A dynamically adapting weather and dispersion model: The Operational Multiscale Environment Model with Grid Adaptivity (OMEGA)

The Operational Multiscale Environment Model with Grid Adaptivity (OMEGA) a nd its embedded Atmospheric Dispersion Model is a new atmospheric simulatio n system for real-time hazard prediction, conceived out of a need to advanc e the state of the art in numerical weather prediction in order to improve the capability to predict the transport and diffusion of hazardous releases . OMEGA is based upon an unstructured grid that makes possible a continuous ly varying horizontal grid resolution ranging from 100 km down to 1 km and a vertical resolution from a few tens of meters in the boundary layer to I km in the free atmosphere. OMEGA is also naturally scale spanning because i ts unstructured grid permits the addition of grid elements at any paint in space and time. In particular, unstructured grid cells in the horizontal di mension can increase local resolution to better capture topography or the i mportant physical features of the atmospheric circulation and cloud dynamic s. This means that OMEGA can readily adapt its grid to stationary surface o r terrain features, or to dynamic features in the evolving weather pattern. While adaptive numerical techniques have yet to be extensively applied in atmospheric models, the OMEGA model is the first model to exploit the adapt ive nature of an unstructured gridding technique for atmospheric simulation and hence real-time hazard prediction. The purpose of this paper is to pro vide a detailed description of the OMEGA model, the OMEGA system, and a det ailed comparison of OMEGA forecast results with data.