The Arctic Oscillation is the dominant mode of variability in the Northern Hemisphere middle latitudes, and this is true all of the year. When we say that something is the “dominant mode,” we mean that if we formally measure the variance and then try to describe the variance by recognizable patterns, then the single largest way to describe the variance is with the Arctic Oscillation.
RickyRood, • 11:12 PM GMT on August 18, 2013