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JAEA Reports

Ocean current data obtained by Acoustic Doppler Current Profiler across the Tsugaru Strait (Joint research)

Kawamura, Hideyuki; Hirose, Naoki*; Nakayama, Tomoharu*; Ito, Toshimichi

JAEA-Data/Code 2021-004, 34 Pages, 2021/05

JAEA-Data-Code-2021-004.pdf:3.72MB

The Japan Atomic Energy Agency measured the ocean current across the Tsugaru Strait using an Acoustic Doppler Current Profiler attached on a ferryboat from October 1999 to January 2008. The characteristics of the ocean current in the Tsugaru Strait must be understood for predicting oceanic dispersion of radioactive materials released from nuclear facilities around the strait. Furthermore, it is critical to elucidate the mechanism of the Tsugaru Warm Current from an oceanography viewpoint. The dataset obtained in this investigation consists of daily ocean current data files that record the components of the current speed in the east-west and north-south directions from the surface layer to the bottom layer. The dataset stores 2,211 daily ocean current data files, despite some data periods missing from October 1999 to January 2008. In this study, information on the dataset is described for users to analyze the dataset properly for their purposes. Section 1 provides the background and purpose of the ocean current measurement, Section 2 explains the methodology of measurement using an Acoustic Doppler Current Profiler, and Section 3 explains the record format of the daily ocean current data files and data acquisition rate and presents analysis results. Finally, Section 4 concludes this study.

Journal Articles

Numerical experiment for strontium-90 and cesium-137 in the Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Hirose, Naoki*; Togawa, Orihiko

Journal of Oceanography, 66(5), p.649 - 662, 2010/10

 Times Cited Count:2 Percentile:6.23(Oceanography)

A numerical experiment is performed to reproduce a distribution of concentrations of $$^{90}$$Sr and $$^{137}$$Cs and estimate their total amounts in the Japan Sea. The concentrations of $$^{90}$$Sr and $$^{137}$$Cs in the surface layer is in the range of 1.0-1.5 Bq/m$$^{3}$$ and 2.0-2.5 Bq/m$$^{3}$$. The concentrations in the intermediate and deep layer are higher than those observed in the northwestern Pacific Ocean, indicating active winter convection in the Japan Sea. The total amounts of $$^{90}$$Sr and $$^{137}$$Cs in the seawater is evaluated to be 1.34 PBq (1 PBq = 10$$^{15}$$ Bq) and 2.02 PBq, which demonstrates an estimation by observational data in the Japan Sea expeditions between 1997 and 2002 by Japan Atomic Energy Agency. The total amounts of $$^{90}$$Sr and $$^{137}$$Cs vary corresponding to deposition at the sea surface with the maximums of 4.86 PBq for $$^{90}$$Sr and 7.33 PBq for $$^{137}$$Cs in the mid-1960s.

Journal Articles

Simulation of concentrations of anthropogenic radionuclides in the Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Hirose, Naoki*; Togawa, Orihiko

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 4 Pages, 2010/10

This study aims to demonstrate many findings in the Japan Sea expeditions by Japan Atomic Energy Agency between 1997 and 2002 making use of an ocean general circulation model. A numerical experiment is performed between 1945 and 2000 with deposition at the sea surface by global fallout as main source of anthropogenic radionuclides. The concentrations of $$^{90}$$Sr and $$^{137}$$Cs in the surface layer are approximately in the range of 1.0-1.5 Bq/m$$^{3}$$ and 2.0-2.5 Bq/m$$^{3}$$ and they exponentially decrease with depth from the sea surface to the sea bottom. Total amounts of $$^{90}$$Sr and $$^{137}$$Cs in the seawater of the Japan Sea are estimated to be about 1.34 PBq (1 PBq = 10$$^{15}$$ Bq) and 2.02 PBq in the numerical experiment, which demonstrates observational estimations in the Japan Sea expeditions. Time series of the total amounts show that they attain the maximums of 4.86 PBq for $$^{90}$$Sr and 7.33 PBq for $$^{137}$$Cs in 1964.

Journal Articles

Modeling of the branches of the Tsushima Warm Current in the eastern Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Hirose, Naoki*; Takikawa, Tetsutaro*; Yoon, J.-H.*

Journal of Oceanography, 65(4), p.439 - 454, 2009/08

 Times Cited Count:5 Percentile:15.47(Oceanography)

This study aims at reproducing branches of the Tsushima Warm Current making use of an ocean general circulation model, which is important for movement of pollutants in the Japan Sea. The model was laterally exerted by volume transports measured by ADCP through the Tsushima Straits and the Tsugaru Strait. Sea level variation measured by coastal tide-stations as well as satellite altimeters is assimilated into the numerical model. It was demonstrated that an assimilation of sea level variation at the coastal tide-stations is useful to simulate oceanic condition in the nearshore region.

Journal Articles

Sequential forecasting of the surface and subsurface conditions in the Japan Sea

Hirose, Naoki*; Kawamura, Hideyuki; Lee, H. J.*; Yoon, J.-H.*

Journal of Oceanography, 63(3), p.467 - 481, 2007/06

 Times Cited Count:29 Percentile:54.45(Oceanography)

This study estimates and forecasts a realistic change of the Japan Sea by assimilating satellite measurements into an eddy-resolving circulation model. Suboptimal but feasible assimilation schemes of approximate filtering and nudging play essential roles in a system. The sequential updates of error covariance significantly outperforms the asymptotic covariance due to irregular sampling patterns from multiple altimeter satellites. The best estimate shows an average rms difference of 1.2 $$^{circ}$$C only to the radiometer data, and also explain about half of sea level variances measured by the microwave observation. It is demonstrated that a forecast persistency strongly depends on variable, depth, and location.

Journal Articles

Oil spill simulation in the Japan Sea

Kawamura, Hideyuki; Kobayashi, Takuya; Hirose, Naoki*; Ito, Toshimichi; Togawa, Orihiko

WIT Transactions on Ecology and the Environment, Vol.88, p.273 - 278, 2006/00

An assessment system of marine environment in the Japan Sea is being constructed in the Japan Atomic Energy Agency. It is composed of an ocean general circulation model (RIAMOM), a particle random-walk model (SEA-GEARN) and a radiation dose assessment model (COLDOS). This study aims to confirm a validity of the assessment system by reproducing a movement of spilled oil at an incident of Russian tanker Nakhodka, in January 1997. Realistic reproduction of ocean conditions is a significant factor for accurate simulations of the movement of spilled oil. In this study, one of data assimilation techniques, an approximate Kalman filter, was introduced by combining RIAMOM with sea level measurements of satellite data. The assimilated results were in good agreement with observed oceanic phenomena both qualitatively and quantitatively. Using the calculated ocean currents, simulations of behaviour of spilled oil was performed with SEA-GEARN. The tanker was ruptured in a storm about 100 km north of the Oki Islands in Shimane Prefecture, Japan, on January 2, 1997. Most of oil spread over off Hyogo, Kyoto, Fukui and Ishikawa Prefecture, meanwhile a part of it reached a coast of Niigata Prefecture detouring around Noto Peninsula by January 21, 1997. The most important feature in these regions is considered to be a branch of the Tsushima Warm Current (TWC). Owing to a variability of TWC, ocean eddy activities and a sea surface wind, the spilled oil dispersed widely in space. On the other hand, the strong northeastward component of TWC was likely to drive the spilled oil to Niigata Prefecture. A number of experiments with different parameters and situations showed that the assimilated daily ocean currents with wind drift gave the best effect on simulation for the movement of spilled oil.

JAEA Reports

Construction of STACY(Static Experiment Critical Facility)

Murakami, Kiyonobu; ; Hirose, Hideyuki; ; *; *; Sakuraba, Koichi; ; ; *; et al.

JAERI-Tech 98-033, 70 Pages, 1998/08

JAERI-Tech-98-033.pdf:2.25MB

no abstracts in English

JAEA Reports

Annual report of STACY in 1995; 600mm diameter cylindrical core and 10% enriched uranyl nitrate solution

; ; Hirose, Hideyuki; *; *; Ono, Akio; Sakuraba, Koichi; Izawa, Naoki; Tonoike, Kotaro; *; et al.

JAERI-Tech 97-005, 107 Pages, 1997/03

JAERI-Tech-97-005.pdf:3.26MB

no abstracts in English

Oral presentation

The Development of assessment system for marine environment in the Japan Sea

Kawamura, Hideyuki; Kobayashi, Takuya; Hirose, Naoki*; Ito, Toshimichi; Togawa, Orihiko

no journal, , 

no abstracts in English

Oral presentation

Sequential state estimation using remote-sensing measurements in the Japan/East Sea

Hirose, Naoki*; Kawamura, Hideyuki; Yamamoto, Masaru*

no journal, , 

This presentation reports our assimilation modeling efforts in the Japan/East Sea. An eddy-resolving, free-surface ocean circulation model is driven by daily meteorological forcing of JMA regional forecast at the surface and monthly measurement data at the horizontal boundary. The top layer is restored to the remotely-sensed temperature. The SST assimilation reduces the average residual variance from 4.55 to 2.09 degC$$^{2}$$ and presents small-scale features even finer than the original data set. An approximate Kalman filter corrects the subsurface density and velocity conditions based on the difference between the observation and the model at the sea surface height. The sequential updates of the error covariance require more computational overheads than the steady covariance but significantly corrects high-frequency barotropic changes of the northern waters. The assimilated results show realistic upper circulations such as the separation of the East Korean Warm Current or the quasi-biennial oscillation in comparison to in-situ subsurface measurements. The study also demonstrates that the assimilated estimates of the JES improve winter atmospheric conditions from meso to seasonal scales. The sharp frontal structure of the assimilated SST strongly modifies the mesoscale features over the southern JES as simulated by a non-hydrostatic atmospheric model. It is also found that the total amount of the DJF precipitation is lead by the regional NDJ SST and is further controlled by autumn transport of the Tsushima Warm Current.

Oral presentation

Non-steady Kalman filtering for the forecasting model in the Sea of Japan

Hirose, Naoki*; Kawamura, Hideyuki

no journal, , 

no abstracts in English

Oral presentation

A Forecasting system of RIAM for the Japan/East Sea

Hirose, Naoki*; Sergey, V.*; Watanabe, Tatsuro*; Kawamura, Hideyuki; Yamamoto, Masaru*

no journal, , 

The Japan Sea holds many features that are similar to world's oceans. We have been developing an ocean data assimilation and prediction system. There are currently two versions of the model aiming at short- and long-term forecasts. The short-term version is driven by tidal forcings and atmospheric predictions, and enables accurate forecasts for up to five days including tidal changes. Short-term outputs will be used for material drift simulations such as an oil spill. The long-term version is sequentially corrected by assimilating the sea surface temperature and height of satellites by the nudging and reduced-order Kalman filter, respectively. The assimilated model estimates realistic nowcast and forecast for a few months. We are also successful to predict a migration of giant jellyfish in 2005. The system will be extended to the East Asian Marginal Seas in the near future.

Oral presentation

Modeling of the nearshore branch of the Tsushima Warm Current with data assimilation

Kawamura, Hideyuki; Ito, Toshimichi; Hirose, Naoki*; Yoon, J.-H.*; Takikawa, Tetsutaro*

no journal, , 

An assessment system for oceanic environment in the Japan Sea has been developed at Japan Atomic Energy Agency. Realistic reproduction of oceanic condition such as current and temperature is necessary to calculate movement of materials in the ocean. A circulation in the Japan Sea is strongly effected by the Tsushima Warm Current through the Tsushima Straits and the Tsugaru Warm Current through the Tsugaru Strait. In this study, an ocean general circulation model was drived by realistic volume transports of the Tsushima Warm Current and the Tsugaru Warm Current observed by Kyushu University and JAEA, respectively. In addition, the satellite altimeter data and sea surface height at coastal stations were assimilated by the Kalman filter. Model results well reproduced current field along the Japanese coast observed from September to October in 2000.

Oral presentation

Data assimilation research of the east Asian marine system; Preliminary results

Hirose, Naoki*; Moon, J.-H.*; Kawamura, Hideyuki; Okei, Noriyuki*

no journal, , 

To study comprehensively the marine system in the East Asian region, we are currently extending the prediction model of the Japan/East Sea to the broader northwestern Pacific region. Because we find that tide gauge data improves coastal current significantly, a new gauge is installed at Hegura Island in this summer. Strong sea level changes are found in coastal region of the East China Sea associated with the local wind variation and the river discharge.

Oral presentation

The Numerical experiment of distribution of anthropogenic radionuclides in the Japan Sea

Kawamura, Hideyuki; Ito, Toshimichi; Kobayashi, Takuya; Otosaka, Shigeyoshi; Hirose, Naoki*

no journal, , 

Observation had been carried out to clarify distribution of anthropogenic radionuclides in the Japan Sea in the period between 1997 and 2002 by Japan Atomic Energy Agency. This study aims at reproducing the distribution of anthropogenic radionuclides with a numerical model and clarifying their movement in the Japan Sea. Deposition densities by global fallout are applied as boundary conditions for strontium 90 and cesium 137 at the sea surface. Numerical results show that concentration of strontium 90 and cesium 137 is compared with the observed one in the surface layer and the intermediate layer, although the concentration below 1000 m depth is quite low. More numerical experiments will be performed modifying parameters and boundary conditions of the numerical model in the future.

Oral presentation

Development of the ocean forecast system in the Japan Sea (JADE), 4; Assimilation of tide data

Takayama, Katsumi*; Hirose, Naoki*; Kawamura, Hideyuki; Shimizu, Daisuke*; Watanabe, Tatsuro*

no journal, , 

An ocean general circulation model in the Japan Sea has been being developed to reproduce and forecast movement of pollutants at JAEA. It was demonstrated that an assimilation of sea level variation at tide stations along the Japanese coast is effective to reproduce oceanic condition in the nearshore region. In this study, an effect of assimilation of satellite altimeter data, CTD data and tide data is quantitatively surveyed. As a result, it was demonstrated that this assimilation scheme improves the oceanic condition.

Oral presentation

Development of a material circulation model in the Japan Sea

Kawamura, Hideyuki; Kobayashi, Takuya; Ito, Toshimichi; Otosaka, Shigeyoshi; Togawa, Orihiko; Onitsuka, Go*; Hirose, Naoki*

no journal, , 

Japan Atomic Energy Agency has been developing a material circulation model in the Japan Sea to confirm aspect of observational results. The material circulation model consists of three numerical models, an ocean general circulation model, a particle random-walk model and a lower trophic ecosystem model. A preliminary numerical experiment shows that vertical profile and total amount of Sr-90 and Cs-137 are well compared with observational results.

Oral presentation

Development of ocean current data measured by acoustic doppler current profiler across the Tsugaru Strait

Kawamura, Hideyuki; Hirose, Naoki*; Nakayama, Tomoharu*; Ito, Toshimichi

no journal, , 

We developed ocean current data measured by an Acoustic Doppler Current Profiler attached on a ferryboat across the Tsugaru Strait from October 1999 to January 2008 in this study. It is useful to understand the characteristics of the ocean current in the Tsugaru Strait for predicting oceanic dispersion of radioactive materials released from nuclear facilities around the strait and for understanding the mechanism of the Tsugaru Warm Current. The database cosists of 2,211 daily data files from October 1999 to January 2008. The data files record the components of the current speed in the east-west and north-south directions, quafifying flags and so on. The ocean current data was frequently acquired in summer compared with winter. The strong eastward ocean current corresponding to the Tsugaru Warm Current was confirmed by analyzing the ocean current data. We expect that the database will be used by many users for oceanographical study.

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