Turbulent dissipation rates across the Summer Monsoon Current

Nayak, AA and N, VP and George, JV (2022) Turbulent dissipation rates across the Summer Monsoon Current. In: Ocean Dynamics .

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Abstract

During the summer monsoon, the southern Bay of Bengal (BoB) hosts a cyclonic circulation known as Sri Lanka Dome (SLD) and the swift Summer Monsoon Current (SMC), which advects high salinity (> 35 psu) Arabian Sea water into the BoB. This study presents observations of vertical microstructure across SLD and SMC along 8ͦ N extending from 85.3ͦ E to 88ͦ E measured during July 2016. Arabian Sea water was observed across the section as a subsurface high salinity core (HSC) between 50 and 140 m, sandwiched in the ambient fresher and relatively cooler BoB water. Microstructure shear and temperature gradient observations were used to estimate dissipation rates for turbulent kinetic energy (ε) and temperature gradient variance (X). SLD stations showed patches with elevated values of ε of O(10− 8–10− 7 W kg− 1) and X of O(10− 7–10− 6ͦC2 s− 1) below the mixed layer due to shear instabilities. SMC stations showed elevated patches of ε and X suggesting turbulent mixing, but also showed patches of χ with concomitant relatively weaker ε patches, which suggest mixing due to salt fingering. Below 50 m, turbulent heat fluxes were between 0.1 and 1 W m− 2 at SMC and between 0.01 and 0.1 W m− 2 at SLD. Turbulent salt fluxes were of O(10− 8–10− 7 kg m− 2 s− 1) within HSC. Salt fluxes were in the upward direction from the upper part of HSC and downward from the lower part due to opposing salinity gradients at the top and bottom of HSC. The magnitudes of subsurface salt fluxes were 0.5–1 order smaller at SLD and upward in direction. This study suggests that turbulent and salt fingering processes, constantly encountered across the SMC, transport salt in the subsurface layers below the mixed layer and contribute to the salt balance of the BoB.

Item Type:	Journal Article
Publication:	Ocean Dynamics
Publisher:	Springer Science and Business Media Deutschland GmbH
Additional Information:	The copyright for this article belongs to Springer Science and Business Media Deutschland GmbH.
Keywords:	Atmospheric thermodynamics; Barium compounds; Domes; Kinetic energy; Kinetics; Microstructure; Mixing; Seawater, 'current; Bay of Bengal; High salinity; Salt fingering; Sri Lanka; Sri lanka dome; Summer monsoon; Summer monsoon current; Turbulent flux; Vertical turbulent flux, Thermal gradients
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	13 Oct 2022 05:12
Last Modified:	13 Oct 2022 05:12
URI:	https://eprints.iisc.ac.in/id/eprint/77321

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