Comparison between Eulerian and Lagrangian Atmospheric Transport Models

Two numerical atmospheric models are tested and compared both in backward and forward modes to study the transport and dispersion of radioactive gases in the framework of the Comprehensive Test Ban Treaty. The first one (LMDZ) has been developed at the Laboratoire de Meteorologie Dynamique in Paris,it calculates eulerian large-scale advection based upon finite-volume methods and parametrization of turbulent mixing and convection. The second one (HYSPLIT), developed by the Air Resources Laboratory of NOAA, is lagrangian and calculated 3D trajectories of particules, taking also into account dispersion due to wind shear. Concentrations of particules are compared at stations of the CTBT network for a fictitious source in the Pacific Ocean, that is assumed to be punctual in time and space. In the backward mode, concentrations are calculated and compared over 15 days from a point source at Tahiti to determine the field of regard for this station. Sensitivity tests are carried out by varying the spatial resolution of models.