Model verification using GAW observations

Near-Real-Time Model Validation with Global Atmospheric Watch (GAW) Station Data

For an evaluation of the global model performance, modelled gas concentrations are validated with surface in-situ measurements. Station data is provided by Global Atmospheric Watch (GAW) stations in near- real-time (submission ranging from 1 day to 1 month). In order to compare modelled and observed values, modelled concentrations of CO and O3 at the stations' location are interpolated linearly from the model gridded data in the horizontal domain. In the vertical, modelled gas concentrations are extracted at the model level that matches the Global Atmospheric Watch (GAW) stations' real altitude. This is equivalent to matching the mean pressure of model level and the ground station. The comparison of surface in-situ data with global model output comprises several issues of representativeness: In the horizontal scale, the estimation of errors is rather uncomplicated. In the vertical scale, however, representative matching of measured and modelled values remains critical. Especially for mountainous stations, the chosen model level (matching the GAW station's real altitude) may lack topographic effects. Generally, stations in flat terrain are less critical. For evaluation of model performance, scores for the displayed period are printed on top of each figure. Currently, the online validation service operates with 12 GAW stations, which are delivering hourly data of tropospheric CO and O3. The data are preliminary and have not been extensively quality checked. For detailed information, please contact info.mohp@dwd.de.