The Effect of Solar Flux Variations and Trace Gas Emissions on Recent Trends in Stratospheric Ozone and Temperature

Trend analyses of satellite and ground-based observations clearly indicate that temperatures and ozone concentrations in the upper stratosphere are undergoing longterm changes. Variations in solar ultraviolet radiation during the 11-year solar cycle are influencing stratospheric temperatures and photochemistry from above. Forcings from below result from the increasing atmospheric concentrations of long-lived trace constituents, such as carbon dioxide, methane, nitrous oxide, several chlorofluorocarbons and other halocarbons. Using the LLNL two-dimensional chemical-radiative-transport model of the global atmosphere, we evaluate the influences of these external forcings on the middle atmosphere. Our calculations include recent estimates of the variations in solar ultraviolet radiation since 1974. Model results for the solar cycle effects on total ozone, upper stratospheric ozone and temperature are within the uncertainty (in some cases, large) range of observational data analyses. The model calculations including both solar variability and the effects of changing trace gas emissions can explain much of the observed trends in upper stratospheric ozone and temperature from 1979 to 1986.