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

Study key findings & significance

• The heavy rainfall at intraseasonal timescale is intensified over the northeastern Arabian Sea (AS)

• Increased intraseasonal rainfall is linked to the intensified upward moisture transport by the intraseasonal vertical wind velocity

• The AS warming and poleward movement of low-level jet jointly strengthen the cyclonic wind convergence in the planetary boundary layer

Plain Language Summary

The changes in the spatial distribution of Indian summer monsoon (ISM) rainfall pose significant risks of extreme weather events in the Indian subcontinent and Arabian Peninsula. Monsoon intraseasonal oscillation (MISO) plays a key role in the intraseasonal distribution of the ISM rainfall, and changes in MISO determine the ISM rainfall patterns in the warming climate as well. However, the trend in MISO remains unclear in recent decades. Here, we find that the variance of MISO has an increasing trend from 1982 to 2017 over the northeastern Arabian Sea (AS), accompanied by increasing intraseasonal rainfall. The enhancement in rainfall is mainly nourished by the increasing moisture supply, with a major contribution from the upward moisture advection. The intensified intraseasonal upward motions are mainly responsible for the upward moisture advection, which is excited by the enhanced wind convergence in the planetary boundary layer (PBL) over the northeastern AS. Moreover, the poleward movement of the low-level jet and the acceleration of AS warming jointly lead to the strengthening trend in PBL wind convergence. Thus, the MISO accompanying the intraseasonal rainfall displays an increasing trend over the northeastern AS. The results could assist the understanding and better projections of spatial pattern of rainfall during the ISM.