Abstract
In order to determine the response of the atmosphere to winter sea surface temperature (SST) anomalies in the North Atlantic area, we carried out ensemble runs of 20 years, forced with constant, perturbed, SST patterns using the climate version of the ARPEGE AGCM, at T42 resolution. A Monte Carlo technique was applied, in such a way that the control experiment, forced with observed climatological temperatures, and the four scenario experiments, forced with perturbed SSTs are equivalent to a length of 20 independent winters. Four anomalous winter North Atlantic sea surface temperature (SST) fields have been constructed by considering the observed SST variability in the main basins, namely the Labrador Sea and the Greenland Sea. Two patterns are of the `seesaw' type, while the two others have same the polarity in both basins. The patterns have been reinforced by a factor of 5–6 compared to presently observed multi-annual anomalies, in order to get SST anomalies which may have occurred during periods of the Little Ice Age. The differences between each of the four winter simulations with perturbed SSTs and the control run are analyzed in terms of tropospheric thickness, mean-sea-level pressure and storm activity. The `seesaw' type patterns give a weaker response in the tropospheric thickness fields than the two others. This is expected from simple considerations. In the mean circulation and synoptic activity, it appears that the Labrador Sea SST is important in determining the atmospheric response. This is probably due to enhanced temperature gradients east of New Foundland which enhances the storm activity.
Published Version
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