The GRIPS solar intercomparison project presented here is part of the “GCM Reality Intercomparison Project for SPARC (GRIPS)” focusing only on the influence of 11-year solar-cycle variations on the atmosphere. The aim of the present comparison is to assess the problems related to the simulation of the solar influence in order to better define future experiments. Results from different GCMs will be presented to investigate whether there is any consistency between them or with existing model studies and observations. Each of the different GCMs used the same wavelength-dependent solar irradiance changes as well as the resulting ozone changes calculated with 2-D chemical models enabling a better intercomparison of the different GCMs. It turns out that each model response is different and that the model results are dependent on the model climatologies that vary widely both among themselves and with observations.
One of the major problems encountered during the comparison is the lack of reliable observational evidence for the solar influence on climate (e.g., temperature, ozone). There are also important uncertainties of the forcings used for the model simulations (solar energy spectrum, ozone).