Trapping of Wind Momentum in a Salinity-Stratified Ocean

Chaudhuri, D and Sengupta, D and D�Asaro, E and Shivaprasad, S (2021) Trapping of Wind Momentum in a Salinity-Stratified Ocean. In: Journal of Geophysical Research: Oceans, 126 (12).

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Abstract

We study the nature of ocean currents forced by summer monsoon winds in the Bay of Bengal using data from two cruises within a pool of low-salinity (<32 psμ) river water, and one cruise outside the low-salinity pool. Upper ocean (5�70 m) temperature, salinity, and velocity profiles were measured at sub-kilometer horizontal resolution along the 800�1800-km-long cruise tracks. We find that beneath the river water, density stratification at 5�15 m depth can be 10 times stronger than typically seen in much of the subtropical or tropical ocean. The shallow salinity-dominated stratification suppresses shear-induced turbulence, thereby �trapping� momentum input from monsoon winds in the uppermost 20 m of the ocean. Estimates of directly wind-forced ocean currents are consistent with Ekman depth scaling as (Formula presented.), where N0 is stratification at the base of the mixed layer and f is Coriolis frequency. In the presence of river water, cruise-mean wind-forced currents resemble tightly surface trapped Ekman-like spirals: The shallowest measured current at 5 m depth has a speed of nearly 0.2 m/s, directed 80° to the right of the wind. Outside the pool of river water, wind momentum penetrates to 40 m depth. © 2021. 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 > Divecha Centre for Climate Change
Date Deposited:	12 Jan 2022 05:47
Last Modified:	12 Jan 2022 05:47
URI:	http://eprints.iisc.ac.in/id/eprint/70933

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