The geomagnetic storm prompted officials in the United States and Canada to warn airline passengers and crew members that they could be exposed to abnormally high levels of radiation.
The Federal Aviation Administration in the United States has warned passengers on some aircraft that they would accumulate about 2 millirems of radiation per hour, or two days` worth of normal radiation exposure on the ground.
Dr Robert Barish, a medical radiation specialist whose 1996 book The Invisible Passenger deals with in-flight radiation, said the exposure to passengers and crew members was at a level that would be subject to government regulation if it occurred on the ground.
Instead of the equivalent of a chest X-ray for every three or four hours of flight, he said, `it`s two every hour`.
Dr John Kohl, an astrophysicist at the Harvard-Smithsonian Centre for Astrophysics, said: `We`re going to be seeing pretty high levels of radiation over the coming days.`