Intraseasonal variation of rainfall characteristics and latent heating profiles during southwest and northeast monsoon seasons over the Arabian Sea and Bay of Bengal

Abstract

Recent studies emphasize the significance of precipitation characteristics at intraseasonal time scales for better predicting the monsoonal rainfall. In this connection, to understand the differences in characteristics of the vertical structure of precipitation during wet and dry spells over the Arabian Sea (AS) and Bay of Bengal (BOB) from the southwest monsoon (SWM) to northeast monsoon (NEM) using 16 years of tropical rainfall measuring mission (TRMM) version#7 datasets. On average, the wet and dry spells durations are more during NEM (> 5 days) than SWM (4 days) over BOB, while the durations are identical (5 days) in all spells over AS. Irrespective of the season, shallow systems' occurrence and rain fraction are more in dry spells than the respective wet spells over AS and BOB. During the dry spells of BOB, both rain fraction and occurrence of stratiform and convective rain decreases while shallow rain increases from SWM to NEM. The increase in shallow systems occurrence results bimodal distribution (3 and 5.5 km) in storm height and reflectivity distributions. During wet spells, for different rain types, the occurrence and rain fraction changes are minimal in both seasons and seas. The prevalence of deeper systems than shallow systems is due to changes in atmospheric background conditions from dry to wet spells. The latent heating distributions are broader during SWM than NEM in both spells of two seas. The observed bimodal distribution of latent heating profiles in the dry spells during SWM and NEM over AS, and only during NEM over BOB results from a higher occurrence of shallow rain in these spells.