[img_assist|nid=2292|title=click for animation|desc=|link=none|align=center|width=523|height=235]
High resolution Global system Mercator: PSY4
The 1/12° global ocean system Mercator PSY4 has been operated at Mercator Océan since February 2011. This system produces weekly a 14-day hindcast and a 7-day forecast. In this area close to the Japanese coast, PSY4 has a horizontal resolution of 6-7 km which enables a good description of important eddies and current meanders. The system is run in real-time and assimilates continuously ocean observations (satellite and in-situ).The Kuroshio Current plays along the Japanese Eastern coast a role similar to the Gulf Stream in the Atlantic along the US coast: it can strongly advect the particles far East in the open ocean.
The Kuroshio appears to be the boundary between two different zones: the cold and fresh waters coming from the Subarctic Gyre in the North, and the warm and salty subtropical waters in the South. Within the movie, the Kuroshio meanders appear in white.
Methodology
We have been calculated the Lagrangian drift of water particles from the analysis provided by the system PSY4 since March 12, 2011. For that we coloured a set of water particles near the Fukushima nuclear power plant between 0 and 30m deep, and we followed their drift with a monthly update, this is done using the computational tool ARIANE1 (B. Blanke, S. Raynaud, 1997). For each update we start from the water particle positions of the previous simulation.
Results
The green square represents the location of the Fukushima nuclear power plant. The yellow dots represent the coloured water particles. The simulation shows that, from the accident until 31st August, the coastal currents carry the coloured particles along the Kuroshio Current with dispersion towards the North of the current and East of the basin. The water particle dispersion is more significant in energetic areas of the current, especially up to 160°E where eddies are intense. The water particles seemed to stay mostly in the area located North of the current, between 34 and 43°N, except until May. After that, we began to observe coloured particles in the area South of the current.