How South Asian Thunderstorm-Driven Transport Affects the Atmospheric Composition Over the Tibetan Plateau and Stratosphere

Abstract

The Tibetan Plateau (TP) is an important gateway for tropospheric substances enter the stratosphere. South Asia, especially its northwesternmost part, is emerging as a global hotspot for thunderstorms and lightning, driven by dynamic interactions between the orography of the TP and the South Asian Summer Monsoon (SASM). This study used TRMM satellite observations from 1998 to 2013, combined with ERA-5 reanalysis data and the HYSPLIT trajectory model, to comprehensively investigate how thunderstorms in the region impact the atmospheric composition over the TP. The findings reveal that thunderstorms in the region predominantly occur during the SASM. Spatially, these thunderstorms are concentrated along the southern Himalayan front, especially in the westernmost indentation between the TP and the Iranian Plateau, an area also characterized by heavy anthropogenic pollution. By employing the HYSPLIT model to trace transport pathways associated with the thunderstorm, the study demonstrates a clear convergence of pollutants from the South Asia boundary layer into thunderclouds. Furthermore, three principal transport pathways were identified for substances originating from the tops of thunderstorms entering the TP. These pathways are closely linked to the tropospheric westerlies, the anticyclonic circulation of the South Asian High, and processes penetrating the tropopause, accounting for approximately 58%, 33%, and 9% of thunderstorms, respectively. Notably, the impact of these thunderstorm-driven transport processes on the TP and even the lower stratosphere is expected to intensify as thunderstorms become more frequent and pollution levels rise in South Asia due to global warming and local social development.