http://www.spacedai ly.com/reports/ Auroras_In_ Broad_Daylight_ 999.html

SOLAR SCIENCE
Auroras In Broad Daylight
An artist's concept of NASA's Polar satellite observing Earth.by Staff
Writers
Greenbelt MD (SPX) Mar 07, 2008

Imagine living on a planet where Northern Lights fill the heavens at all
hours of the day. Around the clock, even in broad daylight, luminous
curtains shimmer and ripple across the sky, mesmerizing anyone who
bothers to look. News flash: Astronomers have discovered such a planet.
Its name is Earth.

"Our own planet has auroras 24 hours a day," says Jim Spann of the
Marshall Space Flight Center, "and we can see them even in broad
daylight." The trick, he explains, is picking the right wavelength. "If
we look at Earth from space using an ultraviolet (UV) filter, we see
there are auroras underway at all times. It is a beautiful sight."

The extent of the phenomenon was revealed twelve years ago by NASA's
Polar satellite. As its name suggests, Polar orbits over Earth's poles,
slowly arcing as high as 57,000 km above the arctic where it can take a
good long look at the auroras below. Polar is equipped with special UV
filters that allow it to photograph auroras through the glare of
sunlight and "we were amazed to see Northern and Southern Lights active
non-stop," says Spann, one of the scientists who led development of the
satellite's UV instrumentation.

As an example he offers this movie of a June 2007 auroral display over
Antarctica. Just before the video, a solar wind gust buffeted Earth's
magnetic field causing a mild geomagnetic storm. Visible light
auroras-the kind we see with the human eye--were weak, but "Polar's UV
camera picked up a magnificent outburst," says Spann.

Watch the movie again; it highlights an ancient mystery. Long ago,
arctic sky watchers noticed that mild auroras-the ho-hum kind they saw
almost every night--would sometimes erupt without warning in a stunning
riot of light and color. 20th-century scientists called these events,
with some understatement,

"substorms." A good substorm can unleash a hundred thousand billion
(1014) Joules of energy, as much as a magnitude 5 earthquake. Although
auroras, generally speaking, are understood (they are caused by solar
activity), the sudden power of substorms is one of the biggest mysteries
of space science.
The June 2007 outburst is a classic substorm. "We see plenty of them at
UV wavelengths, " says Spann. "Polar's ability to monitor both night and
day allows us to catch substorms that other satellites might miss."

This ability is being put to good use. Polar is now assisting THEMIS, a
fleet of five spacecraft launched by NASA in Feb. 2007 to solve the
mystery of the substorm. What triggers the events? Where does their
power come from? These are some of the questions THEMIS has set out to
answer.

The five THEMIS satellites are equipped with sensors to map the complex
ebb and flow of particles and fields in Earth's magnetosphere. (The
magnetosphere is a vast magnetic bubble around Earth. It is the "force
field" that protects us from solar wind, and which lights up with
auroras when solar wind gusts come crashing into it.) While a single
spacecraft might be confused by the magnetosphere' s suddenly shifting
electrodynamics, the THEMIS quintet, working together, is able make
sense out of very complicated events. Researchers hope this will lead to
an understanding of the substorm phenomenon.

Polar is valuable because no other spacecraft can match its global view
of the auroras. "We provide the big picture while THEMIS sorts out the
crucial details."
At an age of 12 years, Polar is well past its design lifetime. "It's
amazing that we're still in business," notes Spann. Moreover, by joining
THEMIS, the veteran spacecraft is on the verge of new discovery.

Even for Polar, however, the auroras must stop sometime. During the
writing of this story, the spacecraft ran out of fuel, limiting its
ability to track Earth's poles. Nevertheless, mission planners believe
they can squeeze another one or two month's worth of observing out of
Polar in support of THEMIS. Its final images may be key pieces to the
auroral puzzle.

Farewell, Polar--and thanks for all the substorms!

SOLAR SCIENCE
Spring Is Aurora Season
Los Angeles CA (SPX) Mar 06, 2008
What are the signs of spring? They are as familiar as a blooming
daffodil, a songbird at dawn, a surprising shaft of warmth from the
afternoon sun. And, oh yes, don't forget the aurora borealis. Spring is
aurora season. For reasons not fully understood by scientists, the weeks
around the vernal equinox are prone to Northern Lights.