A model intercomparison of atmospheric 137Cs concentrations from the Fukushima Daiichi Nuclear Power Plant accident, phase III: Simulation with an identical source term and meteorological field at 1-km resolution. (October 2020) - Sato, Yousuke
Abstract: The third model intercomparison project (MIP) for investigating the atmospheric behavior of atmospheric caesium-137 ( 137 Cs) emitted from Fukushima Daiichi Nuclear Power Plant (FDNPP) (3rd FDNPP-MIP), Japan, in March 2011, was conducted. A finer horizontal grid spacing (1 km) was used than in the previous FDNPP-MIP (2nd FDNPP-MIP, Sato et al., 2018; 3 km) to evaluate the models' performance for high-concentration events measured near FDNPP. Nine of the models used in the 2nd FDNPP-MIP were also used in the 3rd FDNPP-MIP, and all models used identical source terms and meteorological fields. The performance of the models was evaluated through a comparison with observational data. Our analyses indicated that most of the observed high atmospheric 137 Cs concentrations (plumes) were reasonably well simulated by the models, and the good performance of some models improved the performance of the multimodel, highlighting the advantage of using a multimodel ensemble. The analyses also confirmed that the use of a finer grid resolution resulted in the meteorological field near FDNPP being better reproduced in the 3rd FDNPP-MIP, and the performance of the models was better than that of the 2nd FDNPP MIP. The good representation of the wind field resulted in the reasonable simulation of the narrow distribution of high deposition amount to the northwest of FDNPP and the reduction of the overestimation in deposition amount over the area to the south of FDNPP compared to the 2nd FDNPP MIP. In contrast, the performance of the models in simulating plumes observed over the Nakadori area, the northern part of Gunma, and the Tokyo Metropolitan Area (TMA) was slightly worse than in the 2nd FDNPP-MIP. Highlights: A model intercomparison for atmospheric 137 Cs with fine resolution was conducted. The models showed better performance in the vicinity of FDNPP. Multimodel ensemble showed better performance than that of each model.