A.W. Robertson, C.-C. Ma, M. Ghil and C.R. Mechoso
Two multi-year simulations with a coupled ocean-atmosphere general circulation m odel (GCM)\121totaling 45 years\121are used to investigate interannual variabili ty at the equator. The model consists of the UCLA global atmospheric GCM coupled to the GFDL oceanic GCM dynamically active over the tropical Pacific. Multi-cha nnel singular spectrum analysis along the equator identifies ENSO-like quasi-bie nnial (QB) and quasi-quadrennial (QQ) modes. Both consist of predominantly stand ing oscillations in sea-surface temperature and zonal wind stress that peak in t he central or east Pacific, accompanied by an oscillation in equatorial thermocl ine-depth that is characterized by a phase shift of about 90o across the basin, with west leading east. Simulated interannual variability is weaker than observe d in both simulations. One of these is dominated by the QB, the other by the QQ mode, although the two differ only in details of the surface-layer parameterizat ions.