Sensitivity of Cloud Microphysics on the Simulation of a Monsoon Depression Over the Bay of Bengal

Abstract

In this study, we have examined the role of implicit and explicit representation of cloud microphysics on the simulation of a monsoon depression formed over the Bay of Bengal and the associated rainfall from 0000 UTC of 13 August to 0000 UTC of 17 August 2018 using the Weather Research and Forecast model. Five different WRF model simulations are performed by changing the Cloud Micro Physics (CMP) schemes: WSM6, Goddard, Thompson, Morrison, and Thompson Scheme with Aerosol aware options in both explicit and implicit cloud models. WRF simula15 tions are conducted by initializing the NCEP GFS analysis at 0000 UTC of 13 August 2018 and integrated up to 96-h. The boundary conditions are updated at 6-hourly intervals with the respective GFS forecasts. Our results of sensitivity simulations suggest that the Thompson Scheme with Aerosol aware scheme, followed by Goddard microphysics, captured the features of monsoon depres21 sion and associated rainfall. Microphysics schemes have an influence on the simulation of low level westerly jet, and upper level easterly jet. Implicit and explicit cloud microphysics options are able to reproduce the convection over the west-coast, but the implicit option failed in producing the prolonged convection over the east coast. The comparison of model rainfall with rain-gauge, and satellite merged rainfall estimates reveals that the large scale off-shore precipitation is better captured in CMP with the inclusion of explicit cumulus parameterization. The orographic rainfall over the wind-ward and lee-ward sides of the Eastern and Western Ghats is well predicted in the implicit CMP. The vertical distribution of the hydrometeors and rainfall analysis suggest that the Thompson Scheme with Aerosol aware scheme with the cloud-resolving explicit mode is suitable for simulating the monsoon depressions formed over the Bay of Bengal and the associated heavy rainfall over the east coast of India.