Simple data assimilation of precipitation for atmospheric advection diffusion simulations of radioactive materials and investigation on formation of the hotspot

Abstract

Due to the Great East Japan Earthquake occurred in March 2011, Fukushima Daiichi Nuclear Power Plant was severely damaged and radioactive materials were released in the air. The materials were transported and deposited directly or with precipitation. Simulations of atmospheric numerical models are expected to give us information of the spatio-temporal distribution of the materials. However, its accuracy is still not enough because of uncertainties especially for the hotspot in Kanto region. In this study, we used IsoRSM with the tracers of ¹³¹I and ¹³⁷Cs and applied simple data assimilation of observed precipitation and improved the accuracy of simulating the hotspot. In addition, using 2 hours shifted vertical accumulated radioactive materials for the simulations, we concluded hotspot would have been formed in the morning on March 21^st in 2011.