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Solar cannibalism

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11:39am, April 25, 2001
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Billion-ton parcels of charged gas hurled from the sun can overtake and eat their

slower-moving gaseous brethren, according to researchers who presented their

findings March 27 at a meeting of the European Geophysical Society in Nice,

France.

Cannibalism among these clouds of charged particles, known as coronal mass

ejections (CMEs), is more than an astronomical curiosity. CMEs can harm

communications and power systems on Earth. Commenting about the work, Ernest

Hildner, director of the National Oceanic and Atmospheric Administration's Space

Environment Laboratory in Boulder, Colo., says that combined CMEs can act

differently from single ejections. Astronomers may have to take that into account

when they predict earthly effects, he notes.

The collision of two CMEs could generate, for example, a single, more powerful

punch, slow the speed of the faster eruption, or direct the merged CME toward or

away from Earth.

Natchimuthuk Gopalswamy of the Catholic University of America in Washington, D.C.,

and his colleagues base their findings on observations by two spacecraft. Several

years ago, NASA's Wind craft recorded a group of puzzling, intense radio bursts

far from the sun. Images taken by the Solar and Heliospheric Observatory, a

NASAEuropean Space Agency mission, have revealed that the bursts occurred when

one solar eruption swallowed another, creating energetic, radio-emitting

electrons.

"It is not very surprising that CMEs should interact," notes Gopalswamy, who is

based at NASA's Goddard Space Flight Center in Greenbelt, Md., but the radio

outbursts suggest that the interaction is extremely violent and can occur millions

of kilometers from the sun. Scientists expect such collisions to be much more

common now, at the peak of the sun's 11-year activity cycle, when the sun can

jettison CMEs in relatively rapid succession.

The collisions occur "when a slow CME is expelled before a fast one from the same

general region on the sun," says Gopalswamy. "The fast CME simply gobbles up the

slow one." His team has identified 21 instances of CME cannibalism since 1997.

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