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

Yousuke Sato,Masayuki Takigawa,Denis Quélo,Junya Uchida,Mizuo Kajino,Sheng Fang,Arnaud Quérel,Tsuyoshi Thomas Sekiyama,Hiroaki Terada,Yu Morino,Hiroaki Kondo,Masanao Kadowaki,Daisuke Goto,Hiromi Yamazawa

doi:10.1016/j.aeaoa.2020.100086

Abstract

Abstract The third model intercomparison project (MIP) for investigating the atmospheric behavior of atmospheric caesium-137 (137Cs) 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 137Cs 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

Large amounts of radionuclides, including caesium-137 (137Cs), were emitted to the atmosphere after the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan, which was triggered by an earthquake and seismic sea wave in March 2011
We evaluated the averaged model performance during the whole calculation period and over the whole calculation domain to provide an overview of the results of the 3rd model intercomparison project (MIP)
A new model intercomparison targeting the atmospheric 137Cs emitted from FDNPP in March 2011 (3rd MIP) was conducted using the same meteorological field (Sekiyama and Kajino, 2020) and emission inventory (Katata et al, 2015)

Summary

Introduction

Large amounts of radionuclides, including caesium-137 (137Cs), were emitted to the atmosphere after the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan, which was triggered by an earthquake and seismic sea wave in March 2011. A number of studies investigated the behavior of the atmospheric 137Cs through observations (e.g., Adachi et al, 2013; Honda et al, 2012; Igarashi et al, 2015; Kaneyasu et al, 2012; Moriizumi et al, 2019; Oura et al, 2015; Sanada et al, 2018; Science Council of Japan, 2014; Terasaka et al, 2016; Tsuruta et al, 2014, 2018) and modeling (e.g., Chino et al, 2011; Draxler et al, 2015; Hu et al, 2014; Kajino et al, 2016; Katata et al, 2012; Korsakissok et al, 2013; Mathieu et al, 2018; Morino et al, 2011; Stohl et al, 2012; Takemura et al, 2011; Terada et al, 2012; Yasunari et al, 2011) These studies demonstrated that modeling is a powerful tool for understanding the behavior of 137Cs. the numerical models themselves contained uncertainties originating from various factors, e. Due to these uncertainties, simulated atmospheric 137Cs typically differed from model to model

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