Impacts of northern Tibetan Plateau on East Asian summer rainfall via modulating midlatitude transient eddies

Abstract

AbstractRoles of the Tibetan Plateau (TP) in forming and changing the seasonal Asian climate system have been widely explored. However, little is known about modulation effects of the TP on extratropical transient eddies (TEs) and subsequent synoptic responses of the East Asian rainfall. In this study, the Community Atmosphere Model version 5.1 coupled with a slab ocean model is employed to highlight the important role of the TP in regulating the upper‐tropospheric transient wave train. Comparison between sensitivity experiments with and without the TP shows that the northern TP excites a strong anomalous anticyclone, which shifts the upper‐level East Asian westerly jet northward and helps transfer barotropic and baroclinic energy from the mean flow to the synoptic TE flow. The transient wave train is primarily shifted northward by northern TP and is forced to propagate southeastward along the eastern flank of the TP until reaching eastern China. Before the strengthening of monsoonal southerlies, the TP‐modulated transient wave train cools the troposphere, which decreases the static stability over northern China. Meanwhile, the associated anomalous warm advection induces ascending motion, leading to excessive rainfall by releasing unstable energy as the southerly strengthens. Due to the southeastward propagation of the wave train, anomalous heavy rainfall subsequently appears over eastern China from north to south, which increases day‐to‐day rainfall variation in this region. Additionally, occurrence of this upper‐tropospheric transient wave train associated with low‐level southerly peak is substantially increased by northern TP.