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On the Influence of the Bay of Bengal's Sea Surface Temperature Gradients on Rainfall of the South Asian Monsoon

Sheehan, PMF and Matthews, AJ and Webber, BGM and Sanchez-Franks, A and Klingaman, NP and Vinayachandran, PN (2023) On the Influence of the Bay of Bengal's Sea Surface Temperature Gradients on Rainfall of the South Asian Monsoon. In: Journal of Climate, 36 (18). pp. 6499-6513.

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The southwest monsoon delivers over 70 of India's annual rainfall and is crucial to the success of agriculture across much of South Asia. Monsoon precipitation is known to be sensitive to sea surface temperature (SST) in the Bay of Bengal (BoB). Here, we use a configuration of the Unified Model of the Met Office coupled to an ocean mixed layer model to investigate the role of upper-ocean features in the BoB on southwest monsoon precipitation. We focus on the pronounced zonal and meridional SST gradients characteristic of the BoB; the zonal gradient in particular has an as-yet unknown effect on monsoon rainfall. We find that the zonal SST gradient is responsible for a 50 decrease in rainfall over the southern BoB (approximately 5 mm day21), and a 50 increase in rainfall over Bangladesh and northern India (approximately 1 mm day21). This increase is remotely forced by a strengthening of the monsoon Hadley circulation. The meridional SST gradient acts to decrease precipitation over the BoB itself, similarly to the zonal SST gradient, but does not have comparable effects over land. The impacts of barrier layers and high-salinity subsurface water are also investigated, but neither has significant effects on monsoon precipitation in this model; the influence of barrier layers on precipitation is felt in the months after the southwest monsoon. Models should accurately represent oceanic processes that directly influence BoB SST, such as the BoB cold pool, in order to faithfully represent monsoon rainfall. © 2023 American Meteorological Society.

Item Type: Journal Article
Publication: Journal of Climate
Publisher: American Meteorological Society
Additional Information: The copyright for this article belongs to the authors.
Keywords: Atmospheric temperature; Atmospheric thermodynamics; Oceanography; Rain; Submarine geophysics; Surface waters, Atmosphere-ocean interactions; Bay of Bengal; General circulation model; Indian ocean; Monsoon; Sea surface temperature; Sea Surface Temperature gradients; Sea surfaces; Southwest monsoon; Surface temperatures, Surface temperature, air-sea interaction; atmosphere-ocean coupling; general circulation model; Hadley cell; marine atmosphere; mixed layer; monsoon; rainfall; sea surface temperature; temperature effect; temperature gradient, Bangladesh; Bay of Bengal; India; Indian Ocean; Indian Ocean
Department/Centre: Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited: 24 Nov 2023 05:31
Last Modified: 24 Nov 2023 05:31
URI: https://eprints.iisc.ac.in/id/eprint/83238

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