宁夏“5·16”强对流天气跟踪分析及预报模型建立

利用逐时自动站资料、WRF模式数值产品、卫星云图、雷达产品等资料对2009年5月16日宁夏冰雹、短时强风等强对流天气进行了跟踪预报分析。结果表明：利用水汽通量散度数值产品中大气低层水汽通量的辐合或辐散可作为对流活动产生的重要依据之一。而卫星云图中的强对流云团的识别和新一代天气雷达基本反射率强度、液态水含量、冰雹指数、中尺度气旋产品是短时冰雹天气及短时雷雨大风天气预报的有利工具。并对2004—2008年出现的冰雹天气进行统计分析,建立了宁夏冰雹天气预报预警模型。     

Assessment of the WRF model in reproducing a flash-flood heavy rainfall event over Korea

This study examines the ability of the cloud-resolving weather research and forecasting (WRF) model to reproduce the convective cells associated with the flash-flooding heavy rainfall near Seoul, South Korea, on 12 July 2006. A triply nested WRF model with the highest resolution of 3-km horizontal grid spacing was integrated with conventional analysis data. The WRF model simulated the initiation of isolated thunderstorms, and the formation of a convective band, cloud cluster, and squall line at nearly the right time. The corresponding precipitation simulation was also reasonably reproduced in its distribution, although the amount was underestimated. A sensitivity experiment that excludes the orography over the peninsula revealed that orographic forcing over the peninsula is responsible for about 20% increase in precipitation over the heavy rainfall region. It was identified that in addition to the up-lifting local orographic forcing to the west of the mountain range in South Korea, anticyclonic circulation due to the presence of the Gaema Heights in North Korea contribute to the confinement of convective activities in the heavy rainfall region.     

Dynamic downscaling of summer precipitation prediction over China in 1998 using WRF and CCSM4

To study the prediction of the anomalous precipitation and general circulation for the summer(June–July–August) of1998, the Community Climate System Model Version 4.0(CCSM4.0) integrations were used to drive version 3.2 of the Weather Research and Forecasting(WRF3.2) regional climate model to produce hindcasts at 60 km resolution. The results showed that the WRF model produced improved summer precipitation simulations. The systematic errors in the east of the Tibetan Plateau were removed, while in North China and Northeast China the systematic errors still existed. The improvements in summer precipitation interannual increment prediction also had regional characteristics. There was a marked improvement over the south of the Yangtze River basin and South China, but no obvious improvement over North China and Northeast China. Further analysis showed that the improvement was present not only for the seasonal mean precipitation, but also on a sub-seasonal timescale. The two occurrences of the Mei-yu rainfall agreed better with the observations in the WRF model,but were not resolved in CCSM. These improvements resulted from both the higher resolution and better topography of the WRF model.     

浙江一次强飑线系统结构特征的数值研究

利用常规观测资料、自动气象站资料、NCEP再分析资料和高分辨率WRF模式,对2016年5月5日发生在浙江地区的一次强飑线过程进行模拟研究。结果表明,切变线是影响此次强飑线过程的主要天气系统,飑线发生在充沛的水汽,较弱的对流有效位能和中等强度垂直风切变大气环境下。WRF模式对此次飑线的演变过程和降水分布有较好的模拟能力。通过进一步分析模拟资料发现,雷暴高压和地面冷池是此次飑线风暴的重要边界层特征,边界层辐合线有利于飑线的发展和维持。飑线后侧对流层中层以下的强下沉气流,是造成此次雷暴大风的关键因素。     

一次飑线过程的数值模拟及诊断分析

利用NCAR、NCEP和FSL/NOAA等共同研制的WRF中尺度数值模式,对2009年6月3日河南地区发生的一次飑线过程进行数值模拟,并利用模式输出的高分辨率资料对该次过程进行诊断分析。结果表明:WRF模式成功地再现了高低空环流形势演变及强对流的分布发展特征,高空冷涡后部冷空气南下,近地层较暖,形成了上冷下暖的位势不稳定层结及地面辐合线是这次强对流和飑线天气过程的触发机制。强对流发生时,该地区出现的低空增温增湿、低空急流的爆发及低层急流核向东南快传、高空急流轴稳定在强对流天气发生地上空,对流有效位能积累和释放随时间的演变过程及垂直螺旋度大值中心等对此次强对流天气过程有较好的指示意义。     

机器学习在强对流监测预报中的应用进展

近年来,机器学习理论和方法应用蓬勃发展,已在强对流天气监测和预报中广泛应用.各类机器学习算法,包括传统机器学习算法(如随机森林、决策树、支持向量机、神经网络等)和深度学习方法,已在强对流监测、短时临近预报、短期预报领域发挥了积极的重要作用,其应用效果往往明显优于依靠统计特征或者主观经验积累的传统方法.机器学习方法能够更...     

Validating a regional climate model’s downscaling ability for East Asian summer monsoonal interannual variability

Performance of a regional climate model (RCM), WRF, for downscaling East Asian summer season climate is investigated based on 11-summer integrations associated with different climate conditions with reanalysis data as the lateral boundary conditions. It is found that while the RCM is essentially unable to improve large-scale circulation patterns in the upper troposphere for most years, it is able to simulate better lower-level meridional moisture transport in the East Asian summer monsoon. For precipitation downscaling, the RCM produces more realistic magnitude of the interannual variation in most areas of East Asia than that in the reanalysis. Furthermore, the RCM significantly improves the spatial pattern of summer rainfall over dry inland areas and mountainous areas, such as Mongolia and the Tibetan Plateau. Meanwhile, it reduces the wet bias over southeast China. Over Mongolia, however, the performance of precipitation downscaling strongly depends on the year: the WRF is skillful for normal and wet years, but not for dry years, which suggests that land surface processes play an important role in downscaling ability. Over the dry area of North China, the WRF shows the worst performance. Additional sensitivity experiments testing land effects in downscaling suggest the initial soil moisture condition and representation of land surface processes with different schemes are sources of uncertainty for precipitation downscaling. Correction of initial soil moisture using the climatology dataset from GSWP-2 is a useful approach to robustly reducing wet bias in inland areas as well as to improve spatial distribution of precipitation. Despite the improvement on RCM downscaling, regional analyses reveal that accurate simulation of precipitation over East China, where the precipitation pattern is strongly influenced by the activity of the Meiyu/Baiu rainfall band, is difficult. Since the location of the rainfall band is closely associated with both lower-level meridional moisture transport and upper-level circulation structures, it is necessary to have realistic upper-air circulation patterns in the RCM as well as lower-level moisture transport in order to improve the circulation-associated convective rainfall band in East Asia.     

一次强对流天气过程的诊断分析和数值模拟

利用常规资料和WRF模拟结果分析了2007年4月17日发生在广州白云机场附近的强对流天气过程.结果表明,此次天气过程发生于高低层系统有利配置、南海季风涌活跃和低空急流等低层系统加强使得华南地区具备充足水汽和不稳定条件的环境中.热力作用、地形和锋面的抬升作用促使冰雹和飑线等强对流天气生成和发展.数值模式输出的局地强降水和雷达强度回波等产品对保障航空安全有很好的指示作用.     

淮北地区一次弱天气尺度强迫背景下MCS过程分析与模拟

利用多源观测资料和WRF中尺度数值模式对2016年8月7日淮北地区一次中尺度对流系统（Mesoscale Convective Systerm,MCS）过程进行诊断分析和模拟。结果表明,本次MCS过程发生在弱天气尺度强迫背景场下,系统性上升运动较弱,对流层低层存在较弱的源自西北太平洋的偏东风转东南风的水汽输送作用;MCS移动和形态变化与地面辐合线演变特征较为一致,地面流场的演变与降水强度之间有着密切的联系;WRF模式较好地模拟出本次降水的分布特征以及MCS演变过程中对流活动和地面辐合线相互作用的特征。模拟结果表明,本次过程中MCS在逐渐南移过程中完成了对流单体的更替,地面辐合线在此过程中发挥重要作用,并且处于不同发展阶段的对流单体环境场的对流不稳定度的垂直分布存在明显差异。     

基于WRF模式和CloudSat卫星资料对黄淮下游一次强对流天气过程的诊断分析和数值模拟

利用Cloud Sat卫星资料和WRF中尺度模式,结合NCEP再分析资料及FY2G静止气象卫星资料,研究了发生在黄淮地区的一次深对流天气过程,分析了此次过程的天气特征、动力结构,重点分析了该次强对流过程中各水成物的时空演变特征。结果表明:(1)黄淮下游地区处于副高西北边缘,温度高,湿度大,对流潜势好。在地面冷锋和低层切变线的抬升触发下,气流不断辐合上升,同时高层冷平流与低层暖湿空气为强对流的发展提供了热力不稳定条件;(2)使用静止卫星TBB产品可以很好的定位、追踪深对流系统,但单一的TBB产品无法分辨深对流云和较厚的高云。本文结合Cloud Sat卫星资料和TBB产品把剖面上的云分为3种:非对流云(NDC),一般深对流云(DC),深对流核(DCC);(3)深对流云核(DCC)位于对流系统南部边缘,在3种云中DCC中冰相粒子粒径大、数浓度多、冰水含量大,且其最大值区域都位于12 km高度附近,这一区域可能是对流云内冰晶凝华增长、凇附增长、聚并增长形成大冰相粒子的关键发生区;(4)耦合了NSSL双参方案的WRF模式对于本次过程体现了较好的模拟效果,并通过模拟再现了此次天气过程中水成物的分布特征,发现本次过程深对流云中存在过冷水累积带特征。冰核核化形成的冰晶通过碰并过程形成雪晶,霰又由雪晶碰撞冻结过冷水滴以及过冷雨滴冻结产生,之后不断增长转化形成冰雹,雹增长到足够大后降落,其中雪晶和过冷水累积带对霰(雹胚)及雹的产生及增长至关重要。     

雷达热动力反演资料的高分辨率同化模拟试验

目前,北京地区的天气预报系统对局地对流性定量降水预报能力较弱,远不能满足人们生产、生活和防灾、减灾工作的需要。针对北京地区对提高0-12 h短时临近天气,尤其是夏季局地对流性降水预报能力的需求,基于中国气象局北京城市气象研究所变分多普勒雷达分析系统（VDRAS）的雷达热动力反演资料,建立了WRF模式初始化模块,采用四维资料同化（FDDA）方法,将VDRAS系统高时空分辨率三维热动力结构分析场资料同化到WRF模式中,实现了北京地区VDRAS分析场资料在WRF中尺度模式系统中的应用。通过降水个例的高分辨率同化模拟试验分析了雷达热动力反演资料同化对模式预报结果的影响。研究结果表明:雷达热动力反演资料的同化能够提高模式系统对近地面温、湿、风大气要素和降水过程的模拟能力,改善2 m比湿、降水落区、降水量级、降水时间的预报效果,减少降水漏报的现象。温度和比湿的同化比风的同化对模拟降水结果的改善更重要。虽然研究表明雷达热动力反演资料在WRF模式中的同化能够明显改善模式对选取降水个例的模拟效果,但其对模式尤其是数值业务模式系统预报效果的影响需要进一步更全面、更系统的检验,为业务化应用奠定更坚实的基础。      

宁夏一次短时暴雨天气的跟踪预报分析

用卫星云图、雷达对2008年8月7日强对流天气产生的暴雨过程跟踪观测资料,结合自动站地面降水实况和WRF模式风场资料进行短时预报分析.结果表明:扩散东移冷空气和副热带高压边缘偏南暖湿气流的共同影响下,大气层结不稳定发生强烈的强对流天气;利用卫星云图,新一代天气雷达基本反射率强度图、0.5°仰角基本速度图和风廓线产品跟踪监测,综合分析预报短时暴雨天气是有效的方法.     

天津地区080625强对流天气过程的分析

强对流降水是天津地区重要的灾害性天气,为了研究该类天气发生发展的动力学、热力学机制,利用NCEP/NCAR再分析资料和FY-2C卫星逐时TBB资料对2008年6月25日天津的强对流降水过程进行研究,然后利用WRF（weather research and forecasting）中尺度数值模式对该次强对流降水过程进行数值模拟和诊断分析。结果表明：中尺度露点锋是该次强对流降水的重要机制,其对应的低层气流辐合所形成的强烈上升运动及相对应的强烈发展的对流云团,是此次天津强对流降水的直接影响系统;对流有效位能等参数的变化非常好地反映出此次强降水天气的发生和发展特征;较大的相对螺旋度与此次强对流天气的发生对应也较好。由此认为,中尺度露点锋锋生的动力学、热力学过程是此次强对流降水天气发生发展的重要机制。     

对流天气预报中的环境场条件分析

中尺度对流天气的分析包括以天气型识别和中尺度过程分析为主的主观分析,以及以动力热力物理参数诊断为主的客观分析。利用"配料法"预报的思路,通过诊断有组织的深厚中尺度对流系统发生、发展的4个条件(水汽、不稳定、抬升和垂直风切变),开发了中尺度对流天气的环境场条件分析技术(对流天气图分析和客观物理量诊断技术),并应用于中国国家气象中心的强对流天气预报。以中尺度对流天气的天气图分析方法为例,介绍如何利用高低空观测资料,分析对流天气发生发展的环境场条件;并以数值模式释用为主的强对流特征物理量诊断分析为例,介绍如何动态诊断对流天气的动力热力条件演变。     

Impact of surface observations on simulation of rainfall over NCR Delhi using regional background error statistics in WRF-3DVAR model

In this study, efforts are made to improve the simulation of heavy rainfall events over National Capital Region (NCR) Delhi during 2010 summer monsoon, using additional observations from automatic weather stations (AWS). Two case studies have been carried out to simulate the relative humidity, wind speed and precipitation over NCR Delhi in 48-h model integrations; one from 00UTC, August 20, 2010, and the other from 00UTC, September 12, 2010. Several AWS installed over NCR Delhi in the recent past provide valuable surface observations, which are assimilated into state-of-the-art weather research and forecasting (WRF) model using the three-dimensional variational data assimilation (3DVAR). The quality of background error statistics (BES) is a key component in successful 3DVAR data assimilation in a mesoscale model. In this study, the domain-dependent regional background error statistics (RBS) are estimated using National Meteorological Center method in the months of August and September 2010 and then compared with the global background error statistics (GBS) in the WRF model. The model simulations are analyzed and validated against AWS and radiosonde observations to quantify the impact of RBS. The root mean square differences in the spatial distributions of precipitation, relative humidity and wind speed at the surface showed significant differences between both the global and regional BES. Similar differences are also observed in the vertical distributions along the latitudinal cross section at 28.5°N. Model-simulated fields are analyzed at five different surface stations and one upper air station located in NCR Delhi. It is found that in 24-h model simulation, the RBS significantly improves the model simulations in case of precipitation, relative humidity and wind speed as compared to GBS.     

Parameterized Forward Operators for Simulation and Assimilation of Polarimetric Radar Data with Numerical Weather Predictions

Many weather radar networks in the world have now provided polarimetric radar data(PRD)that have the potential to improve our understanding of cloud and precipitation microphysics,and numerical weather prediction(NWP).To realize this potential,an accurate and efficient set of polarimetric observation operators are needed to simulate and assimilate the PRD with an NWP model for an accurate analysis of the model state variables.For this purpose,a set of parameterized observation operators are developed to simulate and assimilate polarimetric radar data from NWP model-predicted hydrometeor mixing ratios and number concentrations of rain,snow,hail,and graupel.The polarimetric radar variables are calculated based on the T-matrix calculation of wave scattering and integrations of the scattering weighted by the particle size distribution.The calculated polarimetric variables are then fitted to simple functions of water content and volumeweighted mean diameter of the hydrometeor particle size distribution.The parameterized PRD operators are applied to an ideal case and a real case predicted by the Weather Research and Forecasting(WRF)model to have simulated PRD,which are compared with existing operators and real observations to show their validity and applicability.The new PRD operators use less than one percent of the computing time of the old operators to complete the same simulations,making it efficient in PRD simulation and assimilation usage.     

“0730”上海强对流天气个例的中尺度观测分析及数值模拟

利用上海多普勒雷达、中尺度自动站等资料和中尺度数值模式WRF模拟结果,分析了2005年7月30发生,在上海地区的一次强对流天气(简称"0730")的发生、发展过程。结果表明,边界层中尺度辐合线和扰动能够在弱冷空气南下和局地中小尺度斜压不稳定的背景下产生,中尺度扰动不稳定随垂直运动上传、触发对流;低层高湿度梯度的大气层结、垂直风向剧烈非均匀切变和能量锋区的耦合配置,促进了强对流的迅速发展。结合数值模拟和诊断分析初步揭示了这次强对流过程发生冰雹、暴雨、大风等天气的原因。     

北京地区强对流天气展望预报方法研究

该文依据1983～1992年6～8月间276次强对流天气过程，研究北京地区强对流天气的形成条件及其展望预报方法。通过500 hPa逐日分型，将影响北京地区的大尺度环流型划分为5种类型。在各型中随机抽取出现和不出现强对流天气样本共298个，分别作合成分析，研究各环流型出现和不出现强对流天气的合成形势及差异。结果表明，出现和不出现强天气的环流系统特征、结构及物理量分布都有明显不同，从而概括出概念模式，导出各环流型预报着眼点。在此基础上，从各型计算的数十个物理量参数中，筛选出最佳预报因子，采用判断树预报流程，逐     

基于SWCWARR模式的一次重庆江北机场对流天气过程分析

基于常规观测与雷达观测资料,应用西南区域数值模式SWCWARR和重庆RUC模式,对2019年4月27～28日重庆江北国际机场出现的一次强对流天气过程进行对比分析.结果表明:本次天气过程是高空槽后冷空气与低层西南暖湿气流相遇后形成切变,受地面辐合锋面和前倾槽系统共同影响的一次对流过程.SWCWARR模式的预报效果更优,该...     

ＷＲＦ-ＥｎＳＲＦ同化系统的效果检验及其应用

利用自主构建的针对风暴尺度资料同化的WRF-EnSRF同化系统同化多普勒天气雷达资料,检验其在2003年一次梅雨锋暴雨以及2009年一次强对流天气过程的同化性能.结果显示,在两个例中该同化系统均表现出有效的同化能力,经过60 min同化的分析场和以该分析场集合做初值的30 min的集合预报结果都比较接近实际观测.在同化过程中,径向速度和反射率因子的观测增量均方差分别达到3～4 m/s和9-11 dBz.本文考察了初始扰动时全场扰动与对流区域局部扰动,以及扰动环境风场与否对同化效果的影响.试验结果表明,对流区局部扰动相对于全场扰动并没有提高同化效果;对于尺度较大的梅雨锋暴雨来说,扰动环境风场时同化效果较好.为了考察分析场在降水预报中的表现,在暴雨个例中,以分析场为初值做6 h降水预报,经过同化的集合预报和确定性预报结果都比没有经过同化的控制试验预报结果准确.