Importance of Seasonally Evolving Near-Surface Salinity Stratification on Mixed Layer Heat Budget During Summer Monsoon Intraseasonal Oscillation in the Northern Bay of Bengal in 2019

Sherin, VR and Girishkumar, MS and Shivaprasad, S and Sureshkumar, N and Farrar, JT and Athulya, K and Ashin, K and Rama Rao, EP and Sengupta, D and Venkatesan, R and Ravichandran, M (2023) Importance of Seasonally Evolving Near-Surface Salinity Stratification on Mixed Layer Heat Budget During Summer Monsoon Intraseasonal Oscillation in the Northern Bay of Bengal in 2019. In: Journal of Geophysical Research: Oceans, 128 (11).

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Abstract

The discharge of freshwater from major rivers into the northern Bay of Bengal (BoB) increases dramatically during the summer monsoon season, reaching a peak in August�September, and there is a corresponding increase in the vertical salinity gradient in the upper ocean. Here we study the impact of seasonally evolving near-surface salinity stratification on the response of ocean mixed layer temperature (MLT) to Summer Monsoon Intraseasonal Oscillations (MISO), using accurate surface fluxes and high vertical resolution (�2 m) hydrographic measurements from a mooring in the northern BoB (17.8°N, 89.5°E) during June�September 2019. Prominent MLT warming and cooling with a range of 1.5°C is observed between suppressed (clear skies, calm winds) and active (cloudy, windy) phases of MISO convection. However, the intraseasonal MLT response to the active phase of a late-season MISO event is minimal compared to MISO events in early summer. We infer this is primarily due to the much smaller contribution from oceanic vertical processes (�6 Wm�2) in late summer 2019, compared to their role in early summer (�15 to �55 Wm�2). During the active phase of the MISO event of late summer 2019, the combined effect of reduced entrainment and weak vertical temperature gradients associated with a barrier layer inhibits near-surface cooling. Conversely, the near-surface salinity stratification and the barrier layer are weak during MISO events in the early summer of 2019�these hydrographic conditions lead to enhanced MLT cooling in response to MISO, apparently through a freer turbulent exchange of cool thermocline water with the surface layer. © 2023. American Geophysical Union. All Rights Reserved.

Item Type:	Journal Article
Publication:	Journal of Geophysical Research: Oceans
Publisher:	John Wiley and Sons Inc
Additional Information:	The copyright for this article belongs to John Wiley and Sons Inc.
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	28 Feb 2024 12:59
Last Modified:	28 Feb 2024 12:59
URI:	https://eprints.iisc.ac.in/id/eprint/83665

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