The European Tracer Experiment ETEX: A Comparison of Long Range Atmospheric Dispersion Models in Different Weather Conditions

In fall 1994 two long range tracer experiments were conducted in Europe over a distance of 1,800 km. For 12 hours an inert, non-depositing tracer was released at Rennes, Brittany, France. The releases took place at the surface and the tracer was sampled at 168 stations throughout Europe. The sampling stations were run by the National Meteorological Services and the whole experiment was sponsored by the EC, the WMO and the IAEA. 24 Institutions took part in the real-time forecasting of the cloud evolution with 28 long range dispersion models. They simulated surface concentration evolution at the locations where the tracer was sampled. The results of these calculations were compared for both experiments with the measurements, using a number of statistical parameters. The results of this comparison (see Archer et al., 1995 for details) indicated for the first release that a limited group of models (7–8) were capable to obtain a good reproduction of the cloud displacement throughout Europe for any time intervals between 24 to 60 hours after the release start. Large differences were however found when examining the predicted tracer concentration at a particular location. In this paper some results for the second release are also presented, similarities and differences with the first are evidenced and tentative explanations are proposed for the differences in model performance.