EFFECTS OF CONDENSATION HEATING AND SURFACE FLUXES ON THE DEVELOPMENT OF A SOUTH CHINA MESOSCALE CONVECTIVE SYSTEM (MCS)

A sensitive numerical simulation study is carded out to investigate the effects of condensation heating and surface fluxes on the development of a South China MCS that occurred during 23 - 24 May 1998. The results reveal the following： （1） Condensation heating plays an important role in the development of MCS. In every different stage, without condensation heating, MCS precipitation is significantly reduced, and quickly dissipates. （2） Condensation heating demonstrates most importantly during the early development stages of MCS vortex; as the vortex develops stronger, the condensation heating effects reduces. （3） By affecting the MCS development processes, condensation heating also influences the formation of MCS mesoscale environment structure features such as low-level jet （mLLJ）, upper-level divergence. （4） By changing the antecedent environmental circulation, the surface fluxes also play an important role in the development of MCS. Because of the surface heating, pressure declines over the heavy rainfall and MCS happening regions, which results in the intensification of southerly flows from the ocean along the South China coastline areas, and leads to the enhancement of horizontal convergence and increase of vapor amount in the lower layer. All of these make the atmosphere more unstable and more favorable for the convection.

Understanding the Split Characteristics of the Tropical Mesoscale Convective System (MCS) of April 9, 2018, in Northern Ghana Using Infrasound Data

The split characteristics of the tropical Mesoscale Convective System (MCS) of April 9, 2018, in northern Ghana were studied using infrasound data measured by the mobile array (I68CI) which was deployed by C?te d’Ivoire National Data Center (NDC) in collaboration with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). These infrasound measurements were made during a measurement campaign from January 1st, 2018 to December 31, 2018, in northeast Cote d’Ivoire, precisely in Comoe National Park. Graphic Progressive Multi-Channel Correlation (GPMCC) method based on a progressive study of the correlation functions was used to analyze and visualize data. The infrasound detection from this MCS shows clearly a division of the MCS structure into 2 distinct subsystems under the effect of internal and external constraints not well known but related to convection;a smaller subsystem in the north, associated with an area of intense rainfall of about 30 mm/hour and located at 9.5°N - 2°E with an azimuth of 70° and, a large subsystem in the south, associated with a zone of high rainfall of about 96 mm/hour and located at 8.8°N - 1.4°E with an azimuth of 90°. These two subsystems were located 200 km and 260 km from the I68CI station with frequencies of 2.3 Hz and 1 Hz respectively. The mesoscale convective systems in this region are moving from East to West and including several storm cells.

Locating Parent Lightning Strokes of Sprites Observed over a Mesoscale Convective System in Shandong Province,China

In this paper, we report the location results for the parent lightning strokes of more than 30 red sprites observed over an asymmetric mesoscale convective system(MCS) on 30 July 2015 in Shandong Province, China, with a long-baseline lightning location network of very-low-frequency/low-frequency magnetic field sensors. The results show that almost all of these cloud-to-ground(CG) strokes are produced during the mature stage of the MCS, and are predominantly located in the trailing stratiform region, which is similar to analyses of sprite-productive MCSs in North America and Europe. Comparison between the location results for the sprite-producing CG strokes and those provided by the World Wide Lightning Location Network(WWLLN) indicates that the location accuracy of WWLLN for intense CG strokes in Shandong Province is typically within 10 km, which is consistent with the result based on analysis of 2838 sprite-producing CG strokes in the continental United States. Also, we analyze two cases where some minor lightning discharges in the parent flash of sprites can also be located, providing an approach to confine the thundercloud region tapped by the sprite-producing CG strokes.

THE FORMATION AND DEVELOPMENT OF A MESOSCALE CONVECTIVE SYSTEM WITH HEAVY RAINFALL ALONG SOUTH CHINA COASTAL AREA

Observational analysis shows that a Mesoscale Convective System (MCS) occurred on May 13-14 2004 along the coastal area in South China. The MCS initiated among the southwesterly flows within a west-east orientation low-level shear line. Associated with the system, in its subsequent development stages, no distinct vortex circulation developed in low-level. Instead, a cyclonic flow disturbance was observed in the mid-troposphere. How the convection starts to develop and evolve into a MCS With observational analysis and numerical simulation, the problem has been studied. The high-resolution MM5 simulation shows that topographic convergence along the coastal line and the nearby mountains in western South China plays an important role to initiate the MCS convection. Once the convection occurs, due to the condensation heating, a cooperative interaction between the preexisting mid-level disturbance and convection is created, which may greatly affect the MCS development during periods when the system continues moving eastward. Compared to some typical MCS that happen in Southern China, which are usually accompanied with upward development of cyclonic vorticity, the development and evolution of the investigated MCS shows distinguishing features. In this article, the physical mechanisms responsible for the intensification of mid-level disturbance are discussed, and a viewpoint to interpret the effects of mid-level disturbance on the MCS organizational development is proposed.

Analysis and Comparison of Mesoscale Convective Systems over the Qinghai-Xizang (Tibetan) Plateau

A series of mesoscale convective systems (MCSs) occurred daily over the Qinghai-Xizang Plateau during 25–28 July 1995. In this paper, their physical characteristics and evolutions based on infrared satellite imagery, their largescale meteorological conditions, and convective available potential energy (CAPE) are analyzed. It is found that similar diurnal evolution is present in all these MCSs. Their initial convective activities became active at noon LST by solar heating, and then built up rapidly. They formed and reached a peak in the early evening hours around 1800 LST and then abated gradually. Among them, the strongest and largest is the MCS on 26 July, which developed under the conditions of the great upper-level nearly-circular Qinghai-Xizang anticyclonic high and driven by the strong low-level thermal forcing and conditional instability. All these conditions are intimately linked with the thermal effects of the plateau itself. So its development was mainly associated with the relatively pure thermal effects peculiar to the Qinghai-Xizang Plateau. The next strongest one is the MCS on 28 July, which was affected notably by the baroclinic zone linked with the westerly trough. There are different features and development mechanisms between these two strongest MCSs.

A Numerical Case Study on a Mesoscale Convective System over the Qinghai-Xizang (Tibetan) Plateau

A mesoscale convective system (MCS) developing over the Qinghai-Xizang Plateau on 26 July 1995 is simulated using the fifth version of the Penn State-NCAR nonhydrostatic mesoscale model (MM5). The results obtained are inspiring and are as follows. (1) The model simulates well the largescale conditions in which the MCS concerned is embedded, which are the well-known anticyclonic Qinghai-Xizang Plateau High in the upper layers and the strong thermal forcing in the lower layers. In particular, the model captures the meso-α scale cyclonic vortex associated with the MCS, which can be analyzed in the 500 hPa observational winds; and to some degree, the model reproduces even its meso-β scale substructure similar to satellite images, reflected in the model-simulated 400 hPa rainwater. On the other hand, there are some distinct deficiencies in the simulation; for example, the simulated MCS occurs with a lag of 3 hours and a westward deviation of 3–5° longitude. (2) The structure and evolution of the meso-α scale vortex associated with the MCS are undescribable for upper-air sounding data. The vortex is confined to the lower troposphere under 450 hPa over the plateau and shrinks its extent with height, with a diameter of 4° longitude at 500 hPa. It is within the updraft area, but with an upper-level anticyclone and downdraft over it. The vortex originates over the plateau, and does not form until the mature stage of the MCS. It lasts for 3–6 hours. In its processes of both formation and decay, the change in geopotential height field is prior to that in the wind field. It follows that the vortex is closely associated with the thermal effects over the plateau. (3) A series of sensitivity experiments are conducted to investigate the impact of various surface thermal forcings and other physical processes on the MCS over the plateau. The results indicate that under the background conditions of the upper-level Qinghai-Xizang High, the MCS involved is mainly dominated by the low-level thermal forcing. The simulation described here is a good indication that it may be possible to reproduce the MCS over the plateau under certain large-scale conditions and with the incorporation of proper thermal physics in the lower layers.

卫星遥感揭示的青藏高原上MCS活动特征及东移传播

利用 1998年 6— 8月日本GMS红外辐射亮温 (Tbb)资料 ,对高原上中尺度对流系统 (MCS)的活动进行了自动追踪 ,得到了高原上夏季MCS的大小、强度、活动区域及生命史、形状特征。在此基础上 ,利用国家气象中心高分辨率有限区域分析预报系统 (HLAFS)的数值分析格点值 ,研究了MCS的东移传播与其周围环境场物理量之间的关系 ,建立了 4 0 0hPa和 5 0 0hPa两个层次上有利于MCS移出高原的物理量场概略模型图。

凝结加热和地表通量对华南中尺度对流系统(MCS)发生发展的影响

通过有无凝结加热和地表通量影响的数值模拟对比研究,分析了非绝热过程对一次华南暴雨MCS发生发展过程的影响。结果表明:(1)凝结加热对MCS的降水影响很大,在MCS发展的各个时期,如不考虑凝结加热,MCS的降水强度很快减弱,无法继续发展。(2)凝结加热在MCS涡旋的形成期最为重要,在涡旋形成之后,影响相对减弱。(3)凝结加热通过对MCS发展过程的影响从而也影响了MCS环境场中尺度低空急流、高层辐散等中尺度结构特征的形成。(4)地表感热、潜热通量等边界层非绝热过程对MCS的形成也有重要影响;在暴雨MCS发生前期,地表非绝热过程造成气压下降,导致华南南部来自海洋的偏南风加大,辐合加强,从而使低层的湿度增大,气层变得更加不稳定,有利于对流的启动。

江苏一次锢囚状MCS和相关中涡旋MCV的观测分析

利用常规地面和高空气象观测资料,结合气象卫星云图和雷达回波,分析了2009年6月14日15—23时（北京时,下同）,造成江苏强对流天气的一个中尺度对流系统（MCS）的锢囚状特征的形成过程及其垂直结构。地面中尺度分析表明,雷暴高压东侧在飑前倒槽北端发展的闭合低压环流的东南气流将暖湿空气输送到冷性雷暴高压的北侧形成东南一西北向的暖舌,从而形成锢囚状的结构。长三角探空网资料的垂直结构分析表明,在对流层下部地面到850 hPa为冷性的雷暴高压,在对流层中部700 hPa为冷性的α中尺度涡旋（MCV）,而500 hPa已转变为暖性的MCV。静力学关系可以说明MCV仅仅存在于700~500 hPa的原因和MCS下冷上暖的热力结构密切相关。

多源探测资料在一次非线状MCS分析中的综合应用

用多种加密观测资料和NCEP日再分析资料分析了2010年7月14日强降水期间咸宁地区一次非线状MCS活动造成短时强降水的发生发展机制。结果表明,14日13—18时非线状MCS回波结构组织性差,强对流单体散乱地分布在大片层状回波中,准静止地维持在湖北咸宁地区大约5 h,造成了短时强降水。该MCS发生在梅雨锋锋面附近的地面涡旋环流中,高空冷空气侵入和锋前抬升运动是对流的主要触发机制,切变线南侧不稳定的暖湿气流在长江中游地区辐合集中、局地的地面气流辐合和边界层有利的风切变是该非线状MCS发展维持在咸宁地区的有利条件。高时空分辨率探测资料对MCS演变过程有较好的分析能力。

“12.7.22”四川暴雨的MCS特征及对短时强降雨的影响

利用FY2D卫星云图云顶亮温(TBB)资料、雷达回波产品和常规气象观测资料、地面自动站降水资料及NCEP 1°×1°逐6 h再分析资料,对2012年7月21-22日四川暴雨中的中尺度对流系统(MCS)特征及其对短时强降雨影响进行分析,结果表明:(1)这次暴雨过程在21日00-06时和21日21时至22日03时有两个明显的6 h短时强降雨阶段。第一阶段中,500 hPa高原涡与700 hPa低涡切变线、低空急流作用,引发盆地西部短时强降雨;第二阶段中,500 hPa高原涡与700 hPa西南涡作用,引发盆地南部短时强降雨。(2)短时强降雨通常由MCS中的深对流特征造成,水平尺度多为β中尺度或更小的γ中尺度系统,具有云顶亮温低、雷达反射率因子大和垂直累积液态水含量高等特点。(3)探空资料分析表明,MCS增长初期,大气不稳定能量高,存在风垂直切变,在低层冷暖平流交汇明显且温度梯度大的区域,有利于激发MCS生成,另外高低层系统作用产生的深厚正涡度对其发生发展亦具有重要作用。在演变过程中MCS具有低层正涡度、负散度,高层负涡度、正散度的垂直结构,且上升速度明显,这种结构特征可能是MCS发展维持的重要因素,亦是产生强降雨的机制之一。

流形群运动目标自动识别与跟踪技术研究——以MCS自动追踪方法为例

从流形群运运目标的形状特征及其本质属性出发 ,提出了多种适合计算机自动识别与跟踪流形群运运目标的匹配模板的构建技术。充分顾及流形群运动目标的区域整体描述、几何形状特征、不变矩特性 ,以及流形群目标的本质属性 (纹理特征 ) ,通过最大欧几里得贴近度的择近原则 ,实现模板匹配 ,完成目标识别 ;通过交替更新匹配模板元素参量及交叉匹配算法 ,实现目标跟踪。应用这种算法 ,对 1 998年 6月至 8月的青藏高原上空中尺度对流系统 (MCS)进行了识别与跟踪实验。实验结果表明 ,这种技术较适合计算机自动识别和跟踪类似MCS的流形群运动目标 ,与专家目测屏幕扫描跟踪法相比 ,准确率达 90 %。同Arnaud等人提出的面积重叠跟踪法相比 。

2007年夏季川渝与江淮流域MCS分布与日变化特征

2007年夏季川渝地区及江淮流域持续性降水、极端强降水和强对流事件频发。利用强暴雨发生时段2007年6月28日至7月26日逐时FY-2C红外TBB资料对这两个地区及周边区域(25°～38°N、100°～130°E)进行普查,共获得570个生命史≥3小时的中尺度对流系统(MCS)。MCS的定义为-52℃TBB闭合等值线内TBB≤-52℃的面积≥400km2,不区分形状与生命史。MCS识别由计算机自动完成,MCS追踪由人工完成。普查结果发现,云南西北部至四川西部、四川东部与重庆、云贵高原东部和广西北部山区至洞庭湖、淮河流域四个区域是MCS活跃区,但淮河流域又有三个波动状MCS活跃中心。普查区域内总体MCS和川渝地区活动最频繁的MCS持续时间为3～7小时,但江淮流域活动最频繁的MCS生命史为4～9小时。按时间尺度将570个MCS分成三类,第一类MCS生命史3～5小时,第二类MCS生命史6～11小时,第三类MCS生命史≥12小时。三类MCS的地理分布特征及触发机制各不相同:第一、二类MCS在西太平洋副高平均位置的内、外侧都有发生,它们的发生、发展及移动受中尺度因素影响明显,可能与地形、中尺度辐合线等有关;第三类MCS发生在西太平洋副热带高压平均位置的外侧,其发生、发展及移动路径受天气尺度环境控制因素显著。三类MCS日变化具有明显不同的日变化特征。三类MCS的形成高峰都出现在午后。第一类MCS无显著的夜发性特征,第二、三类MCS有较显著的夜发性特征。第一、二类MCS在午后最活跃,但第三类MCS活动最活跃时段在下半夜(18UTC)。川渝地区和江淮流域的MCS都具有多峰型日变化特征,但二者的活跃时段有所不同。本文还给出了2个引发强降水的MCS典型个例及1个长生命史MCS演变特征。

一次局地大暴雨过程中两个不同MCS成因分析

利用常规观测资料、地面加密自动站资料、雷达资料、湖北地形资料及NCEP、ECMWF再分析资料,针对一次数值模式漏报的局地大暴雨过程进行分析,结果表明:高空槽前,低层切变线北侧,地面弱冷空气侵入暖倒槽是本次过程的大尺度天气背景。边界层强辐合中心和订正后高对流有效位能在预报中值得关注。两个大暴雨中心分别由两个不同的中尺度对流系统(Mesoscale Convective System,MCS)造成的,其演变形式和加强维持机制明显不同。松滋地区MCS受阵风锋触发,加强于边界层强辐合中心附近,在局地锋生作用下演变为中尺度涡旋结构,雷达上表现为人字形回波形态,大暴雨中心位于人字形回波交点处,50 mm/h雨强维持3 h。长阳地区MCS在边界层辐合区边缘,受边界层辐合气流触发,由加强的偏东气流在迎风坡上产生较强的地形强迫抬升而增强,最大雨强达102 mm/h。

云南切变线类短时强降水MCS特征分析

利用云南省125个国家级自动气象站及3042个区域站降水数据、FY-2E/G云图数据以及探空观测数据,统计2015—2019年由切变线系统影响的云南短时强降水过程,对短时强降水时空分布、中尺度对流系统(Mesoscale Convective System,MCS)系统特征、MCS系统发生发展的环境特征以及对流云系演变特征进行分析.结果表明,云南切变线类短时强降水频次有4个大值中心,分别是云南南部边缘地区、曲靖南部至文山北部、华坪、德宏西部,傍晚至凌晨是强降水发生的主要时段;云南切变线类短时强降水对流云系分成新生对流云团、M_(α)CS和M_(β)CS和带状MCS共4类,75%的切变线类短时强降水是由M_(α)CS和M_(β)CS系统造成,M_(α)CS和M_(β)CS系统中低于–32℃冷云区呈椭圆形,平均面积分别为1.8万km^(2)、10.4万km^(2),存在1个或2个中心,中心云顶亮温低于–52℃.M_(α)CS持续平均时间为3.3 h,其中最长时间为6 h;M_(β)CS持续平均时间为2.3 h,其中最长时间是5 h.短时强降水位于M_(α)CS和M_(β)CS强中心附近或者发展方向梯度大值区.综合分析了高低空系统配置的结合、对流发生的条件、MCS的发生及消退和降水特征,旨在建立由切变线引起的4种短时强降水过程的概念模型,从而为云南省短时强降水的预测提供关键技术支持.

2008年春夏华南地区MCS时空分布和活动特征分析

利用2008年3—8月FY2号地球静止卫星逐小时红外亮温（TBB）资料对我国华南地区春夏中尺度对流系统（MCS）的分布和活动特征进行了统计分析，并采用动态合成分析方法，讨论MCS初生前、初生、成熟和消亡四个阶段的大尺度环境场特征。研究发现：（1）两广沿海地区和海南岛北部是两个主要MCS活跃区，从两广沿海往北，随纬度增加和深入内陆MCS发生频率降低；（2）MCS活动分布具有明显的月际变化特征，3—6月对流活动逐渐增强并北扩，6月对流活动最活跃，之后又逐渐减弱南退；（3）华南地区MCS日变化呈现双峰分布，午后到傍晚前是MCS全天发生的最高峰，傍晚前后MCS达到成熟高峰，MCS消亡高峰则出现在傍晚到晚上，另外清晨有一个MCS发生、成熟、消亡的次高峰；（4）MCS平均生命史为4．7h，3-7h的MCS占总数的90％，平均移速为25km／h，以向东移动为主，向南和向西次之；（5）华南MCS发生的大尺度环境场特征主要表现为：对流层高层，MCS被南亚高压东部的反气旋环流控制，云团北侧存在西风急流，造成较强的风切变；中层，MCS形成于副热带高压西北侧的西风槽上，云团内部出现局部中性层结；低层则有西南急流将水汽输送至华南，急流左侧（对应MCS发生处）形成低涡，水汽易在此大量堆积。

一次梅雨锋强降水过程中MCS数值模拟与分析

文章以2005年梅汛期一次影响闽浙两省的大暴雨天气过程为研究对象,对梅雨锋上的多个MCS(中尺度对流系统)进行了中尺度数值模拟,利用模式输出的高时空分辨率数据集分析了MCS的发生发展演变机制,及其与梅雨锋暴雨的关系。

近16年暖季青藏高原东部两类中尺度对流系统(MCS)的统计特征

利用日本高知大学提供的逐小时分辨率静止卫星云顶黑体亮温(TBB)资料,使用模式匹配算法对2000~2016年(2005年除外)暖季(5~9月)青藏高原东部的两类中尺度对流系统(MCS)进行了识别和追踪,并利用人工验证订正了结果。基于此,利用NOAA的CMORPH(Climate Prediction Center Morphing)降水资料和NCEP的CFSR(Climate Forecast System Reanalysis)再分析资料对高原东部两类MCS进行了统计和对比研究。研究发现,7月和8月是高原东部MCS生成最活跃的季节,然而,此两个月能够东移出高原MCS的比例最小;5月虽然MCS生成数最少,但是移出率高达近40%。对比表明,能够东移出高原的MCS(V-MCS)比不能移出的MCS(N-MCS)生命史更长,触发更早,短生命史个例占比更低。暖季各个月份,相比于N-MCS,V-MCS的对流更旺盛且发展更快,然而,由于其发生频数远低于N-MCS,总体而言,V-MCS对高原东部的降水贡献率仅为15%左右,是N-MCS相应数值的一半左右。高原东部两类MCS的环流特征差异显著,有利于V-MCS发生、维持和东移的因子主要位于对流层中低层(西风带短波槽、西风引导气流、低层风场切变),而在对流层高层,N-MCS拥有更好的高空辐散条件(其对应的南亚高压更强)。

一次MCS的尺度分离动能分析

利用尺度分离动能方法对１９９４年６月１１日０９ＵＴＣ－１２日１０ＵＴＣ影响湖南省的一次ＭＣＳ进行了研究，结果表明：１．大尺度运动中非地转风以及两种尺度间风场与气压场的相互作用产生的动能，是这次ＭＣＳ的主要能源；２．中尺度动能以及两种尺度风场相互作用的动能，随ＭＣＳ发展（减弱）而增加（减小）；３．在ＭＣＳ的整个发展阶段，高层的总体动能锐减。

2014年5月8—9日引发珠江口区域强降水的两个长生命史MCS特征分析

2014年5月8日上午至9日白天,广东中南部珠江口地区连续受MCS-A1、MCS-A2两个长生命史中尺度对流系统影响,形成长时间强降水。其中5月8日午后华南内陆地区MCS-A1逐步增强,从广西东部向广东珠江口方向移动,陆上活动时间超过11h;MCS-A2从9日凌晨至上午持续影响珠江口沿海地区,维持时间超过9 h,导致珠江口沿海地区出现400 mm以上单站降水量。过程发生前,8日早上华南南部地区具有弱地面温度梯度,中午MCS-A1对流触发与广西南部地面南风增强、华南南部云开大山—云雾山中尺度地形抬升有紧密关系;在弱斜压环境条件下,MCS-A1从层云伴随线状对流结构演变为中尺度涡旋组织结构。8日夜间MCS-S1入海后,与陆上遗留冷池相关的地面温度边界稳定在珠江口西侧沿海地区;9日凌晨西南低空急流增强后,MCS-A2在珠江口沿海残留冷池边界附近开始发展,在向上游迎风方向传播的过程中,逐步形成多条平行β中尺度线状对流组织结构,对流系统整体移动缓慢,造成珠江口沿海地区出现较高的总降水量。计算表明MCS-A2冷池边界扩张速度与低层垂直切变相对平衡,有利于形成较为直立的对流单体,增强的边界层水汽输送、更高的对流单体高度有利于产生较高的降水强度。通过总结这两个华南地区长生命史MCS发生发展过程,表明通过分析对流反馈造成的边界层/近地面层热动力特征变化,对于分析MCS发展特征、提高华南前汛期中尺度暴雨预报能力具有重要意义。