Tsunami/Nuclear radionuclide spreading

March 11, 2011, was a tragic day for Japan and the world. The earthquake in Tohoku, Japan, caused a tsunami, and the resulting tsunami-induced inundation has placed Japan into crisis. The radiation released in the nuclear accident has threatened the coastal environment with potential impacts on the Pacific Ocean. An international research team was established to study the mechanism of the tsunami, simulate the inundation and assess the impact of radionuclides on the surrounding countries around the Pacific. The team members include Dr. Changsheng Chen (Physical Oceanographer), Dr. Zhigang Lai (Physical Oceanographer), and Ms. Huichan Lin (Physical Oceanographer) at University of Massachusetts-Dartmouth (UMASSD)-USA, Dr. Robert C. Beardsley(Physical Oceanographer), Dr. Jian Lin (Geologist) and Dr. Rubao Ji (Biologist) at Woods Hole Oceanographic Institution (WHOI)-USA, and Dr. Jun Sasaki at Yokohama National University-Japan (the current contact address is the University of Tokyo). The ocean model used for this activity is the global-coastal nested FVCOM system. The Experiments were done with initial fields provided by five seismic rupture models under realistic conditions with the inclusion of the Kuroshio, tides, and wind forcing (Chen et al., 2014). We also used the FVCOM dye module to track the initial spread of ¹³⁷Cs over the eastern shelf of Japan. The ¹³⁷Cs were tracked as a conservative tracer (without radioactive decay) in the three-dimensional model flow field from 26 March–31 August 2011. The results clearly show that the model-predicted spreading of ¹³⁷Cs was sensitive to model resolution and the FNPP seawall structure. A coarse-resolution (∼ 2 km) model simulation led to an overestimation of lateral diffusion and, thus, faster dispersion of ¹³⁷Cs from the coast to the deep ocean. At the same time, advective processes played a more significant role when the model resolution at and around the FNPP was refined to ∼ 5 m. By resolving the pathways from the leaking source to the southern and northern discharge canals, the high-resolution model better predicted the ¹³⁷Cs spreading in the inner shelf where in situ measurements were made at 30 km off the coast. The overestimation of ¹³⁷Cs concentration near the coast is thought to be due to the omission of sedimentation and biogeochemical processes, as well as uncertainties in the amount of ¹³⁷Cs leaking from the source in the model. As a result, a biogeochemical module should be included in the model for more realistic simulations of the fate and spreading of ¹³⁷Cs in the ocean.

Block 1

The animation reappears the fields of near-surface currents and temperatures over the east coast of Japan over the period from 00:00 March 1 to 05:00:00 March 11, 2011, before the earthquake.

The animation reappears the tsunami generalized by March 11, 2011 earthquake. The simulation was done using the nonhydrostatic version of the global-Japan-nested FVCOM with a horizontal resolution of up to ~5 m. Note: The red color along the coast at the initial was a graphical problem due to the image process between the wet-dry boundary. The model does not produce it (Chen et al., 2014).

The animation reappears how the March 11, 2011 tsunami wave propagated onto the Fukushima Nuclear Power Plant. To make the image viewable, we reduced the number of vectors when the animation was made (Chen et al., 2014).

The animation reappears the fields of near-surface currents and temperatures over the east coast of Japan over the period from 00:00 March 1 to 05:00:00 March 11, 2011, before the earthquake.

Block 2

The animation displays the projected trajectories of 100 neutral buoyancy water particles released and tracked at the fixed depths of the surface, 50, 100, 200, 400, 600, 800, and 1200 m. The release time: 00:00 GMT, March 12, 2011. The tracking period: 7 years. The flow field is the daily output of the Global-FVCOM driven by the climatologically-averaged meteorological forcings.

Surface

50 m

100 m

200 m

400 m

600 m

800 m

1200 m

Block 3

The animation displays the projected trajectories of 100 neutral buoyancy water particles released at the surface, 50, 100, 200, 400, 600, 800, and 1200 m. The tracking considered the vertical motion of particles. The release time: 00:00 GMT, March 12, 2011. The tracking period: 7 years. The flow field is the daily output of the Global-FVCOM driven by the climatologically-averaged meteorological forcings.