Dispersion Simulations of Radionuclides in the Ocean
Yukio Masumoto(The University of Tokyo ; JAMSTEC)
+ Contributors to the model intercomparison
Why do we need dispersion simulations?
- Models can show detailed distribution in a large area and can interpolate/extrapolate sparse observed distributions
- Models can be used for predictions of radionuclide dispersions
- Model results may suggest important processes responsible for the dispersion
(Bq/m3)
- Models show their own worlds, with a certain degree of uncertainty
Model (a)
Model (b)Observation
1. Model results for regional dispersion off Tohoku area
2. Model results for basin-scale dispersion in the North Pacific
• Regional model intercomparison
- Originally started as one of the activities of “the Earthquake Disaster Response Working Group” under the Oceanographic Society of Japan. Now continuing under a working group of the Science Council of Japan.
- To understand similarities and discrepancies among model results and to identify important oceanic processes responsible for the radionuclide dispersion.
- Only a few models have been used for the basin-scale dispersion simulation
Regional Model Intercomparison
11 models are participating in the intercomparison (6 from Japan, 5 from abroad)
Note: Domain, resolution, discharge scenario, and atmospheric depositions are all different among the models.
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Model Domains
Surface distribution of 137Cs (Apr.21-30)
Observation
• Anticyclonic meso-scale eddy off Ibaraki prevents radionuclides to spread southward
• Currents along the coast determine the direction of initial dispersion
• Location of the Kuroshio axis differs significantly among the models
137Cs activity (Surface) in June, 2011
(1.58) (1.33) (4.15)
(3.06)(3.52)(1.78)
(4.52)(4.01)(1.57)
(4.17)
Inventory : 1.9 ~ 2.1 PBq
R/V Ka’imikai-o-Kanaloa(Buesseler et al., 2012)
Observed reference:
Inventory Summary
(PBq)
Inset value for each panel shows the Inventory in
each model
Apr., 2012
Jan.-Mar./Feb.15, 2012
Observations : Aoyama et al. (2013)Simulation : Tsumune et al., (2013)
Simulation : Rossi et al., (2013)
Two model results for basin-scale Cs distributions (Bq/m )137 3
• Rossi et al. adopted the direct discharge of 22 PBq, with no atmospheric deposition
• Tsumune et al. employed 3.6 PBq of the direct discharge, together with 3.0 PBq of the atmospheric deposition
Summary
• Dispersion simulation of radionuclides is a useful tool to understand how the radionuclides are transported and distributed over time
• Each model shows reasonable agreement with observations, but significant discrepancy exists among the models, due to the different model settings and source scenarios
• Need to be aware of model uncertainty when describing the model results