Development of observed meteorological database to understand the wet deposition and dispersion processes over Fukushima, Japan in March 2011

The atmospheric transportation and diffusion of the radioactive pollutants from the Fukushima-Daiichi nuclear power plant caused a disaster for the residents in and around Fukushima. Studies have sought to understand the transportation, diffusion, and deposition processes, and to understand the movements of the radioactive pollutants through the soil, vegetation, rivers, and groundwater. However, detailed simulations and understanding of the distribution of radioactive compounds depends on the accurate simulation of precipitation and on information regarding the timing of the emission of these radioactive pollutants from the power plant. Furthermore, both the precipitation type and its quantity affect the various transportation processes of the radioactive nuclides. Hence, this study first examines the qualitative pattern and timing of precipitation in March 2011, using X-band radar data from Fukushima University and the three-dimensional C-band radar data network of the Japan Meteorological Agency. Second, by collecting rain gauge and other surface meteorological data, we quantitatively estimate the precipitation according to the same method used to create the APHRODITE daily gridded precipitation (Yatagai et al., 2012) and its type (rain/snow) (Yasutomi et al., 2011). For example, the data verified that snowfall was observed on the night of March 15 into the morning of March 16 throughout Fukushima Prefecture. This had an important effect on the pattern of radioactive contamination across Fukushima Prefecture. The precipitation pattern itself does not show direct correlation with the contamination pattern. As the pollutants transported to the northeast of the power plant and through North Kanto (about 200 km southwest of Fukushima and 100 km north of Tokyo) went to the northeast, the timing of the precipitation causing the fallout is important.Although the hourly Radar-AMeDAS 1-km-mesh precipitation data of the JMA are available publically, they do not represent accurately the precipitation pattern in Nakadori, in central Fukushima Prefecture. Hence, we used the 10-minute-interval X-band radar, located in north Nakadori to determine the start and detailed spatial pattern (120-m mesh) of the precipitation. The developed data set of precipitation and other meteorological information will be released to the project Fukushima-IRIS site (http://firis.stelab.nagoya-u.ac.jp/). The project aims to establish a database to further the understanding of the initial meteological condition. Various useful sites with meteorological data and other physical information from March 2011 have already been linked to the site. This project is being supported by the Disaster Prevention Research Institute of Kyoto University.