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Apr 4, 2007

GPS Outage Due to Solar Flare; Are More to Come?

An unprecedented solar eruption last December caused large numbers of GPS receivers to stop tracking the signal, and may foreshadow worse outages in the future. That was the finding of the Space Weather Enterprise Forum at its first meeting today in Washington, D.C.

On December 5 and 6, forecasters at the National Oceanic and Atmospheric Administration (NOAA), observed two powerful solar flares. These solar flares injected high-energy electrons into the solar upper atmosphere which produced radio waves that spread to Earth, covering a broad frequency range. Those radio waves acted as noise that degraded the signal used by GPS and other navigational systems.

This phenomenon has been experienced before, though at much lower levels. Studies at Cornell University led to the prediction that large solar radio bursts would disturb GPS receiver operation for some users.

However, the disruptions experienced in December were worse than had been anticipated. “...December's solar flare produced as much as 10 times more radio noise than the previous record,” reported Dr. Dale Gary, from the New Jersey Institute of Technology. “Measurements with NJIT’s solar radiotelescope confirmed, at its peak, the burst produced 20,000 times more radio emission than the entire rest of the Sun. This was enough to swamp GPS receivers over the entire sunlit side of Earth.”

The concern is that December's solar flare occurred during the solar minimum, a time of lesser solar disruption. If that event could cause such widespread outages, what could a solar flare do if it came during the solar maximum, a time when solar activity is at its peak? “In December, we found the effect on GPS receivers were more profound and wide spread than we expected,” Dr. Paul Kintner, a professor at Cornell University, reported, “Now we are concerned more severe consequences will occur during the next solar maximum.”

The National Space Weather Program, a multi-agency task force will continue studying the matter, with the ultimate goal of being able to predict such events in the future. However, right now it's not known if December's event was a one time occurrence, or an indication of future solar activity that could prove to be a major disruption to GPS and other navigational systems. Dr. Anthea Coster, from MIT observed, "...the size and timing of this burst were completely unexpected and the largest ever detected. We do not know how often we can expect solar radio bursts of this size or even larger.”

Pictured is an eruptive prominence, previously captured by the Extreme ultraviolet Imaging Telescope on board the SOHO spacecraft. (Courtesy of SOHO, a project of international cooperation between ESA and NASA)