Study of rain episode in the desert region of the Indian summer monsoon trough

A rain episode over the desert region of the summer monsoon trough during the period 1–4 July 1990 is discussed in the study. The fine structure observations of this unique event reveal that the atmosphere was hot like that of over a desert, but very moist like the monsoon air mass with specific humidity, constant or even increasing with height in the planetary boundary layer. A cold core by adiabatic cooling from vertical advection, abrupt increase of specific humidity and latent heat flux as the disturbance moved in, are some of the features noticed. The equivalent potential temperature surface was found to be raised at all levels above the surface with virtually no overturning, like that of tropical cyclones. The role of the turbulent eddies in the surface layer in destroying the moisture gradients within and making it homogeneous during pre-rain period and pumping out moisture during rain-episode are highlighted. A study into analysis of such anomalies over the past several years, and follow up through numerical modelling is suggested.