梅雨暴雨与高空急流的统计与动力分析

Statistic and Dynamic Analysis to the Relation between Meiyu Storm and High Level Jet

对1991、1996、1998年梅雨暴雨与高空急流进行了统计与合成分析。结果表明,大尺度环流形势稳定是1991、1998年梅雨期局部降水时间较长的主要原因,1996年环流形势多变,难以在局地长久维持。梅雨暴雨与高空急流关系密切,暴雨多出现在西北风高空急流的右前方或西南风高空急流的右后方。西南风高空急流造成梅雨暴雨的高层辐散场多由经向风辐散形成,西北风高空急流多出现纬向风辐散,当其与南亚高压东部的经向风辐散配合时往往会造成较强的暴雨,1998年这类情况出现最多。南亚高压东北象限的偏北风对雨区南侧季风反环流的形成有重要作用。

Correlation and composite analysis are carried out to reveal the relation between Meiyu storm of 1991,1996,1998 and high level jet in this study. Results show that the stable large-scale circulation pattern is the main reason for lasting local precipitation in 1991 and 1998, and the unstable large-scale circulation pattern makes the precipitation difficult to last long in one place in 1996. It is also found that Meiyu storm has close relation with high level jet. The storm is likely to occur right to where the high level NW jet exits or SW jet enters. The high level divergence field which leads to Meiyu storm under SW jet is mainly composed of meridional wind, and NW jet composed of zonal wind which could lead to storm when working with meridional wind divergence east to the South Asia High together,a situation happening frequently in 1988. Northerly of South Asia High NW quadrant plays an important role in forming of monsoon anti-circulation south to rain zone.