The East-west Difference of Precipitation near the Zonal Shear Line over the Tibetan Plateau in Summer and Its Mechanism

Summer Precipitation over the Tibetan Plateau (TP) exhibits uneven distribution in the east-west direction. The zonal shear line (ZSL) over the TP is the primary synoptic system in summer precipitation, and it is the only synoptic system that can basically span the TP from east to west, having obvious implications for the distribution of summer precipitation over the TP. The existence of the east-west difference of precipitation near ZSL and its underlying mechanism deserves in-depth research. Utilizing hourly ERA5 reanalysis data from 1980 to 2019, a composite study was conducted on 11 cases of ZSL that caused heavy precipitation over the TP from the perspective of the rotational and divergent components of the horizontal atmospheric motion. The results revealed that the precipitation is obviously greater in the eastern section of ZSL (ZSL_ES, east of 88.5°E) than in the western section of ZSL (ZSL_WS, west of 88.5°E). The anticyclonic and divergent intensity of the wind field in the ZSL_ES are obviously stronger than observed in the ZSL_WS at upper levels, the ZSL_ES exhibits a deeper convergence layer, resulting in an upward velocity of the ZSL_ES approximately twice that of the ZSL_WS. The net water vapor income of the whole layer near the ZSL_ES is 7.7 times that of the ZSL_WS, because the water vapor near the ZSL is mainly transported through the Yarlung Zangbu Grand Canyon, and converges on the southern ZSL_ES. The stronger upward velocity lifts more water vapor near ZSL_ES, resulting in notably greater precipitation than that observed in the ZSL_WS.