A Comparison of the Solar Cycle Signature in Vertical Ozone and Temperature Profiles Seen by SAGE II With Coupled Chemistry-Climate Model Results

Solar variability is known to affect the Earth's climate. However, the exact mechanisms whereby small changes in extra-terrestrial solar irradiance over the 11 year solar cycle affect the climate are poorly understood. One of the primary objectives of the SOLar Impacts on Climate and the Environment (SOLICE) project is to assess the impact of solar variability on stratospheric ozone, radiative forcing and surface UV using coupled chemistry-climate models. Comparisons of model results and observations are expected to advance understanding of the mechanisms of solar-climate links. Global vertical ozone profiles (version 6.1) from the Stratospheric Aerosol and Gas Experiment II (SAGE II), together with co-located NCEP/NCAR temperature profiles, have been examined for the solar cycle signature from October 1984 to June 2001 as a function of altitude/pressure and latitude. In addition to solar cycle forcing, ozone concentrations and temperatures may also be influenced by the Quasi-Biennial Oscillation (QBO), volcanic eruptions, the El Niño-Southern Oscillation (ENSO), tropopause height variations, and the solar zenith angle (time of day) at the measurement location [Bodeker et al., JGR, vol. 103, 28661-28681, 1998]. These confounding effects must be eliminated before the solar cycle signal can be quantitatively identified. Two different approaches have been used:

1) Outside of volcanically perturbed periods, the QBO is expected to be the largest source of variability. Ozone and temperature profiles are sorted according to the phase of the QBO before profile differences between solar maximum and minimum are calculated.

2) A regression model, incorporating all forcings as basis functions, is applied to the ozone and temperature profiles and the amplitude of the solar cycle basis function is extracted.

These results are compared with output from the UMETRAC (Unified Model with Eulerian TRansport And Chemistry) coupled chemistry-climate model.