Plume forecast for Japan: 4/2

Plume will impact land areas north and somewhat northwest of the reactor site during the day through 10 PM  Friday April 1 Japan Standard Time (JST).  After that, the plume is projected to turn offshore through the morning of Saturday April 2 (JST). [Plume images are a research tool; contours are arbitrary units for visualization purposes.]

Intermittent releases are expected to continue at the site, but the exact timing of those releases and the associated radiation levels have not been consistently conveyed by officials. Thus the plume plots below show the most likely trajectory of material that might be released at the reactor site.  The spread of the plume north and northwestward occurred two times recently (see posts for 3/28 and 3/25) and most likely resulted in the high levels of radiation in areas 25 miles north of the site.  The IAEA has recommended that the evacuation zone of 12 miles be reconsidered.

The forecast fields are from the Naval Research Laboratory’s COAMPS weather prediction model.  The model is nested down to 5 km resolution and assimilates all available local weather observations.  The prediction system makes detailed and accurate forecasts of coastal regions, including large-scale (synoptic) weather patterns, but it also is skillful at simulating local coastal processes such as the influence of cold upwelled ocean waters, and sea breezes, when there is no strong synoptic forcing.

The tracer shows what direction a radioactive plume could take from the reactors, with the lighter shades of gray indicating the highest concentrations.  Note that 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 still much uncertainty in the source term, as the releases of radiation likely fluctuate with explosions and other events at the reactors (So although modeled as such, the plume in actuality is not a continuous release.)

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