Are solar spectral variations a drive for climatic change?

Abstract

Observations of the Sun from satellite and rocket platforms have provided good evidence that solar radiation varies noticeably in the UV portion of the spectrum over a solar rotation period of 27 d^1,2. There is also less conclusive evidence for such variations on the time scale of the 11 -yr sunspot cycle^1,2. We investigate here the possible effects of these UV variations on atmospheric ozone content and climate for time scales encompassing the 27-d solar rotation period, the sunspot period, twice this period (solar magnetic period) and much longer times. We conclude that (1) solar UV variations on time scales of weeks to months can occasionally perturb total ozone and stratospheric temperatures by noticeable amounts, but they result in only very minor changes in the troposphere; (2) the above cited estimates of UV variation over the 11-yr solar cycle are inconsistent with measured changes in total ozone; (3) with UV variations being limited by long-term trends in total ozone, only very small variations in surface temperature are expected over the 11-yr solar cycle, but possibly significant ones could occur over the 22-yr cycle; (4) solar spectral changes might be partially responsible for century-long variations in climate, which have been empirically correlated with changes in solar activity^3,4.