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The seasonal cycle in coupled ocean-atmosphere general circulation models

The seasonal cycle in coupled ocean-atmosphere general circulation models
The seasonal cycle in coupled ocean-atmosphere general circulation models
We examine the seasonal cycle of near-surface air temperature simulated by 17 coupled ocean-atmosphere general circulation models participating in the Coupled Model Intercomparison Project (CMIP). Nine of the models use ad hoc “flux adjustment” at the ocean surface to bring model simulations close to observations of the present-day climate. We group flux-adjusted and non-flux-adjusted models separately and examine the behavior of each class. When averaged over all of the flux-adjusted model simulations, near-surface air temperature falls within 2?K of observed values over the oceans. The corresponding average over non-flux-adjusted models shows errors up to ?6?K in extensive ocean areas. Flux adjustments are not directly applied over land, and near-surface land temperature errors are substantial in the average over flux-adjusted models, which systematically underestimates (by ?5?K) temperature in areas of elevated terrain. The corresponding average over non-flux-adjusted models forms a similar error pattern (with somewhat increased amplitude) over land. We use the temperature difference between July and January to measure seasonal cycle amplitude. Zonal means of this quantity from the individual flux-adjusted models form a fairly tight cluster (all within ?30% of the mean) centered on the observed values. The non-flux-adjusted models perform nearly as well at most latitudes. In Southern Ocean mid-latitudes, however, the non-flux-adjusted models overestimate the magnitude of January-minus-July temperature differences by ?5?K due to an overestimate of summer (January) near-surface temperature. This error is common to five of the eight non-flux-adjusted models. Also, over Northern Hemisphere mid-latitude land areas, zonal mean differences between July and January temperatures simulated by the non-flux-adjusted models show a greater spread (positive and negative) about observed values than results from the flux-adjusted models. Elsewhere, differences between the two classes of models are less obvious. At no latitude is the zonal mean difference between averages over the two classes of models greater than the standard deviation over models. The ability of coupled GCMs to simulate a reasonable seasonal cycle is a necessary condition for confidence in their prediction of long-term climatic changes (such as global warming), but it is not a sufficient condition unless the seasonal cycle and long-term changes involve similar climatic processes. To test this possible connection, we compare seasonal cycle amplitude with equilibrium warming under doubled atmospheric carbon dioxide for the models in our data base. A small but positive correlation exists between these two quantities. This result is predicted by a simple conceptual model of the climate system, and it is consistent with other modeling experience, which indicates that the seasonal cycle depends only weakly on climate sensitivity.
0930-7575
775-787
Covey, C.
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Abe-Ouchi, A.
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Boer, G.J.
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Boville, B.A.
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Cubasch, U.
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Fairhead, L.
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Flato, G.M.
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Gordon, H.
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Guilyardi, E.
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Jiang, X.
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Johns, T.C.
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Le Treut, H.
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Madec, G.
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Meehl, G.A.
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Miller, R.
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Noda, A.
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Power, B.
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Roeckner, E.
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Russell, G.
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Schneider, E.K.
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Stouffer, R.J.
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Terray, L.
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von Storch, J-S.
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Covey, C.
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Abe-Ouchi, A.
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Boer, G.J.
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Boville, B.A.
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Cubasch, U.
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Fairhead, L.
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Flato, G.M.
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Gordon, H.
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Guilyardi, E.
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Jiang, X.
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Johns, T.C.
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Le Treut, H.
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Madec, G.
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Meehl, G.A.
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Miller, R.
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Noda, A.
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Power, B.
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Roeckner, E.
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Russell, G.
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Schneider, E.K.
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Stouffer, R.J.
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Terray, L.
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von Storch, J-S.
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Covey, C., Abe-Ouchi, A., Boer, G.J., Boville, B.A., Cubasch, U., Fairhead, L., Flato, G.M., Gordon, H., Guilyardi, E., Jiang, X., Johns, T.C., Le Treut, H., Madec, G., Meehl, G.A., Miller, R., Noda, A., Power, B., Roeckner, E., Russell, G., Schneider, E.K., Stouffer, R.J., Terray, L. and von Storch, J-S. (2000) The seasonal cycle in coupled ocean-atmosphere general circulation models. Climate Dynamics, 16 (10-11), 775-787. (doi:10.1007/s003820000081).

Record type: Article

Abstract

We examine the seasonal cycle of near-surface air temperature simulated by 17 coupled ocean-atmosphere general circulation models participating in the Coupled Model Intercomparison Project (CMIP). Nine of the models use ad hoc “flux adjustment” at the ocean surface to bring model simulations close to observations of the present-day climate. We group flux-adjusted and non-flux-adjusted models separately and examine the behavior of each class. When averaged over all of the flux-adjusted model simulations, near-surface air temperature falls within 2?K of observed values over the oceans. The corresponding average over non-flux-adjusted models shows errors up to ?6?K in extensive ocean areas. Flux adjustments are not directly applied over land, and near-surface land temperature errors are substantial in the average over flux-adjusted models, which systematically underestimates (by ?5?K) temperature in areas of elevated terrain. The corresponding average over non-flux-adjusted models forms a similar error pattern (with somewhat increased amplitude) over land. We use the temperature difference between July and January to measure seasonal cycle amplitude. Zonal means of this quantity from the individual flux-adjusted models form a fairly tight cluster (all within ?30% of the mean) centered on the observed values. The non-flux-adjusted models perform nearly as well at most latitudes. In Southern Ocean mid-latitudes, however, the non-flux-adjusted models overestimate the magnitude of January-minus-July temperature differences by ?5?K due to an overestimate of summer (January) near-surface temperature. This error is common to five of the eight non-flux-adjusted models. Also, over Northern Hemisphere mid-latitude land areas, zonal mean differences between July and January temperatures simulated by the non-flux-adjusted models show a greater spread (positive and negative) about observed values than results from the flux-adjusted models. Elsewhere, differences between the two classes of models are less obvious. At no latitude is the zonal mean difference between averages over the two classes of models greater than the standard deviation over models. The ability of coupled GCMs to simulate a reasonable seasonal cycle is a necessary condition for confidence in their prediction of long-term climatic changes (such as global warming), but it is not a sufficient condition unless the seasonal cycle and long-term changes involve similar climatic processes. To test this possible connection, we compare seasonal cycle amplitude with equilibrium warming under doubled atmospheric carbon dioxide for the models in our data base. A small but positive correlation exists between these two quantities. This result is predicted by a simple conceptual model of the climate system, and it is consistent with other modeling experience, which indicates that the seasonal cycle depends only weakly on climate sensitivity.

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Published date: October 2000

Identifiers

Local EPrints ID: 64840
URI: https://eprints.soton.ac.uk/id/eprint/64840
ISSN: 0930-7575
PURE UUID: d9ecf1d5-9c4b-41f9-a803-f44c891634c7

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Date deposited: 16 Jan 2009
Last modified: 13 Mar 2019 20:20

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Contributors

Author: C. Covey
Author: A. Abe-Ouchi
Author: G.J. Boer
Author: B.A. Boville
Author: U. Cubasch
Author: L. Fairhead
Author: G.M. Flato
Author: H. Gordon
Author: E. Guilyardi
Author: X. Jiang
Author: T.C. Johns
Author: H. Le Treut
Author: G. Madec
Author: G.A. Meehl
Author: R. Miller
Author: A. Noda
Author: B. Power
Author: E. Roeckner
Author: G. Russell
Author: E.K. Schneider
Author: R.J. Stouffer
Author: L. Terray
Author: J-S. von Storch

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