中文摘要：

利用卫星云图Tbb资料、常规观测资料和NCEP／NCAR再分析资料，按照Jirak对中尺度对流系统（MCS）的分类方法，将华南MCS分为MCC（中尺度对流复合体）、PECS（线状或长条状MCS）、MBCCS和MpECS（即β尺度的MCC和β尺度的PECS）4种类型，对华南前汛期MCS的时空变化特征、发生发展的组织形式和天气学背景进行了分析。结果表明：PECS是华南地区MCS的主要发展形式。4—6月MCS的发生个数逐月增多。MCS的日变化呈单峰型，主要集中于下午到上半夜形成，傍晚到半夜之间发展成熟。但具体到不同的4种类型，其日变化特征有一定差异。MCS活动分布特征与地形没有明显对应关系，全区都可有PECS发生。MCS主要以东移为主，其次的移动方向4种不同类型分别略有不同。MCS的发生发展有3种主要天气形势：500hPa槽前西南风场型、850hPa切变线南侧的西南风场型和地面低槽配合的I型；500hPa西北风场型、850hPa切变线型和地面低槽配合的Ⅱ型；500hPa西风槽过境型、850hPa切变线南侧的西南风场型和地面低槽配合的Ⅲ型。孤立发展和合并增长是华南MCS的主要组织发展形式。

英文摘要：

By using infrared satellite imageries, conventional observation data and NCEP/NCAE reanalysis data, mesoscale convective systems （MCSs） over South China during the first rainy season in 2001-2006 were divided into four kinds according to Jirak＇s paper. There are MCC, PECS, MβCCS and MβECS. Then, the spatial and temporal characteristics, the organizing form of evolution and the synoptic background of MCSs were studied. The results show as follows： PECS is the most among the four kinds of MCSs. MCSs increase from April to June. The diurnal variation of MCSs is unimodal and mainly occurs in the afternoon and before midnight, become matured between evening and midnight, and dissipates during the evening to sometime after midnight. But there are some differences in diurnal variation among the four kinds. The occurrence of MCSs almost has nothing to do with terrain. PECS may occur anywhere of the domain. MCSs are mainly eastward, but the direction of secondary movement is slightly different among the four kinds. Three main synoptic patterns are easily brought about on MCSs, which are pattern I （southwest wind ahead of a west trough at 500 hPa, south and southwest wind ahead of a shear at 850 hPa, and a trough at surface）, pattern II （northwest wind at 500 hPa, a shear line at 850 hPa, a trough at surface） and pattern III（a west trough at 500 hPa, south and southwest wind ahead a shear at 850 hPa, a trough at surface）. Independent growth and merger are the important organizing forms of MCSs.