Cloud burst over the complex terrain of Sauni Binsar, Uttarakhand: I. Appraisal of collision efficiencies.

Cloudburst events are characterized by very high rainfall rates (100 mm h−1) over a small area (~10×10 km). It catastrophically damages the properties and causes loss of lives. Therefore, it is essential to understand the nature of the microphysical processes that contributed to producing such a high rain rate. Collision processes inside the cloud are vital in determining the rainfall rate. Hence, in the present study, we have evaluated a comparative performance of disparate collision efficiencies based on different formulations during the cloud burst event of 10 June 2021 over Sauni Binsar, Uttarakhand, at 11:45 AM IST (06:15 UTC 10 June 2021). The lifting condensation level (LCL), lifting deposition level (LDL), and lifting freezing levels (LFL) have been calculated using the ERA5 dataset. The collision efficiencies were determined on 100 levels between the lifting condensation and freezing levels. The appraisal of eight formulations shows that Onishi, Beard and Grover, Bohm, and Jin formulations yielded higher collision efficiencies during the cloudburst event, which is expected. Meanwhile, the estimated collision efficiency based on Ahmad's formulation is high for specific bins only. The formulations by Barnet, Long, and Lee and Baik, however, yielded very low values of collision efficiencies during the cloud burst event. Research highlights: Collision processes inside the cloud are vital in determining the rainfall rates especially during cloud burst. Eight collision efficiency formulations have been apprised during the cloud burst event of Sauni Binsar, Uttarakhand, India. The complex interaction between synoptic systems and orography caused atmosphere over Sauni Binsar to be convective and moist few hours before the cloud burst event. Collision efficiency formulation by Onishi, Beard and Grover, Bohm, and Jin estimated higher collision efficiencies, which is appropriate, while Ahmad estimated high values for specific bins only. Collision efficiency formulation by Barnet, Long, and Lee and Baik estimated very low values. [ABSTRACT FROM AUTHOR]