Solar cycle modulation of the North Atlantic Oscillation: Implication in the spatial structure of the NAO

The spatial extent of the North Atlantic Oscillation (NAO) is investigated. The results suggest that the spatial structure of the NAO differs significantly according to the phase of the solar cycle. During the solar maximum phases, the NAO has a hemispherical structure extending into the stratosphere, which is similar to the Arctic Oscillation (AO) except for the Pacific sector. However, during the minimum phase, the NAO is confined to the eastern Atlantic sector in the troposphere. Whether or not the NAO is modulated by the solar cycle, these results may shed new light on the controversy of the physical reality of the two modes of variability, the NAO and the AO.