Numerical experiments on dispersion of radionuclides in the ocean released from the Fukushima Daiichi Nuclear Power Plant; An Application of GOV product to marine environmental emergency responses

Kawamura, Hideyuki  ; Kobayashi, Takuya ; Furuno, Akiko   ; Usui, Norihisa*; Kamachi, Masafumi*

Numerical experiments on oceanic Cs dispersion were intensively conducted in order to assess an effect on the North Pacific, focusing on long-term variation of Cs concentration after the Fukushima disaster occurred in March, 2011. The numerical experiments were carried out using the oceanic dispersion model SEA-GEARN and the three-dimensional variational data assimilation system MOVE-NP and MOVE-WNP (GOV Japan National System). It was suggested that main radioactive cesium clouds reached the central part of the North Pacific exceeding the 170th meridian West one year later after the Fukushima disaster. The radioactive cesium had been efficiently diluted by meso-scale eddies along the Kuroshio Extension regime since the Fukushima disaster, declining the concentration below pre-Fukushima background value in the wide area within the North Pacific one year later after the Fukushima disaster.