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

In this work we report the results of HYSPLIT numerical simulations of the Chernobyl ¹³⁷Cs atmospheric transport, dispersion, and deposition on the regional scale (~1000 km from the source) with the main focus on the analysis of the deposition processes. In the simulations we used three different gridded datasets of input meteorology and three release scenarios previously published in the literature. The resistance method and the predefined constant value of the deposition velocity (0.005 m/s) were applied to calculate dry depositions whereas 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 the territory of Ukraine. Our simulations show considerable dependence of the HYSPLIT-predicted accumulated deposition pattern on both the input meteorology and source parameterizations. The best performance of HYSPLIT was obtained with the ERA Interim reanalysis data and the source model of Talerko (2005) and the constant deposition velocity. This simulation reproduced fairly well the spatial structure of the ¹³⁷Cs contamination on the territory of Ukraine with good evaluation statistics. However, not all significant local maxima of the contamination pattern were captured clearly. Our simulations also show that dry removal processes account for approximately 50% of the total depositions in Ukraine. Both wet in-cloud and below-cloud removal mechanisms had roughly equal influence on the total amount of ¹³⁷Cs radionuclides deposited on the territory of Ukraine.