A THERMAL OSCILLATION UNDER A RESTORATIVE FORCING

The authors report an interdecadal oscillation in a wind-and thermally -driven ocean general circulation model (OGCM). The oscillation is tan talizing in that it occurs under a relatively strong thermal damping ( 26.3 W m(-2) K-1). Examinations involving a two-dimensional OGCM, a si mple thermal 'flipflop' model, and a three-dimensional OGCM with and w ithout the nonlinear effect of temperature in the state equation of se a water demonstrate that the oscillation is not driven by mechanisms s uch as the so-called convective oscillator, or the advective overshoot ing oscillator. Instead, the oscillation is associated with the propag ation of modelled long Rossby-waves with westward phase velocity. It i s found that the north-south basin extent of the OGCM is an important factor; a larger north-south basin extent is conducive to the generati on of thermal wind flows crucial for initiating the propagation of dis turbances. The geophysical relevance of these results is discussed.