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The sensitivity of a coupled climate model to its ocean component

The sensitivity of a coupled climate model to its ocean component
The sensitivity of a coupled climate model to its ocean component
The control climates of two coupled climate models are intercompared. The first is the third climate configuration of the Met Office Unified Model (HadCM3), while the second, the Coupled Hadley–Isopycnic Model Experiment (CHIME), is identical to the first except for the replacement of its ocean component by the Hybrid-Coordinate Ocean Model (HYCOM). Both models possess realistic and similar ocean heat transports and overturning circulation. However, substantial differences in the vertical structure of the two ocean components are observed, some of which are directly attributed to their different vertical coordinate systems. In particular, the sea surface temperature (SST) in CHIME is biased warm almost everywhere, particularly in the North Atlantic subpolar gyre, in contrast to HadCM3, which is biased cold except in the Southern Ocean. Whereas the HadCM3 ocean warms from just below the surface down to 1000-m depth, a similar warming in CHIME is more pronounced but shallower and confined to the upper 400 m, with cooling below this. This is particularly apparent in the subtropical thermoclines, which become more diffuse in HadCM3, but sharper in CHIME. This is interpreted as resulting from a more rigorously controlled diapycnal mixing in the interior isopycnic ocean in CHIME. Lower interior mixing is also apparent in the better representation and maintenance of key water masses in CHIME, such as Subantarctic Mode Water, Antarctic Intermediate Water, and North Atlantic Deep Water. Finally, the North Pacific SST cold error in HadCM3 is absent in CHIME, and may be related to a difference in the separation position of the Kuroshio. Disadvantages of CHIME include a nonconservation of heat equivalent to 0.5 W m?2 globally, and a warming and salinification of the northwestern Atlantic.
0894-8755
5126-5150
Megann, A.P.
4fd92e77-5512-487d-bb28-8476afafdeaf
New, A.L.
69c2be8b-c6c2-408f-9612-6980b1a25802
Blaker, A.T.
94efe8b2-c744-4e90-87d7-db19ffa41200
Sinha, B.
544b5a07-3d74-464b-9470-a68c69bd722e
Megann, A.P.
4fd92e77-5512-487d-bb28-8476afafdeaf
New, A.L.
69c2be8b-c6c2-408f-9612-6980b1a25802
Blaker, A.T.
94efe8b2-c744-4e90-87d7-db19ffa41200
Sinha, B.
544b5a07-3d74-464b-9470-a68c69bd722e

Megann, A.P., New, A.L., Blaker, A.T. and Sinha, B. (2010) The sensitivity of a coupled climate model to its ocean component. Journal of Climate, 23 (19), 5126-5150. (doi:10.1175/2010JCLI3394.1).

Record type: Article

Abstract

The control climates of two coupled climate models are intercompared. The first is the third climate configuration of the Met Office Unified Model (HadCM3), while the second, the Coupled Hadley–Isopycnic Model Experiment (CHIME), is identical to the first except for the replacement of its ocean component by the Hybrid-Coordinate Ocean Model (HYCOM). Both models possess realistic and similar ocean heat transports and overturning circulation. However, substantial differences in the vertical structure of the two ocean components are observed, some of which are directly attributed to their different vertical coordinate systems. In particular, the sea surface temperature (SST) in CHIME is biased warm almost everywhere, particularly in the North Atlantic subpolar gyre, in contrast to HadCM3, which is biased cold except in the Southern Ocean. Whereas the HadCM3 ocean warms from just below the surface down to 1000-m depth, a similar warming in CHIME is more pronounced but shallower and confined to the upper 400 m, with cooling below this. This is particularly apparent in the subtropical thermoclines, which become more diffuse in HadCM3, but sharper in CHIME. This is interpreted as resulting from a more rigorously controlled diapycnal mixing in the interior isopycnic ocean in CHIME. Lower interior mixing is also apparent in the better representation and maintenance of key water masses in CHIME, such as Subantarctic Mode Water, Antarctic Intermediate Water, and North Atlantic Deep Water. Finally, the North Pacific SST cold error in HadCM3 is absent in CHIME, and may be related to a difference in the separation position of the Kuroshio. Disadvantages of CHIME include a nonconservation of heat equivalent to 0.5 W m?2 globally, and a warming and salinification of the northwestern Atlantic.

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Published date: October 2010
Organisations: Marine Systems Modelling

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Local EPrints ID: 166795
URI: http://eprints.soton.ac.uk/id/eprint/166795
ISSN: 0894-8755
PURE UUID: c712d345-b7ce-4eab-a835-9d80a07a2874

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Date deposited: 02 Nov 2010 11:29
Last modified: 14 Mar 2024 02:14

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Contributors

Author: A.P. Megann
Author: A.L. New
Author: A.T. Blaker
Author: B. Sinha

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