Effects of the solar cycle on the earth's atmosphere

Abstract

Until recently it was generally doubted that the solar variability in the 11-year sunspot cycle (SSC), as measured by satellites, has a significant influence on weather and climate variations. But several studies, both empirical and modelling, have in recent years pointed to probable and certain influences. For instance, Labitzke suggested in 1982 that the sun influences the intensity of the north polar vortex (i.e., the Arctic Oscillation (AO)) in the stratosphere in winter, and that the Quasi-Biennial Oscillation (QBO) is needed to identify the solar signal. At present there is no agreement about the mechanism or mechanisms through which the solar variability effect is transmitted to the atmosphere. But there is general agreement that the direct influence of the changes in the UV part of the solar spectrum (6 to 8% between solar maxima and minima) leads to more ozone and warming in the upper stratosphere (around 50 km) in solar maxima. This leads to changes in the vertical gradients and thus in the wind systems, which in turn lead to changes in the vertical propagation of the planetary waves that drive the global circulation. Therefore, the relatively weak, direct radiative forcing of the solar cycle in the stratosphere can lead to a large indirect dynamical response in the lower atmosphere. © 2007 Springer-Verlag.