The Structure of the Warm Shear-Line Type Jianghuai Meiyu Front and the Mechanism of Its Formation and Maintenance
暖切变型江淮梅雨锋结构及其形成和维持机制

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.