The impact of the 1997/98 El Nino event on the Atlantic Ocean

The El Nino-Southern Oscillation (ENSO) has far-reaching impacts on global climate via "teleconnections'' associated with wavelike or other disturbanc es that are excited in the tropical Pacific. These teleconnections may infl uence the air-sea heat fluxes, either by altering the latent and sensible h eat fluxes through a change in low-level wind speed or direction or by alte ring the degree of cloud cover and thus the radiation budget. The anomalous fluxes can generate sea surface temperature (SST) anomalies that can in tu rn feed back on the atmospheric circulation. These effects are explored for the 1997/98 ENSO event using a novel and powerful modeling technique in wh ich a coupled ocean-atmosphere model (the U.K. Hadley Centre HadCM3 model) is forced to follow observed tropical Pacific SSTs using a strong thermal r elaxation, while elsewhere the model is allowed to vary freely. This is an extension of previous studies in which the impact of ENSO was investigated using an atmospheric model coupled to an ocean mixed layer model. The autho rs focus on the impact of ENSO on the Atlantic Ocean. Model results are com pared both with historical records of the Atlantic response to El Nino and with SST observations during the 1997/98 event. The model simulates well th e warming of the tropical North Atlantic that is typical of El Nino events. In addition, it identifies a significant positive anomaly in the South Atl antic in the autumn of 1997/98 that was also observed and appears to be a f eature of the Atlantic response to El Nino that has not previously been not ed. The results suggest that many other large SST anomalies observed in the Atlantic during 1997/98 were not part of the response to El Nino.