The Effect of SST and NAO on Recent Changes in the Location and Intensity of the North Atlantic Storm Track

An increasing amount of evidence suggests a poleward shift of the storm tracks as the climate warms. A coherent picture of the physical processes responsible for the storm track shift is, however, still lacking, and the overall aim of this study is to better understand these processes. Specifically we quantify the relationship between the North Atlantic sea surface temperature (SST) and storm track location with a focus on the seasonal variability. The Climate Forecast System Reanalysis (CFSR) products from 1979-2014 are used. Extra-tropical cyclones are tracked using the University of Melbourne Cyclone Tracking Scheme, and the relationships between SST and track density are assessed through correlation analyses. The results show clear seasonal variability. In winter the areas of positive correlations between SST and track density are spatially more extensive than during summer, when increases in the SST are associated with decreases in the track density over most of the North Atlantic. However, a consistent positive correlation between SST and track density is observed in every season along the Arctic sea-ice margin and over the Gulf Stream area. In these areas the SST gradient is strong throughout the year. The role of the North Atlantic Oscillation (NAO) is also considered. A southeast-northwest shift in the area of influence of NAO from winter to summer is detected and, in contrast to previous studies, we found that correlations between NAO and storm track location are as strong in summer as in winter. Different mechanisms potentially responsible for the seasonal variability in the correlation between SST and storm track location will also be discussed, such as changes in the SST gradient.