An objective method for predicting occurrence of pre-monsoon (March-May) thunderstorm events over Delhi using stability indices

Abstract

In this paper an attempt has been made to investigate different stability indices in relation to the occurrence of thunderstorms in order to determine the critical values of these indices for Delhi (28.35° N / 77.12° E) using pre monsoon data for the years 1999 - 2004. The study shows that the critical values of Showalter Index (SI), Lifted Index (LI), K Index (KI), Total Totals Index (TTI), and Sweat Index (SWI) are respectively < 2 °C, < 0 °C, > 24 °C, > 44.5 °C and > 100 for the thunderstorm to occur over Delhi. The corresponding common critical ranges of Lifted Condensation Level (LCL), Level of Free Convection (LFC), Equilibrium Level (EL) and Precipitable Water (PW) are respectively 923 hPa – 695 hPa, 856 hPa – 504 hPa, 545 hPa – 109 hPa and 18 mm – 54 mm. Testing of critical values of indices and the corresponding common critical ranges of LCL, LFC, EL and PW during pre-monsoon seasons of the years 2005 and 2006 shows that they are matching well with the respective critical values/ranges in most of the thunderstorm days.