Mechanisms and Impacts of South Asian Thunderstorm-Driven Transport on the Atmospheric Composition over the Tibetan Plateau and Stratosphere

The Qinghai-Tibet Plateau (TP), the world's highest and most complex plateau, serves as a critical gateway for tropospheric substances entering the stratosphere. Northwestern South Asia, particularly the region encompassing the steep terrain of the westernmost indentation between the TP and the Iranian Plateau, is a global hotspot for frequent and energetic convective storms. Therefore, it is vital to investigate how these thunderstorms impact the atmospheric composition over the pristine TP, especially for short-lived species. Using TRMM satellite observations (1998-2013), ERA-5 reanalysis data, and the HYSPLIT trajectory model, this study comprehensively examines the transport mechanisms associated with these storms. Our findings reveal that thunderstorms predominantly occur during the SASM and are concentrated along the southern Himalayan front. 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, we identify three principal transport pathways for substances from thunderstorm tops into the TP atmosphere, closely linked to larger-scale circulations: (1) the tropospheric westerlies (~58% of cases), (2) the anticyclonic circulation of the South Asian High (~33%), and (3) tropopause-penetrating processes (~9%). These results clarify the mechanisms—primarily associated with westerlies and the South Asian High—through which intense South Asian thunderstorms influence the TP. The impact of this thunderstorm-driven transport on the TP and the lower stratosphere is projected to intensify with increasing thunderstorm frequency and pollution levels in South Asia under global warming and continued local development.