Evaluating the Impact of Topography on Initiation of Nor’westers over Eastern India

Pre-monsoon thunderstorms are a common source of natural destruction over eastern India, commonly known as Nor'westors. Meteorologists studied these Nor'westers for more than a century over India. Various studies highlighted that the Chota Nagpur plateau, situated in Jharkhand state, acts as a triggering source for initiating these thunderstorms. The present study attempts to evaluate the topographical variations of the Chota Nagpur plateau for initiating the Nor'westors. The current research simulated ten thunderstorm events over the Kolkata region, West Bengal, by changing the Chota Nagpur plateau's topography (increasing and decreasing along with natural topography). The study uses the Weather Research and Forecasting model (WRF ARW 3.9.1) with a triple nested domain. The innermost domain has a resolution of 3 km across eastern India. The simulated model variables are validated against vertical profiles and surface observations of point locations obtained from the India Meteorological Department's radiosonde and automatic weather station data sets. The model simulations significantly capture the observational (surface and vertical profile) characteristics. Thermodynamic indices obtained from simulations revealed that the plateau's changed (increased/decreased) topography alters the values considerably below/above thresholds for thunderstorms over the region.

Keywords: Thunderstorms; Topography; Numerical Simulation; Thermodynamic Indices