What makes the northern lights dance discovered
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Friday » July
25 » 2008
>When Earth's rubber band snaps
Canadian and U.S. Scientists say they have discovered what makes the
northern lights dance
MARGARET MUNROCanwest News Service
Friday, July 25, 2008
[image: The northern lights dance across a starry night sky at the
Yellowknife boat launch on Great Slave Lake in the Northwest
LARRY WONG, CANWEST NEWS SERVICEThe northern lights dance across a starry
night sky at the Yellowknife boat launch on Great Slave Lake in the
An international team has discovered that when Earth's magnetotail snaps out
in space, the northern lights start dancing across Canada's skies.
One explosive release in February - which occurred about 127,000 kilometres
away, or one-third of the way to the moon - sent enormous amounts of energy
hurdling toward Earth. A minute-and-a-half later, a spectacular aurora
display lit up the skies, say the scientists, whose work with five NASA
satellites and 20 ground stations across Canada and Alaska is
revolutionizing our understanding of space weather.
"We discovered what makes the northern lights dance," lead investigator
Vassilis Angelopoulos of the University of California (Los Angeles) said in
announcing the discovery yesterday.
Scientists have been trying to figure out for decades what makes the aurora
swirl and undulate through the northern and southern skies.
The $200-million system of satellites and ground stations has, in effect,
allowed them to "fly into the eye of the storm," said space physicist Ian
Mann of the University of Alberta, a member of the team that has published
its new findings online in the journal Science.
They say explosive short-circuits, or reconnections, in Earth's magnetic
field lines, trigger the onset of so-called "substorms" which cause the
aurora to suddenly brighten and dance.
Earth's magnetic field, which protects the planet from harsh solar
radiation, absorbs energy from the solar wind, which is constantly buffeting
the planet. The wind stretches Earth's magnetic field lines far off into
space, producing the magnetotail, NASA scientist David Sibeck said.
(A magnetotail is the narrow and elongated region of the magnetosphere of
Earth that extends in the direction away from the sun.)
But Sibeck said the magnetic field lines can only be stretched so far before
they snap "like rubber bands."
"You build up these big currents, you store lots of energy and then suddenly
bang!, they snap," Sibeck told a media teleconference. Vast amounts of
energy are then flung back toward Earth, powering up the aurora in both the
northern and southern hemispheres.
Such "substorms" typically occur several times a day. They vary greatly in
intensity, with some dumping so much energy into Earth's atmosphere that
they can damage satellites, endanger astronauts and disrupt power lines and
communications on the ground, said the scientists, who hope their work will
lead to better space weather forecasts.
To try to find out what causes the spectacular light shows, NASA and its
partners launched a flotilla of five identical satellites, the size of
washing machines, in February 2007.
The satellites line up on the same side of Earth once every four days and
can pinpoint where and when substorms begin. They can also track the
corresponding disturbances "spreading like wildfires in space," Sibeck said.
The satellites are coupled with 20 ground stations, which have magnetometers
and sophisticated cameras pointing skyward. They measure the currents and
aurora swirling through the heavens during substorms.
"We're talking about million-amp currents pumped into Earth's atmosphere,"
The cameras snap pictures every three seconds, enabling the scientists to
follow aurora shows across the continent from Alaska to Newfoundland.
The system was perfectly aligned to catch the Feb. 26 substorm.
One satellite was on the far side of the magnetic field lines that snapped,
or reconnected, 127,000 kilometres from Earth. The other four were closer to
Earth and measured the resulting power surge as it raced back toward the
planet. The ground stations caught the aurora lighting up about 11/2 minutes
after the initial explosion, Angelopoulos said.
"It's a quite a beautiful sequence of cause and effect," Mann said.
"We can pinpoint where the action was right at the beginning of the boom,
and then we can see the effect twang down toward the planet and release
energy in the form of the northern lights over Canada and Alaska."
It's "pretty wild" to think reconnecting magnetic field lines more than
100,000 kilometres away can get the aurora dancing overhead, says Eric
Donovan of the University of Calgary, who heads the Canadian component of
He said the finding is just "a taste of what's to come" from the mission,
which is revolutionizing understanding of the aurora.
"It is going to change the field of space physics forever," said Donovan,
noting there are all kinds of strange and mysterious features in the
northern lights. "What we don't know outnumbers what we do know."
(c) The Gazette (Montreal) 2008
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