台风“利奇马”远距离暴雨的关键动力因子和水汽来源

Analysis of key dynamical factors and water vapor sources influencing remote heavy rainfall produced by typhoon Lekima

基于地面加密观测、ERA5再分析、ECMWF全球集合预报等多源资料,利用敏感性分析方法、涡度收支诊断方法以及拉格朗日水汽追踪方法,探讨1909号台风“利奇马”造成远距离暴雨的关键动力因子和水汽来源。结果表明,对流层低层短波槽的加深有利于台风远距离降水(Tropical cyclone Remote Precipitation,TRP)区南北两侧的气流共同增强TRP区域内的低层相对涡度,从而增强TRP。尤其相对涡度的散度项是影响TRP增强或减弱的关键作用项。在TRP增强阶段,有利于暴雨增强的正涡度主要由散度项贡献。负的散度项贡献导致相对涡度减小,TRP雨强也随即减弱。在水汽方面,TRP雨强和区域内的水汽含量密切相关。500 hPa上TRP区域内的水汽由局地和台风“利奇马”共同贡献;700 hPa的水汽主要由“利奇马”台风贡献;850 hPa的水汽则由局地和两个台风共同输送,其中台风“罗莎”的贡献更大一些。

This study investigates the primary dynamic forcing factors and sources of water vapor influencing remote heavy rainfall over North China,generated by Typhoon Lekima on August 10,2019.We utilize surface rain gauge data,ERA5 reanalysis data,and ECWMF ensemble forecast data.Ensemble sensitivity analysis reveals that low-level relative vorticity over the remote typhoon precipitation(TRP)area plays a pivotal role as the most significant dynamic factor facilitating TRP.The intensification of low-level relative vorticity closely correlates with the strengthening northerly winds in the northern region,induced by the deepening of the low-level short-wave trough.These winds are jointly related to the reinforcement of low-level southerly winds between the TRP and typhoon precipitation(TP)areas.The divergence term of relative vorticity emerges as the crucial dynamic process governing the periods of TRP strengthening and weakening.During the phase of TRP enhancement,positive vorticity is primarily attributed to positive divergence,while negative divergence leads to the reduction of relative vorticity and the weakening of TRP intensity.At 500 hPa,water vapor in the TRP region mainly originates from the local area and Typhoon Lekima,while 60%of the water vapor at 700 hPa is sourced from Typhoon Lekima.At 850 hPa,40%of the water vapor is contributed by Typhoon Rosa,with the remaining 60%of water vapor being transported from Typhoon Lekima and the local area.