Seasonal and interannual variability in a hybrid coupled GCM
- Univ. of California, Los Angeles, CA (United States)
A hybrid coupled model for the tropical Pacific ocean-atmosphere system is used to simulate El Nino-Southern Oscillation (ENSO) interannual variability and to investigate the role of coupling in the season cycle. An ocean GCM (OGCM) is coupled to an empirical atmospheric model that specifies a wind stress field from a given sea surface temperature (SST) field. The stress is estimated by singular value decomposition of the covariance between observed surface wind stress and SST fluctuations. Two versions of the atmospheric model are employed; one includes only spatial patterns of the atmospheric feedbacks associated with interannual variability, whereas the other also includes spatial patterns associated with the annual cycle. In the latter version wind stress coupling in the seasonal cycle is modeled on the same basis as in the interannual variability. The seasonal cycle enters through prescribed heat flux and is modified by momentum-flux feedbacks. In the OGCM, two vertical mixing schemes-Philander-Pacanowski (PP) and a modified scheme-are used. Simulated ENSO anomalies have a reasonable spatial structure compared to observation, and the form is not strongly sensitive to the atmospheric model or mixing scheme. SST anomalies evolve largely as a standing oscillation, though with some westward propagation; heat content evolution is characteristic of subsurface memory, consistent with a mixed SST-ocean dynamics mode regime. In the absence of the seasonal cycle, the ENSO period is affected by vertical mixing: about 2.3 years for the modified scheme and slightly less than 2 years for the PP scheme. Indications of irregular or multifrequency behavior are also found. Interaction with the seasonal cycle frequency locks the interannual signal to a quasi-biennial period. The seasonal cycle in the eastern Pacific is well simulated by the coupled model. 56 refs., 25 figs.
- OSTI ID:
- 115208
- Journal Information:
- Journal of Climate, Vol. 8, Issue 9; Other Information: PBD: Sep 1995
- Country of Publication:
- United States
- Language:
- English
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