The National Oceanic and Atmospheric Administration â€œobserved two powerful solar flares on December 5 and 6, 2006, emanating from a large cluster of sunspots,â€ according to the article. â€œA giant radio burst followed, causing large numbers of receivers to stop tracking the GPS signal.â€
The flare has researchers worried about the next â€œsolar maximumâ€ peak, expected sometime between 2010 and 2012. The sun goes through 11-year cycles of minimum and maximum phases of charged particle ejection that can disrupt satellite communication. The last solar maximum occurred in 2000, but "in December, we found the effect [of solar flares] on GPS receivers were more profound and widespread than we expected," said Paul Kintner, a professor of electrical and computer engineering at Cornell University in New York.
Before the December storm, researchers from the National Center for Atmospheric Research in Boulder, Colo., warned the next solar maximum peak would be "30 percent to 50 percent stronger than the previous one," said researcher Mausumi Dikpati, in this 2006 NASA article.