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Release: Thursday, May 28, 1998
UI's Louis Frank observes northern lights hugging Earth's coastlines
IOWA CITY, Iowa -- The northern lights, like some species of birds,
sometimes prefer to soar above the Earth's coastlines.
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
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, which is embargoed
until 1:30 p.m. EDT, Thursday, May 28 at: http://www-pi.physics.uiowa.edu/www/vis/coastlines/)