13. Uncertainty in Simulation of Global Transport of Radioactive Tracer Emitted from Fukushima Daiichi Nuclear Power Plant

Global transport of radioactive tracers emitted from Fukushima Daiichi Nuclear Power Plant was simulated by using an atmospheric transport model, and the levels of uncertainties in the results were investigated. These uncertainties are attributed to the reanalysis atmospheric data used as the input of the transport model and imprecision of the details of the radiation flux time series. Simulation results were found using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, the atmospheric general circulation model for the Earth Simulator—local ensemble transform Kalman filter experimental ensemble reanalysis 2 (ALERA2) data, the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA Interim data, and the Japan Meteorological Agency Climate Data Assimilation System (JCIDAS) data. The standard deviation of the simulation results using these data sets was larger than the standard deviations (which were within 10 % of the mean values) of the results using the data of the ALERA2 ensemble members. Simulation results of 1-day emissions showed a clear difference in the transport of the emitted tracer and suggest the availability of an inverse method to estimate a detailed flux time series.