The Impact of Solar Variability on Climate

Abstract

A general circulation model that simulated changes in solar irradiance and stratospheric ozone was used to investigate the response of the atmosphere to the 11-year solar activity cycle. At solar maximum, a warming of the summer stratosphere was found to strengthen easterly winds, which penetrated into the equatorial upper troposphere, causing poleward shifts in the positions of the subtropical westerly jets, broadening of the tropical Hadley circulations, and poleward shifts of the storm tracks. These effects are similar to, although generally smaller in magnitude than, those observed in nature. A simulation in which only solar irradiance was changed showed a much weaker response.

Response of global upper ocean temperature to changing solar irradiance

“…Other mechanisms have been proposed that alter the atmosphere directly and the upper ocean indirectly. One such mechanism has been proposed by Haigh [1996], who finds the UV portion of peak solar irradiance increasing ozone production, leading to stratospheric heating and to poleward displacements in the stratospheric and tropospheric wind systems. Another mechanism has been proposed by Svensmark and FriisChristensen (submitted manuscript, 1996) who find peak solar irradiance decreasing global cloud cover through its influence upon cosmic ray activity and tropospheric ionization.…”

“…The l 1-year solar irradiance cycle occurs because bright solar faculae and dark sunspots modulate the A major question impacting this study is whether changing solar irradiance influences global-average upper ocean temperature directly through solar insolation or whether it influences it indirectly through its impact upon the intervening atmospheric wind and cloud patterns. Haigh [1996] examined the influence of the ultraviolet (UV) portion of changing solar irradiance upon stratospheric ozone in an atmospheric general circulation model, finding subsequent heating altering stratospheric and tropospheric winds, displacing them poleward during peak solar irradiance. H. Svensmark and E. FriisChristensen (Variation of cosmic ray flux and global cloud covcrage--A missing link in solar-climate relationships, submitted to Journal of Atmospheric and Terrestrial Physics, 1996) (hereinafter referred to as Svensmark and Friis-Christensen, submitted manuscript, 1996) examined the influence of changing solar irradiance upon cosmic ray activity (i.e., responsible for ionization in the troposphere), finding it modulating global cloud cover, decreasing it during peak solar irradiance.…”

On the ambiguous nature of the 11 year solar cycle signal in upper stratospheric ozone

“…In this mechanism, increased UV radiation enhances ozone production via O 2 photolysis, thereby altering middle atmosphere (stratosphere and mesosphere) temperatures. This modifies the upward propagation of planetary waves [Kodera and Kuroda, 2002], which drive the middle atmospheric circulation, and also influence the tropospheric circulation [e.g., Haigh, 1996].…”

Do Models Underestimate the Solar Contribution to Recent Climate Change?

“…Although our study indicates that there could be an enhanced global-scale temperature response to solar forcing, convincing evidence for a mechanism remains elusive. Potentially the largest amplification of solar forcing could result from modulation of stratospheric ozone by variations in solar ultraviolet, which could influence the troposphere via modulation of planetary waves (Shindell et al 1999b) or modulation of the Hadley circulation (Haigh 1996), although none of the published studies indicate that ozone feedback could enhance solar radiative forcing by more than a factor of one-half (J. D. Haigh 2003, personal communication). Alternatively, solar effects on climate could be mediated by cosmic rays, the intensity of which has declined at the earth as the interplanetary magnetic field increased during the twentieth century.…”