Causes and Analysis on Heavy Precipitation in Xizang Induced by the Storm"Sitrang"in the Bay of Bengal

Gongga; Yu Yanqun; Danzeng Wangdui

doi:10.3969/j.issn.1004-3403.2025.05.006

Abstract：The causes of rainstorms and snowstorms as well as characteristics of moist potential vorticity(MPV)during the impact of tropical storm"Sitrang"in the Bay of Bengal on Xizang in October,2022 were analyzed by us-ing conventional observation data,ground-based encrypted data and reanalysis data ERA-5.The results showed that the heavy precipitation weather during the impact of"Sitrang"was caused by the interaction of its peripheral circula-tion,cold air from the north,branch trough in the south and damp-warm air from the southwest.Diagnostic analysis on the physical quantity fields and MPV during the impact of"Sitrang"revealed that the establishment and strength-ening of low-level and low-altitude rapids were conducive to the water-vapor transport in south Xizang.Strong water-vapor convergence centers corresponded to strong precipitation centers,and convergence center movement was in-dicative of the changes in precipitation centers.When strong vertical uplift motion corresponded to unstable high-en-ergy θse zones,precipitation intensity increased,conducive to the occurrence of rainstorms and snowstorms.The un-stable high-energy zones and strong vertical uplift motion zones had a relatively good correspondence with the rain-storm and snowstorm occurrence zones.During the occurrence of rainstorms and snowstorms,MPV1＜0 at 500hpa and MPV2＞0 was simutaneously satisfied.In the wet troposphere upper level,MPV1＞0,and in the lower level,MPV1＜0.The stronger the center was,the more frequently high MPV value was transmitted downward in the up-per troposphere with increasing instability,leading to the weakening of atmospheric stability at the bottom of the tro-posphere,which in turn triggered the release of convective instable energy,conducive to the formation and develop-ment of rainstorms and snowstorms.The centers of rainstorms and snowstorms occured beneath the positive and nega-tive MPV columnsat high and low altitudes.