Compound Impacts of Monsoon and Westerlies on Summer Precipitation over Tibetan Plateau

Abstract

Abstract South Asian summer monsoon (SASM) and westerlies are essential to the precipitation over Tibetan Plateau (TP) by transporting water vapor. Based on the latest reanalysis datasets, we investigate the compound mechanisms of SAMS and westerlies influencing summer precipitation over the TP. The results show that the summer precipitation over the TP is mainly modulated by two meridional Rossby wave trains which are linked to the compound impacts of SASM and westerlies over the TP (TPW). When both the SASM and the TPW are stronger, a cyclone over India and an anticyclone over Southeast Asia could jointly enhance the transport of warm and moist airflow to the TP along its southern boundary. Meanwhile, a cyclone over the northwestern TP and an anticyclone over the northeastern TP could induce the southward invasion of cold airflow. Consequently, the convergence of warm and cold airflows can result in more summer precipitation over the southern TP. On the contrary, when both the SASM and the TPW are weaker, a reversed pattern of above wave trains is stimulated, leading to more precipitation over the northeastern TP. Besides, with the stronger SASM and the weaker TPW configurated, anomalous moisture convergence (divergence) and ascending (descending) motion are found over the eastern (western) TP, producing more (less) precipitation over the eastern (western). Contrarily, with the weaker SASM and the stronger TPW configurated, the summer precipitation will be increased over the western TP. Overall, the compound impacts of SASM and TPW on the TP summer precipitation are significantly related to the dynamical processes instead of thermodynamic processes. These findings provide scientific basis and clues for the predictions of summer precipitation over the TP.