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

Abstract

The ocean-atmosphere interactions of sea surface temperature and the North Atlantic Oscillation as an atmospheric phenomenon are examined in an ensemble of climate change simulations. The principal task concentrates on the common climate change signals, the lead-lag relationship, the time-space covariability, and the aspect of predictability. The study is based on Monte Carlo experiments of the German coupled climate model ECHAM-3/LSG with increasing greenhouse-gas concentrations according to IPCC scenario A. The Atlantic SST variability is mainly determined by the greenhouse-gas induced warming signal with maximum temperature rise in the low latitudes whereas in the Icelandic region the CO 2 influence is blotted out by intense natural variability. On a monthly time scale, the North Atlantic SST field is regionally affected by the NAO. An oceanic impact cannot be observed on this short time scale. The main oceanic response occurs in the Sargasso Sea, the Irminger Sea, and less pronounced in the subtropical North Atlantic building 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 temperature and sea level pressure in the North Atlantic sector amounts to 26 % of total variance.