Analysis of Water Vapor Transport Characteristics during Persistent Heavy Rainfall in Xizang in the Midsummer of 2021

Bianma Luobu; Xire Luzhu; Zhaxi Dunzhu; Luosang Zhaxi

doi:10.3969/j.issn.1004-3403.2024.10.005

Abstract：Based on the NCEP and ERA5 reanalysis data,the large-scale circulation background and water vapor transport characteristics of the persistent heavy rainfall weather process from July 8 to 11,2021 were first analyzed,and then the NOAA trajectory model HYSPLIT was introduced to quantitatively analyze the water vapor transport characteristics of heavy precipitation.The results indicate that(1)This persistent heavy rainfall is mainly caused by changes of the 500 hPa plateau shear line and the position of the subtropical high pressure.A stable high and low alti-tude influence system is conducive to the formation of continuous precipitation,and the warm and humid airflow in the south and the dry and cold airflow in the north continue to converge in the heavy rainfall area.After 10 days,the southerly airflow over 700 hPa at a low altitude guided the water vapor from the Bay of Bengal northward to the southeastern part of the plateau,which formed convective rainfall due to the special topographic amplification,which was also an important reason for the persistence of heavy precipitation in Xizang.(2)The backtracking and clustering of water vapor trajectories showed that the main source of water vapor leading to heavy precipitation in Xi-zang were formed from the Arabian Sea and the Bay of Bengal,then a part formed by the special topography near the plateau or locally,and a last part of the water vapor traveled south to the plateau with cold air from the north.(3)Ac-cording to the analysis of water vapor flux in each layer,it was found that the main sources of water vapor at 700hPa were near Somalia in Africa and the western Pacific Ocean;the main sources of water vapor at 600 hPa were the ocean surface of southern Indian and the western Pacific Ocean;and the main sources of water vapor at 500 hPa were the ocean near India and the western Pacific Ocean.The water vapor flux weakened significantly from the lower layer(700 hPa and 600 hPa)to the upper plateau,and there was obvious vertical water vapor in the middle layer(500 hPa)transported to the east and south,which also provided sufficient water vapor for the persistent heavy precipitation.