Increase in Intraseasonal Rainfall Driven by the Arabian Sea Warming in Recent Decades

Abstract

AbstractIntraseasonal oscillation (ISO) is the dominant variability during the Indian summer monsoon (ISM). In this study, it is found that ISOs accompanying intraseasonal rainfall are substantially enhanced over the northeastern Arabian Sea (AS) in the past three decades. The rise in rainfall agrees with the variation in moisture loading. The strengthening of the wind convergence in the planetary boundary layer (PBL) triggers the changes in vertical velocity, intensifying the advection of background moisture by the intraseasonal vertical velocity, which contributes the most to intensified moisture supply over the northeastern AS. In addition, the faster warming of the AS and the increasing cyclonic vorticity associated with the poleward movement of the summer mean low‐level jet are responsible for the increasing trend in PBL convergence. This recent intensified intraseasonal rainfall over the AS has contributed to the trend in the mean and extremes over the central‐western parts of the Indian subcontinent.