进入杭州湾的两个台风降水特征及成因分析

本文利用FY-4A红外云图和ERA5再分析等资料对"云雀"和"温比亚"两个台风的强降水进行诊断分析。结果表明:"云雀"影响华东期间,西太平洋副热带高压(WPSH)不断加强西伸,台风路径右侧辐散环流维持,台风中心附近垂直风切变指向偏西方向,导致强降水始终集中在台风路径左侧。"温比亚"登陆前,台风中心附近垂直风切变指向西北方向,台风左侧垂直速度强于右侧,有利于强降水发生在台风路径左侧。"温比亚"登陆后,垂直风切变转为指向东北方向,台风右侧垂直速度强于左侧,有利于强降水发生在台风路径右侧。进一步分析指出,"云雀"登陆时期的垂直风切变和WPSH南侧偏东风气流有关;而"温比亚"登陆后WPSH减弱东退和中高纬高空脊东移,垂直风切变指向变化和高空脊后部的西南气流有关。

Precipitation distributions and possible mechanisms of tropical cyclones entering in Hangzhou Bay

The asymmetric feature and possible mechanism of tropical cyclone precipitation of Jongdari (1812) and Rumbia (1818) were diagnosed by using merged grid precipitation data from CMA, FY-4A imagine, and ERA5 reanalysis dataset. Results show that during the affecting period of Jongdari (1810) in eastern China, the enhanced divergence flow at lower level associated with continuously westwards of Western Pacific Subtropical High (WPSH), as well as the westward direction of wind shear favored the asymmetric precipitation on the left side of Jongdari during the whole period. The vertical shear of ambient wind pointed northwest before landfall, and turned southeast after landfall of Rumbia, which favor the transition of asymmetric circulation and precipitation. Further analyses show the relation between wind shear and deep circulation of WPSH during the period the Jongdari, while an eastward migration of upper high ridge at mid-high latitudes play important role in the transition of wind shear during the period the Rumbia.