Modeling the response of the atmosphere to solar variability (Invited Speaker)

Numerous observations have documented the impact of solar variability on the Earth's atmosphere, ranging from the short-term response of the mesosphere and lower thermosphere to changes associated with the 11-year solar cycle that appear to be present even in the lower atmosphere. Understanding of such variability often requires numerical modeling, but computational limitations have precluded detailed calculation of the interactions among radiation, dynamics and chemistry, which can be particularly important in the middle atmosphere. This paper describes a series of studies carried out with NCAR's Whole Atmosphere Community Climate Model, designed to elucidate mechanisms of atmospheric response to solar variability, with emphasis on the 11-year solar cycle. It is shown that observations throughout the upper stratosphere and the MLT are well reproduced and may be understood in terms of current knowledge of atmospheric chemistry and dynamics. Responses in the lower stratosphere and troposphere are smaller, often statistically insignificant, and only partly consistent with observations, even in long model runs and ensembles of runs. Possible reasons for the failure to reproduce observations in the lower atmosphere are discussed, together with suggestions for model improvements that may help resolve this issue.