Atmospheric drivers of post-monsoon and winter thunderstorms in Central India

The rise in frequency of severe weather events cause significant socio-economic challenges in the Indian sub-continent. Understanding the causative mechanisms driving these heavy rainfall events is still unclear. Using the state-of-the-art C-band Doppler weather radar at Bhopal and reanalysis data, this study explored the storm-scale characteristics and the driving mechanisms of thunderstorms that occurred on 17 October 2021 (post-monsoon thunderstorm) and 06 January 2022 (winter thunderstorm) over Central India. The radar reflectivity exceeds 45 dBZ, indicating intense convection during thunderstorms. The thunderstorm associated with post-monsoon season is deeper (top heights beyond 12 km) compared to winter thunderstorm. The disdrometer observations showed that the winter thunderstorm is very intense reaching upto 158 mm/h with a short duration of about 30-min. Among the two thunderstorms, the post-monsoon thunderstorm is associated with a mesoscale convective system. The atmospheric water vapour transport from the surrounding oceans (Bay of Bengal and Arabian Sea) is a potential contributor to moisture advection. However, the vertical extent of the storm is regulated by the moistening of midtroposphere prior to the thunderstorm. The cyclonic circulation induced by the low-pressure system plays a major role in the vertical development of the thunderstorm during post-monsoon season. In contrast, the horizontal mass convergence between cold air from high latitudes and warm, moist air from the Bay of Bengal is the key to thunderstorm development for the winter case. The present findings would have profound significance in improving the simulations of these heavy rainfall events by the regional climate models.