A new interactive chemistry-climate model:: 1.: Present-day climatology and interannual variability of the middle atmosphere using the model and 9 years of HALOE/UARS data -: art. no. 4290

The newly developed middle atmosphere general circulation model with interactive photochemistry, Middle Atmosphere European Centre/Hamburg Model 4 with Chemistry (MA-ECHAM4-CHEM), has been applied for several 20 year "time slice'' experiments using fixed boundary conditions typical of the early and late 1990s, the 1960s, and the near future, including sensitivity runs to study effects of sea surface temperature and greenhouse gas concentration changes. In part 1 we compare the results for the early and late 1990s with 9 years of data of the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite, some presented for the first time, and other satellite and radiosonde data. We show a statistical analysis as well as snapshots of a set of chemical species for typical situations. The model captures the main features of temperature and ozone distributions including the interannual variability of the Arctic and Antarctic vortices and homogeneous and heterogeneous ozone destruction. A detailed comparison of modeled and observed chlorine and nitrogen species including denitrification and chlorine repartitioning in the polar vortices is presented, showing generally good agreement. This holds also for chemical ozone budgets derived from the model and from satellite data. Computed stratospheric and mesospheric water vapor agrees with the satellite data within about 10%, including dehydration in the Antarctic winter. However, in the tropical lower stratosphere, the concentrations of the source gases are underestimated, presumably because of numerical deficiencies in transport. It is shown that interactive photochemistry is important to get agreement with observed temperatures in the lower stratosphere in high-latitude spring. Our coupled model provides a powerful tool to investigate chemical-radiative-dynamical feedback mechanisms of anthropogenic trace gas emissions and natural variability on climate and stratospheric ozone, at least for quasi-steady-state conditions.