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.

�3*+0!+73098.32�*+,6++7�

�.74+67.3213*+0�8;4+

�81374-+6.)�'00398

�.6+)8�*.7)-'6,+

�!�� � �����:����� �90+6 �!�� � �!�� ��8;4+���� �5�

�����! ����:����� �90+6 ��� �278'28�6+0+'7+��� �5�

�!"� �����:��� � �90+6 �!"��4& �!"��� �� �5�

���� �����:���� �',6'2,.'2 ���� �����8;4+���� �5�

��� �# �� �:��� �90+6 ���"#�� �!�� ��8;4+�� �� �5�

���"# �� ��:��� � �90+6 ��� �����8;4+���� �5�

�3(+�$ ��/1�:���/1 �90+6 ��� �!�� ��8;4+�� �� �5�

�""� ����� �:������ �',6'2,.'2 ��� �!�� ��8;4+����� �5�

���" ����:���� �90+6 ���" �!�� ��8;4+��� �5�

%����� �����:����� �',6'2,.'2"83-0�+8�'0�����

�����8;4+��� � �5�

%����� �����:����� �',6'2,.'2 ��� �����8;4+��� � �5�

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