Abstract
Abstract. At MeteoSwiss an integrated modelling system is used to simulate the dispersion of radioactive material in emergency situations. For the prediction of the atmospheric flow, the COSMO numerical weather prediction model is used. The model is run operationally at 6.6 and 2.2 km horizontal resolution, respectively and uses a 1.5 order turbulence closure with a prognostic equation for turbulent kinetic energy. Both versions of the COSMO model are coupled off-line with a Lagrangian particle dispersion model (LPDM). The aim of this study is to investigate the sensitivity of the dispersion model to different interfacing approaches between LPDM and the COSMO model. The diagnosed turbulence variables are validated on an ideal convective case and two measurement campaigns. Simulations of hypothetical pollutant releases show that the different interfacing approaches can lead to substantial changes in the forecasted concentrations.
Highlights
2 MethodologyLagrangian particle dispersion models are among the most sophisticated tools to simulate atmospheric dispersion of pollutants
The mean meteorological variables can directly be extracted from a numerical weather prediction (NWP) model but turbulence characteristics have to be parameterized
The impact of two different interfacing approaches on dispersion has been studied with the COSMO–Lagrangian particle dispersion model (LPDM) system operationally used at MeteoSwiss
Summary
Lagrangian particle dispersion models are among the most sophisticated tools to simulate atmospheric dispersion of pollutants. The mean wind component is taken directly from the COSMO model, while the turbulent component is computed using the Langevin equation (Legg and Raupach, 1982) Evaluation of this equation requires the following turbulence variables at the particle’s position: autocorrelation function and the Lagrangian timescale (parameterized according to Taylor (1921), and the standard deviation of the wind fluctuations (σk). The latter are derived from the turbulent kinetic energy (e), which is taken directly from the COSMO model: σk = 2mke,. A different approach to diagnose the turbulence variables for a dispersion model is to apply similarity theory considerations In this case usually the surface fluxes and a diagnosed planetary boundary layer (PBL) height is needed from the NWP model. For the present purpose both approaches (the bulk Ri and the TKE methods) to determine the boundary layer heights are employed in Sect. 4 as a sensitivity test
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