Simulation of Nor'westers using Doppler weather radar wind observations in a mesoscale model

Abstract

Severe thunderstorms form over the Eastern and Northeastern parts of India, i.e., Gangetic West Bengal, Jharkhand, Orissa, Assam and parts of Bihar during the pre-monsoon months (April-May). These storms are known as Nor'wester as they move from Northwest to Southeast. In this study we have made numerical simulations of 10 thunderstorms that formed over the West Bengal region during April-May of 2005 and 2006. Numerical simulations have been carried out using MM5 mesoscale model (at 10 km resolution) using conventional and non-conventional observations from Doppler Weather Radar (DWR) and satellites. Composite characteristics of the Nor'wester have been made based upon the simulations. Results indicate that the Nor'westers occur generally when the CAPE increases above 1500 J Kg -1 . They have updraft speeds up to 3-4 m s -1 , while the downdrafts have magnitudes of about 0.4 - 0.5 m s -1 . The updrafts can extend up to 8-9 km altitudes. The total amount of hydrometeors simulated inside the Nor'westers is up to 600-800 mg kg -1 . Large amount of ice and snow exist at upper levels, while liquid water is present in the lower levels. The magnitudes of the ice, snow and liquid water depend on the stage of their life cycle.