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The upper Bay of Bengal salinity structure in a high-resolution model

The upper Bay of Bengal salinity structure in a high-resolution model
The upper Bay of Bengal salinity structure in a high-resolution model
Salinity in the Bay of Bengal is highly heterogeneous, with extremely fresh waters found at the surface in the Northern part of the basin, and saltier waters at subsurface as well as to the south. This paper investigates the seasonal structure of sea surface salinity of the Bay in a regional high-resolution model forced by ERA-Interim reanalysis and various precipitation products. Surface circulation is believed to drive the spreading of northern Bay of Bengal fresh waters to the rest of the Indian Ocean. We first present a series of experiments to infer the sensitivity of modeled circulation to various numerical choices. Surface circulation is found to be sensitive to the horizontal resolution of the model, with the 1/12° version appearing much more realistic than the 1/4° version. The sidewall boundary condition is also drastically influencing the characteristics of the western boundary current simulated. We then investigate the sensitivity of the salinity response to the various precipitation products. We observe that ERA-Interim excess precipitation induces a fresh bias in the surface salinity response. Spaceborne precipitation products are more satisfactory. We then identify the pathways of the northern Bay freshwater mass, based on passive tracers experiments. Our model suggests that over timescales of a few months, vertical exchanges between the upper fresh layer and the underlying saltier layer appear to be the main export pathway for the freshwater. The horizontal circulation within the mixed layer also acts to convey fresh waters out of the Bay at these timescales, but in a lesser quantity compared to the vertical export. Beyond its intrinsic interest for the understanding of Bay of Bengal physics, this study highlights the need for a careful design of any realistic numerical model, in three key aspects: the choice of the resolution of the model, the choice of the sub-grid scale parameterizations, and the choice of the forcing fluxes.
1463-5003
36-52
Benshila, Rachid
b619ab45-9f42-46eb-bada-547c9262198a
Durand, Fabien
41544cb3-3ad8-4db4-97fc-69330ad81072
Masson, Sébastien
3c93954e-649f-478b-a35e-d06879fb5d12
Bourdallé-Badie, Romain
5e441c1f-83ce-40c4-b64f-a1273782274f
de Boyer Montégut, Clement
ad2acbaa-80e6-413a-89b1-2afa082c75d1
Papa, Fabrice
7cd53c9c-52b0-4286-be73-ebf408c2aff5
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Benshila, Rachid
b619ab45-9f42-46eb-bada-547c9262198a
Durand, Fabien
41544cb3-3ad8-4db4-97fc-69330ad81072
Masson, Sébastien
3c93954e-649f-478b-a35e-d06879fb5d12
Bourdallé-Badie, Romain
5e441c1f-83ce-40c4-b64f-a1273782274f
de Boyer Montégut, Clement
ad2acbaa-80e6-413a-89b1-2afa082c75d1
Papa, Fabrice
7cd53c9c-52b0-4286-be73-ebf408c2aff5
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864

Benshila, Rachid, Durand, Fabien, Masson, Sébastien, Bourdallé-Badie, Romain, de Boyer Montégut, Clement, Papa, Fabrice and Madec, Gurvan (2014) The upper Bay of Bengal salinity structure in a high-resolution model. Ocean Modelling, 74, 36-52. (doi:10.1016/j.ocemod.2013.12.001).

Record type: Article

Abstract

Salinity in the Bay of Bengal is highly heterogeneous, with extremely fresh waters found at the surface in the Northern part of the basin, and saltier waters at subsurface as well as to the south. This paper investigates the seasonal structure of sea surface salinity of the Bay in a regional high-resolution model forced by ERA-Interim reanalysis and various precipitation products. Surface circulation is believed to drive the spreading of northern Bay of Bengal fresh waters to the rest of the Indian Ocean. We first present a series of experiments to infer the sensitivity of modeled circulation to various numerical choices. Surface circulation is found to be sensitive to the horizontal resolution of the model, with the 1/12° version appearing much more realistic than the 1/4° version. The sidewall boundary condition is also drastically influencing the characteristics of the western boundary current simulated. We then investigate the sensitivity of the salinity response to the various precipitation products. We observe that ERA-Interim excess precipitation induces a fresh bias in the surface salinity response. Spaceborne precipitation products are more satisfactory. We then identify the pathways of the northern Bay freshwater mass, based on passive tracers experiments. Our model suggests that over timescales of a few months, vertical exchanges between the upper fresh layer and the underlying saltier layer appear to be the main export pathway for the freshwater. The horizontal circulation within the mixed layer also acts to convey fresh waters out of the Bay at these timescales, but in a lesser quantity compared to the vertical export. Beyond its intrinsic interest for the understanding of Bay of Bengal physics, this study highlights the need for a careful design of any realistic numerical model, in three key aspects: the choice of the resolution of the model, the choice of the sub-grid scale parameterizations, and the choice of the forcing fluxes.

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More information

Published date: February 2014
Organisations: Marine Systems Modelling

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Local EPrints ID: 362958
URI: http://eprints.soton.ac.uk/id/eprint/362958
ISSN: 1463-5003
PURE UUID: b375048c-4fc0-49a2-b87d-b6ceacff0e76

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Date deposited: 10 Mar 2014 14:15
Last modified: 14 Mar 2024 16:16

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Contributors

Author: Rachid Benshila
Author: Fabien Durand
Author: Sébastien Masson
Author: Romain Bourdallé-Badie
Author: Clement de Boyer Montégut
Author: Fabrice Papa
Author: Gurvan Madec

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