Space-shuttle astronauts were the first to see these strange
displays of light similar to auroras, more than 500 miles above
our planet’s surface. Their sightings were later dismissed
because auroras typically extend from only 60 to several hundred
miles above the Earth. Known as the northern and southern lights,
these colorful auroras, are most commonly visible from the
surface of our planet in the high northern and southern latitudes.
They
are caused by fluxes of charged particles, mostly electrons,
emanating from the sun. These particles sometimes overload
the radiation belts during periods of high solar flare activity
and
are then discharged into the atmosphere. As they collide with
air molecules in the lower portions of the atmosphere, they
produce shimmering displays of colorful light.
But if these are seen only in the lower atmosphere what were
the astronauts seeing far above in space?
UCSD solar physicists may have the answer. They recently reported
that they had identified the unmistakable signature of what they
call “high-altitude auroras.” They discovered them
while combing through the first images from the Solar Mass Ejection
Imager, an orbiting instrument designed to view the clouds of
energetic electrons that emanate from solar flares.
Scientists have long believed that at a height of 500 miles,
air molecules are not plentiful enough to collide with charged
particles and therefore produce auroras. So what’s producing
these high-altitude auroras?
“
It’s a mystery,” admits Bernard Jackson of UCSD’s
Center for Astrophysics and Space Sciences. “This is far
higher than anyone had ever expected. It may be that nitrogen
from the ionosphere is ejected into the higher altitudes during
a coronal mass ejection.”
Coronal mass ejections are the giant clouds of energetic electrons
that emanate from solar flares and speed through space at up
to two million miles an hour. They can interrupt satellite communications,
produce destructive surges in power grids and even increase radiation
exposure to people flying in planes.
Space forecasters have been
unable to
accurately predict whether or not these destructive clouds will
affect Earth. So Jackson and UCSD solar physicist Andrew Buffington
designed and built the
Solar Mass Ejection Imager, together with scientists at the Air Force Research
Laboratory, University of Birmingham in the United Kingdom, Boston College and
Boston University.
The Imager was launched in January 2003 and, as scientists viewed
the first pictures of coronal mass ejections, Buffington noticed
a bright source of light. It was
100 times brighter than the scattering of sunlight from the electrons, and
he and Jackson concluded that it came from high-altitude auroras.
While the UCSD scientists say they
still don’t understand the process causing these auroras, they note that
researchers
at the Air Force Research Laboratory are presently studying the data to come
up with some possible explanations. 
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