Solar influence on a major mode of atmospheric variability

Abstract

We find that the North Annular Mode (NAM) of the wintertime geopotential height anomalies between 10 and 1000 hPa is influenced by solar changes and that the effect is statistically significant. This evidence suggests that a mechanism of solar influence on climate operates through the excitation of this mode. The influence depends on the phase of the quasi-biennial oscillation (QBO). In early winter for the west QBO and late winter for the east QBO the solar changes affect the NAM in both the stratosphere and the troposphere almost equally. The results are compared with earlier studies of the role of the QBO and solar UV changes on near-polar temperatures and geopotential heights. Thus the late winter effect for the west QBO found by Labitzke and van Loon [1988] is clearly evident in the NAM in the stratosphere but does not appear in the troposphere. Copyright 2002 by the American Geophysical Union.