The effect of ocean thermodynamics on interannual climate variability in the tropical Atlantic is investigated by using an atmospheric general circulation model (CCM3) coupled to an ocean mixed layer model which is forced by heat content anomalies.

A series of experiments has been conducted by coupling an ocean mixed layer model with fixed (prescribed) ocean heat transport to an atmospheric GCM. After a 20 year long spin up we have investigated the ensemble mean response to heat content anomaly in the tropical Atlantic. We contrast the findings of four experiments, two had anomalies north of the equator and two in the southern hemisphere. In each hemisphere one experiment looks at the coupled response in a small box and the response to a broad region akin to the EOF of interannual SST anomalies. An ensemble of 6-10 runs for each experiment has been run. We find a significant dynamical atmospheric response wich at times amplifies the initial heat content anomaly. In most cases the SST signal persists for up to six month and influences the position and strength of the ITCZ. The proposed mechanism is that an off equatorial warm SST anomalie tends to reduce the strength of the trade winds and thereby reduces the local and downwind latent heat flux. This wind evaporation SST feedback seems strong and is hypothesised to be responsible for the long persistence of SST in the subtropical Atlantic. The role of active ocean dynamics in reducing the persistence will be discussed.