2nd Atmospheric Model Intercomparison Project for Fukushima Daiichi Nuclear Power Plant Accident on March 2011 (2nd FDNPP-MIP)

The second intercomparison of atmospheric model targeting on the physical process radionuclides (i.e., 137-cesium: ¹³⁷Cs) released from Fukushima Daiichi Nuclear Power Plant (FDNPP) on March 2011 is conducted. Thirteen atmospheric models, which include both the Langrangian-based (dispersed) model and the Eulerian-based model, participate in this model intercomparison project (MIP). The purposes of this MIP are to 1: understand the transport process of the radionuclide in atmosphere, 2: estimate the uncertainties in wet and dry deposition process among the models, 3: reveal the essential key processes to reproduce the plume of ¹³⁷Cs, 4: assess the muti-model ensemble mean, and 5: obtain the knowledge for improving the physical processes of the models.

To exclude the uncertainties of the model results originated from the emission inventory, all models used the same emission inventory (Katata et al. 2015). The meteorological data with fine spatiotemporal resolution, which was calculated by the simulation of Japanese operational weather forecast model (JMANHM, Saito et al. 2006) coupled with the local ensemble transform Kalman Filter (LETKF) data assimilation system (NHM-LETKF), was applied for all models to reduce the uncertainties originated from the difference in the meteorological field. These points are one of the distinct differences of 2nd FDNPP-MIP from the first model intercomparson of FDNPP (Science Council of Japan, 2014), in which each model used the different emission inventory and different meteorological data. As well as the comparison among the models, the comparison between the models and in-situ measurement obtained from the aerosol sampling of the national suspended particle matter (SPM) network (Oura et al. 2015) are conducted.

The comparisons between the model results and SPM data indicate that the ¹³⁷Cs concentration near the FDNPP transported without precipitation process was relatively well reproduced by using the meteorological data with fine spatiotemporal resolution. On the contrary, ¹³⁷Cs concentration accompanied with precipitation has large inter-model spread. In the presentation, we will discuss the more detailed analyses about the physical process to determine the ¹³⁷Cs concentration.

Reference

• Katata, G., and Coauthors, 2015: Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model. Atmos. Chem. Phys., 15, 1029–1070, doi:10.5194/acp-15-1029-2015. http://www.atmos-chem-phys.net/15/1029/2015/.

• Oura, Y., and Coauthors, 2015: A database of hourly atmospheric concentrations of radiocesium (¹³⁴Cs and ¹³⁷Cs) in suspended particulate matter collected in March 2011 at 99 air pollution monitoring stations in eastern Japan. J. Nucl. Radiochem. Sci., 15, 2_1-2_12, doi:10.14494/jnrs.15.2_1. http://www.radiochem.org/j-online152.html.

• Saito, K., and Coauthors, 2006: The operational JMA nonhydrostatic mesoscale model. Mon. Weather Rev., 134, 1266–1298, doi:10.1175/MWR3120.1. http://journals.ametsoc.org/doi/abs/10.1175/MWR3120.1.

• Science Council of Japan, 2014: A review of the model comparison of transportation and deposition of radioactive materials released to the environment as a result of the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant accident. http://www.scj.go.jp/ja/info/kohyo/pdf/kohyo-22-h140902-e1.pdf