Click to animate this plume of fallout from the Fukushima nuclear disaster in Japan, as produced by ZAMG (Zentralanstalt für Meteorologie und Geodynamik, Viennese Central Institute for Meteorology and Geodynamics, Vienna Austria). Via the Harvard Japan Sendai Earthquake Data Portal.
Note that this is not the hoax map "Nuclear fallout" described by Snopes.
Of the map, the authors write (in German)
Zur Farbskalierung ist zu sagen, dass die rote Skala Gebiete kennzeichnet, die seit Beginn des Unfalles mit einer Effektivdosis von maximal 100 Milli-Sievert pro Stunde belastet waren (laut Informationen der IAEO). Die violette Skala zeigt daher maximal 100 Nano-Sievert pro Stunde an. Dieser Wert ist, selbst über ein Jahr summiert, niedriger als die natürliche Belastung, der jeder Mensch ausgesetzt ist.
as translated
Regarding the colour scaling of the simulation, one needs to keep in mind that the red colour marks areas around the plant where the effective dose rates were, at the absolute maximum, 100 Milli-Sievert per hour (according to information released by IAEA in Vienna). The violet colour thus shows areas with estimated effective dose rates of 100 Nano-Sievert (maximum) per hour. Summed up over a period of one year, this would still be less than the natural radiation exposure of an average citizen.
Note that this is a simulation, and based on dispersion calculations. Actual measurements of observed nucleotides have been collected from locations monitoring the Comprehensive Nuclear Test Ban Treaty, as noted in this March 16 post "CTBTO Messnetz misst erste Radioaktivitätswerte über Japan/ Korrektur".
Nature Magazine has a story, Radiation data from Japanese disaster starts to filter out, (March 17) which describes the release of this data by the Austrian organization ZAMG.
More maps here.
