MEDIA—An Eulerian Model of Atmospheric Dispersion: First Validation on the Chernobyl Release

Jean Philippe Piedelievre Direction de la Météorologie Nationale, SCEM/D/ES, Paris, France

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Lue Musson-Genon Direction de la Météorologie Nationale, SCEM/D/ES, Paris, France

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François Bompay Direction de la Météorologie Nationale, SCEM/D/ES, Paris, France

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Abstract

At the time of the Chernobyl accident, only a trajectory model was available at the French Weather Service to operationally forecast the movements of such a radioactive cloud. Thus, it was decided to develop a tridimensional model of the atmospheric dispersion of pollutants.

This paper presents the model that was applied using the data collected during and after the Chernobyl release. The transport-diffusion of a pollutant concentration field is computed using the wind, temperature, and precipitation fields already predicted by an operational weather forecasting model, which makes the computing time of this model very low. Turbulent diffusion is modeled using exchange coefficients, Louis' formulation for vertical diffusion and constant parameters for horizontal diffusion. A scavenging ratio is used for wet deposition, and dry deposition is parameterized in terms of deposition velocity. The operational objective of our work has led us to use well-documented numerical techniques (a Crank-Nicholson scheme combined with a splitting technique). Results obtained for the Chernobyl release show that the model is able to describe with a reasonable accuracy the time-evolution of the polluted cloud, as soon as the weather conditions are forecasted well.

The model has been operational at the French Weather Service coupled with EMERAUDE (a global weather forecasting model) or PERIDOT (a limited area forecasting model with a 35-km mesh, centered on France and covering the whole of western Europe).

Abstract

At the time of the Chernobyl accident, only a trajectory model was available at the French Weather Service to operationally forecast the movements of such a radioactive cloud. Thus, it was decided to develop a tridimensional model of the atmospheric dispersion of pollutants.

This paper presents the model that was applied using the data collected during and after the Chernobyl release. The transport-diffusion of a pollutant concentration field is computed using the wind, temperature, and precipitation fields already predicted by an operational weather forecasting model, which makes the computing time of this model very low. Turbulent diffusion is modeled using exchange coefficients, Louis' formulation for vertical diffusion and constant parameters for horizontal diffusion. A scavenging ratio is used for wet deposition, and dry deposition is parameterized in terms of deposition velocity. The operational objective of our work has led us to use well-documented numerical techniques (a Crank-Nicholson scheme combined with a splitting technique). Results obtained for the Chernobyl release show that the model is able to describe with a reasonable accuracy the time-evolution of the polluted cloud, as soon as the weather conditions are forecasted well.

The model has been operational at the French Weather Service coupled with EMERAUDE (a global weather forecasting model) or PERIDOT (a limited area forecasting model with a 35-km mesh, centered on France and covering the whole of western Europe).

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