Diurnal variation of deep convective clouds over Indian monsoon region and its association with rainfall

Abstract Diurnal cycle of deep convective clouds (DCC) over the Indian Summer Monsoon Region is studied. A harmonic analysis has been applied on the 3 hourly deep convective cloud fraction estimated from satellite observations to derive diurnal and semi-diurnal amplitudes of deep convective clouds. The daily cycle of deep convective clouds shows seasonal variations and amplitudes which are stronger during the northern hemispheric summer than winter and exhibits prominence over land as compared to ocean. Irrespective of seasons, deep convection peaks in the late evening hours over land whereas the peak is in the afternoon hours over majority of the oceanic regions considered in our study. The reason for the difference is attributed to the semi-diurnal oscillation which determine the oceanic diurnal cycle of deep convection. Various parameters which represent the tropospheric instability are equally affected by the semi-diurnal oscillation as in deep convective clouds over ocean. These results suggest that diurnal tides could play a key role in governing the daily cycle of deep convective clouds over oceanic regions. The relation between diurnal amplitudes of DCC and rainfall is also explored and it is shown that the strength of the daily cycle of DCC has a strong bearing on the amount of rainfall observed over the Indian summer monsoon region.