SAN
FRANCISCO -- Vivid
eruptions of the Northern Lights raced through Earth's atmosphere earlier this
year, breaking speed and energy expectations.
A new
NASA spacecraft caught the show, called an aurora, and has shed light on
the source of the magnetic storm's energy.
On March
23, an auroral substorm erupted over Alaska and Canada and produced spectacular
auroras for more than two hours, caught on camera by NASA's THEMIS
satellite. These THEMIS' observations were presented here today at a meeting of
the American Geophysical Union.
"The
auroras surged westward twice as fast as anyone thought possible, crossing 15
degrees of longitude in less than one minute," said mission scientist Vassilis
Angelopoulos. "The storm traversed an entire polar time zone, or 400 miles, in
60 seconds flat."
The
satellite observed the substorm's development and witnessed small staccato
explosions within the storm that each lasted about 10 minutes. Some of the
outbursts died out, while others went on to become major auroral events.
The power
of the storm blew scientists away; they estimate the total energy of the
two-hour event at five hundred thousand billion Joules, or the energy of one
5.5-magnitude earthquake.
The THEMIS
observations also shed light on just where the substorms get their tremendous
energy.
"The
satellites have found evidence of magnetic ropes connecting Earth's upper
atmosphere directly to the sun," said David Sibeck of NASA's Goddard Space Flight Center in Maryland. "We believe that solar wind
particles flow in along these ropes, providing energy for geomagnetic storms
and auroras."
Spacecraft
have detected hints of magnetic ropes (essentially twisted bundles of magnetic
fields) before, but THEMIS provided the first 3-D look at a ropes' structure.
"THEMIS
encountered its first magnetic rope on May 20," said Sibeck. "It was very
large, about as wide as Earth, and located approximately 40,000 miles (70,000
kilometers) above Earth's surface in a region called the magnetosphere."
(The
magnetosphere is where the solar wind slams into Earth's magnetic field.)
The
explosions detected in the substorm happened "where the solar wind first feels
the effects of Earth's magnetic field," Sibeck said. "Sometimes a burst of
electrical current within the solar wind will hit the bow shock and--Bang! We
get an explosion."
advertisement
