Oceanic forcing of the wintertime North Atlantic Oscillation and European climate

Abstract

The weather over the North Atlantic Ocean, particularly in winter, is often characterized by strong eastward air-flow between the ‘Icelandic low’ and the ‘Azores high’, and by a ‘stormtrack’ of weather systems which move towards western Europe. The North Atlantic Oscillation — an index of which can be defined as the difference in atmospheric pressure at sea level between the Azores and Iceland — is an important mode of variability in the global atmosphere¹,² and is intimately related to the position and strength of the North Atlantic stormtrack owing to dynamic processes internal to the atmosphere³,⁴. Here we use a general circulation model of the atmosphere to investigate the ocean's role in forcing North Atlantic and European climate. Our simulations indicate that much of the multiannual to multidecadal variability of the winter North Atlantic Oscillation over the past half century may be reconstructed from a knowledge of North Atlantic sea surface temperature. We argue that sea surface temperature characteristics are ‘communicated’ to the atmosphere through evaporation, precipitation and atmospheric-heating processes, leading to changes in temperature, precipitation and storminess over Europe. As it has recently been proposed that there may be significant multiannual predictability of North Atlantic sea surface temperature patterns⁵, our results are encouraging for the prediction of European winter climate up to several years in advance.