Covariability and interaction of North Atlantic sea surface temperature and North Atlantic Oscillation in ECHAM3 greenhouse-gas scenario simulations

The ocean-atmosphere interactions of sea surface temperature and the North Atlantic Oscillation as an atmospheric phenomenon are examined in an ensemb le of climate change simulations. The principal task concentrates on the co mmon climate change signals, the lead-lag relationship, the time-space cova riability, and the aspect of predictability. The study is based on Monte Ca rlo experiments of the German coupled climate model ECHAM-3/LSG with increa sing greenhouse-gas concentrations according to IPCC scenario A. The Atlantic SST variability is mainly determined by the greenhouse-gas ind uced warming signal with maximum temperature rise in the low latitudes wher eas in the Icelandic region the CO2 influence is blotted out by intense nat ural variability. On a monthly time scale, the North Atlantic SST field is regionally affected by the NAO. An oceanic impact cannot be observed on thi s short time scale. The main oceanic response occurs in the Sargasso Sea, t he Irminger Sea, and less pronounced in the subtropical North Atlantic buil ding a tripole structure. A climatological index is defined indicating the main response of North Atlantic SST to the atmospheric forcing. This index is largely coherent with the index of the North Atlantic Oscillation on the interannual and decadal time scale. The covariability of sea surface tempe rature and sea level pressure in the North Atlantic sector amounts to 26% o f total variance.