Response of the Bay of Bengal to 3-7-Day Synoptic Oscillations During the Southwest Monsoon of 2019

Abstract

The satellite-derived precipitation over central India (73-78�E, 20-25�N) during the 2019 southwest monsoon season reveals that high-amplitude 3-7-day synoptic oscillations dominated the other intraseasonal oscillations and contributed to the excess seasonal monsoon rainfall. In this paper, we address the contribution of 3-7-day synoptic oscillations in atmospheric and oceanic parameters during the 2019 southwest monsoon season over the Bay of Bengal (BoB). Our study reveals that both satellite observations and the Nucleus for European Modeling of the Ocean (NEMO) model simulations show high-amplitude 3-7-day synoptic scale events during the 2019 monsoon. The upper 300 m of the water column responds to the basin-scale 3-7-day synoptic oscillations as revealed in the vertical structures of NEMO model simulated temperature, salinity, and currents in the BoB. The synoptic scale wind stress drives strong currents in the shallow mixed layer due to salinity stratification in the northern BoB. The northward propagation of the synoptic scale oscillations is evident across the BoB but is capped to the base of the mixed layer, above which the propagation is affected by wind stress and the spread of freshwater flux. The 3-7-day synoptic scale oscillations in NEMO sea surface height appear to be related to synoptic scale wind-driven convergence and divergence of waters through mesoscale eddy circulations that in turn contribute to thermocline variability, rather than the temperature and salinity in the mixed layer