Evaluation of the operational multiscale environment model with grid adaptivity against the European tracer experiment

The Operational Multiscale Environment Model with Grid Adaptivity (OMEGA) i s a multiscale nonhydrostatic atmospheric simulation system based on an ada ptive unstructured grid. The basic philosophy behind the OMEGA development has been the creation of an operational tool for real-time aerosol and gas hazard prediction. The model development has been guided by two basic desig n considerations in order to meet the operational requirements: 1) the appl ication of an unstructured dynamically adaptive mesh numerical technique to atmospheric simulation, and 2) the use of embedded atmospheric dispersion algorithms. An important step in proving the utility and accuracy of OMEGA is the full-scale testing of the model using simulations of real-world atmo spheric events and qualitative as well as quantitative comparisons of the m odel results with observations. The main objective of this paper is to prov ide a comprehensive evaluation of OMEGA against a major dispersion experime nt in operational mode. Therefore, OMEGA was run to create a 72-h forecast for the first release period (23-26 October 1994) of the European Tracer Ex periment (ETEX). The predicted meteorological and dispersion fields were th en evaluated against both the atmospheric observations and the ETEX dispers ion measurements up to 60 h after the start of the release. In general, the evaluation showed that the OMEGA dispersion results were in good agreement in the position, shape, and extent of the tracer cloud. However, the model prediction indicated that there was a limited spreading of the predictions around the measurements with a small tendency to underestimate the concent ration values.