Surface air temperature and SST in wide regions across the North Atlantic basin, in eastern North America, the Arctic, Eurasia and the Mediterranean, are significantly correlated with NAO variability.
Temperature changes over northern Africa, the Middle East and the southeast U.S. are also notable.
They hypothesize that stratospheric increases in CO2 result in enhanced radiative cooling of the polar stratosphere in winter, leading to a strengthening of the polar vortex. They then invoke stratosphere-troposphere interaction to explain the recent positive trend in the NAO index through enhancement of tropospheric stationary waves. Changes in mean circulation patterns over the North Atlantic are accompanied by pronounced shifts in the storm tracks and associated synoptic eddy activity. Drier than normal conditions occur during high NAO index winters over much of central and southern Europe, the northern Mediterranean countries, and west North Africa. At the same time, wetter than normal conditions occur from Iceland through Scandinavia.