Analyse multivariée de la réponse atmosphérique simulée aux températures de surface océanique (1961–1994)

Abstract

The ECHAM-4 atmospheric circulation model has been forced with the observed sea surface temperatures (SST) and sea-ice coverage through the period 1901–1994 (with three experiments starting from different initial conditions). Multivariate analyses, based on singular value decomposition, allow the large-scale pattern to be identified which maximizes the skill relative to the observations and the reproducibility between the experiments, that is the proximity between the runs, forced by the same boundary conditions but starting from different initial atmospheric conditions. This leads to the forced component of the atmospheric variability, mainly by SST, which is theoretically predictable from it at seasonal time scales. The spatio-temporal variability of the first observed mode of sea level pressure (December–March) is well simulated for the Tropics but also for North America. The forcing in both cases comes primarily from the ‘Global Tropical’ SST mode. The situation in Europe and in the northeast Atlantic is less clear. Although the spatial behaviour of the observed pattern is well simulated, the reproducibility is weak.