Tropical Atlantic air-sea interaction and its influence on the NAO

An atmospheric general circulation model (AGCM) is forced with a prescribed SST dipole anomaly in the tropical Atlantic to investigate the cause of cr ossequatorial SST gradient (CESG) variability and its teleconnection tb the extratropics. The model response bears a striking resemblance to observati ons in both the tropics and extratropics. The tropical response is robust a nd can act to reinforce the prescribed SST anomalies through wind-induced e vaporation. A new feedback mechanism involving low-level stratiform clouds in the subtropics is also identified in the model and observations. The tro pical SST dipole forces a barotropic teleconnection into the extratropics t hat projects onto the North Atlantic Oscillation (NAO). It further induces the extratropical portion of the North Atlantic SST tripole when the AGCM i s coupled with an ocean mixed layer model. CESG variability thus appears to be the centerpiece of a pan-Atlantic climate pattern observed to extend fr om the South Atlantic to Greenland.