The Impact of the 1997/98 El Niño Event on the Atlantic Ocean

Abstract

The El Niño?Southern Oscillation (ENSO) has far-reaching impacts on global climate via ?teleconnections? associated with wavelike or other disturbances that are excited in the tropical Pacific. These teleconnections may influence the air?sea heat fluxes, either by altering the latent and sensible heat fluxes through a change in low-level wind speed or direction or by altering the degree of cloud cover and thus the radiation budget. The anomalous fluxes can generate sea surface temperature (SST) anomalies that can in turn feed back on the atmospheric circulation. These effects are explored for the 1997/98 ENSO event using a novel and powerful modeling technique in which a coupled ocean?atmosphere model (the U.K. Hadley Centre HadCM3 model) is forced to follow observed tropical Pacific SSTs using a strong thermal relaxation, 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 authors focus on the impact of ENSO on the Atlantic Ocean. Model results are compared both with historical records of the Atlantic response to El Niño and with SST observations during the 1997/98 event. The model simulates well the warming of the tropical North Atlantic that is typical of El Niño events. In addition, it identifies a significant positive anomaly in the South Atlantic in the autumn of 1997/98 that was also observed and appears to be a feature of the Atlantic response to El Niño that has not previously been noted. The results suggest that many other large SST anomalies observed in the Atlantic during 1997/98 were not part of the response to El Niño.