一次强降水过程的中尺度对流系统模拟研究

1998年5月23～24日在珠江三角洲地区发生的特大暴雨过程是华南暴雨试验(HUAMEX)加密观测期间的一个典型个例,卫星云图与降水分布表明这是锋面附近与锋前暖区发生的两个中尺度对流系统(简称MCS)造成的强降水。使用非静力原始方程模式MM5较为成功地模拟了这次暴雨过程。根据数值模拟的结果,本文着重分析了发生在锋面上和锋前暖区的两类MCS的中尺度特征,并探讨了这两类MCS的差别。结果表明,两类MCS具有某些共同的中尺度特征,即对流系统的底层和顶部分别存在β尺度的低压和高压中心;低层流场辐合而在对流雨团的顶部辐散出流;对流系统内部具有暖心结构等,但锋面上的MCS较暖区中的对流系统具有更强的斜压性;二者内部的流场与三维运动结构也具有不同的特征,来自西南和偏南方向的空气从底部流入锋前暖区MCS时受到中低压的气压梯度力作用而加速;而锋面上MCS中不仅有来自锋前的暖湿空气,而且还有来自锋后的冷空气参加对流。MCS高空反气旋式发散气流和空气的加速运动反映出MCS顶部存在中尺度高压及向外的气压梯度力,轨迹分析也证明了MCS上空气流的这种非地转特征。     

Diurnal Variation of MCSs over Asia and the Western Pacific Region

Mesoscale convective systems (MCSs) are severe disaster-producing weather systems. Radar data and infrared satellite image are useful tools in MCS surveillance. The previous method of MCS census is to look through the printed infrared imagery manually. This method is not only subjective and inaccurate, but also inefficient. Different from previous studies, a new automatic MCS identification (AMI) method, which overcomes the above disadvantages, is used in the present study. The AMI method takes three steps: searching potential MCS profiles, tracking the MCS, and assessing the MCS, so as to capture MCSs from infrared satellite images. Finally, 47468 MCSs are identified over Asia and the western Pacific region during the warm seasons (May-October) from 1995 to 2008. From this database, the geographical distribution and diurnal variation of MCSs are analyzed. The results show that different types of MCSs have similar geographical distributions. Latitude is the main control factor for MCS distribution. MCSs are most frequent over the central Tibetan Plateau; meanwhile, this area also has the highest hail frequency according to previous studies. Further, it is found that the diurnal variation of MCSs has little to do with MCSs’ size or shape; MCSs in different areas have their own particular diurnal variation patterns. Based on the diurnal variation characteristics, MCSs are classified into four categories: the whole-day occurring MCSs in low latitude, the whole-day occurring MCSs in high latitude, the nocturnal MCSs, and the postmeridian MCSs. MCSs over most places of mainland China are postmeridian; but MCSs over the Sichuan basin and its vicinity are nocturnal. This conclusion is coincidental with the hail climatology of China.     

基于静止卫星红外云图的MCS普查研究进展及标准修订

基于静止卫星红外云图的MCS普查标准不统一不利于各种MCS普查结果的对比分析, 该文在总结MCS普查研究进展的基础上, 依据Orlanski尺度分类标准对MβCS普查的最小尺度标准作了修订, 即修订为TBB≤-32 ℃的连续冷云区直径≥20 km。根据马禹等的MβCS普查标准和该文修订的MβCS普查标准, 利用GOES-9卫星红外云图普查了2003年6月19日—7月22日淮河大水期间的MCS, 结果发现共有10个MαCS和24个MβCS, 并对24个MβCS作了普查标准修订前后的统计结果对比, 发现新的普查标准比根据马禹等的MβCS普查标准获得的结果多7个MβCS, 并且这7个MβCS中有6个都引起强降水, 因此这种对比分析结果表明:新MβCS普查标准对揭示淮河大水和MCS的关系更具合理性。此外, 还分析了3个因MβCS而引起局地强降水的典型个例, 这些MβCS的直径尺度只有几十至一百多公里, 不符合马禹等的MβCS普查标准。对这3个MβCS分析结果表明:该文新MβCS普查标准有助于对产生剧烈天气的MCS的普查研究和预报。     

The Characteristics of Mesoscale Convective Systems (MCSs) over East Asia in Warm Seasons

Mesoscale convective system (MCS) cloud clusters,defined using an objective recognition analysis based on hourly geostationary infrared satellite data over East Asia during the warm seasons of 1996-2008 (except 2004),were investigated in this study.The geographical pattern of MCS distribution over East Asia shows several high-frequency centers at low latitudes,including the Indo-China peninsula,the Bay of Bengal,the Andaman Sea,the Brahmaputra river delta,the south China coastal region,and the Philippine Islands.There are several middle-frequency centers in the middle latitudes,e.g.,the central-east of the Tibet Plateau,the Plateau of west Sichuan,Mount Wuyi,and the Sayan Mountains in Russia;whereas in Lake Baikal,the Tarim Basin,the Taklimakan Desert,the Sea of Japan,and the Sea of Okhotsk,rare MCS distributions are observed.MCSs are most intensely active in summer,with the highest monthly frequency in July,which is partly associated with the breaking out and prevailing of the summer monsoon in East Asia.An obvious diurnal cycle feature is also found in MCS activities,which shows that MCSs are triggered in the afternoon,mature in the evening,and dissipate at night.MCS patterns over East Asia can be characterized as small,short-lived,or elongated,which move slowly and usually lead to heavy rains or floods.     

The 2001 Mesoscale Convective Systems over Iberia and the Balearic Islands

Summary This paper characterizes Mesoscale Convective Systems (MCSs) during 2001 over Iberia and the Balearic Islands and their meteorological settings. Enhanced infrared Meteosat imagery has been used to detect their occurrence over the Western Mediterranean region between June and December 2001 according to satellite-defined criteria based on the MCS physical characteristics. Twelve MCSs have been identified. The results show that the occurrence of 2001 MCSs is limited to the August–October period, with September being the most active period. They tend to develop during the late afternoon or early night, with preferred eastern Iberian coast locations and eastward migrations. A cloud shield area of 50.000 km² is rarely exceeded. When our results are compared with previous studies, it is possible to assert that though 2001 MCS activity was moderate, the convective season was substantially less prolonged than usual, with shorter MCS life cycles and higher average speeds. The average MCS precipitation rate was 3.3 mm·h⁻¹ but a wide range of values varying from scarce precipitation to intense events of 130 mm·24 h⁻¹ (6 September) were collected. The results suggest that, during 2001, MCS rainfall was the principal source of precipitation in the Mediterranean region during the convective season, but its impact varied according to the location. Synoptic analysis based on NCEP/NCAR reanalysis show that several common precursors could be identified over the Western Mediterranean Sea when the 2001 MCSs occurred: a low-level tongue of moist air and precipitable water (PW) exceeding 25 mm through the southern portion of the Western Mediterranean area, low-level zonal warm advection over 2 °C·24 h⁻¹ towards eastern Iberia, a modest 1000–850 hPa equivalent potential temperature (θ_e) difference over 20 °C located close to the eastern Iberian coast, a mid level trough (sometimes a cut-off low) over Northern Africa or Southern Spain and high levels geostrophic vorticity advection exceeding 12·10⁻¹⁰ s⁻² over eastern Iberia and Northern Africa. Finally, the results suggest that synoptic, orographic and a warm-air advection were the most relevant forcing mechanisms during 2001.     

湖北三类组织形态强对流系统造成的地面强对流大风特征

利用湖北省2012~2017年区域自动站、天气雷达和周边探空站观测资料,对三类不同组织形态的中尺度对流系统(Mesoscale Convective System, MCS)(线性MCS、非线性MCS和孤立对流风暴)造成的地面强风(极大风速≥17 m/s)的时空分布、移动与传播、对流环境特征等方面进行了统计对比分析,并结合个例讨论了地面入流大风的成因及其对对流系统发展、组织的影响。结果表明:(1)大量的非线性MCS可能是由更早发生在山区和丘陵的孤立对流风暴向平原地区移动过程中组织形成的,孤立对流风暴造成的地面大风出现的峰值时间在17:00(北京时,下同)前后,非线性MCS地面大风的峰值时间在19:00左右;线性MCS造成的强对流大风主要出现在平原地区。(2)非线性MCS和孤立对流风暴是造成湖北省地面大风的主导系统,其中,非线性MCS造成的地面大风站次数占强对流大风站次总数的41.9%,而39.3%的地面强对流大风站次是由孤立对流风暴造成的。(3)虽然大于17 m/s的地面入流大风占所有强对流大风的比例很小,但存在地面入流大风的强对流系统的影响范围、持续时间均远大于同一类型对流系统的平均值。基于一次长生命史线性MCS(飑线)造成强对流大风事件的分析表明:雷暴系统前侧的地面入流大风是由对流强烈发展造成,这支暖湿入流又进一步增强了对流风暴的发展,同时地面入流大风的形成进一步加强了垂直风切变,因而强的地面入流更有利于对流系统的组织化发展。(4)虽然暖季强对流系统的平均引导气流均以西南风为主,但线性MCS主要自西向东移动、非线性MCS以自西南向东北移动为主、孤立对流风暴的移动方向则更具多样性,也更易出现后向传播现象。孤立对流风暴相对组织化的强对流系统而言,往往发生在更不稳定或更干的层结大气中,且环境垂直风切变更弱、风速更小。     

Modes of Mesoscale Convective System Organization During Meiyu Season over the Yangtze River Basin

Mesoscale convective systems （MCSs） are classified and investigated through a statistical analysis of composite radar reflectivity data and station observations during June and July 2010-2012. The number of linear-mode MCSs is slightly larger than the number of nonlinear-mode MCSs. Eight types of linear-mode MCSs are identified： trailing stratiform MCSs （TS）, leading stratiform MCSs （LS）, training line/adjoining stratiform MCSs （TL/AS）, back-building/quasi-stationary MCSs （BB）, parallel stratiform MCSs （PS）, bro- ken line MCSs （BL）, embedded line MCSs （EL）, and long line MCSs （LL）. Six of these types have been identified in previous studies, but EL and LL MCSs are described for the first time by this study. TS, LS, PS, and BL MCSs are all moving systems, while TL/AS, BB, EL, and LL MCSs are quasi-stationary. The average duration of linear-mode MCSs is more than 7 h. TL/AS and TS MCSs typically have the longest durations. Linear-mode MCSs often develop close to the Yangtze River, especially over low-lying areas and river valleys. The diurnal cycle of MCS initiation over the Yangtze River valley contains multiple peaks. The vertical distribution of environmental wind is decomposed into storm-relative perpendicular and parallel wind components. The environmental wind field is a key factor in determining the organizational mode of a linear-mode MCS.     

河南省对流性暴雨云系特征与概念模型

利用2005—2010年FY-2C/E和MODIS卫星资料、A0报文、自动气象站降水资料及常规观测资料,修订了河南省对流性暴雨中尺度对流系统标准,统计分析了暴雨中尺度对流系统的活动规律和降水特征,初步建立了河南省典型对流性暴雨概念模型。河南省对流性暴雨中尺度对流系统主要包括新生对流云团、β中尺度对流系统、α中尺度对流系统及带状中尺度对流系统。对流性暴雨易产生于中尺度对流系统的发生、发展期,多发于中尺度对流系统云顶亮温低中心附近及后侧梯度大值区, 云系上云光学厚度高值区为中尺度对流系统发展潜势区。低槽 (涡) 切变型和低槽型过程中干冷气团对中尺度对流系统的发生、发展起触发作用;高压后部型与午后边界层辐射增温关系密切,能量锋、边界层辐合线是中尺度对流系统的触发系统;切变型过程中干线的作用较重要。河南省对流性暴雨中尺度对流系统多发展于山区附近,移动路径有东移、东北移和东南移型,高层云导风可为中尺度对流系统的移动发展提供预报信息。     

STATISTIC CHARACTERISTICS OF MCSS OVER ASIA AND WESTERN PACIFIC REGION

Mesoscale convective systems (MCSs) are severe disaster-producing weather systems. Previous attempts of MCS census are made by examining infrared satellite imageries artificially, with subjectivity involved in the process unavoidably. This method is also inefficient and time-consuming. The disadvantages make it impossible to do MCS census over Asia and western Pacific region (AWPR) with an extended span of time, which is not favorable for gaining a deeper insight into these systems. In this paper, a fire-new automatic MCS identification (AMI) method is used to capture four categories of MCSs with different sizes and shapes from numerical satellite infrared data. 47,468 MCSs are identified over Asia and western Pacific region during the warm season (May to October) from 1995 to 2008. Based on this database, MCS characteristics such as shape, size, duration, velocity, geographical distribution, intermonthly variation, and lifecycle are studied. Results indicate that the number of linear MCSs is 2.5 times that of circular MCSs. The former is of a larger size while the latter is of a longer duration. The 500 hPa steering flow plays an important role in the MCS movement. MCSs tend to move faster after they reach the maximum extent. Four categories of MCS have similar characteristics of geographical distribution and intermonthly variation. Basically, MCSs are zonally distributed, with three zones weakening from south to north. The intermonthly variation of MCSs is related to the seasonal adjustment of the large-scale circulation. As to the MCSs over China, they have different lifecycle characteristics over different areas. MCSs over plateaus and hill areas, with only one peak in their lifecycle curves, tend to form in the afternoon, mature at nightfall, and dissipate at night. On the other hand, MCSs over plains, which have several peaks in their lifecycle curves, may form either in the afternoon or at night, whereas MCSs over the oceans tend to form at midnight. Affected by the sea-land breeze circulation, MCSs over coastal areas of Guangdong and Guangxi always come into being at about 1500 or 1600 (local time), while MCSs over the Sichuan Basin, affected by the mountain-valley breeze circulation, generally initiate nocturnally.     

西南山区5—8月产生突发性暴雨事件的中尺度对流系统的时空分布特征

利用逐时的风云静止卫星黑体亮温(TBB)资料和国家级地面站降水观测资料,根据中尺度对流系统(MCS)的逐时云顶覆盖范围是否包含突发性暴雨事件,识别出2010—2018年5—8月与中国西南山区突发性暴雨事件相关的中尺度对流系统(AHR-MCS),并得到其统计特征.结果表明,该地区AHR-MCS在7月出现最频繁,存在四川盆...     

梅雨锋暴雨中尺度对流系统触发和组织化的观测分析

利用观测和NCEP再分析资料,对2015年6月26-28日江淮流域梅雨锋暴雨天气对流的触发和中尺度对流系统（MCS）的组织方式进行了分析。结果表明:梅雨锋附近发展的2个线状中尺度对流系统是暴雨的直接制造者。MCS2的发展有2种组织方式,26日夜间到27日凌晨,东西向雨带的不断后部建立和随后对流单体的列车效应是其发展的主要方式。27日凌晨到白天,初期新单体不断在线状MCS2的南缘触发,形成多个近乎平行的东北-西南向短雨带,后期梅雨锋锋面雨带从西部不断东移,经过强降水区;对流元有2种尺度的组织方式:新生对流单体沿着单个雨带向东北方向的列车效应以及东北-西南向雨带沿线状中尺度对流系统向东平移的"列车带"效应;持续的后部建立型和沿着同一路径不断的"列车带"效应使MCS2发展和维持。梅雨锋前不稳定空气的地形抬升和边界层辐合上升是初始对流的主要触发机制;26日夜间对流产生的冷池对对流的触发和MCS2的组织化及维持起重要作用,中尺度对流系统的组织特征和发生、发展受近地面环境场制约。      

A MASCOTTE-based characterization of MCSs over Spain, 2000–2002

A 3-year Mesoscale Convective Systems (MCSs) database, which extends from 2000 to 2002, has been built for the Iberian Peninsula and the Balearic Islands using the objective method MASCOTTE (MAximum Spatial COrrelation Technique). It was originally developed to track the evolution of convective systems over the Amazon region; after modifications, it is able to track MCS evolution even with an hour and a half of missed images and provides essential information of both dynamical and morphological characteristics of MCSs. MASCOTTE is tested against a visual and subjective method, and is found to offer advantages such as automation and a simple and efficient operation that make it very useful for building large MCS databases.Thirty-five MCSs were found between June and October, most of them originated along the Mediterranean coast and near the Pyrenees, showing an increasing occurrence from June to September, when the maximum is found. The regions most influenced by MCS occurrences are Balearic Islands, Valencia, Catalonia, Murcia and the Basque Country. The MCSs tend to be small, short-lived and linear, usually moving eastward or northeastward with low velocities.The MCSs-associated precipitation presents high variability, ranging from 80 to 0 mm h⁻¹ as maximum hourly records. Two different convective regions are identified based on MCS behavior in extreme precipitation events: Northern Spain (the Basque Country) with abundant and continuous precipitation regime but little MCS influence, and the Mediterranean coast, where precipitation is sporadic but much more intense.     

梅雨锋上两类中尺度对流系统形成的边界层特征

采用具有较高时空分辨率的地面观测资料以及WRF（Weather reasearch and forecasting）模式输出资料,分析了2009年6月29一-30日梅雨锋暴雨过程中两类不同的中尺度对流系统（rnesoscale convective system,MCS）边界层特征及边界层对两类MCS的触发维持机理,重点分析了海平面气压场特征、边界层冷池、干线及其在MCS中的影响。结果表明：两类中尺度对流系统的海平面气压特征存在着明显的差异,对流爆发阶段地面风场存在辐合线,再次激发阶段气压场呈“跷跷板”型的中尺度扰动,即由前置中低压和后置中高压组成,最强的对流带位于中低压和中高压之间的过渡区内;边界层辐合线是第一类中尺度对流系统（MCSl）维持的重要因素;MCSl爆发后边界层冷池生成,冷池前的冷出流与低层环境风产生的强辐合触发了第二类中尺度对流系统（MCS2）;存在于中低压和中高压之间的中尺度干线是MCS2的重要特点之一。     

A Diagnostic Case Study on the Comparison Between the Frontal and Non-Frontal Convective Systems

Two major mesoscale convective clusters of different characters occurred during the heavy rainfall event in Guangxi Region and Guangdong Province on 20 June 2005,and they are preliminarily identified as a frontal mesoscale convective system(MCS1;a frontal cloud cluster) and a non-frontal MCS(MCS2;a warm sector cloud cluster).Comparative analyses on their convective intensity,maintenance mechanism, and moist potential vorticity(MPV) structure were further performed.The convective intensity analysis sugges...     

"05.6"东北暴雨中尺度对流系统研究Ⅰ:常规资料和卫星资料分析

应用常规气象资料与卫星资料相结合的办法,研究了2005年6月10日午后在黑龙江省中东部发生的暴雨中尺度对流系统(MCSs)的大尺度环流背景、大气层结演变特征、下垫面条件以及中尺度对流系统。结果表明:此次暴雨(简称“05.6”东北暴雨)是发生在高空槽东移加深过程中的一次对流天气过程。中尺度对流系统处于前倾疏散的高空槽槽前,高空辐散,低空辐合,为MCS发生提供了有利的大尺度动力条件。暴雨发生前对流层低层有西南—东北走向的湿舌,为暴雨提供了有利的水汽条件。高空干冷平流与低空的暖湿平流形成的差动平流,造成此处大气的层结不稳定度增强。此外,从地面接收到的太阳辐射能量分布情况来看,下垫面不均匀加热引起的热力环流是这次暴雨过程中尺度对流系统发生发展的一个重要的触发机制。研究地面中尺度切变线演变与此次暴雨对流系统发生发展的关系发现,切变线上对流强弱分布是不均匀的,其中在弧形切变线曲率最大处的对流最强,与沙兰河上游暴雨有关的对流云团就出现在这个地区。以上事实表明,地面中尺度切变线可能是此次暴雨发生发展的另一个关键因素,而造成切变线上对流发展不均匀的原因可能和切变线走向与环境风场的配置有较大关系。     

A Case Study of the Initiation of Parallel Convective Lines Back-Building from the South Side of a Mei-yu Front over Complex Terrain

Parallel back-building convective lines are often observed extending to the southwest of some mesoscale convective systems(MCSs)embedded in the mei-yu front in China.The convective lines with echo training behavior can quickly develop into a stronger convective group of echoes,resulting in locally heavy rainfall within the mei-yu front rainband.The initiation mechanism of the back-building convective lines is still unclear and is studied based on high-resolution numerical simulation of a case that occurred during 27?28 June 2013.In the present case,the new convection along the convective lines was found to be forced by nonuniform interaction between the cold outflow associated with the mei-yu front MCSs and the warm southerly airflow on the south side of the mei-yu front,which both are modified by local terrain.The mei-yu front MCSs evolved from the western to the eastern side of a basin surrounded by several mesoscale mountains and induced cold outflow centered over the eastern part of the basin.The strong southwest airflow ahead of the mei-yu front passed the Nanling Mountains and impacted the cold outflow within the basin.The nonuniform interaction led to the first stage of parallel convective line formation,in which the low mountains along the boundary of the two airflows enhanced the heterogeneity of their interaction.Subsequently,the convective group quickly developed from the first stage convective lines resulted in apparent precipitation cooling that enhanced the cold outflow and made the cold outflow a sharp southward windshift.The enhanced cold outflow pushed the warm southerly airflow southward and impacted the mountains on the southeast side of the basin,where the roughly parallel mountain valleys or gaps play a controlling role in a second stage formation of parallel convective lines.     

中尺度对流系统红外云图云顶黑体温度的分析

采用ＧＭＳ卫星红外云图的云顶黑体温度（ＴＢＢ）等值线分析方法，对１９９２年８月初在中国３个地区，不同环流背景下发生的中尺度对流系统（ＭＣＳ），即西南低涡内、西太平洋副热带高压的西北边缘和副高内部的ＭＣＳ进行了分析。结果表明，ＴＢＢ等值线分析方法能较细致地揭示ＭＣＳ的形成过程。冷云盖周围ＴＢＢ等值线疏密所反映的云顶温度梯度，对ＭＣＳ的发展有很好的指示意义。文中还给出了一个在消散阶段出现涡旋状结构的ＭＣＳ。这种涡旋结构不同与北美发现的中层中尺度气旋，它可能是凝结加热所产生的对流层高层的高压反气旋环流的反映。     

Distribution and Diurnal Variation of Warm-Season Short-Duration Heavy Rainfall in Relation to the MCSs in China

Short-duration heavy rainfall（SDHR） is a type of severe convective weather that often leads to substantial losses of property and life. We derive the spatiotemporal distribution and diurnal variation of SDHR over China during the warm season（April–September） from quality-controlled hourly raingauge data taken at 876 stations for 19 yr（1991–2009）, in comparison with the diurnal features of the mesoscale convective systems（MCSs） derived from satellite data. The results are as follows. 1） Spatial distributions of the frequency of SDHR events with hourly rainfall greater than 10–40 mm are very similar to the distribution of heavy rainfall（daily rainfall 50 mm） over mainland China. 2） SDHR occurs most frequently in South China such as southern Yunnan, Guizhou, and Jiangxi provinces, the Sichuan basin, and the lower reaches of the Yangtze River, among others. Some SDHR events with hourly rainfall 50 mm also occur in northern China, e.g., the western Xinjiang and central-eastern Inner Mongolia. The heaviest hourly rainfall is observed over the Hainan Island with the amount reaching over 180 mm. 3） The frequency of the SDHR events is the highest in July, followed by August. Analysis of pentad variations in SDHR reveals that SDHR events are intermittent, with the fourth pentad of July the most active. The frequency of SDHR over mainland China increases slowly with the advent of the East Asian summer monsoon, but decreases rapidly with its withdrawal. 4） The diurnal peak of the SDHR activity occurs in the later afternoon（1600–1700 Beijing Time（BT））, and the secondary peak occurs after midnight（0100–0200 BT） and in the early morning（0700–0800 BT）; whereas the diurnal minimum occurs around late morning till noon（1000–1300 BT）. 5） The diurnal variation of SDHR exhibits generally consistent features with that of the MCSs in China, but the active periods and propagation of SDHR and MCSs difer in diferent regions. The number and duration of local maxima in the diurnal cycles of SDHR and MCSs also vary by region, with single, double, and even multiple peaks in some cases. These variations may be associated with the diferences in large-scale atmospheric circulation, surface conditions, and land-sea distribution.     

青藏高原上中尺度对流系统(MCSs)的个例分析及其比较

对1995年7月25—28日高原上连续数日出现MCSs的现象进行了红外云图特征及其演变、大尺度环境背景场和对流有效位能的分析。可以发现，所有这些MCSs有着相似的日变化演变过程；它们的初始对流在中午由于日射加热开始活跃，之后迅速发展，这些MCSs在后下午形成，在傍晚达到最强，之后逐渐减弱。其中26日MCS最为强大，它是在单一的强大的近于圆形的高原反气旋高压背景下受强的低层热力强迫和条件不稳定的驱动而发生的。这些发生条件都与高原本身的热力作用紧密相关，所以它的发生发展主要与高原特有的较为纯粹的热力因子相联系。28日MCS是另一个很强的MCS，它明显地受到中纬度西风槽的斜压区的影响，这二个很强的MCS有着不同的发展机制和显著不同的表现特征。     

Cloud-to-ground lightning and Mesoscale Convective Systems

This work analyzes some physical and microphysical properties of Mesoscale Convective Systems (MCSs) and cloud-to-ground lightning. Satellite data from the GOES-10 infrared and NOAA-18 and TRMM microwave channels and lightning information from the Brazilian lightning detection network (BrasilDAT) were utilized for the period from 2007 to 2009. Based on an automatic MCSs detection method, 720 MCSs life cycles were identified during the period and in the region of study, with a lightning detection efficiency of over 90%. During the diurnal cycle, maximum electrical activity occurred close to the time of maximum convective cloud fraction (18 UTC), and 3 h after the maximum normalized area expansion rate. Diurnal cycles of both properties were modulated by diurnal heating, and thus could be used to monitor diurnal variability of lightning occurrence. The electrical activity was more intense for the widest (Pearson’s correlation of 0.96) and deeper (Pearson’s correlation of 0.84) clouds, which reached 390 km size and 17 km maximum cloud top height. Area growth during the initial phase of MCSs exerted a strong influence on their size and duration, and thus also showed a potential for defining the possibility of electrical activity during their life cycle. The average lightning life cycle exhibited a maximum close to MCSs maturation, while the maximum average lightning density occurred in the MCSs initial life cycle stage. The growth rate of electrical activity during the early stages can indicate the strength of convection and the possible duration of systems with lightning occurrence. Strong condensation processes and mass flux during the growth phase of the systems can provide favorable conditions for cloud electrification and lightning occurrence. A comparison of high microwave frequencies with lightning data showed a strong relationship of vertically integrated ice content and particle size with lightning occurrence, with Pearson's correlation of 0.86 and 0.96, respectively. The polarization difference in the 85 GHz channel showed that electrical activity increases linearly with polarization reduction, associated with a high value of Pearson's correlation coefficient (above 0.90). This suggests that regions with more intense electrical activity are predominantly located in areas with a high concentration of larger ice particles that are vertically oriented, due to the existence of intense updrafts and the electric field. These results demonstrate the potential use of thermodynamic, dynamic and microphysical characteristics for analyzing thunderstorms severity, and as additional information for nowcasting and monitoring electrical activity over large regions that lack ground-based lightning sensors.