Monday 21 March between 4-6 pm Japan Standard Time (JST) smoke billows occurred at reactors 2 and 3. Although there are reports of no increase in radiation 500 m northwest of the site, the plume maps below show that elevated radiation is not expected to the northwest. Instead, any release that may have occurred with the smoke would be drifting southwest and impact the greater Tokyo area during the day Tuesday 22 March (between 7 AM and 4 PM JST). Japanese officials confirmed a 4-fold increase in radiation levels 1 km west of the reactor site and associate this with the smoke/steam. U.S. Navy carrier USS Washington left port at Yokohama (just southwest of Tokyo) to move offshore. There has also been a setback in repairs at the plant that will further delay the containment efforts. [Plume images are a research tool; contours are arbitrary units for visualization purposes.] (See more details below the figure.)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.)
COAMPS is the Coastal Ocean-Atmosphere Mesoscale Prediction System, a high-resolution atmospheric model run by the Naval Research Laboratory. We collaborate with NRL and have utilized the model to make detailed and accurate forecasts of coastal regions, including processes such as large-scale (synoptic) weather patterns, but 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.
A useful source of additional information on the regional weather conditions and long-range transport is the blog atWeatherUnderground.