Simulation of a heavy rainfall event over Chennai in Southeast India using WRF: Sensitivity to microphysics parameterization

Chennai City on the southeast coast of India experienced record heavy rainfall on 1 Dec 2015 during the Northeast Monsoon. In this study, numerical simulations of this event are performed using the Advanced Research and Weather Research and Forecasting (WRF-ARW) model, with a cloud-resolving grid resolution of 1 km. Five simulations are performed to study the model sensitivity to cloud microphysics parameterizations on the heavy rainfall prediction. Model results are compared with the available surface and Doppler weather radar (DWR) observations. Results show that the microphysics significantly influenced the rainfall simulation due to variation in mixing ratios of different hydrometeors and the associated dynamic and thermodynamic parameters. The Thompson scheme, followed by the Morrison scheme captured the location of maximum rainfall, its spatial distribution, and its time of occurrence in close agreement with the observations. All the other schemes simulated the event with lesser intensity and at a later time. Results suggest that the Thomson scheme captured the time evolution of different hydrometeors that led to produce the observed pattern of rainfall both spatially and temporally. It is also found that the Thompson scheme correctly produced high vertical motions associated with high instability, strong mid-level convergence and upper air divergence associated with strong cyclonic vorticity, which led to the observed feature of the intense precipitation over Chennai.