Impact of extremely warm Tibetan Plateau in spring on the rare rainfall anomaly pattern in the regions west and east to Plateau in late summer 2022

Abstract

In late summer 2022, regions to the southwest and southeast of the Tibetan Plateau (TP) suffer historically unusual precipitation since 1979. Precipitation in these two regions shows a distinct dipole pattern during 1979–2022. In this study, the role of spring thermal conditions over TP in inducing such dipole precipitation pattern and its mechanism are investigated. Analysis suggests that warm TP in spring leads to enhanced meridional winds in the western Indian Ocean and migrates the East Asian westerly jet (EAWJ) northward in late summer. The enhanced meridional winds in the western Indian Ocean are conducive to increased precipitation in the region to the southwest of TP. The northward shift of the EAWJ leads to easterly winds anomalies over the research domain. The anomalous easterly winds inhibit water vapor transportation from the Indian Ocean to the region to the southeast of TP and reduce water vapor outputs from the region to the southwest of TP, finally resulting in the opposite change in precipitation. In spring 2022, warming over the TP reaches its highest record since 1979, leading to the northernmost location of the EAWJ in late summer and further inducing the extreme dipole pattern of precipitation anomalies to the southwest and southeast of TP in the following summer of 2022. Meanwhile, the extremely warm TP in spring 2022 drives the northeastward shift of the South Asian high and the northwestward movement of the western Pacific subtropical high, contributing to the overlap of the South Asian high and the western Pacific subtropical high in the vertical direction, which favors anomalous anticyclone and reducing precipitation to the southeast of TP. This study implies the spring thermal condition over TP is of tremendous value in predicting extreme summer precipitation over these regions months in advance.