Modelling transport and deposition of caesium and iodine from the Chernobyl accident using the DREAM model

[摘要] A tracer model, DREAM (the Danish Rimpuff and Eulerian Accidental releaseModel), has been developed for modelling transport, dispersion and deposition(wet and dry) of radioactive material from accidental releases, as the Chernobyl accident. The model is a combination of a Lagrangian model, thatincludes the near source dispersion, and an Eulerian model describing the long-range transport. The performance of the transport model has previouslybeen tested within the European Tracer Experiment, ETEX, which included transport and dispersion of an inert, non-depositing tracer from a controlledrelease. The focus of this paper is the model performance with respect to thetotal deposition of¹³⁷Cs, ¹³⁴Cs and ¹³¹I fromthe Chernobyl accident, using different relatively simple and comprehensiveparameterizations for dry- and wet deposition. The performance, compared tomeasurements, of using different combinations of two different wet depositionparameterizations and three different parameterizations of dry deposition hasbeen evaluated, using different statistical tests. The best model performance, compared to measurements, is obtained when parameterizing thetotal deposition combined of a simple method for dry deposition and a
subgrid-scale averaging scheme for wet deposition based on relativehumidities. The same major conclusion is obtained for all the three differentradioactive isotopes and using two different deposition measurement databases. Large differences are seen in the results obtained by using thetwo different parameterizations of wet deposition based on precipitation rates and relative humidities, respectively. The parameterization based onsubgrid-scale averaging is, in all cases, performing better than the parameterization based on precipitation rates. This indicates that thein-cloud scavenging process is more important than the below cloud scavengingprocess for the submicron particles and that the precipitation rates are relatively uncertain in the meteorological model compared to the relativehumidity. Relatively small differences are, however, seen in the statisticaltests between the three different parameterizations of dry deposition.

[学科分类] 大气科学