Effect of Submesoscale Eddies on Oceanic Dispersion of Materials in a Coastal Area off Fukushima Analyzed with a Downscaling System

Recent studies suggested that turbulent mixing by submesoscale eddies is prominent for oceanic dispersion of materials in continental shelves and nearshore areas. A multiple nesting methodology enables us to reproduce submesoscale eddies in order to investigate their effect on surface mixing and associated material transport. In this study, downscaling simulations in a coastal area off Fukushima with a horizontal resolution of 1 km were conducted by using the Regional Ocean Modeling System (ROMS). Initial and boundary conditions for oceanic field such as temperature and salinity were given by reanalysis data calculated by an ocean data assimilation system MOVE developed at Japan Meteorological Agency (JMA).

A comparison with the satellite altimetry data demonstrated a good agreement with measurement and the capability of reproducing the Kuroshio and 3D oceanic structure quite well. Analysis of surface normalized relative vorticity suggested that meso- and submeso-scale eddies are enhanced as a horizontal resolution is finer. In addition, we simulated oceanic dispersion of Fukushima tracer to investigate the effect of submesoscale eddies on transport of Fukushima-derived radioactive materials. It was demonstrated that movement of Fukushima tracer in the coastal area depends on horizontal resolution, which suggests an importance of submesoscale eddies to evaluate oceanic pollution associated with the Fukushima disaster.