PERFORMANCE OF THE OPA ARPEGE-T21 GLOBAL OCEAN-ATMOSPHERE COUPLED MODEL/

The climatology of the OPA/ARPEGE-T21 coupled general circulation mode l (GCM) is presented. The atmosphere GCM has a T21 spectral truncation and the ocean GCM has a 2 degrees x 1.5 degrees average resolution. A 50-year climatic simulation is performed using the OASIS coupler, wit hout flux correction techniques. The mean state and seasonal cycle for the last 10 years of the experiment are described and compared to the corresponding uncoupled experiments and to climatology when available . The model reasonably simulates most of the basic features of the obs erved climate. Energy budgets and transports in the coupled system, of importance for climate studies, are assessed and prove to be within a vailable estimates. After an adjustment phase of a few years, the mode l stabilizes around a mean state where the tropics are warm and resemb le a permanent ENSO, the Southern Ocean warms and almost no sea-ice is left in the Southern Hemisphere. The atmospheric circulation becomes more zonal and symmetric with respect to the equator. Once those syste matic errors are established, the model shows little secular drift, th e small remaining trends being mainly associated to horizontal physics in the ocean GCM. The stability of the model is shown to be related t o qualities already present in the uncoupled GCMs used, namely a balan ced radiation budget at the top-of-the-atmosphere and a tight ocean th ermocline.