Northward transport, with some inland spreading, is expected to continue through Friday April 15 Japan Standard Time (JST). As mentioned in a post on ocean radiation, the sustained northward winds that have occurred lately are a factor in driving the ocean plume toward the north as well.
High temperatures plague reactor 4’s spent fuel storage pool and produced radiation values ~20 feet above the pool: 84 millisievert/hr vs. normal reading of 0.1 millisievert/hr. The temperature was higher than on March 15 when a hydrogen explosion and fire created significant radiation emissions. TEPCO continued to spray water on the pool.
The Naval Research Laboratory’s skillful data-assimilating triply nested (45 km/15 km/5 km) mesoscale meteorological model COAMPS produced the fields above, using a passive tracer to map the expected plume trajectory. Lighter gray contours show more concentrated material. Each shade of gray represents a factor of 10 difference in tracer concentration. [Plume images are a research tool; contours are arbitrary units for visualization purposes.] The modeled “plume” is a tracer that is released at a constant concentration, simply follows the air flow, and (a) does not settle due to gravity, (b) does not get deposited with rain, and (c) does not have any radioactive decay. These neglected factors typically dramatically reduce the effects of radiation when it travels over distances of hundreds of miles. There is much uncertainty in the source term, as the releases of radiation that occurred in the past were highly intermittent. (So although modeled as such, the plume in actuality was not a continuous release.) We have utilized COAMPS to make detailed and accurate forecasts of various coastal regions, including large-scale (synoptic) weather patterns. It also is skillful at simulating local coastal processes such as the influence of cold upwelled ocean waters, or sea breezes, when there is no strong synoptic forcing. We have previously used the model to simulate the movement of hypothetical releases along the east coast of Japan.