雷达反射率资料的三维变分同化研究

应用天气研究和预报模式(WRF)三维变分系统中一种新的雷达反射率资料间接同化方法来进行反射率资料的三维变分同化研究,评估雷达反射率资料对夏季短时定量降水预报的作用.该方法不直接同化雷达反射率资料,而是同化由反射率资料反演出的雨水和估计的水汽.以2009年夏季北京地区发生的4次强降水过程为例,考察了北京市气象局业务运行的快速更新循环同化预报系统对京津冀地区雷达网的雷达反射率资料的同化性能以及雷达反射率资料和径向风资料同时同化的效果.数值试验结果表明:(1)同化反演雨水或水汽都能改善降水预报,但同化反演水汽对降水预报效果的改善起了更重要的作用;(2)同化反射率资料能极大地提高短时降水预报的效果,其稳定的正面效果可以延伸到6h的预报时效,而同化径向风资料不能得到稳定的正效果;(3)同化雷达资料时,应用快速更新循环同化预报系统是提高短时定量降水预报的一个有效途径.     

雷达与雨量计联合估测降水的相关性分析

在对比分析质量控制前后雷达估测降水量与自动雨量计降水量之间相关性的基础上,采用雷达-雨量计联合校准方法,对14种不同密度雨量计校准雷达估测降水的效果进行分析。结果表明:在使用雷达资料和雨量计资料前有必要对资料的质量进行分析与控制。联合雨量计校准雷达能明显提高雷达对降水的估测能力;采用不同密度雨量计校准雷达,随着校准雨量计密度的加大,雷达估测降水的精度不断提高并趋于稳定。校准雷达的效果及所需雨量计密度与降水类型有关,当校准效果相同时,积云强降水过程需要的雨量计密度最大,积混对流性降水过程次之,层云稳定性降水过程需要的雨量计密度最小。不同方法的校准效果不同,卡尔曼滤波方法适合于对稳定性降水的校准,或在雨量计密度低的地区对雷达进行校准;变分校准法和最优插值法的校准效果相当,适合对积混对流性降水的校准,或在雨量计密度高的地区对雷达进行校准。     

三维变分和物理初始化方法相结合同化多普勒雷达资料的试验研究

以美国新近研发的天气研究预报模式(WRF)配置的三维变分(3D-Var)同化系统WRF 3D-Var为平台,结合物理初始化方法(Physical Initialization,简称PI)来同化多普勒雷达径向风和回波强度观测资料.其基本做法是首先用物理初始化方法由雷达回波资料估计出比湿、云水混合比和垂直速度,然后用估计的比湿和云水混合比对模式的相应变量进行调整,最后再将估计出的垂直速度作为一种新的观测类型添加到现有的WRF 3D-Var目标函数中,同时以WRF 3D-Var提供的方法直接同化径向风.针对2002年6月19日的一次强对流性降水过程和2003年7月5日的一次梅雨锋暴雨过程进行了一组同化多普勒雷达径向风和回波资料的试验研究.同化结果表明:分析变量的增量场和观测的雷达回波有很好的对应关系.在雷达回波区,有正的比湿增量、云水含量增量和垂直速度增量,并且水平风增量在此辐合;在没有雷达回波的地方有负的垂直速度增量.预报结果表明,调整云水含量对降水预报改善不明显,调整比湿对降水预报改进明显,直接用物理初始化估计出的垂直速度替代模式的初始垂直速度,对降水预报改进不明显,但以新的方案同化雷达资料能有效地缩短模式的起转时间(spin-up time),明显改进短时降水预报.     

同化多普勒雷达风资料的两种方法比较

以美国新近研发的天气研究预报模式(WRF)配置的三维变分同化系统WRF 3D-Var为平台,比较了两种不同的同化多普勒雷达径向风资料的方法。一种是WRF 3D-Var系统现有的径向风资料直接同化方法;另一种是首先用两步变分法由多普勒资料反演出水平风,再同化反演风场。针对2003年7月4~5日的一次淮河暴雨过程进行的同化试验结果表明,同化了雷达风资料后得到的水平风场包含了更多的中尺度特征;从降水预报评分和预报的雷达回波来看,两种方法都能够明显改进降水预报,这种正作用能维持6 h左右;相对而言,同化反演的水平风场的效果略优于直接同化雷达径向风的效果。     

The WRF 3DVar System Combined with Physical Initialization for Assimilation of Doppler Radar Data

The three-dimensional variational data assimilation (3DVar) system of the Weather Research and Forecasting (WRF) model (WRF-Var) is further developed with a physical initialization (PI) procedure to assimilate Doppler radar radial velocity and reflectivity observations. In this updated 3DVar system, specific humidity, cloud water content, and vertical velocity are first derived from reflectivity with PI, then the model fields of specific humidity and cloud water content are replaced with the modified ones, and finally, the estimated vertical velocity is added to the cost-function of the existing WRF-Var (version 2.0) as a new observation type, and radial velocity observations are assimilated directly by the method afforded by WRF-Var. The new assimilation scheme is tested with a heavy convective precipitation event in the middle reaches of Yangtze River on 19 June 2002 and a Meiyu front torrential rain event in the Huaihe River Basin on 5 July 2003. Assimilation results show that the increments of analyzed variables correspond well with the horizontal distribution of the observed reflectivity. There are positive increments of cloud water content, specific humidity, and vertical velocity in echo region and negative increments of vertical velocity in echo-free region where the increments of horizontal winds present a clockwise transition. Results of forecast experiments show that the effects of adjusting cloud water content or vertical velocity directly with PI on forecast are not obvious. Adjusting specific humidity shows better performance in forecasting the precipitation than directly adjusting cloud water content or vertical velocity. Significant improvement in predicting precipitation as well as in reducing the model's spin-up time are achieved when radial velocity and reflectivity observations are assimilated with the new scheme.     

多普勒天气雷达资料对中尺度模式短时预报的影响

利用中尺度模式ARPS(The Advanced Regional Prediction System)及其资料分析系统ADAS(ARPS Data Analysis System),将国内新一代多普勒雷达(CINRAD)反射率及径向风资料直接用于中尺度数值模拟,通过一次华北地区暴雨过程的模拟对比试验,分析了雷达资料对初始场的改进效果及其对模拟结果的影响,结果表明:(1)利用雷达径向风资料对初始风场进行调整后,自近地面到对流层顶的u,v,w都发生了变化,调整后的初始风场在对流层中层变化最大.(2)利用雷达反射率进行微物理调整和云分析能调整初始场中的云水信息,使得雷达回波附近3 km以下的水汽混合比(qv)增加,4 km以下的雨水混合比(qr)增加,对流层(约10 km以下)的云水混合比(qc)增加,4～9 km的对流层上部云冰混合比(qi)和雪混合比(qs)增加.ADAS通过非绝热初始化调整温度场,从而得到了一个动力和热力上平衡的初始场.(3)模拟的1 h雨量与实况的对比表明,同时利用雷达反射率和径向风改进过的初始场能明显增强3 h内的降水强度和落区预报,改善中尺度数值模式短时定量降水预报.模拟的1 h流场对比分析表明,经雷达径向风调整后,能够在初始场中增加气旋性涡旋等中小尺度风信息,明显减少模式的spin-up时间.(4)通过对雷达径向风和反射率对模式初始场和模拟结果影响的对比分析发现,雷达径向风主要是改进初始风场,而雷达反射率主要是改进初始场中的湿度参数,增加初始场中云水等的含量,调整温度场.通过模拟的6 h降水对比发现,利用雷达径向风调整初始场后,对降水模拟有一定的改进,但效果不甚明显,而雷达反射率资料对定量降水预报改进效果明显,同时使用雷达径向风和反射率资料改进初始场后对降水的模拟效果最明显.     

集合卡尔曼滤波同化多普勒雷达资料的数值试验

利用集合卡尔曼滤波(EnKF)在云数值模式中同化模拟多普勒雷达资料,并考察了不同条件下EnKF同化方法的性能.结果显示,经过几个同化周期后,EnKF分析结果非常接近真值.单多普勒雷达资料EnKF同化对雷达位置不太敏感,双雷达资料同化结果在同化的初期阶段比单雷达资料同化结果准确.同化由反射率导出的雨水比直接同化反射率资料更有效,联合同化径向速度和雨水有利于提高同化分析效果.协方差对EnKF同化效果起着非常重要的作用,考虑模式全部预报变量与径向速度协方差的同化效果比仅考虑速度场与径向速度协方差的同化效果好.雷达资料缺值降低了同化效果,此时增加地面常规观测资料的同化可以明显提高同化分析效果.EnKF同化技术对雷达观测资料误差不太敏感.初始集合对同化分析有较大影响.EnKF同化受集合大小和观测资料影响半径.同化对模式误差较敏感.利用EnKF同化双多普勒雷达资料,分析了一次梅雨锋暴雨过程的中尺度结构.结果表明,EnKF同化技术能够从双多普勒雷达资料反演暴雨中尺度系统的动力场、热力场和微物理场,反演的风场是较准确的,反演的热力场和微物理场分布也是基本合理的.中低层切变线是此次暴雨的主要动力特征,对流云表现为低层辐合、高层辐散并有垂直上升运动伴随,其热力特征表现为低层是低压区,高层为高压区,中部为暖区而上、下部为冷区,水汽、云水和雨水分别集中在对流云体内、上升气流区和强回波区.     

Statistics of the <Emphasis Type="Italic">Z</Emphasis>–<Emphasis Type="Italic">R</Emphasis> Relationship for Strong Convective Weather over the Yangtze–Huaihe River Basin and Its Application to Radar Reflectivity Data Assimilation for a Heavy Rain Event

The relationship between the radar reflectivity factor (Z) and the rainfall rate (R) is recalculated based on radar observations from 10 Doppler radars and hourly rainfall measurements at 6529 automatic weather stations over the Yangtze–Huaihe River basin. The data were collected by the National 973 Project from June to July 2013 for severe convective weather events. The Z–R relationship is combined with an empirical q_r–R relationship to obtain a new Z–q_r relationship, which is then used to correct the observational operator for radar reflectivity in the three-dimensional variational (3DVar) data assimilation system of the Weather Research and Forecasting (WRF) model to improve the analysis and prediction of severe convective weather over the Yangtze–Huaihe River basin. The performance of the corrected reflectivity operator used in the WRF 3DVar data assimilation system is tested with a heavy rain event that occurred over Jiangsu and Anhui provinces and the surrounding regions on 23 June 2013. It is noted that the observations for this event are not included in the calculation of the Z–R relationship. Three experiments are conducted with the WRF model and its 3DVar system, including a control run without the assimilation of reflectivity data and two assimilation experiments with the original and corrected reflectivity operators. The experimental results show that the assimilation of radar reflectivity data has a positive impact on the rainfall forecast within a few hours with either the original or corrected reflectivity operators, but the corrected reflectivity operator achieves a better performance on the rainfall forecast than the original operator. The corrected reflectivity operator extends the effective time of radar data assimilation for the prediction of strong reflectivity. The physical variables analyzed with the corrected reflectivity operator present more reasonable mesoscale structures than those obtained with the original reflectivity operator. This suggests that the new statistical Z–R relationship is more suitable for predicting severe convective weather over the Yangtze–Huaihe River basin than the Z–R relationships currently in use.     

Analysis and very short range forecast of cyclone “AILA” with radar data assimilation with rapid intermittent cycle using ARPS 3DVAR and cloud analysis techniques

In this study, both reflectivity and radial velocity are assimilated into the Weather Research and Forecasting (WRF) model using ARPS 3DVAR technique and cloud analysis procedure for analysis and very short range forecast of cyclone ÁILA. Doppler weather radar (DWR) data from Kolkata radar are assimilated for numerical simulation of landfalling tropical cyclone. Results show that the structure of cyclone AILA has significantly improved when radar data is assimilated. Radar reflectivity data assimilation has strong influence on hydrometeor structures of the initial vortex and precipitation pattern and relatively less influence is observed on the wind fields. Divergence/convergence conditions over cyclone inner-core area in the low-to-middle troposphere (600–900 hPa) are significantly improved when wind data are assimilated. However, less impact is observed on the moisture field. Analysed minimum sea level pressure (SLP) is improved significantly when both reflectivity and wind data assimilated simultaneously (RAD-ZVr experiment), using ARPS 3DVAR technique. In this experiment, the centre of cyclone is relocated very close to the observed position and the system maintains its intensity for longer duration. As compared to other experiments track errors are much reduced and predicted track is very much closer to the best track in RAD-ZVr experiment. Rainfall pattern and amount of rainfall are better captured in this experiment. The study also reveals that cyclone structure, intensification, direction of movement, speed and location of cyclone are significantly improved and different stages of system are best captured when both radar reflectivity and wind data are assimilated using ARPS 3DVAR technique and cloud analysis procedure. Thus optimal impact of radar data is realized in RAD-ZVr experiment. The impact of DWR data reduces after 12 h forecast and it is due to the dominance of the flow from large-scale global forecast system model. Successful coupling of data assimilation package ARPS 3DVAR with WRF model for Indian DWR data is also demonstrated.     

云分析系统在台风莫拉菲数值模拟中的应用

借鉴美国CAPS开发的中尺度ARPS模式的资料分析系统ADAS,设计了基于GRAPES_Meso的云分析系统,实现了地面云观测资料、卫星云图、多普勒雷达反射率资料在GRAPRS模式中的综合融合应用。通过对登陆台风莫拉菲 (0906) 数值模拟检验云分析系统的性能。结果表明:云分析系统通过地面云观测资料、卫星红外云图、可见光云图、多普勒雷达反射率的同化,能够反演出合理的三维云覆盖状况;在三维云覆盖的基础上结合云底云顶高度,进而反演出云水、云冰、雨水、雪、霰等云微物理量,并显著改善模式初始湿度场;在台风登陆过程的模拟中,虽然对台风路径的预报有所偏差,但对比控制试验,在台风登陆地点、台风强度、路径的预报中云分析发挥了正作用;通过对云分析后初始场反演的雷达回波进行检验,验证了云分析的可行性与正确性,对整体的降水预报效果也有明显改善。     

毫米波云雷达功率谱密度数据的检验和 在弱降水滴谱反演中的应用研究

本文首先利用数值模拟的方法,分析了利用毫米波云雷达功率谱密度反演雨滴谱时,降水粒子米散射效应、空气湍流、空气上升速度等对雨滴谱和液态水含量等参数反演的影响;建立了功率谱密度处理及其直接反演雨滴谱、液态水含量、降水强度和空气上升速度的方法;并利用2012年7月在云南腾冲观测的二次弱降水数据,采用毫米波雷达和Ku波段微降水雷达观测的回波强度、径向速度垂直廓线以及780 m高度上的功率谱密度对比的方法,以及毫米波云雷达观测的780 m高度上功率谱密度、回波强度与地面雨滴谱计算得到的这些量的对比方法,分析了毫米波雷达数据的可靠性;并将780 m高度上毫米波雷达反演的雨滴谱与地面雨滴谱数据进行了对比,分析了毫米波雷达反演的雨滴谱的准确性;分析了毫米波雷达回波强度偏弱的原因,讨论了该高度以下降水对毫米波雷达衰减的影响。结果表明:空气湍流对弱降水微物理参数反演影响不大,而空气上升速度和米散射效应均对反演结果有一定影响;毫米波雷达观测到的径向速度和功率谱密度与微降水雷达比较一致,回波强度的垂直廓线的形状与微降水雷达也比较一致,但毫米波雷达观测的回波强度偏弱;与雨滴谱计算值相比,毫米波雷达观测的低层的回波强度也偏弱,天线上的积水是造成毫米波雷达回波强度变弱的主要原因。毫米波雷达观测的低层的功率谱密度与地面雨滴谱观测的数据形状比较一致,但有一定的位移。毫米波雷达反演的雨滴谱与地面观测的谱型和粒子大小也比较一致。这些结果初步验证了毫米波雷达观测的功率谱密度及其反演方法的可靠性。     

云分析方法对浙江省一次强对流天气数值模拟的应用初探

基于云分析方法,利用WRF-ARW模式设计一套快速更新循环同化方案,对2019年3月21至22日发生在浙江省的一次强对流天气过程进行模拟研究。通过设计两组对比试验,对云分析同化雷达反射率效果进行诊断分析。在控制试验中,模拟降水落区和降水量与实况差别较大,而采用云分析方法同化雷达反射率（CA-DA）的模拟试验中,降水模拟效果相对较好,雨带明显东移,强度与实况接近。初步结果表明,利用云分析同化雷达反射率因子可以改进模式初始场的风、温度、水汽场以及水凝物等信息,进而缩短模式spin-up时间,提高降水落区及强度的预报。     

雷达资料同化对2016年6月23日阜宁龙卷模拟的改进

基于GSI（Community Gridpoint Statistical Interpolation）同化系统和WRF（Weather Research and Forecasting）模式,探讨了多部多普勒雷达的反射率因子和径向速度资料同化对2016年6月23日江苏阜宁龙卷模拟的改进效果和影响过程。结果表明:（1）仅同化雷达反射率因子和仅同化径向速度均能在一定程度上改进模式对阜宁龙卷及其环境场的模拟,且雷达径向速度同化的改进作用更大;同时同化两种资料改进效果最佳。（2）雷达反射率因子同化是利用复杂云分析技术,直接修正了水凝物含量,增加了潜热释放,对低层大气热力场进行了正温度扰动调整,从而主要改进了初始场的水汽条件和热力条件;而雷达径向速度同化通过三维变分技术直接修正了风场,进而引起水汽输送变化影响水凝物的调整和大气热力场的变化,对初始场的动力条件和热力条件修正较大;同时同化两种资料修正了初始场的动力和热力结构,保证了两者物理上的协调,综合了两者的改进作用,从而取得最佳模拟效果。（3）同时同化雷达反射率因子和径向速度后,模式在阜宁附近模拟出了明显的涡旋结构,尽管涡旋强度和龙卷结构与实况仍有一定差距,但涡旋发生发展过程、路径、地面小时极大风和降水等模拟与实况吻合度均明显高于对照试验。      

Short-range prediction of a heavy precipitation event by assimilating Chinese CINRAD-SA radar reflectivity data using complex cloud analysis

Summary With the ARPS (Advanced Regional Prediction System) Data Analysis System (ADAS) and its complex cloud analysis scheme, the reflectivity data from a Chinese CINRAD-SA Doppler radar are used to analyze 3D cloud and hydrometeor fields and in-cloud temperature and moisture. Forecast experiments starting from such initial conditions are performed for a northern China heavy rainfall event to examine the impact of the reflectivity data and other conventional observations on short-range precipitation forecast. The full 3D cloud analysis mitigates the commonly known spin-up problem with precipitation forecast, resulting a significant improvement in precipitation forecast in the first 4 to 5 hours. In such a case, the position, timing and amount of precipitation are all accurately predicted. When the cloud analysis is used without in-cloud temperature adjustment, only the forecast of light precipitation within the first hour is improved. Additional analysis of surface and upper-air observations on the native ARPS grid, using the 1 degree real-time NCEP AVN analysis as the background, helps improve the location and intensity of rainfall forecasting slightly. Hourly accumulated rainfall estimated from radar reflectivity data is found to be less accurate than the model predicted precipitation when full cloud analysis is used.     

C波段雷达反射率资料的同化与数值模拟

利用ARPS模式(Advanced Regional Prediction System)的资料分析系统ADAS(ARPS Data Analysis Sys-tem),以NCEP GFS资料为背景场对我国西北地区CINRAD-CB\CC型雷达反射率资料进行同化试验研究,并借助于WRF(Weather Research and Forecasting Model)模式,对发生在黄河河套及河北地区的一次天气过程进行个例模拟试验。不同模拟方案模拟结果的对比分析和短时预报检验表明:①C波段雷达反射率资料的引入与S波段雷达反射率资料在空间覆盖上构成互补,与卫星、地面等资料的云综合分析能够分析出与实况更为接近的降水场和垂直结构信息;②同化了C波段雷达反射率资料的试验方案在模拟回波系统演变上优于未同化的,但由于模拟低层暖湿条件不足,系统逐渐衰弱与实况不符;③对比实况降水发现,区域C波段雷达反射率资料的同化对短时降水预报效果有一定改善。     

中尺度分析系统LAPS应用雷达资料的个例研究

武汉暴雨所引进国际先进的中尺度分析系统LAPS, 经成功本地移植后, 该系统能融合华中区域多种非常规观测资料, 提供包含丰富中尺度信息的高分辨率中尺度分析场。针对一次梅雨期强降水过程, 利用LAPS系统进行中尺度分析, 通过对比该系统融合多普勒雷达资料前后各种物理量场的差异, 研究了多普勒雷达资料在该系统中的作用。结果表明, LAPS融合雷达径向风后, 对风场的改善比较明显, 能揭示流场的中尺度信息。融合多种资料后的LAPS中尺度分析场比NCEP再分析场更接近实况, 能清楚地反映中尺度特征, 可作为分析此次强降水过程发生\, 发展的工具。融合雷达资料反射率后, LAPS云分析能提供与实况接近的较细致的云信息, 有利于了解暴雨过程中云参数的演变, 同时也为数值模式热启动提供条件。     

雷达反射率三维拼图观测资料在北方区域数值模式预报系统中的同化应用研究

以业务应用为目标,开展雷达反射率三维拼图观测资料在北方区域数值预报系统中的同化应用研究。采用雷达反射率间接同化方法同化北方雷达反射率拼图观测资料,重点关注其对降水、湿度、温度及风的预报能力影响。首先,基于2017年8月雷达拼图观测资料批量同化和对比试验,对雷达拼图资料同化应用效果进行定量评估,结果表明雷达拼图资料同化虽然加大了地面风场预报误差,但在降水预报和湿度、温度预报等方面有明显的改善作用。其次,选择在业务中预报难度较大的强降水个例开展分析研究,分析表明:（1）同化雷达拼图观测资料有效提高了模式降水预报性能,临近降水发生的循环起报时次预报效果更好;（2）对于短时间多次强降水过程发生的预报,循环同化雷达拼图资料可及时弥补模式中由于前次降水导致的水汽、能量等消耗及热/动力条件削弱,持续支持降水系统发展。最后,通过考察雷达反射率的不同同化方案,发现同化反演水凝物或者估计水汽均能改善模式降水预报性能,但是同化估计水汽对降水预报性能的改善更为明显,联合使用两方案能同时对水凝物分布、热力场等进行调整,可提高模式降水预报性能。      

Assimilating surface observations in a four-dimensional variational Doppler radar data assimilation system to improve the analysis and forecast of a squall line case

This paper examines how assimilating surface observations can improve the analysis and forecast ability of a fourdimensional Variational Doppler Radar Analysis System(VDRAS).Observed surface temperature and winds are assimilated together with radar radial velocity and reflectivity into a convection-permitting model using the VDRAS four-dimensional variational(4DVAR) data assimilation system.A squall-line case observed during a field campaign is selected to investigate the performance of the technique.A single observation experiment shows that assimilating surface observations can influence the analyzed fields in both the horizontal and vertical directions.The surface-based cold pool,divergence and gust front of the squall line are all strengthened through the assimilation of the single surface observation.Three experiments—assimilating radar data only,assimilating radar data with surface data blended in a mesoscale background,and assimilating both radar and surface observations with a 4DVAR cost function—are conducted to examine the impact of the surface data assimilation.Independent surface and wind profiler observations are used for verification.The result shows that the analysis and forecast are improved when surface observations are assimilated in addition to radar observations.It is also shown that the additional surface data can help improve the analysis and forecast at low levels.Surface and low-level features of the squall line—including the surface warm inflow,cold pool,gust front,and low-level wind—are much closer to the observations after assimilating the surface data in VDRAS.     

X波段双线偏振气象雷达反射率的衰减订正

X波段天气雷达的强衰减是影响其探测精度与应用推广的主要问题.本文旨在寻求适用于降水过程中对X波段双偏振雷达进行衰减订正的一种方法.在订正前先对雷达数据进行了质量控制和预处理;在分析了国内外已有订正方法的基础上,选择并改进了自适应约束算法作为雷达反射率进行衰减订正的方法;最后进行方法的效果验证.既对衰减订正前后反射率与同...     

一次冰雹云过程及其冰雹形成机制的模拟研究

利用常规气象资料和多普勒天气雷达资料,从天气形势和雷达回波演变特征等方面对2011年6月24日发生在洛阳嵩县的一次冰雹过程进行了分析,并利用三维弹性冰雹云催化模式对该冰雹云进行了模拟研究,分析其冰雹形成的物理机制。结果表明:本次过程在天气形势上属于下滑冷槽型。多普勒天气雷达资料上表现为单个单体的强对流风暴,最大反射率≥65 dBz,回波顶高达到14 km,降雹前垂直积分液态含水量具有明显的跃增;径向速度场上出现了大范围明显的逆风区。三维冰雹云模式对该冰雹云具有较好的模拟能力,模式模拟的最强回波与实况一致,雹云中含水量中心与强上升气流有很好的配置,在云的发展阶段,主含水量中心是强上升气流的指示。冰雹的雹胚主要来自冻滴和霰,在冰雹形成期间,冻结形成的冻滴和转化产生的霰数量上相差不大,但是冻滴向雹的转化比例却是霰的6倍,即在地面强降雹之前,雹云中的雹胚主要来源于冻滴;而冰雹的增长在前期主要靠收集过冷雨水,后期主要靠收集过冷云水;适量的冰晶、雪和丰富的过冷水的存在对雹的形成和增长极为有利。