Atmospheric response to zonally averaged sea surface temperatures in the North Atlantic - a model study

Abstract

A less dynamically active ocean will most likely lead to a more zonal sea surface temperature (SST) distribution. In order to identify if, and how such an effect affects the atmospheric variability, idealized experiments with an Atmospheric General Circulation Model (AGCM) of intermediate complexity have been conducted. For two different seasons, the atmospheric response to a removal of the longitudinal dependence of the SSTs in the North Atlantic are investigated. The results reveal a response projecting largely on the model's positive 1st mode of intrinsic atmospheric variability characterized by the North Atlantic Oscillation (NAO). In winter, the response is more in accordance with the variability pattern referred to as the East-Atlantic Pattern (EAP). Generally it is found that the tropical part of the ocean circulation is the most important for creating changes in atmospheric circulation, both at lower and higher latitudes. In general, the local interannual atmospheric variability is decreased in most regions, but several areas also experience increased variability. We identify a tendency of the response amplitudes to increase with longer timescales.