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Influence of upper-ocean stratification on tropical cyclone-induced surface cooling in the Bay of Bengal

Influence of upper-ocean stratification on tropical cyclone-induced surface cooling in the Bay of Bengal
Influence of upper-ocean stratification on tropical cyclone-induced surface cooling in the Bay of Bengal
Surface cooling induced by tropical cyclones (TCs) is about three times larger during premonsoon than during postmonsoon season in the Bay of Bengal. We investigate processes responsible for this seasonal contrast using an ocean general circulation model. The model is forced by TC winds prescribed from an analytic vortex using observed TC tracks and intensities during 1978–2007. The simulation accurately captures the seasonal cycle of salinity, temperature, and barrier layer in this region, with fresher waters, deeper upper-ocean stratification, and thicker barrier layers during postmonsoon season. It also reproduces the three times larger TC-induced cooling during premonsoon than during postmonsoon season. This difference is essentially related to seasonal changes in oceanic stratification rather than to differences in TC wind energy input. During the postmonsoon season, a deeper thermal stratification combined with a considerable upper-ocean freshening strongly inhibits surface cooling induced by vertical mixing underneath TCs. On average, thermal stratification accounts for ?60% of this cooling reduction during postmonsoon season, while haline stratification accounts for the remaining 40%. Their respective contributions however strongly vary within the Bay: haline stratification explains a large part of the TC-induced cooling inhibition offshore of northern rim of the Bay (Bangladesh-Myanmar-east coast of India), where salinity seasonal changes are the strongest, while thermal stratification explains all the cooling inhibition in the southwestern Bay. This study hence advocates for an improved representation of upper-ocean salinity and temperature effects in statistical and dynamical TCs forecasts that could lead to significant improvements of TC intensity prediction skill.
Bay of Bengal, air-sea interaction, numerical modeling, ocean stratification, sea surface cooling, tropical cyclone
0148-0227
C12020
Neetu, S.
868b9146-7282-40b6-b609-aef5d408b437
Lengaigne, Matthieu
3f78eafe-bcd2-41c4-9e0e-3b8bb3c55aa4
Vincent, Emmanuel M.
06aa233c-bb5e-438e-8672-7a53b826e014
Vialard, Jérôme
165dd2c7-d5ec-4bd6-9f20-02e182e38f36
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Samson, Guillaume
7c0ea385-6cf7-4740-8937-fd27549cff73
Ramesh Kumar, M.R.
8675eae0-7e2e-4b48-ba7f-2465f42d26be
Durand, Fabien
41544cb3-3ad8-4db4-97fc-69330ad81072
Neetu, S.
868b9146-7282-40b6-b609-aef5d408b437
Lengaigne, Matthieu
3f78eafe-bcd2-41c4-9e0e-3b8bb3c55aa4
Vincent, Emmanuel M.
06aa233c-bb5e-438e-8672-7a53b826e014
Vialard, Jérôme
165dd2c7-d5ec-4bd6-9f20-02e182e38f36
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Samson, Guillaume
7c0ea385-6cf7-4740-8937-fd27549cff73
Ramesh Kumar, M.R.
8675eae0-7e2e-4b48-ba7f-2465f42d26be
Durand, Fabien
41544cb3-3ad8-4db4-97fc-69330ad81072

Neetu, S., Lengaigne, Matthieu, Vincent, Emmanuel M., Vialard, Jérôme, Madec, Gurvan, Samson, Guillaume, Ramesh Kumar, M.R. and Durand, Fabien (2012) Influence of upper-ocean stratification on tropical cyclone-induced surface cooling in the Bay of Bengal. Journal of Geophysical Research, 117 (C12), C12020. (doi:10.1029/2012JC008433).

Record type: Article

Abstract

Surface cooling induced by tropical cyclones (TCs) is about three times larger during premonsoon than during postmonsoon season in the Bay of Bengal. We investigate processes responsible for this seasonal contrast using an ocean general circulation model. The model is forced by TC winds prescribed from an analytic vortex using observed TC tracks and intensities during 1978–2007. The simulation accurately captures the seasonal cycle of salinity, temperature, and barrier layer in this region, with fresher waters, deeper upper-ocean stratification, and thicker barrier layers during postmonsoon season. It also reproduces the three times larger TC-induced cooling during premonsoon than during postmonsoon season. This difference is essentially related to seasonal changes in oceanic stratification rather than to differences in TC wind energy input. During the postmonsoon season, a deeper thermal stratification combined with a considerable upper-ocean freshening strongly inhibits surface cooling induced by vertical mixing underneath TCs. On average, thermal stratification accounts for ?60% of this cooling reduction during postmonsoon season, while haline stratification accounts for the remaining 40%. Their respective contributions however strongly vary within the Bay: haline stratification explains a large part of the TC-induced cooling inhibition offshore of northern rim of the Bay (Bangladesh-Myanmar-east coast of India), where salinity seasonal changes are the strongest, while thermal stratification explains all the cooling inhibition in the southwestern Bay. This study hence advocates for an improved representation of upper-ocean salinity and temperature effects in statistical and dynamical TCs forecasts that could lead to significant improvements of TC intensity prediction skill.

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More information

Published date: 2012
Keywords: Bay of Bengal, air-sea interaction, numerical modeling, ocean stratification, sea surface cooling, tropical cyclone
Organisations: Ocean Technology and Engineering

Identifiers

Local EPrints ID: 350663
URI: http://eprints.soton.ac.uk/id/eprint/350663
ISSN: 0148-0227
PURE UUID: b4e85a0e-6886-4999-8e99-ba89cd92640b

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Date deposited: 27 Mar 2013 16:28
Last modified: 14 Mar 2024 13:30

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Contributors

Author: S. Neetu
Author: Matthieu Lengaigne
Author: Emmanuel M. Vincent
Author: Jérôme Vialard
Author: Gurvan Madec
Author: Guillaume Samson
Author: M.R. Ramesh Kumar
Author: Fabien Durand

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