Results from a reduced gravity, primitive equation, ocean general circulation model (OGCM) are used to examine the mechanisms which control the seasonal and interannual variability of sea surface temperature (SST) in the eastern Pacific warm pool (EPWP). In contrast to the western Pacific warm pool where much of the region is in a one-dimensional radiative equilibrium, the temporal and spatial evolution of EPWP SST is believed to depend on the combined effects of dynamic and thermodynamic forcing, precipitation, advection, and penetrating radiation. Understanding this delicate balance is essential to understanding linkages between the eastern Pacific ocean-land-atmosphere system on timescales from months to decades.
Using a series of complementary OGCM simulations, this study focuses on two main contributors to EPWP SST variability, namely the dynamic and thermodynamic responses. In the base model simulation, the OGCM is forced with monthly wind stress and wind speed (NCEP re-analysis) spanning 1980-2001. The second simulation allows the wind stress to vary interannually, while constraining the wind speeds to their climatological values. The third simulation limits the wind stress to its climatological value while allowing the wind speed, and thus surface fluxes of latent and sensible heat, to vary interannually. The former simulation assesses SST variability arising from variations in the large scale oceanic circulation (the dynamic response), while the latter focuses on the net effects of locally varying surface heat fluxes (the thermodynamic response). The two responses are then compared to the base simulation in an effort to assess the relative roles of each process. To further assess the thermodynamic role, two additional OGCM simulations are performed utilizing climatological wind stress and speed, but including interannual cloud (ISSCP) and precipitation (Xie-Arkin) forcing respectively. In all simulations climatological solar radiation (ERBE) is applied externally and freshwater forcing is used as a natural boundary condition.