40-60 DAY OSCILLATIONS IN THE WESTERN TROPICAL PACIFIC - RESULTS FROM AN EDDY-RESOLVING GLOBAL OCEAN MODEL

Preliminary analyses of results from the Semtner and Chervin [1992] eddy-resolving general circulation model reveal the presence of energetic 40-60 day oscillations in the near-surface layers of the western tropical Pacific. These oscillations have the strongest signal in meridional velocity (maximum amplitudes on the order of 10-20 cm s-1), in latitudinal bands west of the dateline centered at approximately 10-degrees-N and 10-degrees-S. The 40-60 day disturbances have zonal wavelengths of approximately 700 km at 10-degrees-N and 1000 km at 10-degrees-S, and show clear westward phase propagation at speeds of order 15-20 cm/s. Eastward (but slower) energy propagation is also apparent. The oscillations in the model are a result of oceanic instability processes and not a direct response to wind stress anomalies associated with the Madden-Julian oscillation in the atmosphere. Enhanced energy at 40-60 days is also present in the Indian and Atlantic basins, suggesting that the 40-60 day time scale is a preferred scale for variability in the tropical oceans.