Spatial resolution dependence of Fukushima radionuclide simulations using 15-km, 3-km, and 500-m grid models

The nuclear accident on 11 March 2011 at the Fukushima Daiichi nuclear power plant (FDNPP) discharged a lot of artificial radionuclides, which were advected, dispersed, and deposited mainly over eastern Japan and the North Pacific Ocean. To achieve the comprehensive understanding of this radioactive contamination, we need numerical model studies as well as observational studies. However, the simulation of advection, diffusion, and deposition has large uncertainties and difficulties. Therefore the combination of up-to-date weather forecast modeling, chemical transport modeling, data assimilation, and ensemble simulation must be indispensable. As the first step of that combinational study, we conducted a spatial resolution intercomparison of Fukushima Cs-137 simulations with 15-km, 3-km, and 500-m grid models, which were coupled with an ensemble-based data assimilation system using meteorological observation datasets. The grid values such as U, V, T, and precipitation were calculated by the data assimilation system for each resolution simulation (i.e., 15-km/3-km/500-m grid) respectively. The spatial distribution of the Cs-137 contamination was largely influenced by the surrounding geography of FDNPP through the advection, diffusion, and deposition processes, so that the simulation results evidently depended on the model resolution. This simulation results were statistically validated by ensemble analysis.