Ocean-Atmosphere Interaction and the Tropical Climatology. Part II: Why the Pacific Cold Tongue Is in the East

Henk A. Dijkstra Institute for Marine and Atmospheric Research, University of Utrecht, Utrecht, The Netherlands

Search for other papers by Henk A. Dijkstra in
Current site
Google Scholar
PubMed
Close
and
J. David Neelin Department of Atmospheric Sciences, University of California at Los Angeles, Los Angeles, California

Search for other papers by J. David Neelin in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The influence of coupled process on the climatology of the tropical Pacific is studied in a model for the interaction of equatorial SST, the associated component of the Walker circulation, and upper-ocean dynamics. In this part, the authors show how different physical mechanisms affect the spatial pattern of the Pacific warm pool and cold tongue in this coupled climatology. When model parameters give a suitable balance between effects of upwelling and thermocline depth on sea surface temperature and for suitable atmospheric parameters, a good prototype for the observed cold-tongue configuration is produced. This is largely determined by coupled ocean-atmosphere processes within the basin. Presence of an easterly wind s~ component produced by factors external to the Pacific basin can be important in setting up a cooling tendency, but this is magnified and modified by a chain of nonlinear feedbacks between trade winds and ocean dynamics affecting the SST gradient within the basin. These feedbacks determine a preferred spatial pattern that does not strongly depend on the form of the external wind stress and that tends to place the cold tongue in the cast-central basin. Although robust to external influences, this pattern is sensitive to the balance of coupled process. Parameter changes can produce warm-pool-cold-tongue patterns significantly different from observed but resembling some noted in coupled CTCMS.

Abstract

The influence of coupled process on the climatology of the tropical Pacific is studied in a model for the interaction of equatorial SST, the associated component of the Walker circulation, and upper-ocean dynamics. In this part, the authors show how different physical mechanisms affect the spatial pattern of the Pacific warm pool and cold tongue in this coupled climatology. When model parameters give a suitable balance between effects of upwelling and thermocline depth on sea surface temperature and for suitable atmospheric parameters, a good prototype for the observed cold-tongue configuration is produced. This is largely determined by coupled ocean-atmosphere processes within the basin. Presence of an easterly wind s~ component produced by factors external to the Pacific basin can be important in setting up a cooling tendency, but this is magnified and modified by a chain of nonlinear feedbacks between trade winds and ocean dynamics affecting the SST gradient within the basin. These feedbacks determine a preferred spatial pattern that does not strongly depend on the form of the external wind stress and that tends to place the cold tongue in the cast-central basin. Although robust to external influences, this pattern is sensitive to the balance of coupled process. Parameter changes can produce warm-pool-cold-tongue patterns significantly different from observed but resembling some noted in coupled CTCMS.

Save