A coupled model study of the remote influence of ENSO on tropical Atlantic SST Variability.

摘要

To investigate the tropical Atlantic response to the remote El Nino-Southern Oscillation (ENSO) forcing, a Reduced Physics - Coupled Global Circulation Model (RP-CGCM) is developed, and four experiments are carried out. The results show that the RP-CGCM is capable of capturing the major features of Tropical Atlantic Variability (TAV) and its response to ENSO forcing.; The SST response to the remote influence of ENSO may be divided into two stages. In stage one, the ENSO influences the tropical Atlantic SST primarily through the Troposphere Temperature (TT) mechanism, which predicts a uniform warming in the tropical Atlantic following the mature phase of El Nino. In the north tropical Atlantic (NTA), the Walker mechanism and the Pacific-North-American (PNA) mechanism work in concert with the TT-induced warming, giving rise to a robust SST response during the boreal spring in this region. In the south tropical Atlantic (STA), the southeasterly wind anomaly and increased stratus clouds work against the TT-induced warming, resulting in a much weaker SST response in this region. At this stage, the response can be largely explained by the ocean mixed layer response to changes in surface heat fluxes induced by ENSO.; In stage two, ocean dynamics play a more active role in determining the evolution of SST. The cross-equatorial wind anomaly in the western to central equatorial Atlantic can change the SST in the eastern equatorial Atlantic through Bjerknes feedback and the SST in the central equatorial Atlantic through Ekman feedback. These feedback result in a cooling of SST in the equatorial south Atlantic (ESA) region which is so overwhelming that it cancels the warming effect induced by the TT mechanism and reverses the sign of the warm SST anomaly that is formed during stage one in this region.; In general, the horizontal advection of heat plays a secondary role in the SST response to the remote influence of ENSO, except in the regions where the North Equatorial Countercurrent (NECC) dominates and the SST variability is strong. Entrainment is particularly important in maintaining the correct SST structure during boreal summer.