Validation of a Fully Coupled Chemistry-Climate Model

Recently, the fully coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM has been developed (Hein et al. 2001). To check the abilities and deficiencies of the model system a detailed comparison is strongly required with a variety of distinct observations. In this project, an intensive comparison of NO₂ tropospheric columns derived from ERS-2 GOME and results of the interactively coupled model system has been carried out. Nearly five years of GOME measurements (January 1996 to August 2000) have been used. The length of this data series is sufficient to enable a comparison based on climatological averages and with global coverage, focussing on the geographical distribution of the tropospheric NO₂, for the first time. A new approach of analysing regional differences (i.e. on continental scales) calculating individual averages for different environments provides more detailed information about specific NO_X sources and of their seasonal variations. The results obtained enable the validity of the model NO₂ source distribution and the assumptions used to separate tropospheric and stratospheric parts of the NO₂ column amount from the satellite measurements to be investigated. Observations and model results show a qualitative agreement, but also some differences in detail. The method employed to assess the tropospheric column of NO₂ from GOME yields some disadvantages, which must be considered.