Akiyoshi, Hideharu*; Kadowaki, Masanao; Yamashita, Yosuke*; Nagatomo, Toshiharu*
Scientific Reports (Internet), 13, p.320_1 - 320_12, 2023/01
State-of-the-art chemistry climate models (CCMs) have indicated that a future decrease in ozone-depleting substances (ODSs) combined with an increase in greenhouse gases (GHGs) would increase the column ozone amount in most regions except the tropics and Antarctic. However, large Arctic ozone losses have occurred at a frequency of approximately once per decade since the 1990s, despite the ODS concentration peaking in the mid-1990s. To understand this, CCMs were used to conduct 24 experiments with ODS and GHG concentrations set based on predicted values for future years; each experiment consisted of 500-member ensembles. The 50 ensemble members with the lowest column ozone in the mid- and high latitudes of the Northern Hemisphere showed a clear ODS dependence associated with low temperatures and a strong westerly zonal mean zonal wind. Even with high GHG concentrations, several ensemble members showed extremely low spring column ozone in the Arctic when ODS concentration remained above the 1980-1985 level. Hence, ODS concentrations should be reduced to avoid large ozone losses in the presence of a stable Arctic polar vortex. The average of the lowest 50 members indicates that GHG increase towards the end of the twenty-first century will not cause worse Arctic ozone depletion.
Terada, Hiroaki; Nagai, Haruyasu; Kadowaki, Masanao; Tsuzuki, Katsunori
Journal of Nuclear Science and Technology, 22 Pages, 2023/00
It is essential to establish a method for reconstructing the source term and spatiotemporal distribution of radionuclides released into the atmosphere due to a nuclear accident for emergency countermeasures. We examined the dependency of a source term estimation method based on Bayesian inference using atmospheric dispersion simulation and environmental monitoring data on the availability of various monitoring data. Additionally, we examined the applicability of this method to a real-time estimation conducted immediately after an accident. A sensitivity analysis of the estimated source term during the Fukushima Daiichi Nuclear Power Station (FDNPS) accident for combinations of various monitoring data indicated that using monitoring data with a high temporal and spatial resolution and the concurrent use of air concentration and surface deposition data is effective for accurate estimation. A real-time source term estimation experiment assuming the situation of monitoring data acquisition during the FDNPS accident revealed that this method could provide the necessary source term for grasping the overview of surface contamination in the early phase and evaluating the approximate accident scale. If the immediate online acquisition of monitoring data and regular operation of an atmospheric dispersion simulation are established, this method can provide the source term in near-real time.
Kadowaki, Masanao; Furuno, Akiko; Nagai, Haruyasu; Kawamura, Hideyuki; Terada, Hiroaki; Tsuzuki, Katsunori; El-Asaad, H.
Journal of Environmental Radioactivity, 237, p.106704_1 - 106704_18, 2021/10
The source term of Cs for the Fukushima Daiichi Nuclear Power Station (FDNPS) accident was estimated from the results of local-scale atmospheric dispersion simulations and measurements. To confirm the source term's validity for reproducing the large-scale atmospheric dispersion of Cs, this study conducted hemispheric-scale atmospheric and oceanic dispersion simulations. In the dispersion simulations, the atmospheric-dispersion database system Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI)-DB and oceanic dispersion model SEA-GEARN-FDM were used. Compared with the air concentrations of Cs measured by the Comprehensive Nuclear-Test-Ban Treaty Organization, overall, the WSPEEDI-DB simulation reproduced the measurements with some overestimation. Furthermore, the deposition amounts of Cs was investigated using concentrations of Cs in seawater. The simulated seawater concentrations of Cs were underestimated regionally in the North Pacific. The overestimation and underestimation could be improved without contradiction between the air and seawater concentrations of Cs using more realistic precipitation in atmospheric dispersion simulations. This shows that the source term validated in this study could reproduce the spatiotemporal distribution of Cs because of the FDNPS accident in both local and large-scale atmospheric dispersion simulations.
Nakayama, Hiromasa; Yoshida, Toshiya; Terada, Hiroaki; Kadowaki, Masanao
Atmosphere (Internet), 12(7), p.899_1 - 899_16, 2021/07
In this study, first, we conducted meteorological observations by a Doppler LiDAR and simple plume release experiments by a mist spraying system at the site of Japan Atomic Energy Agency. Then, we developed a framework for prediction system of local-scale atmospheric dispersion based on a coupling of large-eddy simulation (LES) database and on-site meteorological observation. The LES-database was also created by pre-calculating high-resolution turbulent flows in the target site at mean wind directions of class interval. We provided the meteorological observed data with the LES database in consideration of building conditions and calculated three-dimensional distribution of the plume by a Lagrangian dispersion model. Compared to the instantaneous shot of the plume taken by a digital camera, it was shown that the mist plume transport direction was accurately simulated. It was concluded that our proposed framework for prediction system based on a coupling of LES-database and on-site meteorological observation is effective.
Kadowaki, Masanao; Terada, Hiroaki; Nagai, Haruyasu
Atmospheric Environment; X (Internet), 8, p.100098_1 - 100098_17, 2020/12
The behaviors of atmospheric I and the global cycle of I remain incompletely understood because the spatiotemporal resolution of monitoring is insufficient and few measurement-based models have been reported. This study aims to quantitatively understand the global budget of I. When quantifying, we conduct global atmospheric I dispersion simulations covering from 2007 to 2010. To achieve this goal, the present study newly incorporated the iodine chemistry processes of two gas-phase chemical reactions, six photolysis reactions, and two heterogeneous reactions into an existing atmospheric I transport model (GEARN-FDM). Besides the aerial release of I from nuclear fuel reprocessing facilities, the model includes the volatilization processes of I compounds from Earth's surface. The net I exchange fluxes from the atmosphere to the Earth's surface of land and ocean were estimated as 18.0 GBq/y and 5.3 GBq/y, respectively. The global I emission from oceans was estimated as 7.2 GBq/y, nearly half of the emission totals were emitted from the English Channel (3.2 GBq/y). In addition, the global I emission from land was estimated as 1.7 GBq/y. The remarkable I emission from land was mainly appeared in Europe, Russia, and North America, and the emission distribution is impacted by the activities of the past and ongoing nuclear fuel reprocessing facilities. The total I emission from ocean and land is lower than the I emission from the model-included nuclear fuel reprocessing facilities (23.3 GBq/y), showing that the aerial release of nuclear fuel reprocessing facilities in operation is still an important I source.
Sato, Yosuke*; Sekiyama, Tsuyoshi*; Fang, S.*; Kajino, Mizuo*; Qurel, A.*; Qulo, D.*; Kondo, Hiroaki*; Terada, Hiroaki; Kadowaki, Masanao; Takigawa, Masayuki*; et al.
Atmospheric Environment; X (Internet), 7, p.100086_1 - 100086_12, 2020/10
The third model intercomparison project for investigating the atmospheric behavior of Cs emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident (FDNPP-MIP) was conducted. A finer horizontal grid spacing (1 km) was used than in the previous FDNPP-MIP. Nine of the models used in the previous FDNPP-MIP were also used, and all models used identical source terms and meteorological fields. Our analyses indicated that most of the observed high atmospheric Cs concentrations were well simulated, and the good performance of some models improved the performance of the multi-model ensemble. The analyses also confirmed that the use of a finer grid resolution resulted in the meteorological field near FDNPP being better reproduced. The good representation of the wind field resulted in the reasonable simulation of the narrow distribution of high deposition amount to the northwest of FDNPP and the reduction of the overestimation over the area to the south of FDNPP. In contrast, the performance of the models in simulating plumes observed over the Nakadori area, the northern part of Gunma, and the Tokyo metropolitan area was slightly worse.
Terada, Hiroaki; Nagai, Haruyasu; Tanaka, Atsunori*; Tsuzuki, Katsunori; Kadowaki, Masanao
Journal of Nuclear Science and Technology, 57(6), p.745 - 754, 2020/06
We have estimated source term and analyzed processes of atmospheric dispersion of radioactive materials released during the Fukushima Daiichi Nuclear Power Station (FDNPS) accident by the Worldwide version of System for Environmental Emergency Dose Information. On the basis of this experience, we developed an dispersion calculation method that can respond to various needs in a nuclear emergency and provide useful information for emergency-response planning. By this method, if a release point is known, it is possible to immediately obtain the prediction results by applying provided source term to the database of dispersion-calculation results prepared in advance. With this function, it is easy to compare results by applying various source term with monitoring data, and to find out the optimum source term, which was applied for the source term estimation of the FDNPS accident. By performing this calculation with past meteorological-analysis data, it is possible to immediately get dispersion-calculation results for various source term and meteorological conditions. This database can be used for pre-accident planning, such as optimization of a monitoring plan and understanding of events to be supposed in considering emergency countermeasures.
Terada, Hiroaki; Nagai, Haruyasu; Tsuzuki, Katsunori; Furuno, Akiko; Kadowaki, Masanao; Kakefuda, Toyokazu*
Journal of Environmental Radioactivity, 213, p.106104_1 - 106104_13, 2020/03
In order to assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station accident in Japan, the spatial and temporal distribution of radioactive materials in the environment is necessary to be reconstructed by computer simulations with the atmospheric transport, dispersion and deposition model (ATDM) and source term of radioactive materials discharged into the atmosphere is essential. In this study, we carried out refinement of the source term and improvement of ATDM simulation by using an optimization method based on Bayesian inference with various measurements (air concentration, surface deposition, and fallout). We also constructed the spatiotemporal distribution of some major radionuclides in the air and on the surface (optimized dispersion database) by using the optimized release rates and ATDM simulations which is used for the comprehensive dose assessment by coupling with the behavioral pattern of evacuees from the accident.
Akiyoshi, Hideharu*; Kadowaki, Masanao; Nakamura, Haruna*; Sugita, Takafumi*; Hirooka, Toshihiko*; Harada, Yayoi*; Mizuno, Akira*
Journal of Geophysical Research; Atmospheres, 123(22), p.12523 - 12542, 2018/11
A reduction of the total ozone over the southern tip of South America lasting 3 weeks occurred in November 2009. Analyses of the ERA-Interim reanalysis data and the total ozone observed by the Ozone Monitoring Instrument indicate that the total ozone reduction event was caused by a migration of the polar vortex toward the South American continent at the time of the vortex breakup. The vortex migration is associated with an enhanced wave flux from the troposphere at 120-150W and 50-60S to the west of the South American continent to the stratosphere over the southern part of the continent, which led to a large negative geopotential height anomaly in the lower stratosphere. In November, a blocking event was diagnosed from the 500-hPa geopotential height over the west of the South American continent. These results suggest a relation between the long-lasting reduction of the total ozone over the southern tip of South America and the blocking phenomenon in the troposphere of the Southern Hemisphere through wave propagation from the blocking region in 2009. Analysis of the total ozone anomaly for 50-60S and 65-75W over the southern tip of South America in November for 1979-2015 indicates that the negative ozone anomaly in November 2009 was one of the largest anomalies in this 37-year period and was associated with the large negative geopotential height anomaly in the lower stratosphere. Analyses of dynamical fields were also conducted for other years with large geopotential height anomalies.
Kadowaki, Masanao; Katata, Genki*; Terada, Hiroaki; Suzuki, Takashi; Hasegawa, Hidenao*; Akata, Naofumi*; Kakiuchi, Hideki*
Atmospheric Environment, 184, p.278 - 291, 2018/07
The long-lived radioactive iodine (I) is a useful geochemical tracer in the atmospheric environment. We recently observed clear seasonal trends in air concentration and deposition of I in Japan. Using these data, we developed a global atmospheric I transport model to reveal key processes for the global atmospheric I cycle. The model generally reproduced the observed seasonal change in air concentration and deposition of I in Japan, and the global distribution of I concentration in rain as presented in past literature. Numerical experiments changing the intensity of anthropogenic and natural sources were conducted to quantify the impact of anthropogenic sources on the global I cycle. The results indicated that the atmospheric I from the anthropogenic sources was deposited in winter and can be accumulated mainly in the northern part of Eurasia. In contrast, the atmospheric I from the natural sources dominated the deposition in summer. These results suggested that the re-emission process of I from the Earth's surface may be important as a secondary impact of I in the global-scaled environment. Furthermore, although wet deposition dominated the total deposition in the Northern hemisphere, dry deposition regionally and seasonally contributed to the total deposition over arctic and northern part of Eurasia in winter, suggesting that the dry deposition may play a key role in the seasonal change of I deposition in the Northern hemisphere high latitudes.
Terada, Hiroaki; Tsuzuki, Katsunori; Kadowaki, Masanao; Nagai, Haruyasu; Tanaka, Atsunori*
JAEA-Data/Code 2017-013, 31 Pages, 2018/01
We developed an atmospheric dispersion calculation method that can respond to various needs for dispersion prediction in nuclear emergency and prepare database of information useful for planning of emergency response. In this method, it is possible to immediately get the prediction results for provided source term by creating a database of dispersion calculation results without specifying radionuclides, release rate and period except release point. By performing this calculation steadily along with meteorological data update, it is possible to immediately get calculation results for any source term and period from hindcast to short-term forecast. This function can be used for pre-accident planning such as optimization of monitoring plan and understanding events to be supposed for emergency response. Spatiotemporal distribution of radioactive materials reproduced by source term estimated inversely from monitoring based on this method is useful as a supplement to monitoring.
Kadowaki, Masanao; Nagai, Haruyasu; Terada, Hiroaki; Katata, Genki*; Akari, Shusaku*
Energy Procedia, 131, p.208 - 215, 2017/12
When radioactive materials are released into the atmosphere due to nuclear accidents, numerical simulations that can reproduce temporal and spatial distribution of radioactive materials are useful to provide the information for emergency responses and radiological dose assessment. In this study, we attempt to improve the atmospheric dispersion simulation using an advanced meteorological data assimilation method and reconstruct the spatiotemporal distribution of radioactive materials released due to the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The atmospheric dispersion simulations were carried out by the Lagrangian particle dispersion model GEARN developed by Japan Atomic Energy Agency. To obtain meteorological fields for GEARN calculation, we used the Weather Research and Forecasting model WRF with meteorological data assimilation using four-dimensional variational method (4D-Var). GEARN calculations of the surface deposition and air concentration of radionuclides were compared with measurements. In the area close to FDNPS, the spatial distribution of the deposition of Cs-137 and I-131 simulated by GEARN agreed with the measured one. The accuracy of modeled deposition in northwest and south directions from FDNPS was particularly improved. This results were mainly attributed to the better reproducibility of wind field by using the meteorological data assimilation with 4D-Var. The improvement of the accuracy of modeled deposition distribution of Cs-137 in the East Japan area was also apparent under the meteorological fields modified by 4D-Var. The information of atmospheric dispersion processes reconstructed in this study is used for updating the existing assessment of radiological dose resulting from the FDNPS accident based on atmospheric simulations by our previous studies. It can also provide useful suggestions to make emergency response plans for nuclear facilities in Japan.
Kadowaki, Masanao; Katata, Genki; Terada, Hiroaki; Nagai, Haruyasu
Atmospheric Pollution Research, 8(2), p.394 - 402, 2017/03
We developed a dispersion model based on the finite difference method, GEARN-FDM, for long-range dispersion, which solves the advection-diffusion equation using numerical schemes with low artificial diffusion. The advection and diffusion terms are modeled using a fully mass conservative scheme and the Crank-Nicolson method, respectively. GEARN-FDM was validated using the dataset from the European Tracer Experiment. In the entire domain throughout the simulation period of the observed dataset, GEARN-FDM showed high performance with factors of 2 and 5 of 39% and 78%, respectively. While testing the sensitivity of the horizontal diffusivity with this model, the simulated horizontal diffusivity was distributed heterogeneously in the model domain. High diffusivity was primarily seen over the coastal and mountainous regions. Therefore, for the long-range simulations of radionuclides, we need to consider to the transport caused by horizontal diffusion.
no journal, ,
A numerical simulation is highly important to estimate temporal and spatial distributions of radionuclides in the atmosphere and ocean. NSEC (Nuclear Science and Engineering Center), Research Group for Environmental Science have developed the atmospheric advection-diffusion model GEARN and the oceanic dispersion model SEA-GEARN. In this presentation, we introduce the detail of our models, the research results which were conducted using the models and the joint research system. Our simulation issues, for instance, the atmospheric model designed by semi-Lagrangian advection scheme, ensemble forecasting simulations for radionuclides, coastal ocean simulations and nudging of radionuclide concentrations for the ocean model, are also discussed.
Kadowaki, Masanao; Terada, Hiroaki; Katata, Genki; Furuno, Akiko; Nagai, Haruyasu
no journal, ,
In case of a nuclear accident or radiological emergency, a simulation with numerical models is a powerful means in order to predict distributions of the polluted air. Although a particle model that WSPEEDI has introduced shows advantage in the synoptic scale, it costs computationally because of the large amount of airborne particles. Moreover, the model has problems with uncertainties in the calculations on long range, due to exponentially increasing errors. For the reason, in this study the atmospheric transport modeling with a finite difference method: GEARN-FDM is proposed in order to improve WSPEEDI. The advection and diffusion in the atmosphere were calculated by using a mass conservative and monotonic manner scheme (Walcek, 2000) and Crank-Nicolson method, respectively. The distributions of tracer were good agreement with the first ETEX measurements. In this session the validation and comparison will be discussed.
Kadowaki, Masanao; Nagai, Haruyasu; Terada, Hiroaki; Katata, Genki; Akari, Shusaku*
no journal, ,
When radioactive materials are released into the atmosphere due to nuclear accidents, numerical simulations that can reproduce temporal and spatial distribution of radioactive materials are useful to provide the information for radiological dose assessment. However, the uncertainties in meteorological field predictions to simulate the atmospheric dispersion becomes a major problem. In this study, we attempt to improve the accuracy of atmospheric dispersion simulation for the Fukushima Daiichi Nuclear Power Station accident using WRF. The meteorological fields were simulated by WRF with and without four-dimensional data assimilation. This data assimilation was conducted by WRFDA using four-dimensional variational method (4D-Var). Under the meteorological fields of two runs, the dispersion simulations for radioactive materials were examined by the Lagrangian atmospheric dispersion model GEARN developed by Japan Atomic Energy Agency. The GEARN calculations of the surface deposition and air concentration of Cs-137 were compared with measurements. In this presentation, we will demonstrate the improvement of the accuracy of GEARN simulation when the data assimilation method is applied to WRF.
Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Katata, Genki; Ota, Masakazu; Furuno, Akiko; Kadowaki, Masanao; Akari, Shusaku*
no journal, ,
no abstracts in English
Kadowaki, Masanao; Katata, Genki; Terada, Hiroaki
no journal, ,
no abstracts in English
Kadowaki, Masanao; Katata, Genki*; Terada, Hiroaki; Suzuki, Takashi; Hasegawa, Hidenao*; Akata, Naofumi*; Kakiuchi, Hideki*
no journal, ,
Iodine-129 (I) has been shown as a useful isotope for dating of water, tracing of marine sediments and investigating the geochemical cycle of iodine. Main sources of atmospheric I are volatilization from ocean and discharge from nuclear fuel reprocessing facilities. Although released I is globally transported in the atmosphere and deposited to the Earth's surface, spatial and temporal distributions of atmospheric I are still not well understood. In this study, we developed an atmospheric global transport model of I which includes the processes such as advection and turbulent diffusion, dry and wet deposition, discharge from nuclear fuel reprocessing facility, volatilization from ocean and atmospheric chemical reactions (atmospheric photolysis and gas-particle conversion). Input meteorological fields of three-dimensional components of wind, air temperature, atmospheric pressure, and turbulent diffusion coefficient were calculated using WRF (Weather Research and Forecasting) with ERA-Interim dataset. The simulation period was set to be from 1 Jan 2006 to 31 Dec 2010. For model validation, we used air concentration and deposition of gaseous and particulate forms of I measured at Rokkasho in Japan from 2006 to 2010 and past measurements of I concentration in rain water in Europe, Asia, and North America. The model successfully reproduced the seasonal variations of measured air concentration and deposition of I at Rokkasho as maximum and minimum values during the wintertime and summertime, respectively. Furthermore, spatial patterns of simulated I concentration in globe were similar to those of measurements. In the presentation, key factors in controlling the spatiotemporal distribution of airborne I and its cycle in the atmosphere suggested by model results will be discussed.
Furuno, Akiko; Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Nakayama, Hiromasa; Kadowaki, Masanao
no journal, ,
SPEEDI (System for Prediction of Environmental Emergency Dose Information) is a computer system that quickly predicts the atmospheric dispersion and the environmental impact of radioactive substances released into the atmosphere in a nuclear accident. During the Fukushima accident in 2011, SPEEDI calculation was executed according to the monitoring guideline by the former Nuclear Safety Commission, but prediction results were not utilized for evacuation planning by decision makers. The Nuclear Regulation Authority concluded that it is not adequate to use SPEEDI for the judgment of protective measures in emergency because it is difficult to accurately predict the timing and amount of release. However, the usefulness of SPEEDI has not been denied, and the local government can utilize SPEEDI with their own judgment and responsibility. We will also present our activities for the Fukushima accident, mainly about the release amount estimation.