基于雨滴谱仪和S波段雷达的X波段相控阵雷达反射率观测质量定量分析

使用深圳市求雨坛X波段相控阵雷达数据,与深圳市竹子林雨滴谱仪数据和深圳市求雨坛S波段雷达数据进行了定量对比,分析X波段相控阵雷达反射率的观测质量。结果表明,整体而言X波段相控阵雷达反射率与雨滴谱仪计算得到的反射率及S波段雷达反射率均较为一致,相关系数均超过0.75,相对平均误差接近于0,不存在明显偏差,且在不同强度降水时段表现较为稳定。但X波段雷达反射率在不同强度下偏差情况不一致,小于25 dBz时,X波段相控阵雷达反射率偏强,大于25 dBz时,X波段相控阵雷达反射率偏弱,且偏弱程度随反射率强度增加逐渐加大,在反射率超过50 dBz时,平均偏弱强度可达8~10 dB。

The Longmen Cloud Physics Field Experiment Base, China Meteorological Administration

Aiming at the needs of mechanism analysis of rainstorms and development of numerical prediction models in south China, the Guangzhou Institute of Tropical and Marine Meteorology of China Meteorological Administration and the Chinese Academy of Meteorological Sciences jointly set up the Longmen Cloud Physics Field Experiment Base,China Meteorological Administration. This paper introduces the instruments and field experiments of this base, provides an overview of the recent advances in retrieval algorithms of microphysical parameters, improved understanding of microphysical characteristics, as well as the formation mechanisms and numerical prediction of heavy rainfalls in south China based on the field experiments dataset.

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 mm),leading to higher rain rates.The mean values of Dmand lgNwof WR events are higher than that of FR events.The microphysical characteristics in different rain rate classes(C1:R~5-20 mm h-1,C2:R~20-50 mm h-1,C3:R~50-100 mm h^(-1),and C4:R> 100 mm h^(-1)) for WR and FR events are also different.Raindrops from C3 contribute the most to the precipitation of WR events,and raindrops from C2 contribute the most to the precipitation of FR events.For C2 and C3,compared with FR events,WR events have higher concentration of D <1 mm and D~3-4.5 mm.Moreover,the shape and slope(μ-A) relationships and the radar reflectivity and rain rate(Z-R) relationships of WR and FR events are quite different in each rain rate class.The investigation of the difference in microphysical characteristics between WR and FR events provide useful information for radar-based quantitative precipitation estimation and numerical prediction.

Thermodynamics and Microphysical Characteristics of an Extreme Rainfall Event Under the Influence of a Low-level Jet over the South China Coast

In this paper,the data of Automatic Weather Stations(AWSs),ERA5 reanalysis,sounding,wind profile radar,and dual-polarization radar are used to study an extreme rainfall event in the south China Coast on 11 to 12 May 2022 from the aspects of thermodynamics and microphysical characteristics under the influence of low-level jets(LLJs).Results show that:(1)The extreme rainfall event can be divided into two stages:the first stage(S1)from 0000 to 0600 LST on May 12 and the second stage(S2)from 0700 to 1700 LST on the same day.During S1,the rainfall is mainly caused by the upper-level shortwave trough and the boundary layer jet(BLJ),characterized by strong upward motion on the windward side of mountains.In S2,the combined influence of the BLJ and synoptic-system-related low-level jet(SLLJ)increases the vertical wind shear and vertical vorticity,strengthening the rainstorm.In combination with the effect of topography,a warm and humid southwest flow continuously transports water vapor to farther north,resulting in a significant increase in rainfall over the study area(on the terrain’s windward slope).From S1 to S2,the altitude of a divergence center in the upper air decreases obviously.(2)The rainfalls in the two stages are both associated with the mesoscale convergence line(MCL)on the surface,and the wind field from the mesoscale outflow boundary(MOB)in S1 is in the same direction as the environmental winds.Due to a small area of convergence that is left behind the MOB,convection moves eastward quickly and causes a short duration of heavy rainfall.In S2,the convergence along the MOB is enhanced,which strengthens the rainfall and leads to strong outflows,further enhancing the surface convergence near the MOB and forming a positive feedback mechanism.It results in a slow motion of convection and a long duration of heavy rainfall.(3)In terms of microphysics,the center of a strong echo in S1 is higher than in S2.The warm-rain process of the oceanic type characterizes both stages,but the convective intensity in S2 is significantly stronger than that in S1,featuring bigger drop sizes and lower concentrations.It is mainly due to the strengthening of LLJs,which makes small cloud droplets lift to melting levels,enhancing the ice phase process(riming process),producing large amounts of graupel particles and enhancing the melting and collision processes as they fall,resulting in the increase of liquid water content(LWC)and the formation of large raindrops near the surface.

Comparison of Microphysical Characteristics of Warm-sector,Frontal and Shear-line Heavy Rainfall During the Pre-summer Rainy Season in South China

Warm-sector heavy rainfall(WR),shear-line heavy rainfall(SR),and frontal heavy rainfall(FR)are three types of rainfall that frequently occur during the pre-summer rainy season in south China.In this research,we investigated the differences in microphysical characteristics of heavy rainfall events during the period of 10-15 May 2022 based on the combined observations from 11 S-band polarimetric radars in south China.The conclusions are as follows:(1)WR has the highest radar echo top height,the strongest radar echo at all altitudes,the highest lightning density,and the most active ice-phase process,which suggests that the convection is the most vigorous in the WR,moderate in the FR,and the weakest in the SR.(2)Three types of rainfall are all marine-type precipitation,the massweighted mean diameter(Dm,mm)and the intercept parameter(Nw,mm^(-1) m^(-3))of the raindrops in the WR are the largest.(3)The WR possesses the highest proportion of graupel compared with the FR and SR,and stronger updrafts and more abundant water vapor supply may lead to larger raindrops during the melting and collision-coalescence processes.(4)Over all the heights,liquid and ice water content in the WR are higher than those in the SR and FR,the ratio of ice to liquid water content in the WR is as high as 27%when ZH exceeds 50 dBZ,definitely higher than that in the SR and FR,indicating that the active ice-phase process existing in the WR is conducive to the formation of heavy rainfall.

Study on the Formation Mechanism and Microphysical Characteristics of WarmSector Convective System with Multiple-Rain-Bands Organizational Mode

Based on ERA5 reanalysis data and multi-source observations,including polarimetric radar and automatic weather stations,this study analyzes the formation mechanism and microphysical characteristics of a warm-sector heavy rainfall event caused by a convective system with multiple-rain-bands organizational mode over the western coast of south China.In the early stage,under the influence of coastal convergence and topography,convection was triggered in the coastal mountainous areas and moved north-eastwards.Nocturnal cooling induced the north winds in the inland mountainous area.A mesoscale convergence line was formed in the middle of Yangjiang city between the inland north and coastal south winds,which facilitated the developing and merging of convective storms into a linear convective band along the convergence line.This relatively long convective band presented a quasi-stationary state in the south of Mt.Ehuangzhang and Mt.Tianlu,which results in the first precipitation peak.At this stage,the convection developed to a higher level,with relatively larger raindrops,producing larger amounts of rainfall,which was probably related to the active merging of convection.In the later phase,as the environmental winds shifted,convective bands tended to move southeastwards,accompanied with the cold pools.At the same time,the multiple short convective bands were formed,which were almost parallel to the shear line,and a multiple-rain-bands organizational mode occurred.The mesoscale convergence line maintained due to the outflows of cold pools caused by precipitation in the preceding period,and then gradually moved southwards.Under the influence of the mesoscale convergence and topography,convection was continuously triggered at the southern end of the short convective bands.This back-building characteristic favored the development of the convective system.The multiple rain bands passed through the same place in a“rainband-training”form,resulting in the second peak of precipitation.The collision process was active in the low levels during this event.

中国暴雨的科学与预报:改革开放40年研究成果

总结了改革开放以来中国学者在暴雨科学与预报领域取得的重要研究进展和主要成果。其中,暴雨机理研究成果从重要天气系统、中国主要区域的暴雨、台风暴雨等3个方面分别进行综述,而暴雨预报技术研发与应用则从中国数值天气预报发展和暴雨预报客观方法两方面进行归纳。

广东两次飑线过程的微物理特征分析研究

基于中国气象局龙门云物理野外科学试验基地2DVD(Two-Dimensional Video Disdrometer)雨滴谱观测资料,分析广东地区2017年5月4日(槽前型飑线)和2017年8月22日(东风型飑线)两次不同飑线系统不同降水类型的雨滴谱特征。根据雨强和雷达反射率随时间变化将降水分成对流降水和层云降水,同时以20 mm/h为阈值将对流降水划分为对流前沿、对流中心和对流后沿。结果表明,两次飑线系统在不同降水时期的微物理特征参数变化有所差异。槽前型飑线过程中,对流降水的粒子分布较为分散,中等粒径的粒子比重较高,且对流区前半部分粒子尺寸大于“大陆性”对流特征,后半部分粒子尺寸小于“海洋性”对流特征;层云降水的粒子分布较为集中,小粒径粒子居多。而东风型飑线整个降水时期基本上是由高浓度中小粒径粒子组成,降水粒子粒径分布较为集中,对流降水粒子介于“海洋性”和“大陆性”对流区之间。

2012年7月发生于浙南山地的短飑线过程研究

山区强对流天气的发生条件十分复杂.选取2012年7月5日发生在浙江南部山区的一次短飑线天气过程,分析加密自动站、多普勒雷达和FY2E的TBB资料,并借助数值模拟手段,研究山地强对流天气发生发展的条件.利用自动站资料、叠加雷达和TBB资料,进行地面中尺度分析,对地面散度场特征进行了统计和分类,分析与山地强对流发生发展的关系,揭示山地强对流发生发展的前期特征.结果表明,来自东面海洋的东南气流易于在迎风坡前形成中尺度辐合区,这些低层辐合区是触发对流的有利条件.流场的辐合往往在回波单体出现前20min就已经存在.地面辐合线可造成低云的出现.中尺度山地触发了山地附近对流并沿着山地出现的辐合点和辐合线排列发展,最终形成中尺度的飑线,产生强对流天气.

中小尺度对流系统的高分辨率数值模拟近况和未来挑战

随着高速、大容量、并行计算能力的迅速增长和中尺度数值模式的不断完善,近年来不断涌现使用1 km乃至次千米网格距开展中、小尺度对流系统的数值模拟研究。这些数值模拟工作展现出目前观测手段还无法得到的动力学一致的高分辨率气象信息,大大提高了对一些中、小尺度对流系统内部结构和演变的理解。但高分辨率数值模拟的未来发展也面临着不少问题和挑战。首先回顾提高模式分辨率至1 km乃至次千米模拟中、小尺度对流系统的进展,并综述目前在高分辨率数值模拟中的资料同化和物理过程处理方法,同时指出中尺度模式中处理积云对流、大气边界层和辐射过程时值得注意的分辨率“灰色区”,然后介绍使用1 km和次千米分辨率模拟中、小尺度对流系统的几篇有代表性的工作。最后讨论高分辨率数值模拟的未来发展和挑战。

SANDRA法对北京小时强降水扰动环流场的分型研究

利用cost733class软件中的SANDRA(Simulated ANnealing and Diversified RAndomization)客观分型方法对北京地区2007~2014年暖季5~9月的小时强降水日的500hPa扰动位势高度场进行分型研究。结果显示,所划分的4类环流形势分别在蒙古、东北华北地区、河套地区和俄罗斯远东地区存在扰动低压区。根据4类环流形势的质心,将2007~2014年暖季所有日划归4类,计算每类小时强降水日占各自类型总天数的百分比得出蒙古扰动低压类的小时强降水日出现概率最大。统计小时强降水日的探空廓线得出,925hPa和850hPa的比湿中位数分别为13.01gkg^-1和10.64gkg^-1,这2个层级上最常出现的风向是180°~225°。

北京“623”大暴雨的强降水超级单体特征和成因研究

本文利用雷达、加密地面自动站等高时空分辨率的观测资料,结合NCEP 1°×1°再分析资料、常规观测等资料,对2011年6月23日发生在北京城区的极端强降水事件开展了细致的观测和诊断分析。结果表明,这次极端强降水事件,主要是由向东南移动的东北—西南走向的飑线右端的强降水超级单体(High Precipitation Supercell,简称HPS)造成的,这是目前已有文献记载的中国发生纬度最高的HPS。HPS在移动方向的右后侧和右前侧均有明显的'V'型入流,这不同于已有HPS模型,表明中、低层干冷空气和低层暖湿气流特征显著。在环境条件方面,存在对流层低层逆温层,其能量存储盖作用使得雷暴具有爆发性增强的潜势,但该逆温层是在08:00~14:00(北京时,下同)的6小时内形成的,对业务预报极具挑战性。相对其他大气层结热动力参数,风暴相对螺旋度和粗理查逊数在14:00较08:00显著增大,对HPS的发生具有一定指示作用。高空偏西风急流和低层偏东风活动显著,使得北京地区的水平风垂直切变增强,形成上干下湿的对流不稳定以及次级环流圈。高空急流造成强烈的相当位温差动平流,促进对流不稳定度发展加强。结合复杂地形作用,在北京西部100 m地形高度线附近形成显著的平原暖湿空气与山地干冷空气的干湿分界线以及风场辐合线。水汽供应主要源自低层偏东风和本地水汽积累。当飑线从西北方向侵入北京并向东南方向移动时,在北部山区,由于条件不足,雷暴没有显著发展加强;然而,在西部山区,在湖面、城市热岛、低层偏东风、冷池出流共同作用下,加之其他有利的环境条件,飑线右端雷暴强烈发展加强,特别是当经过100 m地形高度线附近时发展成为HPS,进而造成石景山区模式口站的大暴雨中心。

Assimilation of Polarimetric Radar Data Using an Ensemble Kalman Filter for the Analysis and Forecast of Tropical Storm Ewiniar(2018)

This study explores the potential for directly assimilating polarimetric radar data(including reflectivity Z and differential reflectivity Z_(DR))using an ensemble Kalman filter(EnKF)based on the Weather Research and Forecasting model to improve analysis and forecast of Tropical Storm Ewiniar(2018).Ewiniar weakened but brought about heavy rainfall over Guangdong,China after its final landfall.In the present study,two experiments are performed,one assimilating only Z and the other assimilating both Z and Z_(DR).Assimilation of Z_(DR)together with Z effectively modifies hydrometeor fields,and improves the forecast of the intensity,shape and position of rainbands.Forecast of 24-hour extraordinary rainfall≥250 mm is significantly improved.Improvement can also be seen in the wind fields because of cross-variable covariance.The current study shows the possibility of applying polarimetric radar data to improve forecasting of tropical cyclones,which deserves more research in the future.