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IN THE USA: A coronal mass ejection
(CME) hit Earth on Oct. 24th at approximately 1800
UT (2:00 pm EDT). The impact strongly compressed
Earth's magnetic field, directly exposing geosynchronous
satellites to solar wind plasma, and sparked an
intense geomagnetic storm. As night fell over North
America, auroras spilled across the Canadian border
into the contiguous United States.
"Wow, wow, wow! These were the
best Northern Lights I've seen since 2004,"
says Shawn Malone, who took this picture from the
shores of Lake Superior in Michigan:
"The auroras filled the sky in
every direction--even to the south," he says.
Indeed, the display spread all the
way down to Arkansas. "When I saw the alert,
I ran outside and immediately saw red
auroras," reports Brian Emfinger from the
city of Ozark. "Within a few minutes the auroras
went crazy! It was unbelievable." Update:
Emfinger has assembled a 2h 22m time-lapse movie
of the display: 29
Auroras were seen or photographed
in more than half of all US states including Alabama,
Oregon, Arkansas and California. Many observers,
especially in the deep south, commented on the pure
red color of the lights they saw. These rare all-red
auroras sometimes appear during intense geomagnetic
storms. They occur some 300 to 500 km above Earth's
surface and are not yet fully understood.
The storm is subsiding now. Nevertheless,
high-latitude sky watchers should remain alert for
auroras as Earth's magnetic field continues to reverberate
from the CME impact. Aurora
2011 Aurora Gallery
[previous Octobers: 2010,
INSTIGATING EXPLOSION: The CME
that hit Earth's magnetic field on Oct. 24th left
the sun almost two days earlier. It was propelled
in our direction by an unstable magnetic filament,
which erupted around 0100 UT on Oct. 22nd. This
movie from the Solar and Heliospheric Observatory
shows the cloud expanding toward Earth in the first
hours after the explosion:
Traveling faster than two million
mph, the cloud took about 41 hours to cross the
sun-Earth divide. The CME was so geoeffective because
it contained a knot of south-pointing magnetic fields.
These fields partially cancelled Earth's north-pointing
magnetic field at the equator, allowing solar wind
plasma to penetrate deeply into Earth's magnetosphere.
The rest, as they say in
Alabama, is history.