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Kamachi, Masafumi*; Ishikawa, Yoichi*; Kawamura, Hideyuki; Maximenko, N.*; Hafner, J.*; MacFadyen, A.*
Techno-Ocean 2016 (Techno-Ocean), p.599 - 602, 2016/10
The tsunami that followed the Great East Japan Earthquake in March 2011 caused a large amount of debris to flow out into the North Pacific, mainly from the Tohoku district, Japan. We conducted drift simulations to monitor and predict the trajectory of the tsunami debris. The results suggested that the tsunami debris was mainly transported eastward by the Kuroshio Extension and prevailing westerly winds, spreading in a north-south direction by ocean eddies and storms. As for the tsunami debris with high buoyancy, it was shown to be strongly influenced by ocean surface winds as well as ocean currents, reaching the west coast of the North American continent around the fall of 2011.
Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*
Journal of Environmental Radioactivity, 136, p.64 - 75, 2014/10
Times Cited Count：24 Percentile：53.02(Environmental Sciences)Numerical simulations on oceanic radioactive cesium dispersions in the North Pacific were conducted with a focus on the long-term variation of the radioactive cesium concentration after the Fukushima disaster. It was suggested that the 
Cs concentration had already been reduced to the pre-Fukushima background value in the wide area within the North Pacific 2.5 years after the Fukushima disaster.
Kawamura, Hideyuki; Kobayashi, Takuya; Nishikawa, Shiro*; Ishikawa, Yoichi*; Usui, Norihisa*; Kamachi, Masafumi*; Aso, Noriko*; Tanaka, Yusuke*; Awaji, Toshiyuki*
Global Environmental Research (Internet), 18(1), p.81 - 96, 2014/09
A drift simulation of tsunami debris flushed out from the Tohoku district, Japan, into the North Pacific due to the tsunami on March 11, 2011, has been conducted to monitor and forecast the drift path over the North Pacific. Results showed that tsunami debris was first transported eastward by the intense Kuroshio Extension and westerly, spreading in the north and south directions by both an energetic ocean eddy and a storm track over the ocean. Tsunami debris with larger windage was transported over the North Pacific by ocean surface wind rather than ocean current and arrived at the west coast of the North American Continent in the fall of 2011. Tsunami debris located near the North American Continent migrated, associated with the basin-scale seasonal change in the atmospheric pressure pattern. Our forecast run suggested that the tsunami debris belt will be formed from the North American Continent in the east to the Philippines in the west.
Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*; Nishikawa, Shiro*; Ishikawa, Yoichi*
Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 7 Pages, 2014/08
Numerical simulations on oceanic dispersion of the radioactive cesium in the North Pacific from March 2011 to September 2013 were conducted to clarify the concentration of the radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant. We implemented the oceanic dispersion simulations with two independent ocean reanalysis dataset. It was suggested that the Cs concentration in the North Pacific was lower than the pre-Fukushima background level about two years after the Fukushima disaster. The intercomparison revealed that meso-scale eddies in the Kuroshio Extension region may have efficiently diluted the radioactive cesium concentration at the sea surface. In addition, it was suggested that the enhanced downward current accompanied by the meso-scale eddies played an important role in transporting the radioactive cesium into the intermediate layer.
Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*
no journal, ,
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.
Kamachi, Masafumi*; Kawamura, Hideyuki; Ishikawa, Yoichi*; Usui, Norihisa*
no journal, ,
A drift simulation on the movement of the marine debris has been conducted by a Japanese modeling group (JAMSTEC, JAEA, and MRI) in order to examine the positions of the marine debris in the North Pacific, landing positions on the coast, and landing date after the Great East Japan Earthquake on March 11, 2011. The simulation has been conducted under the Japanese national project and MoE-PICES ADRIFT project. The potential locations of the marine debris were determined by numerical simulations with an ocean data assimilation system MOVE/MRI.COM-WNP and -NP, a coupled atmosphere-ocean data assimilation system K7, and an oceanic dispersion model SEA-GEARN. Data assimilation, dispersion method, current and wind fields, effect of windage, and comparison with sighting observation will be reported.
Cs concentration due to the Fukushima Daiichi Nuclear Power Plant accidentKawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*
no journal, ,
In this study, we conducted numerical experiments on oceanic dispersion of Cs discharged from the Fukushima Daiichi Nuclear Power Plant (FNPP1) in the North Pacific. A oceanic dispersion model (SEA-GEARN) based on difference equations was used in order to clarify surface dispersion as well as intermediate dispersion of Cs. We used reanalysis data calculated by a three-dimensional variational data assimilation system (MOVE) developed at Meteorological Research Institute, Japan Meteorological Agency. It was suggested that highly polluted water discharged from the FNPP1 was efficiently diluted by meso-scale eddies in the Kuroshio extension region. Simultaneously, these meso-scale eddies played an important role to carry Cs into the intermediate layer in the Kuroshio extension region. The directly discharged Cs was fundamentally carried eastward and it attained at approximately 165
W in August, 2012.
Cs in the ocean discharged from the Fukushima Dai-ichi Nuclear Power PlantKawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*
no journal, ,
Numerical experiments on oceanic dispersion of Cs discharged from the Fukushima Dai-ichi Nuclear Power Plant were carried out with an oceanic dispersion model SEA-GEARN developed in Japan Atomic Energy Agency. High quality oceanic reanalysis data was input to the SEA-GEARN, which was calculated by MOVE system developed in Meteorological Research Institute, Japan Meteorological Agency. Although a large portion of results in the numerical experiments was good agreement with observed surface Cs concentration in the northern Pacific Ocean, the calculated concentration was underestimated in some area. It is suggested that Cs was distributed in the wide area of the northern Pacific Ocean due to deposition of Cs released into the atmosphere, which concentration was low on the whole. On the other hand, Cs directly discharged into the ocean was carried to the east along the Kuroshio extension dispersing by mesoscale eddies.
Kawamura, Hideyuki; Kobayashi, Takuya; Nishikawa, Shiro*; Ishikawa, Yoichi*; Usui, Norihisa*; Kamachi, Masafumi*
no journal, ,
Tsunami debris was flushed out due to tsunami accompanied by the Great East Japan Earthquake in March 2011. In this study, simulation on distribution of tsunami debris was carried out in cooperation with Japan Agency for JAMSTEC and MRI, JMA. An ocean dispersion model SEA-GEARN developed at JAEA was used in this study. We used the ocean current and sea surface wind data from March 2011 to September 2013 calculated by an ocean data assimilation system MOVE developed at MRI, JMA. On the other hand, we used them from October 2013 to June 2016 calculated by an atmosphere-ocean coupling data assimilation system K7 developed at JAMSTEC. It was suggested that tsunami debris was transported eastward by the Kuroshio Extension and reached the western U.S. coast. In addition, it was forecasted that a large part of tsunami debris would spread in the southern part of the North Pacific.
