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-SouthernOscillation (ENSO) forcing, a Reduced Physics ?? Coupled Global Circulation Model(RP-CGCM) is developed, and four experiments are carried out. The results show thatthe 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 twostages. In stage one, the ENSO influences the tropical Atlantic SST primarily throughthe Troposphere Temperature (TT) mechanism, which predicts a uniform warming in thetropical Atlantic following the mature phase of El Nino. In the north tropical Atlantic(NTA), the Walker mechanism and the Pacific-North-American (PNA) mechanism workin concert with the TT-induced warming, giving rise to a robust SST response during theboreal spring in this region. In the south tropical Atlantic (STA), the southeasterly windanomaly and increased stratus clouds work against the TT-induced warming, resulting ina much weaker SST response in this region. At this stage, the response can be largelyexplained by the ocean mixed layer response to changes in surface heat fluxes inducedby ENSO.In stage two, ocean dynamics play a more active role in determining theevolution of SST. The cross-equatorial wind anomaly in the western to central equatorialAtlantic can change the SST in the eastern equatorial Atlantic through Bjerknesfeedback and the SST in the central equatorial Atlantic through Ekman feedback. Thesefeedback 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 andreverses the sign of the warm SST anomaly that is formed during stage one in thisregion.In general, the horizontal advection of heat plays a secondary role in the SSTresponse to the remote influence of ENSO, except in the regions where the NorthEquatorial Countercurrent (NECC) dominates and the SST variability is strong.Entrainment is particularly important in maintaining the correct SST structure duringboreal summer.