LONG EQUATORIAL WAVES IN A HIGH-RESOLUTION OGCM SIMULATION OF THE TROPICAL PACIFIC-OCEAN DURING THE 1985-94 TOGA PERIOD

A high-resolution oceanic general circulation model (OGCM) of the thre e tropical oceans is used to investigate long equatorial Rave activity in the Pacific Ocean during the 1985-94 TOGA period. The ARPEGE atmos pheric general circulation model simulated zonal Rind stress forcing a nd the OPA OGCM simulated dynamic height are interpreted using techniq ues previously applied to data. Long equatorial waves of the first bar oclinic mode (Kelvin and first-mode Rossby waves) are detected propaga ting in the model outputs during the entire period. A seasonal cycle a nd interannual anomalies are computed for each long equatorial wave. I n the east Pacific basin, long equatorial wave coefficients are domina ted by seasonal variations, while west of the date line they display s trong interannual anomalies. Interannual long-wave anomalies are then compared to wave coefficients simulated by a simple wind-forced model. The results presented here indicate the major role played by wind for cing on interannual timescales in generating long equatorial waves. Di screpancies between the simple wave model and the OPA first-mode Rossb y coefficients allow one to draw limitations of interpreting sea surfa ce variability in terms of waves pf the first baroclinic mode alone. F inally, the simple wave model cannot fully explain the Kelvin wave amp litude near che western boundary, nor the first-mode Rossby wave ampli tude near the eastern boundary. However, coherency between the Kelvin and first-mode Rossby wave coefficients at both boundaries lead to the conclusion that reflection occurs in this model and contributes to th e wave amplitudes as they propagate away from the boundaries.