A Comparative Study of the Atmospheric Layers below First Lifting Condensation Level for Instantaneous Pre-Monsoon Thunderstorm Occurrence at Agartala (23o30’N, 91o15’E) and Ranchi (23o14’N, 85o14’E) of India

An attempt has been made to investigate the role of vertical wind shear, corrective instability and the thermodynamic parameter (θes - θe) below the first lifting condensation level (FLCL) in the occurrence of instanta-neous premonsoon thunderstorm over Agartala (AGT) and Ranchi (RNC) at 12 GMT Radiosonde data of 1988 have been utilized here. The study has however been confined to 1000 hPa-500 hPa range at most Here the convectively unstable layers with positive vertical wind shear upto 500 hPa have been termed as ‘Fa?vourable Layers’ (FL) and the level at which an initially stable layer turns out to be convectively unstable for the first time has been termed as ‘Transition Level’ (TL). It is observed that the changes in vertical wind shear are positive at TL at the time of occurrence of thunderstorm (TS) and the corresponding change is negative on fair-weather situa?tion Moreover, the 90% confidence interval for (θes - θe) reveals that for AGT the upper layer thermodynamic characteristic is important at the time of occurrence of TS whereas for RNC, the value of (θes - θe) at the surface is much more effective