A GCM study of climate change in response to the 11‐year solar cycle

Abstract A general‐circulation model (GCM) is used to investigate the impact of the 11‐year solar‐activity cycle on the climate of the lower atmosphere. Solar forcing is represented by changes in both incident irradiance and stratospheric ozone concentrations. Experiments are carried out with realistic and factor‐ten enhanced solar irradiance changes and with ozone changes based on two‐dimensional photochemical model results and loosely based on Total Ozone Mapping Spectrometer ozone column data. A pattern of response, consistent across all the experiments, is found in which the tropical Hadley cells weaken and broaden, and the sub‐tropical jets and mid‐latitude Ferrel cells move polewards. This causes sub‐tropical warming and a characteristic vertical banding of mid‐latitudes temperature changes in both the summer and winter hemispheres. the GCM results suggest that the precise response of the atmosphere depends on the magnitude and distribution of the ozone changes. This is confirmed by use of an equal‐area model of the tropical Hadley cells in which the input radiative equilibrium‐temperature anomalies are determined from the downward irradiance (both solar and long wave) at the tropopause as calculated in the GCM. As both the magnitude of the solar irradiance change and, more particularly, the latitude‐height structure of solar‐induced ozone changes over the 11‐year cycle are not yet well established, the GCM study may well underestimate the solar effects.