摘要
南海季风试验（SCSMEX）的观测表明，1998年南海北部夏季风爆发（5月16～20日）的主要特征是中尺度对流活动的突然爆发和降水迅速增加。文章通过讨论大尺度背景下中尺度对流活动及降水形成的物理条件，揭示了该时段中尺度对流系统与中尺度雨带形成的可能机制：（1）在季风爆发初期华南及南海北部地区对流层低层较高的假相当位温与对流不稳定性、低层西南风辐合和高层的辐散为该地区的中尺度对流系统的发展提供了有利的大尺度热力与动力条件；来自孟加拉湾与副热带高压西侧的西南气流为南海北部强降水区提供了大量水汽，形成了该区深厚的湿层和强水汽辐合；（2）来自东亚中高纬地区几次冷空气活动是对流活动发生的重要触发机制，其作用是使对流不稳定能量迅速释放和对流活动在大范围地区突然爆发；（3）通过对南海季风试验期间安装在东沙岛和实验3号科学考察船上的双多普勒雷达资料反演的降水量分析表明，活跃的对流在季风槽和相应的风场切变线作用下，不断地组织并形成一些中尺度对流雨带（MCSs）。1998年5月15～19日季风爆发时段内，可观测到约12次中尺度降水过程，它们的生命期为6～10h或更长；（4）南海季风槽与低层切变线的建立以及其中中尺度低涡的产生和发展是中尺度对流系统形成与维持的必要条件。
The summer monsoon onset over the northern South China Sea （SCS） in 1998 （May 16 to 20） was characterized by abrupt onset of meso-scale convective activities and rapid increase of precipitation. The possible mechanism for formation of the meso-scale rain belts was revealed through discussing the physical conditions of occurrence of meso-scale convective system and precipitation under the large-scale background： （1） The high pseudoequivalent potential temperature and convective instability in the lower troposphere, low-level southwesterly confluence and high-level divergence over South China and the northern SCS provided favorable large-scale thermodynamic and dynamic conditions for development of the meso-scale convective systems. The southwest flow from the bay of bengal interacted with that from the subtropical high, which constituted the major moisture channel, thus bringing about deep wet layers and strong moisture confluence; （2） Trigged by two cold troughs from high and mid latitudes, the convective activities over the northern SCS broke out abruptly; （3）Analysis of retrieved precipitation based on the dual-Doppler radar during South China Sea Monsoon Experiment （SCSMEX） indicated that active convection influenced by the monsoon trough and corresponding wind shear line organized and formed continually some meso-scale convective rain belts. During May 15 to 19, about twelve precipitation processes with 6-12 hours life span or more were observed; （4） Under the favorable synoptic conditions, establishment of the monsoon trough and shear line in the low level, as well as occurrence and development of mesoscale low vortex were all necessary conditions for the continuous formation and maintenance of meso-scale convective systems.
出处
《气象学报》
CAS
CSCD
北大核心
2005年第4期431-442,共12页
Acta Meteorologica Sinica
基金
中国科学技术部攀登项目A"南海季风试验"
