Massive amounts of anthropogenic radionuclides were released from the nuclear reactors located in Fukushima (northeastern Japan) between 12 and 16 March 2011 following the earthquake and tsunami. Ground level air radioactivity was monitored around the globe immediately after the Fukushima accident. This global effort provided a unique opportunity to trace the surface air mass movement at different sites in the Northern Hemisphere.

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The analysis of the air mass forward movements during 12th -16th March showed that the air mass was displaced eastward from the Fukushima area and bifurcated into a northern and a southern branch outside of Japan (Fig. 3). This eastward bifurcation of air masses is in agreement with the simulation of the potential dispersion of the radioactive cloud after the nuclear accident of Fukushima (Weather OnlineWebsite of United Kingdom, UK, 2012).

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The unique global coverage of fallout radiocaesium released from the Fukushima Daiichi Nuclear Power Plant, particularly a fresh injection of 134Cs and 137Cs to the ground air provided a rare opportunity to observe a complete, uninterrupted revolution of the mid-latitude Surface Westerlies of the northern Hemisphere in late March 2011. This revolution took less than 21 days.

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This work clearly demonstrates how little dissipation occurred during this time due to the nature of the rapid global air circulation system, and the Fukushima radioactive plume contaminated the entire Northern Hemisphere during a relatively short period of time.

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