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The seasonal cycle of submesoscale flows

The seasonal cycle of submesoscale flows
The seasonal cycle of submesoscale flows
The seasonal cycle of submesoscale flows in the upper ocean is investigated in an idealised model domain analogous to mid-latitude open ocean regions. Submesoscale processes become much stronger as the resolution is increased, though with limited evidence for convergence of the solutions. Frontogenetical processes increase horizontal buoyancy gradients when the mixed layer is shallow in summer, while overturning instabilities weaken the horizontal buoyancy gradients as the mixed layer deepens in winter. The horizontal wavenumber spectral slopes of surface temperature and velocity are steep in summer and then shallow in winter. This is consistent with stronger mixed layer instabilities developing as the mixed layer deepens and energising the submesoscale. The degree of geostrophic balance falls as the resolution is made finer, with evidence for stronger non-linear and high-frequency processes becoming more important as the mixed layer deepens. Ekman buoyancy fluxes can be much stronger than surface cooling and are locally dominant in setting the stratification and the potential vorticity at fronts, particularly in the early winter. Up to 30% of the mixed layer volume in winter has negative potential vorticity and symmetric instability is predicted inside mesoscale eddies as well as in the frontal regions outside of the vortices.
Submesoscale, mixed layer fronts, frontogenesis, symmetric instability, baroclinic instability, seasonal cycle, Ekman buoyancy flux
1463-5003
69-84
Brannigan, Liam
6093fdb8-8cae-42ee-8a10-9ee87288fed3
Marshall, David P.
70dddf0a-46d1-404f-aa8f-5fb9902ab587
Naveira-Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Nurser, A.J. George
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Brannigan, Liam
6093fdb8-8cae-42ee-8a10-9ee87288fed3
Marshall, David P.
70dddf0a-46d1-404f-aa8f-5fb9902ab587
Naveira-Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Nurser, A.J. George
2493ef9a-21e9-4d8b-9c32-08677e7e145a

Brannigan, Liam, Marshall, David P., Naveira-Garabato, Alberto C. and Nurser, A.J. George (2015) The seasonal cycle of submesoscale flows. Ocean Modelling, 92, 69-84. (doi:10.1016/j.ocemod.2015.05.002).

Record type: Article

Abstract

The seasonal cycle of submesoscale flows in the upper ocean is investigated in an idealised model domain analogous to mid-latitude open ocean regions. Submesoscale processes become much stronger as the resolution is increased, though with limited evidence for convergence of the solutions. Frontogenetical processes increase horizontal buoyancy gradients when the mixed layer is shallow in summer, while overturning instabilities weaken the horizontal buoyancy gradients as the mixed layer deepens in winter. The horizontal wavenumber spectral slopes of surface temperature and velocity are steep in summer and then shallow in winter. This is consistent with stronger mixed layer instabilities developing as the mixed layer deepens and energising the submesoscale. The degree of geostrophic balance falls as the resolution is made finer, with evidence for stronger non-linear and high-frequency processes becoming more important as the mixed layer deepens. Ekman buoyancy fluxes can be much stronger than surface cooling and are locally dominant in setting the stratification and the potential vorticity at fronts, particularly in the early winter. Up to 30% of the mixed layer volume in winter has negative potential vorticity and symmetric instability is predicted inside mesoscale eddies as well as in the frontal regions outside of the vortices.

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More information

Accepted/In Press date: May 2015
Published date: August 2015
Keywords: Submesoscale, mixed layer fronts, frontogenesis, symmetric instability, baroclinic instability, seasonal cycle, Ekman buoyancy flux
Organisations: Marine Systems Modelling, Physical Oceanography

Identifiers

Local EPrints ID: 377439
URI: https://eprints.soton.ac.uk/id/eprint/377439
ISSN: 1463-5003
PURE UUID: 99ffea40-92db-436c-92bb-dbce3638a4bb

Catalogue record

Date deposited: 26 May 2015 11:00
Last modified: 05 Mar 2019 17:32

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