Ocean-atmosphere variability over the Pan-Atlantic basin

Ocean and atmosphere variability is investigated over the whole Atlantic ba sin in a 51-year record of sea surface temperature (SST). In the tropics, S STs variations are separated into two time scales: decadal (8-16 years) and interannual (< 5 years). A strong cross-equatorial gradient mode dominates decadal SST anomalies with centers of action having opposite polarities at 15 degrees N and 15 degrees S, while interannual variations are characteri zed by SST anomalies of the same polarity throughout the tropics. Sea level pressure (SLP) regressions onto the cross-equatorial gradient index reveal extratropical teleconnections associated with the North Atlantic Oscillati on (NAO), and with the South Atlantic. At the same time, a Pan-Atlantic spa tial pattern is also found in SST regressions. Lagged regressions of SLP on the cross-equatorial SST gradient index shows the extratropical decadal os cillation that is out of phase between hemispheres. These results suggest t hat an extratropical forcing could excite the tropical Atlantic variability .