This project considers the response of lower stratospheric and surface climate to the changes in insolation accompanying the 11-year sunspot cycle. Insolation changes are hypothesized to affect stratospheric temperature as increases in solar ultraviolet (UV) radiation cause increases in stratospheric ozone which in turn lead to increases in stratospheric temperature (maximizing over the tropics) and midlatitude zonal winds. The increased stratospheric zonal winds then affect circulation at lower levels through the wave-mean flow interactions associated with the "downward control" mechanism, producing a pattern of sea level pressure anomalies including low pressure over the poles and high pressure over the northern North Pacific. Work conducted under this award would examine this "top down" mechanism for the influence of solar variability on surface climate in simulations from two climate models, one in which the solar-induced ozone anomalies are specified from satellite observations, and another (the Whole Atmosphere Community Climate Model, or WACCM) in which the ozone changes are generated internally by the model in response to the insolation change. In the WACCM simulations, the insolation change will be prescribed according to several estimates of its spectral distribution, to determine the sensitivity of the response to uncertainty in the UV component of the 11-year solar forcing. WACCM simulations will also be used explore the sensitivity of the response to additional factors including the phase of the stratospheric quasi-biennial oscillation.
The work will have broader impacts through the support and training of a graduate student, which will develop the scientific workforce in this scientific area. In addition, a better understanding of the impact of solar variability on climate may prove useful for understanding the sensitivity of climate to external forcing, and the mechanisms which determine the climatic response. Such information may benefit decision makers engaged in policy decisions regarding climate change.
