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Reducing climatology bias in an ocean-atmosphere CGCM with improved coupling physics

Reducing climatology bias in an ocean-atmosphere CGCM with improved coupling physics
Reducing climatology bias in an ocean-atmosphere CGCM with improved coupling physics
The cold tongue in the tropical Pacific extends too far west in most current ocean–atmosphere coupled GCMs (CGCMs). This bias also exists in the relatively high-resolution SINTEX-F CGCM despite its remarkable performance of simulating ENSO variations. In terms of the importance of air–sea interactions to the climatology formation in the tropical Pacific, several sensitivity experiments with improved coupling physics have been performed in order to reduce the cold-tongue bias in CGCMs.
By allowing for momentum transfer of the ocean surface current to the atmosphere [full coupled simulation (FCPL)] or merely reducing the wind stress by taking the surface current into account in the bulk formula [semicoupled simulation (semi-CPL)], the warm-pool/cold-tongue structure in the equatorial Pacific is simulated better than that of the control simulation (CTL) in which the movement of the ocean surface is ignored for wind stress calculation. The reduced surface zonal current and vertical entrainment owing to the reduced easterly wind stress tend to produce a warmer sea surface temperature (SST) in the western equatorial Pacific. Consequently, the dry bias there is much reduced. The warming tendency of the SST in the eastern Pacific, however, is largely suppressed by isopycnal diffusion and meridional advection of colder SST from south of the equator due to enhanced coastal upwelling near Peru. The ENSO signal in the western Pacific and its global teleconnection in the North Pacific are simulated more realistically.
The approach as adopted in the FCPL run is able to generate a correct zonal SST slope and efficiently reduce the cold-tongue bias in the equatorial Pacific. The surface easterly wind itself in the FCPL run is weakened, reducing the easterly wind stress further. This is related with a weakened zonal Walker cell in the atmospheric boundary layer over the eastern Pacific and a new global angular momentum balance of the atmosphere associated with reduced westerly wind stress over the southern oceans.
0894-8755
2344-2360
Luo, Jing-Jia
d17819b4-b29e-4b43-a81f-7465e3c8b628
Masson, Sebastien
2347d09d-6ab2-4b91-992a-7d73e67b7879
Roeckner, Erich
1e72f7c9-69ff-4e98-af4f-2a97cb6034d3
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Yamagata, Toshio
94509afb-faba-4a4b-9709-2d0dbb8f8635
Luo, Jing-Jia
d17819b4-b29e-4b43-a81f-7465e3c8b628
Masson, Sebastien
2347d09d-6ab2-4b91-992a-7d73e67b7879
Roeckner, Erich
1e72f7c9-69ff-4e98-af4f-2a97cb6034d3
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Yamagata, Toshio
94509afb-faba-4a4b-9709-2d0dbb8f8635

Luo, Jing-Jia, Masson, Sebastien, Roeckner, Erich, Madec, Gurvan and Yamagata, Toshio (2005) Reducing climatology bias in an ocean-atmosphere CGCM with improved coupling physics. Journal of Climate, 18 (13), 2344-2360. (doi:10.1175/JCLI3404.1).

Record type: Article

Abstract

The cold tongue in the tropical Pacific extends too far west in most current ocean–atmosphere coupled GCMs (CGCMs). This bias also exists in the relatively high-resolution SINTEX-F CGCM despite its remarkable performance of simulating ENSO variations. In terms of the importance of air–sea interactions to the climatology formation in the tropical Pacific, several sensitivity experiments with improved coupling physics have been performed in order to reduce the cold-tongue bias in CGCMs.
By allowing for momentum transfer of the ocean surface current to the atmosphere [full coupled simulation (FCPL)] or merely reducing the wind stress by taking the surface current into account in the bulk formula [semicoupled simulation (semi-CPL)], the warm-pool/cold-tongue structure in the equatorial Pacific is simulated better than that of the control simulation (CTL) in which the movement of the ocean surface is ignored for wind stress calculation. The reduced surface zonal current and vertical entrainment owing to the reduced easterly wind stress tend to produce a warmer sea surface temperature (SST) in the western equatorial Pacific. Consequently, the dry bias there is much reduced. The warming tendency of the SST in the eastern Pacific, however, is largely suppressed by isopycnal diffusion and meridional advection of colder SST from south of the equator due to enhanced coastal upwelling near Peru. The ENSO signal in the western Pacific and its global teleconnection in the North Pacific are simulated more realistically.
The approach as adopted in the FCPL run is able to generate a correct zonal SST slope and efficiently reduce the cold-tongue bias in the equatorial Pacific. The surface easterly wind itself in the FCPL run is weakened, reducing the easterly wind stress further. This is related with a weakened zonal Walker cell in the atmospheric boundary layer over the eastern Pacific and a new global angular momentum balance of the atmosphere associated with reduced westerly wind stress over the southern oceans.

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Published date: July 2005

Identifiers

Local EPrints ID: 64368
URI: http://eprints.soton.ac.uk/id/eprint/64368
ISSN: 0894-8755
PURE UUID: 79415d39-0462-4485-831d-cc86123148b2

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Date deposited: 10 Dec 2008
Last modified: 15 Mar 2024 11:48

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Contributors

Author: Jing-Jia Luo
Author: Sebastien Masson
Author: Erich Roeckner
Author: Gurvan Madec
Author: Toshio Yamagata

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