Influence of Different Development Periods of the Strong and Weak South Asian Monsoon on the Vertical Circulation over the Qinghai-Xizang （Tibetan） Plateau

Abstract

In order to explore the role of the changes in the strength and weakness of the South Asian monsoon on the vertical circulation of the Qinghai-Xizang （Tibetan） Plateau， the South Asian monsoon index WYI was calculated using the high-resolution JRA55 reanalysis data for the past 30 years from 1990 to 2019 and the strong and weak years of the South Asian monsoon were selected， and the effects of the changes in the strength and weakness of the South Asian monsoon on the vertical circulation of the Qinghai-Xizang （Tibetan） Plateau were analyzed by comparing the three different periods of the pre-monsoon outbreak， outbreak period and late outbreak.The following main conclusions were obtained： （1） The strength and extent of updrafts on the southern side of the plateau in May in WYI strong years are greater than in weak years， the intensity of updrafts on the main and southern sides of the plateau increases in July， and the difference between strong and weak years is not obvious.（2） In May and October， both mass and energy converge to the plateau from the south and north sides of the plateau， while in July， it turns to dissipate mass and energy from the plateau to the north and south sides.the intensity of the upper-level radiation dispersion in the south side of the plateau in the WYI strong year is greater than that in the weak year， and the difference of the irradiation intensity in the lower level is smaller.The difference in the intensity of energy and mass transfer between WYI strong and weak years is greatest in May and least in July.（3） In the WYI strong year， the 100 hPa South Asian high pressure shifts to the western type in October， and the 500 hPa West Pacific subalpine lifts northward， so the wind field on the southern side of the plateau shifts and raises the high altitude temperature， while in the WYI weak year this phenomenon occurs in May， indicating that the South Asian monsoon changes the horizontal circulation situation at high altitude and thus affects the vertical circulation of the plateau.The surface temperature of the main body of the plateau in May， July and October in WYI strong years is greater than that in weak years， indicating that under the influence of the warm and humid airflow brought by the South Asian monsoon， the updraft from the southern side of the plateau lifts to the plateau， and the surface temperature of the plateau increases significantly， and the surface heat of the plateau increases which in turn affects the vertical circulation of the plateau.

Keywords

• qinghai-xizang （tibetan） plateau
• monsoon index
• vertical circulation
• stream function
• mass flow function