THE VARIABILITY OF THE TROPICAL ATLANTIC

In the present work we simulate;he equatorial Atlantic variability at annual and interannual timescales using a coupled mixed layer - isopyc nal ocean general circulation model (OGCM) forced with observations fo r the period 1980-1989. Surface features such as the seasonal variatio ns of the equatorial system of currents or of the temperature are quit e satisfactorily simulated with a relatively coarse model. For the int erannual variability, the model reproduces quite well the observed war mings and coolings of the Gulf of Guinea, except for the 1981 event. T he anomalies appear in the simulation earlier than in observations, an d their magnitude is overestimated. These characteristics of the simul ated interannual variability are shared with other simulations of the tropical Atlantic using a very different OGCM and different setup. The generation of the events is monitored through the anomalous heat cont ent field. Although this generation can be explained in a first approx imation as ''the displacement to the east of warm water accumulated in the west'', there are other mechanisms at work that account for the d ifferences in the generation of the 1984 and 1988 events. Through stat istical analysis the main characteristics of this field are related to other output variables and to signals in the filtered forcings. Merid ional convergence in surface velocities plays a significant part in th e appearance of anomalies at the Gulf of Guinea. Transition from onset stage to peak phase is connected to extraequatorial signals in the no rthwestern tropical Atlantic. Differences between the two simulated ev ents (1984 and 1938) can be related to a signal in the wind forcings n orth of 18 degrees N, and near the coast of Africa.