Following is an update on radiation levels in Japan emanating from quake-stricken units of nuclear installations made as per observations of 2100 hrs IST on Tuesday by Weather Underground and made available to Business Line through the India Meteorological Department.

Dr Ajit Tyagi, Director-General, IMD, has also provided to Business Line the IMD projections for the forward trajectory for radiation drawing upon on US National Oceanographic and Atmospheric Administration’s (NOAA) HYSPLIT model as well as the GFS (global forecast system) forecast system.

Quoting a Weather Underground model, Dr Tyagi said that a low pressure system was located over Japan near Tokyo yesterday (Wednesday, March 16), and the counterclockwise flow of air around this low was bringing easterly winds over the stricken Fukushima Daiichi nuclear plant, which lies to the north-northeast of Tokyo.

Radiation Inland

These easterly winds are blowing radioactivity inland over Japan. As the low tracks northeastward along the coast of Japan today, winds at the Fukushima Daiichi nuclear plant will gradually shift to northeast and then northwest, which will move radiation towards Tokyo for several hours, which may be long enough for some radiation to reach the city.

US National Oceanographic at Atmospheric Administration’s (NOAA’s) HYSPLIT trajectory model shows that for a release of radioactivity at 50 meters altitude beginning at 0230 hrs on Tuesday (when an explosion at the No. 2 reactor was recorded), with repeat releases simulated to occur every two hours thereafter, the plumes will stay to the north of Tokyo (Figure 1.)

Contamination Aloft

However, a more detailed dispersion model being run by the Austrian weather service showed that the plumes could affect much of the Tokyo area on Wednesday. Both models predicted that by mid-night last (Wednesday) night, the threat to Tokyo would have been over, with more westerly winds blowing the radioactive cloud out to sea.

There will be some radiation from Japan lofted to high altitudes by the low pressure system affecting the region, and if the radiation manages to escape being rained out, it could potentially be transported thousands of miles over the next week.

A run of the HYSPLIT model following the path of a radioactive cloud emitted at 1700 hrs IST on Wednesday showed the radioactivity being lofted four to five km in altitude and being transported over Alaska over the coming week.

After a week of transport, this cloud will be considerably diluted, and it is doubtful if the radioactivity would be harmful to human health if rain or snow were to carry it to the ground over Alaska or Canada, assuming that the radiation levels currently being advertised at ground level in Japan are correct.

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