The Spatiotemporal and Structural Characteristics of Zonal Shear Line Over the Tibetan Plateau in Boreal Summer

Abstract

The Tibetan Plateau (TP) zonal shear line (TPZSL) is one of the most typical precipitation-producing weather systems over the TP. In this paper, based on ERA-5 reanalysis data and observation data from June to August 1980–2019, TPZSLs are identified by objective identification technologies and then classified in detail. The spatiotemporal distributions and the dynamic and thermodynamic characteristics of TPZSLs are revealed in different subregions of northeast (NE), northwest (NW), southeast (SE) and southwest (SW) TP. Results show that an average of 93 TPZSLs generate each year with a striking diurnal variation: a preferential genesis during afternoon to night and a wee-hours dissipation peak. TPZSLs occur frequently in the range of 76° ~ 103°E, 29° ~ 36°N and are concentrated in the area of 76° ~ 85°E, 32° ~ 35°N in the central and western TP. TPZSLs are mainly oriented in the east–west direction (72.9%), and the majority of TPZSLs remain stationary (58.7%). The horizontal and vertical scales of TPZSLs vary significantly across subregions, with the largest horizontal scale in the SE and the deepest vertical scale in the SW. Except for the southwestern TPZSLs, TPZSLs incline northward with increasing altitude. All TPZSLs at 500 hPa are within areas of positive vorticity; notably, TPZSLs in NW are positioned north to the maximum vorticity centre, while the remaining TPZSLs intersect the centre. TPZSLs in NW, SW and SE are situated within convergence zones where convergence centres are situated at eastern and western ends of these shear lines. Vertically, TPZSLs in the NW and NE are embedded within ascending airflow. Except for those in the northeastern TP, all TPZSLs are located within the high-temperature and high-moisture areas. This research serves as an essential reference for comprehending the genesis and evolutionary processes of TPZSLs.