Atmospheric circulation and its impact on ice phenology in Scandinavia

Atmospheric circulation is important in affecting surface climate and ecosystems. In this study, we compared the impact of north-atlantic and regional atmospheric circulation, as represented by the North Atlantic Oscillation (NAO) index and a set of regional circulation indices, on ice phenology of 50 Scandinavian lakes. Both ice freeze and ice break-up dates were coherent over the whole region and were significantly correlated with both types of circulation indices. Correlations were especially strong for regional circulation indices. The application of regional indices, here for the first time related with ice data over a large area, allowed the determination of the type (i.e. meridional/zonal wind and cyclonic/anticyclonic conditions) of atmospheric circulation influencing the ice phenology. The results suggest that regional circulation indices are very useful tools, in addition to global circulation, to improve the understanding of the interaction between ecosystem processes and climate.