Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kawamura, Hideyuki; Furuno, Akiko; Kobayashi, Takuya; In, Teiji*; Nakayama, Tomoharu*; Ishikawa, Yoichi*; Miyazawa, Yasumasa*; Usui, Norihisa*
Journal of Environmental Radioactivity, 180, p.36 - 58, 2017/12
Times Cited Count：12 Percentile：35.86(Environmental Sciences)This study simulates the oceanic dispersion of Fukushima-derived Cs-137 by an oceanic dispersion model and multiple oceanic general circulation models. The models relatively well reproduced the observed Cs-137 concentrations in the coastal, offshore, and open oceans. Multiple simulations in the coastal, offshore, and open oceans consistently suggested that Cs-137 dispersed along the coast in the north-south direction during the first few months post-disaster, and were subsequently dispersed offshore by the Kuroshio Current and Kuroshio Extension. Quantification of the Cs-137 amounts suggested that Cs-137 actively dispersed from the coastal and offshore oceans to the open ocean, and from the surface layer to the deeper layers in the North Pacific.
Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*
Journal of Environmental Radioactivity, 136, p.64 - 75, 2014/10
Times Cited Count：23 Percentile：53.93(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.
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.
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.
CsKawamura, Hideyuki; Furuno, Akiko; Kobayashi, Takuya; In, Teiji*; Nakayama, Tomoharu*; Ishikawa, Yoichi*; Miyazawa, Yasumasa*; Usui, Norihisa*
no journal, ,
Oceanic dispersion simulations include errors originated from source terms, oceanographic data, etc. In this study, the oceanic dispersion simulations were carried out with five oceanographic data in order to analyze an effect of oceanographic data on Cs dispersion and clarify Cs dispersion in the coastal area and the open ocean. The high-resolution simulation could well reproduce the observed Cs concentration in Fukushima Prefecture and it suggested that directly-released Cs into the ocean dispersed in the north-south direction during a few months after the Fukushima disaster. The relatively low-resolution simulations could reproduce main currents in the North Pacific and they suggested that the Kuroshio Extension played an important role on Cs transport from the coastal area to the open ocean. Moreover, it was demonstrated that Cs was transported from the mixed layer to the deeper layer 1 year after the Fukushima disaster.
Kawamura, Hideyuki; Furuno, Akiko; Kobayashi, Takuya; In, Teiji*; Nakayama, Tomoharu*; Ishikawa, Yoichi*; Miyazawa, Yasumasa*; Usui, Norihisa*
no journal, ,
This study simulates the oceanic dispersion of Fukushima-derived Cs-137 by an oceanic dispersion model SEA-GEARN-FDM and multiple oceanic general circulation models. The oceanic dispersion simulations relatively well reproduced the measured Cs-137 concentrations in the coastal and offshore oceans during the first few months after the Fukushima disaster, and in the open ocean during the first year post-disaster. It was suggested that Cs-137 dispersed along the coast in the north-south direction during the first few months post-disaster, and were subsequently dispersed offshore by the Kuroshio Current and Kuroshio Extension. The Cs-137 amounts were quantified in the coastal, offshore, and open oceans during the first year post-disaster. It was demonstrated that Cs-137 actively dispersed from the coastal and offshore oceans to the open ocean, and from the surface layer to the deeper layer in the North Pacific.
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.
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.
