Influence of the Atlantic Multidecadal Oscillation on the Northern Hemisphere Climate in Winter

Abstract:

Some recent studies suggest that the long-term variability of the North Atlantic SST may exert a significant influence on the Northern Hemisphere atmospheric circulation in winter. In the observational record, an inverse relationship is found between the polarity of the Atlantic Multidecadal Oscillation (AMO) - that depicts the basin-wide fluctuations of the North Atlantic SST with a period of ~70 years - and the multidecadal trends of the North Atlantic Oscillation (NAO). However, this statistical relationship is uncertain since only two cycles of the AMO are included in the observations. Here we use a set of experiments performed with the Community Atmospheric Model (CAM5) to investigate the response of the atmospheric circulation to AMO-SST anomalies. As in observations, the positive phase of the AMO results in a southward shift of the North Atlantic storm track and more frequent negative NAO and blocking episodes in winter. The role of tropical vs extratropical AMO-SST anomalies is discussed, as well as the sensitivity of the results to the ocean-atmosphere feedback (using a slab-ocean model) and to the representation of the stratosphere (using the high-top version of CAM, WACCM).