INTERANNUAL AND INTERDECADAL VARIABILITIES IN THE PACIFIC IN AN MRI COUPLED GCM

Interannual and interdecadal variabilities in the Pacific are investig ated with a coupled atmosphere-ocean GCM developed at MRI, Japan. The model is run for 70 years with flux adjustments. The model shows inter annual variability in the tropical Pacific which has several typical c haracteristics shared with the observed ENSO. A basin-scale feature of the principal SST variation for the ENSO time scale shows negative co rrelation in the central North Pacific with the tropical SST, similar to that of the observed one. Associated variation of the model atmosph ere indicates an intensification of the Aleutian Low and a PNA-like te leconnection pattern as a response to the tropical warm SST anomaly. T he ENSO time scale variability in the midlatitude ocean consists of th e westward propagation of the subsurface temperature signal and the te mperature variation within the shallow mixed layer forced by the anoma lous atmospheric heat fluxes. For the interdecadal time scale, variati on of the SST is simulated realistically with a geographical pattern s imilar to that for the ENSO time scale, but it has a larger relative a mplitude in the northern Pacific. For the atmosphere, spatial structur e of the variation in the interdecadal time scale is also similar to t hat in the ENSO time scale, but has smaller amplitude in the northern Pacific. Long oceanic spin-up time (> similar to 10 y) in the mid-high latitude, however, makes oceanic response in the interdecadal time sc ale larger than that in the ENSO time scale. The lagged-regression ana lysis for the ocean temperature variation relative to the wind stress variation indicates that interdecadal variation of the ocean subsurfac e at the mid-high latitudes is considered as enhanced ocean gyre spin- up process in response to the atmospheric circulation change at the mi d-high latitudes, remotely forced by the interdecadal variation of the tropical SST.