University of Iowa
Iowa City IA 52242
May 28, 1998
That's the finding of University of Iowa space physicist Louis A. Frank and UI colleagues John B. Sigwarth and David D. Morgan in a paper presented today, Thursday, May 28, at the spring meeting of the American Geophysical Union (AGU) in Boston. The study is based upon some 9,000 images taken in January 1997 by NASA's Polar satellite and one of its three Visible Imaging System (VIS) cameras designed and built by Frank, Sigwarth and their UI imaging team. About 100 to 200 of the images showed aurora following the coastline, sometimes for hundreds of miles.
"The mechanism or reason for such a coastline effect on auroral lights is not known. It would appear that, at certain times, the ionosphere is primed for the generation of thin arcs over the coastlines and that the arcs are tickled into brightening by magnetic or electric fields from ground currents. This is quite remarkable because these auroral lights are occurring at altitudes of 60 to 200 miles above the shores," Frank says.
Auroras result from the interaction of the upper atmosphere with ionized particles flowing outward from the sun -- a stream of very thin gas called the solar wind that is captured by the Earth's magnetic field and drawn toward its magnetic poles.
Frank, an internationally recognized authority on plasma physics who has spent much of his career studying auroras, adds that the same phenomena that create colorful auroras sometimes cause problems on the ground. "It is well-known that large currents exist in the ionosphere at altitudes of about 60 to 100 miles. These high altitude currents induce large currents in the ground, including power lines and oil pipelines. If these ground currents are sufficiently large, then our power grids can be overloaded, resulting in power blackouts," he says.
Although coastline auroras may not be fully understood, the phenomenon was reported by the Russian explorer Admiral Ferdinand Von Wrangel who recorded his observations during his 1820-23 polar expedition over a century and a half ago. Frank said that he was skeptical when he read the Russian literature on coastline auroras years ago, but gratified that his cameras aboard the Polar spacecraft offered the opportunity to resolve the question. "Examination of thousands of pictures revealed, to our dismay, that auroras aligned along coastlines did occasionally occur -- a relatively rare occurrence, but dramatic in the images," he says.
For further information, see the coastline auroras web site at:
http://www-pi.physics.uiowa.edu/www/vis/coastlines/
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