The Global Modeling Initiative Chemistry and Transport Model (CTM) has been used to produce two simulations of the evolution of stratospheric ozone for 1995-2030 using prescribed boundary conditions for chlorofluorocarbons, nitrous oxide and methane. These simulations each recycle a single year’s meteorological fields. The fields are taken from the finite volume general circulation model (FVGCM) and from a new version of the Goddard Earth Observing System data assimilation system (GEOS DAS) that is termed FVDAS because the DAS uses FVGCM at its core The simulations are identical in all other respects. Although aspects of the constituent observations are reflected by fields produced by both simulations, diagnostics of stratospheric transport such as the age of air show that the transport produced by the FVGCM fields is more realistic than that produced by the FVDAS fields.

There are differences in the constituent fields produced by the simulations for 1995-2002, and the seasonal, latitude and altitude dependencies of the catalytic processes contributing to the ozone loss differ as well. This talk will address the differences in the ozone forecast and focusing on interpretation of these differences using diagnostics of the transport and comparisons of the fields with observations for 1995-2002. The seasonal and spatial dependence of photochemical and transport processes and their relative contributions to the ozone tendency will be investigated in the CTM fields. Because the age of air from the CTM using winds from FVGCM is much different from that calculated from the same CTM using winds from FVDAS, we anticipate that the model balance between photochemical and transport contributions to the ozone tendency will depend on the meteorological fields. We also anticipate that the model differences in the two forecasts can be interpreted using the differences in these balances.