Intensity Evolution of Zonal Shear Line over the Tibetan Plateau in Summer: A Perspective of Divergent and Rotational Kinetic Energies
Xiaohong Bao, Xiuping Yao
Abstract
Abstract Based on the ERA5 reanalysis datasets during 1980–2019, a total of eleven zonal shear lines (ZSLs) that caused heavy precipitation and lasted more than 60 hours over the Tibetan Plateau in summer are selected for composite analysis. By decomposing the kinetic energy ( K ) near the ZSL into divergent and rotational kinetic energies ( K D and K R ) and the kinetic energy of interaction between the divergent wind and the rotational wind ( K RD ), the influence of the rotational and divergent winds on the evolution of the ZSL intensity is investigated from the perspective of K D and K R . The main results are as follows. The ZSL is a comprehensive reflection of rotation and convergence. The intensity evolution of ZSL is essentially synchronized with those of K, K R , and K RD but lags behind K D by about three hours. The enhancement of K is mainly contributed by K R , which is governed by the conversion from K D to K R . Furthermore, the increase in the conversion from K D to K R is controlled by the geostrophic effect term Af, which is determined by the joint enhancement of the zonal rotational and meridional divergent wind components ( u R and v D ). Therefore, the joint enhancement of u R and v D controls the increase of the ZSL intensity, leading to increased precipitation.