暖切变型江淮梅雨锋结构及其形成和维持机制

The Structure of the Warm Shear-Line Type Jianghuai Meiyu Front and the Mechanism of Its Formation and Maintenance

对在１９９１年７月上旬特别稳定的梅雨形势下持续１０天的特大暴雨期作了合成和典型过程研究，并进一步探讨了暖切变型江淮梅雨锋天气系统模型。它在自由大气层表现为结构竖立的相当正压切变线和一种不同于经典地转动量近似的带状准二维运动场．边界层的浅层锋生倾斜环流以及偏于切变线轴以南的Ｅｋｍａｎ抽吸与自由大气层中基本上由积云对流加热驱动的竖直环流相互依存和耦合，造成持续的大暴雨。这种系统的初生和中断后复苏的机制可能是由斜压性极弱的副热带高空东移的短波扰动在低层“湿度锋”带紧南侧触发导致的一种带状ＣＩＳＫ。

A ten-day continued extremely heaVy rain process with the especially steady Meiyu drculation patterns in early July 1991 is studied by both compositive analysis and representative daily casestudy. The synoptic model of warm shear-line type Meiyu front is further discussed. Anequivalentbarotropic shear line of upright structure and a banded quasitwo-dimensional motion field,which is different from the geostrophic momentum approximation one in free atmosphere are found. Ashallow slant-wise frontogenetic circulation and the Ekman pumping to the south of the shear line inthe boundary layer are coupled with and interacting with the cumulus convective heating-driven upright circulation in the free atmosphere and result in the continuous heavy rain, The mechanism of genesis and recovery after the break of such a system is probably a kind of banded CISK,which is triggeredto the south of the low-level 'moisture front' by the upper east travelling short-wave disturbance ofvery weak baroclinity in subtropics.