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In this study, we propose a hypothesis, supported by numerical model simulations, concerning the role of cloud microphysical processes and aerosols in the invigoration of an extreme rainfall event over Uttarakhand in June 2013. The interactions among dynamics, thermodynamics and microphysical processes and their feedbacks play a vital role in the occurrence of extreme events. To test the proposed hypothesis, Weather Research and Forecasting (WRF) simulations are carried out with three different microphysical schemes (i.e. WDM6, Morrison, and CLR). The role of aerosol indirect effects in the process of invigoration of precipitation is demonstrated with a high-resolution regional model for the extreme event over the foothills of the Himalayas. The extreme event is characterized by the strong north-south tropospheric temperature gradient and strong moisture convergence. Forced uplift beyond the freezing level initiates a precipitation process which involves cloud ice and mixed-phase cloud microphysics and latent heat release; further, it invigorates convection and enhances precipitation. Results pinpoint that the role of microphysical processes are very crucial during such a type of extreme event. Additionally, the result accentuates the importance of aerosols on the deep convective cloud systems which have influence through invigoration and involvement of complex interactions between aerosol, large-scale dynamics and cloud microphysics.

In this study, an attempt has been made to bring out the observational aspects of vertical wind shear in thunderstorms over Minicoy. Case studies of thunderstorm events have been examined to find out the effect of vertical wind shear and instability on strength and longevity of thunderstorms. Role of vertical wind shear in thunderstorms and its mechanism has been explored in this study. Results reveal that for prolonged thunderstorms high and low instability along with moderate to high vertical wind shear (moderate: 0.003 S −1 ≤ vertical wind shear ≤ 0.005 S −1 and high: > 0.005 S −1 ) play a significant role in longevity and strength of thunderstorms. The mechanism of vertical wind shear in thunderstorms was investigated in a few cases of thunderstorm events where the duration of thunderstorm was covered by the radiosonde/rawin ascent observation taken at Minicoy. Empirical model has been developed to classify thunderstorm type and to determine the strength and longevity of thunderstorms. Model validation has been carried out for selected cases. Model could classify thunderstorm type for most of the cases of thunderstorm events over island and coastal stations.