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Sky watchers at high latitudes are often rewarded with stunning celestial shows known as auroras. Conventional theory holds that large-scale electric currents flowing along the earth's magnetic field lines power the displays. Now findings published today in the journal Science suggest another source of energy for the heavenly exhibitions. Researchers report that Slinky-like wriggling of the magnetic field lines could help fuel aurora borealis events.
Andreas Keiling of the University of Minnesota and currently with the Center for Space Research on Radiation in Toulouse, France, and his colleagues analyzed electric and magnetic field data amassed by NASA's POLAR satellite over a one-year period. In particular, the team examined so-called Alfv¿n waves, which are movements in the magnetic field lines, at altitudes of 25,000 and 38,000 kilometers. According to their calculations, the rippling of the waves through the magnetic field provides sufficient energy to send electrons shooting into the atmosphere. The interaction of these energized electrons with certain atoms then creates the colorful celestial auroras.
"It's a substantial additional source in driving the aurora," Keiling notes. "One third of the energy could be driven by these waves." In addition, the pattern of energy distribution matched the distribution of auroral activity. Although they don't yet know exactly what causes the field lines to wiggle, the authors conclude that "the globally occurring Alfv¿n waves thus provide an important link from the magnetosphere to the aurora."