Atmospheric Transport Simulation of the Chernobyl Accident by a GCM Eulerian Model

The atmospheric transport of radionuclides from a source close to Chernobyl is simulated by the Global Climate Model LMDZ, developed at the Laboratoire de Météorologie Dynamique in Paris. The source has been released at different altitudes and at different times between April 26 and April 28 1986. Simulations with 192x145 grid cells essentially distributed over Western Europe and 19 levels vertically, are carried out in a "nudged" mode, where horizontal velocities and temperature are relaxed towards wind analyses ECMWF, available every 6 hours. Transport is based on mass conservation of the tracer in the atmosphere, taking into account the parameterization of turbulent mixing and convection. Concentration maps for a transport episode of 15 days show that the grid resolution of a few tens of kilometers is necessary in this model. Numerical results show that South-East of France is affected by the radioactive plume on 1st and 2nd May with calculated concentrations close to the estimated ones. Finally, sensitivity tests are carried out for this accident by varying the vertical spatial resolution, by using different precipitation models, and by testing a new vertical parameterization of vertical transport in the boundary layer.