| Abstrakt: |
The collection mechanism inside the cloud is associated with the coalescence process. It controls the rainfall rate in the presence of high moisture content and low cloud condensation nuclei concentrations. The effectiveness of the coalescence mechanism is determined by the magnitude of the coalescence efficiency. This study compared the effectiveness of six coalescence efficiencies to identify the appropriate formulation, which can simulate the cloudburst event of 10 June 2021 over Sauni Binsar, Uttarakhand, at 11:45 IST (06:15 UTC). The coalescence efficiencies have been estimated between the lifting condensation levels and freezing levels over 100 equidistance intervals, with variation in the bins of colliding droplet pairs. The comparative analysis shows that Ochs’s formulation estimated high values of coalescence efficiencies ranging between 60 and 100% for all bins of droplet diameters during the cloudburst event. The maximum values of coalescence efficiency were found to be high for small cloud droplet diameter of 1–100 µm for collector droplet diameter of 50–7000 µm. The estimates provided by Seifert and Chen and Liu were below 80%, while Low and List, Beard and Ochs estimated coalescence efficiency values of up to 70% for all-collector cloud droplet diameters and small cloud droplet diameters. However, the estimated coalescence efficiencies by Brazier–Smith formulation are very low, not exceeding 20%, for all collector cloud droplet diameters and small cloud droplet diameters. The selection of appropriate coalescence parametrization is essential for appropriately simulating rainfall intensities using microphysics parametrization during extreme weather events. Research highlights: The coalescence process plays an important role in determining rain rate, and modelling it is a challenge. Six coalescence efficiencies have been estimated for the cloud burst event of Sauni Binsar, Uttarakhand, India. Ochs’s formulation estimated high values of coalescence efficiencies ranging between 60 and 100% for all bins of droplet diameter, which was expected. Seifert and Chen and Liu formulations estimated coalescence efficiencies below 80%, and Low and List and Beard and Ochs estimated coalescence efficiency up to 70% for the all-collector cloud droplet diameter and small cloud droplet diameter. The estimated coalescence efficiencies by Brazier–Smith formulation are very low, not exceeding 20%. [ABSTRACT FROM AUTHOR] |
