CoPIVEP: a theory-based analysis of coupled processes and interannual variability in the Equatorial Pacific in four coupled GCMs |
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| Authors: | M Pontaud J-P Céron M Kimoto F Pluviaud L Terray A Vintzileos |
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| Institution: | (1) Meteo-France, ENM/UFR, 42 av. G. Coriolis, 31057 Toulouse-Cedex, France, FR;(2) Center for Climate System Research, University of Tokyo, 4-6-1, Komba, Meguro-ku, Tokyo 153-8904 Japan, JP;(3) CERFACS, 42 av. G. Coriolis, 31057 Toulouse-Cedex, France, FR;(4) Institut Pierre-Simon Laplace, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05, France, FR |
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| Abstract: | The interannual variability over the tropical Pacific and a possible link with the mean state or the seasonal cycle is examined
in four coupled ocean-atmosphere general circulation models (GCM). Each model is composed of a high-resolution ocean GCM of
either the tropical Pacific or near-global oceans coupled to a moderate-resolution atmospheric GCM, without using flux correction.
The oceanic subsurface is considered to describe the mean state or the seasonal cycle through the analytical formulations
of some potential coupled processes. These coupled processes characterise the zonal gradient of sea surface temperature (hereafter
SST), the oceanic vertical gradient of temperature and the equatorial upwelling. The simulated SST patterns of the mean state
and the interannual signals are generally too narrow. The grid of the oceanic model could control the structure of the SST
interannual signals while the behaviour of the atmospheric model could be important in the link between the oceanic surface
and the subsurface. The first SST EOFs are different between the coupled models, however, the second SST EOFs are quite similar
and could correspond to the return to the normal state while that of the observations (COADS) could favour the initial anomaly.
All the models seem to simulate a similar equatorial wave-like dynamics to return to the normal state. The more the basic
state is unstable from the coupled processes point of view, the more the interannual signal are high. It seems that the basic
state could control the intensity of the interannual variability. Two models, which have a significant seasonal variation
of the interannual variance, also have a significant seasonal variation of the instability with a few months lag. The potential
seasonal phase locking of the interannual fluctuations need to be examined in more models to confirm its existence in current
tropical GCMs.
Received: 30 July 1999 / Accepted: 25 April 2000 |
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