Numerical simulation of a tornado over Ludhiana (India) using WRF-NMM model

Abstract

A severe thunderstorm produced a tornado (F0 on the Fujita-Pearson scale) close to Ludhiana airport (Punjab), northwest region of India (30.80°N, 76.05°E) on 15 August 2007. Relatively less damage occurred as it passed through the open fields, but there were minor injuries to some cattle and damage to property. In this paper, analysis of meteorological conditions that led to the tornado on 15 August 2007 at 1100 UTC in Ludhiana has been made. An attempt is also made to simulate this rare event using the Non-hydrostatic Mesoscale Model (NMM) core of the Weather Research and Forecasting (WRF) system with a spatial resolution of 3 km for a period of 24 h, starting at 0000 UTC of 15 August 2007. The results are encouraging in terms of timing and location of occurrence of the event. The atmospheric settings as indicated by surface, upper air and radar echo studies are favourable for severe thunderstorm activity over Ludhiana. The simulated instability indices (lifted index, total totals index and CAPE) over Ludhiana during the tornado hour, which act as indicators of severe convective activity, have been found to be in good agreement with the actual analysis. The model-simulated meteorological parameters, relative humidity, mean sea level pressure, rainfall, moisture convergence, pressure vertical velocity and surface wind speed, are favourable for tornado occurrence at 1100 UTC over Ludhiana, and agree reasonably well with the observations.