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It is highly unlikely that any radiation capable of causing harm to people will be left in atmosphere after seven days and 2,000-plus miles of travel distance, says a forecast of trajectories of radioactive emissions/fallout from Japan given by the US National Oceanographic and Atmospheric Administration (NOAA).
India Meteorological Department (IMD) too is planning to run similar trajectory model based on its forecast model, Dr Ajit Tyagi, Director-General, IMD, told Business Line .
CHERNOBYL PRECEDENT
Even the Chernobyl nuclear disaster, which had a far more serious release of radioactivity, was unable to spread significant contamination more than about 1,000 miles (1,609 km), Dr Tyagi said quoting the NOAA.
A good tool to predict the radiation cloud's path is NOAA's HYSPLIT trajectory model. The model uses the GFS (global forecasting system) model's winds to track the movement of a hypothetical release of a substance into the atmosphere.
One can specify the altitude of the release as well as the location, and follow the trajectory for up to two weeks.
However, given the highly chaotic nature of the atmosphere's winds, trajectories beyond about three days have huge uncertainties. One can get only a general idea of where a plume is headed beyond three days.
OVER WATER
A number of runs of HYSPLIT over past few days showed that a great majority of these runs have so far taken plumes of radioactivity emitted from Japan's east coast eastwards over the Pacific, with the plumes staying over water for at least five days.
Some of the plumes move over eastern Siberia, Alaska, Canada, the US and Mexico in five to seven days.
Such a long time spent over water will mean that the vast majority of the radioactive particles will settle out of the atmosphere or get caught up in precipitation and rained out.
Radiation from Japan's stricken Fukushima Daiichi nuclear plant has been detected 100 miles (160.9 km) to the northeast, over the Pacific Ocean, by the US military.
WIND PATTERN
Westerly to southwesterly winds have predominated over Japan the past few days, carrying most of the radiation eastwards out to sea.
The latest forecast for Sendai, Japan, located about 40 miles (64 km) north of the Fukushima nuclear plant, calls for winds with a westerly component to dominate for the remainder of the week, with the exception of a six-hour period on Tuesday.
Thus, any radiation released by the nuclear plant will primarily affect Japan or blow out to sea.
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