Regional HYSPLIT simulation of atmospheric transport and deposition of the Chernobyl 137Cs releases

Özet

In this work we report the results of HYSPLIT numerical simulations of the Chernobyl 137Cs atmospherictransport, dispersion, and deposition on the regional scale (~1000 km from the source) with the main focus onthe analysis of the deposition processes. In the simulations we used three different gridded datasets of inputmeteorology and three release scenarios previously published in the literature. The resistance method and thepredefined constant value of the deposition velocity (0.005 m/s) were applied to calculate dry depositionswhereas an approach based on a scavenging coefficient was used for both wet in-cloud and below-cloud removals.The results were statistically evaluated against the measurements of 137Cs total depositions on theterritory of Ukraine. Our simulations show considerable dependence of the HYSPLIT-predicted accumulateddeposition pattern on both the input meteorology and source parameterizations. The best performance ofHYSPLIT was obtained with the ERA Interim reanalysis data and the source model of Talerko (2005) and theconstant deposition velocity. This simulation reproduced fairly well the spatial structure of the 137Cs contaminationon the territory of Ukraine with good evaluation statistics. However, not all significant local maximaof the contamination pattern were captured clearly. Our simulations also show that dry removal processes accountfor approximately 50% of the total depositions in Ukraine. Both wet in-cloud and below-cloud removalmechanisms had roughly equal influence on the total amount of 137Cs radionuclides deposited on the territory ofUkraine.