南支气流对高原低涡移出青藏高原影响的诊断分析

Diagnosis of Effect of Southwesterlies on Tibetan Vortex Moving East

利用NCEP再分析资料对2001年以来移出青藏高原后活动时间长(>48小时)的3次高原低涡在南支气流影响下移出高原的个例,进行了325°K等熵面分析、500hPa水汽输送、涡度平流的诊断分析,得出了南支气流影响高原低涡移出高原的共同特征与差异,给出了南支气流对高原低涡移出高原影响的综合作用的概念模型。丰富了高原低涡东移的认识,为高原低涡洪涝暴雨的预报提供了科学依据。

Tibetan Plateau Vortices （ TPV）, when moving eastward out of the plateau, usually cause catastrophic weather in East China. This study diagnoses the effect of southwesterly wind along the south periphery of Tibetan Plateau （ often called the south branch of the subtropical westerly jet） on three such unique TPVs moving eastward out of the plateau （ with their lifes- pan 〉48 hrs downstream） by means of the 325K isentropic surface, 500 hPa vapor transfer and cyclonic vorticity advection with NCEP reanalysis data. Evidence suggests that i） the TPVs are located on the NE - SW sloping isentropic surface, with southwesterly flows to the east that are reinforced when the TPVs migrate off. The three TPVs are associated with the Tibetan shear, the transverse shear line to the north of Hetao, and the shear at the trough line end. The southwesterly affects more on the former two than the latter one; ii） The TPVs travel faster when the southwesterly is amplified, shifting eastward and vice verse. When close to the southwesterly, the TPV is displaced quickly with it and vice verse; iii） the TPV - associated sothth- westerly is responsible for transporting vast amounts of vapor into the vortex, invigorating rising motion and producing stronger cyclonic vorticity along with its advection inside, a situation favorable for TPV moving out of the tableland and persisting for long （ 〉 48 hr） downstream. These fruits, thus, expands the scope of knowledge of east -traveling TPVs, providing a scientific basis for predicting TPV - related rainstorms and flooding events in the plateau per se and downstream.