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

Abstract

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 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 enhances 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 lower-level anticyclone over Southeast Asia as a Gill-type response. Thus, a warming tropical Atlantic can intensify 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.

Impact of Thermal Forcing over the Southeast of the Tibetan Plateau on Frequency of Tropical Cyclones Affecting Guangxi during Boreal Summer

“…In addition, some studies also confirmed the relationship between rainfall over southern TP and wave trains at mid-latitudes [28,51]. Lu et al [52] showed that the relationship between summer precipitation over the southern TP and Southeast Asian summer monsoon is enhanced when the SST and convection increase over the tropical Atlantic. How the Atlantic SST or mid-latitude wave train affects Guangxi TCs or the Guangxi TC-RSTP relationship will be further discussed in future work.…”

Enhanced Impacts of ENSO on the Southeast Asian Summer Monsoon Under Global Warming and Associated Mechanisms

“…The Southeast Asian summer monsoon (SEASM), also referred to as the western North Pacific (WNP) monsoon, is an important component of the Asian monsoon system; it has received tremendous attention in the climate research community due to its considerable impacts on both social economy and climate of East Asia (e.g., Lau & Yang, 1997; Lee et al., 2011; Z. Li et al., 2016; M. Lu et al., 2021, 2023; Qian & Yang, 2000; Wang et al., 2001; S. Yang & Lau, 2006). The SEASM usually commences in mid‐May and exists until October, with a main domain around 120°–160°E, 10°–22°N of the WNP region (Lau & Yang, 1997; T. Li & Wang, 2005; Wang & Fan, 1999; Wang & Lin, 2002).…”

Assessing the Regional Climate Response to Different Hengduan Mountains Geometries With a High‐Resolution Regional Climate Model

“…Both data diagnosis and numerical experiments have exhibited that the topography affects the downstream EASM through mid‐latitude Rossby wave propagation and air‐sea interaction (KOSEKI et al., 2008; Duan et al., 2011; Y. Liu et al., 2020; M. Lu et al., 2023; Y. Zhang et al., 2004; Zhao & Chen, 2001). B. Wang et al.…”