Analysis of stability parameters in relation to precipitation associated with pre-monsoon thunderstorms over Kolkata, India

Abstract

The upper air RS/RW (Radio Sonde/Radio Wind) observations at Kolkata (22.65N, 88.45E) during premonsoon season March-May, 2005-2012 is used to compute some important dynamic/thermodynamic parameters and are analysed in relation to the precipitation associated with the thunderstorms over Kolkata, India. For this purpose, the pre-monsoon thunderstorms are classified as light precipitation (LP), moderate precipitation (MP) and heavy precipitation (HP) thunderstorms based on the magnitude of associated precipitation. Richardson number in non-uniformly saturated (Ri *) and saturated atmosphere (Ri); vertical shear of horizontal wind in 0-3, 0-6 and 3-7 km atmospheric layers; energy-helicity index (EHI) and vorticity generation parameter (VGP) are considered for the analysis. The instability measured in terms of Richardson number in non-uniformly saturated atmosphere (Ri *) well indicate the occurrence of thunderstorms about 2 hours in advance. Moderate vertical wind shear in lower troposphere (0-3 km) and weak shear in middle troposphere (3-7 km) leads to heavy precipitation thunderstorms. The wind shear in 3-7 km atmospheric layers, EHI and VGP are good predictors of precipitation associated with thunderstorm. Lower tropospheric wind shear and Richardson number is a poor discriminator of the three classified thunderstorms. © Indian Academy of Sciences.