2017年1月上旬泰国南部暴雨反复发生机制的研究

基于0.25°×0.25°的CMORPH日降水量产品以及ECMWF 0.25°×0.25°的ERA5再分析数据,本文对2017年1月上旬泰国南部反复发生暴雨事件的机制进行了研究,这些暴雨事件造成了Ko Samui和Ko Phangan近三十多年来最强的洪水事件。结果表明,初生于中南半岛西南方,向东北方向移动的一个中尺度涡旋是泰国南部重复发生暴雨事件的直接原因。涡度收支分析表明,水平辐合项是这个中尺度涡旋维持的最有利因子,倾斜项是第二有利的因子,而水平和垂直输送则主要造成了涡旋三维空间范围内正涡度向外的净输出,这是不利于涡旋维持的。进一步的分析表明,倾斜项与垂直涡度输送项分别对涡旋的移动及涡旋周边对流层低层的涡度增长较为敏感,这两个作用项在涡旋维持的两个不同阶段内各自表现出了完全不同的作用。

Mechanisms accounting for the repeated occurrence of torrential rainfall over South Thailand in early January 2017

Based on CMORPH precipitation estimates and ERA5 reanalysis data,this study investigates the mechanisms accounting for the repeated occurrence of torrential rainfall over South Thailand in early January 2017,which induced the strongest floods over Ko Samui and Ko Phangan in the last almost 30 years.It is found that the maintenance of a northeastward-moving mesoscale vortex that formed southwest of the Indochina Peninsula was the direct reason for the series of torrential rainfall events.Analysis of the vorticity budget illustrates that convergence-related horizontal shrinking was the most favorable factor for the maintenance of the vortex.Tilting was the second most favorable factor,whereas horizontal and vertical transport mainly caused a net export of cyclonic vorticity from the vortex’s three-dimensional range,which was detrimental for its maintenance.Further analysis indicates that tilting and vertical vorticity transport were sensitive to the vortex’s displacement and the enhancement of cyclonic vorticity at lower levels around the vortex,respectively,as the two factors showed completely different effects on the persistence of the vortex during two different stages.