Journal Article

Thermal Impact of the Southern Tibetan Plateau on the Southeast Asian Summer Monsoon and Modulation by the Tropical Atlantic SST

Zhu, Congwen, Lin, Shuheng, Yang, Song, Wei, Wei, Lu, Mengmeng, Fan, Hanjie, Wang, Junbin

2023

Overview

While it is commonly accepted that the thermal effect of the Tibetan Plateau (TP) strengthens the Asian summer monsoon, a recent analysis based mainly on idealized model experiments revealed that the TP effect weakened the Southeast Asian summer monsoon (SEASM). Based on both observational analyses and model experiments, the current study further deciphers the physical mechanism for the TP’s thermal impact on the SEASM and the modulation of this impact by the sea surface temperature (SST) in the tropical Atlantic. When diabatic heating is enhanced over the southern TP, the South Asian high (SAH) intensifies and extends eastward, leading to convergence over the southeastern flank of the anomalous upper-level anticyclone and sinking motion that cause downward advection of negative vorticity. Accompanied by this anomalous anticyclonic pattern, the western Pacific subtropical high (WPSH) extends westward and the monsoon over Southeast Asia is weakened. The TP–SEASM relationship is enhanced when SST and convection increase over the tropical Atlantic, which cause an anomalous barotropic wave train propagating southeastward from eastern North America to East Asia, leading to an eastward extension of the SAH and a westward extension of the WPSH. The anomalous heating over the tropical Atlantic also modulates the Walker circulation through two anomalous vertical cells, with ascending motions over the Maritime Continent and the eastern tropical Indian Ocean, inducing a lowerlevel anticyclone over Southeast Asia as a Gill-type response. Thus, a warming tropical Atlantic can intensify the TP’s thermal forcing, weaken the SEASM, and then modulate the TP–SEASM relationship through both the extratropical wave train and the tropical zonal circulation.

• Publisher: American Meteorological Society
• Subject: Advection / Anticyclones / Atmospheric models / Barotropic mode / Circulation / Climate / Convection / Design of experiments / Diabatic heating / Heat / Heating / Interannual variability / Modulation / Monsoons / Plateaus / Precipitation / Regions / Sea surface temperature / South Asian High / Summer / Summer monsoon / Temperature effects / Tropical circulation / Variability / Vertical cells / Vorticity / Walker circulation / Wave packets / Wave propagation / Wave trains / Wind / Zonal flow / Zonal flow (meteorology)