The Meteorological Agency has been calculating its forecasts on the migration once or twice every day since March 11, when the great earthquake hit the Tohoku and Kanto regions.

The agency inputs observation data sent from the IAEA--such as the time when radioactive substances are first released, the duration of the release and how high the substances reach--into the agency's supercomputer, adding the agency's observation data, including wind directions and other data. The supercomputer then calculates the direction in which the radioactive substances will go and how much they will spread.

However, the agency has only been reporting the forecasts to the IAEA and not releasing them to the public at home.

The IAEA analyzes the data from Japan by adding observation data from other countries it similarly asked for cooperation, such as China and Russia, and notifies nuclear authorities of countries, including Japan, of the results.

Whether to announce the IAEA analysis is left to each government's judgment. The Japanese government's Nuclear Emergency Response Headquarters has so far not released the IAEA analysis.