convective regions, respectively, in previous studies. This indicates that the degree of spread between reflectivity and rainfall rate may be strongly dependent on positive and negative magnitudes of vertical air motion. For three categories of vertical air motion (i.e., updrafts, neutral, and downdrafts), physical relations between the retrieved rainfall parameters were examined.     

Observation of snowfall with a low-power FM-CW K-band radar (Micro Rain Radar)

Quantifying snowfall intensity especially under arctic conditions is a challenge because wind and snow drift deteriorate estimates obtained from both ground-based gauges and disdrometers. Ground-based remote sensing with active instruments might be a solution because they can measure well above drifting snow and do not suffer from flow distortions by the instrument. Clear disadvantages are, however, the dependency of e.g. radar returns on snow habit which might lead to similar large uncertainties. Moreover, high sensitivity radars are still far too costly to operate in a network and under harsh conditions. In this paper we compare returns from a low-cost, low-power vertically pointing FM-CW radar (Micro Rain Radar, MRR) operating at 24.1?GHz with returns from a 35.5?GHz cloud radar (MIRA36) for dry snowfall during a 6-month observation period at an Alpine station (Environmental Research Station Schneefernerhaus, UFS) at 2,650?m height above sea level. The goal was to quantify the potential and limitations of the MRR in relation to what is achievable by a cloud radar. The operational MRR procedures to derive standard radar variables like effective reflectivity factor (Z _e) or the mean Doppler velocity (W) had to be modified for snowfall since the MRR was originally designed for rain observations. Since the radar returns from snowfall are weaker than from comparable rainfall, the behavior of the MRR close to its detection threshold has been analyzed and a method is proposed to quantify the noise level of the MRR based on clear sky observations. By converting the resulting MRR-Z _e into 35.5?GHz equivalent Z _e values, a remaining difference below 1?dBz with slightly higher values close to the noise threshold could be obtained. Due to the much higher sensitivity of MIRA36, the transition of the MRR from the true signal to noise can be observed, which agrees well with the independent clear sky noise estimate. The mean Doppler velocity differences between both radars are below 0.3?ms^?1. The distribution of Z _e values from MIRA36 are finally used to estimate the uncertainty of retrieved snowfall and snow accumulation with the MRR. At UFS low snowfall rates missed by the MRR are negligible when comparing snow accumulation, which were mainly caused by intensities between 0.1 and 0.8 mm?h^?1. The MRR overestimates the total snow accumulation by about 7%. This error is much smaller than the error caused by uncertain Z _e?Csnowfall rate relations, which would affect the MIRA36 estimated to a similar degree.     

Comparison of Microphysical Characteristics Between Warm-sector and Frontal Heavy Rainfall in the South of China

During the April-June raining season,warm-sector heavy rainfall(WR) and frontal heavy rainfall(FR) often occur in the south of China,causing natural disasters.In this study,the microphysical characteristics of WR and FR events from 2016 to 2022 are analyzed by using 2-dimensional video disdrometer(2DVD) data in the south of China.The microphysical characteristics of WR and FR events are quite different.Compared with FR events,WR events have higher concentration of D<5.3 mm(especially D <1 ...     

Turbulent transport processes of momentum and sensible heat in the surface layer over a paddy field

A sonic anemometer-thermometer was used to measure turbulent fluxes of momentum and sensible heat and related turbulence statistics just above plant canopies in unstable conditions. The stability dependence of transport processes is presented, using observational data in a wide range of instability. The analysis of joint probability distributions of w – u, w – T, w – wu, and w – wT confirmed that just above plant canopies, downdrafts were remarkably efficient for vertical transport of momentum and scalar quantities in near neutral conditions. Furthermore, it was shown that updrafts became more efficient than downdrafts for vertical transport, especially of scalar quantities, in very unstable conditions.