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A multi-column vertical mixing scheme to parameterize the heterogeneity of oceanic conditions under sea ice

A multi-column vertical mixing scheme to parameterize the heterogeneity of oceanic conditions under sea ice
A multi-column vertical mixing scheme to parameterize the heterogeneity of oceanic conditions under sea ice
The heterogeneity of ocean surface conditions associated with a spatially variable sea ice cover needs to be represented in models in order to represent adequately mixed layer processes and the upper ocean density structure. This study assesses the sensitivity of the ocean-sea ice model NEMO-LIM to a subgrid-scale representation of ice-ocean interactions. The sea ice component includes an ice thickness distribution, which provides heterogeneous surface buoyancy fluxes and stresses. A multi-column ocean scheme is developed to take them explicitly into account, by computing convection and turbulent vertical mixing separately in the open water/lead fraction of grid cells and below each ice thickness category. For the first time in a three-dimensional simulation, the distinct temperature and salinity profiles of the ocean columns are allowed to be maintained over several time steps. It is shown that the model response is highly sensitive to the homogenization time scale between the columns. If the latter are laterally mixed with time scales shorter than 10 h, subgrid-scale effects exist but the mean state is practically unaffected. For longer mixing time scales, in both hemispheres, the main impacts are reductions in under-ice mean mixed layer depths and in the summer melt of sea ice, following decreased oceanic heat flux at the ice base. Large changes in the open water temperature in summer suggest that the scheme could trigger important feedback processes in coupled simulations.
Model, Ice thickness distribution, Subgrid-scale, Ocean vertical mixing, Arctic, Antarctic
1463-5003
28-44
Barthélemy, Antoine
e063bff5-5482-41fe-8abd-674a4a161502
Fichefet, Thierry
7b3028c8-1af9-4671-b041-51022a13bf73
Goosse, Hugues
33c33c55-356b-48ec-be78-3e9eb5d04f29
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Barthélemy, Antoine
e063bff5-5482-41fe-8abd-674a4a161502
Fichefet, Thierry
7b3028c8-1af9-4671-b041-51022a13bf73
Goosse, Hugues
33c33c55-356b-48ec-be78-3e9eb5d04f29
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864

Barthélemy, Antoine, Fichefet, Thierry, Goosse, Hugues and Madec, Gurvan (2016) A multi-column vertical mixing scheme to parameterize the heterogeneity of oceanic conditions under sea ice. Ocean Modelling, 104, 28-44. (doi:10.1016/j.ocemod.2016.05.005).

Record type: Article

Abstract

The heterogeneity of ocean surface conditions associated with a spatially variable sea ice cover needs to be represented in models in order to represent adequately mixed layer processes and the upper ocean density structure. This study assesses the sensitivity of the ocean-sea ice model NEMO-LIM to a subgrid-scale representation of ice-ocean interactions. The sea ice component includes an ice thickness distribution, which provides heterogeneous surface buoyancy fluxes and stresses. A multi-column ocean scheme is developed to take them explicitly into account, by computing convection and turbulent vertical mixing separately in the open water/lead fraction of grid cells and below each ice thickness category. For the first time in a three-dimensional simulation, the distinct temperature and salinity profiles of the ocean columns are allowed to be maintained over several time steps. It is shown that the model response is highly sensitive to the homogenization time scale between the columns. If the latter are laterally mixed with time scales shorter than 10 h, subgrid-scale effects exist but the mean state is practically unaffected. For longer mixing time scales, in both hemispheres, the main impacts are reductions in under-ice mean mixed layer depths and in the summer melt of sea ice, following decreased oceanic heat flux at the ice base. Large changes in the open water temperature in summer suggest that the scheme could trigger important feedback processes in coupled simulations.

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More information

Accepted/In Press date: 21 May 2016
Published date: August 2016
Keywords: Model, Ice thickness distribution, Subgrid-scale, Ocean vertical mixing, Arctic, Antarctic
Organisations: Marine Systems Modelling

Identifiers

Local EPrints ID: 398579
URI: https://eprints.soton.ac.uk/id/eprint/398579
ISSN: 1463-5003
PURE UUID: 638485f0-ca9d-4012-b8c6-a2eef4f05e42

Catalogue record

Date deposited: 27 Jul 2016 08:53
Last modified: 17 Jul 2017 18:30

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Contributors

Author: Antoine Barthélemy
Author: Thierry Fichefet
Author: Hugues Goosse
Author: Gurvan Madec

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