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

• Published in: Journal of geophysical research. Oceans 2020-06, Vol.125 (6), p.n/a
• Main Authors: Subrahmanyam, Bulusu, Roman‐Stork, Heather L., Murty, V. S. N.
• Format: Article
• Language: English
• Subjects: Amplitude; Amplitudes; Atmospheric models; Atmospheric oscillations; Bay of Bengal; Computer simulation; Convergence and divergence; Drought; Eddies; Flooding; Floods; Freshwater; Geophysics; Inland water environment; Intraseasonal oscillation; Mesoscale eddies; Mixed layer; Monsoon rainfall; Monsoon trough; Monsoons; NEMO; Ocean circulation; Ocean currents; Ocean models; Oceans; Oscillations; Rain; Rainfall; Salinity; Salinity effects; Salinity stratification; Satellite observation; Satellites; Sea surface; sea surface height; Seasons; Southwest monsoon; Stress propagation; synotic oscillations; Temperature; Thermocline; Variability; Water circulation; Water column; Wind; Wind oscillations; Wind stress
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2020JC016200

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. Plain Language Summary Intraseasonal oscillations in the Bay of Bengal significantly influence the variability and strength of rainfall associated with the southwest monsoon. The 3‐7‐day synoptic oscillations associated with oscillations in the monsoon trough and low‐pressure systems directly impact the strength and timing of the active (flood) and break (drought) periods of the monsoon. Even during weak or normal monsoon seasons, there can still be significant flooding due to these 3‐7‐day synoptic oscillations. This research explores the variability of these 3‐7‐day synoptic oscillations during the strong 2019 southwest monsoon and their impact in the Bay of Bengal. Monsoon rainfall over central India is found to be significantly influenced by the 3‐7‐day synoptic oscillations, while southern India rainfall was more dominantly controlled by 10‐20 and 30‐90‐day intraseasonal oscillations. We find that strong 3‐7‐day synoptic oscillations in wind stress ove