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

https://doi.org/10.1007/s10872-010-0053-5

A numerical experiment is performed to reproduce a distribution of concentrations of Sr and Cs and estimate their total amounts in the Japan Sea. The concentrations of Sr and Cs in the surface layer is in the range of 1.0-1.5 Bq/m and 2.0-2.5 Bq/m. 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 Sr and Cs in the seawater is evaluated to be 1.34 PBq (1 PBq = 10 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 Sr and Cs vary corresponding to deposition at the sea surface with the maximums of 4.86 PBq for Sr and 7.33 PBq for Cs in the mid-1960s.

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

https://doi.org/10.1007/s10872-009-0039-3

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.

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.

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

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 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.

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.

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.

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.

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.