长江中游两次MCC过程环境流场及物理条件分析

利用常规气象资料、GFS05°×05°再分析资料以及云图资料，分析了2007年长江中游2例中尺度对流复合体（MCC）的大尺度环境场和物理量特征。结果表明：①MCC是低槽云系尾部由几个β、α中尺度云团合并增强结果，合并是其形成最重要的一个因子；②MCC发生在有利的天气形势背景下，中层有短波槽、低层有冷暖切变线和范围宽广的西南急流带，强盛西南急流给暴雨区提供充足的动力、水汽、不稳定条件。西南暖湿气流维持、边界层暖切变线形成且稳定少动对MCC形成起关键作用，在低层冷切尾部和暖切顶部，干冷与暖湿空气交汇出现锋生导致上升运动加强，激发不稳定能量释放，MCC在此处形成。能量锋生与高空急流右后侧辐散气流耦合可能是导致MCC发展主要动力强迫机制；③MCC环境流场表现为对流层上部为反气旋性辐散环流，中层和低层均为气旋性辐合环流，从低层到中层正涡度柱连成一片，形成深厚垂直正涡度柱，中低层深厚辐合为MCC维持提供了有利动力条件。

Analysis of Environmental and Synoptic Physical Conditions of Two MCC Processes over Middle Reaches of Yangtze River

Based on the conventional data, GFS reanalysisi data, and satellite images of FY 2C, two MCC processes in 2007 are analyzed, with emphasis on the environmental flow and synoptic physical conditions. The results demonstrate： several mseo β and meso α scale cloud clusters intensified and merged, from which the MCCs formed; the MCCs developed in the favorable environmental field, with the trough in the middle layer, the warm cold shear and the broad warm wet airflow in the lower layer. The enhancement of the southwestward warm wet airflow and the formation and maintenance of the warm shear line in the lower layer were the key factors to MCC formation; the joint influencing of cold air and moist warm flow led to energy frontogenesis. The coupling of frontogenesis in lower layer and its associated strong divergence in the right rear of the high level jet were the main dynamical mechanisms of MCC formation. There existed anticyclone divergence flow in the upper layer, and cyclone convergence flow in the middle lower layer, and the vertical vorticity column supplied favorable dynamical mechanism in the rainstorm centre.