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Researchers led by Craig DeForest of the Southwest Researcher Institute in Boulder,
Colorado, have announced, in a NASA press conference, that they have followed the
entire path of a solar storm for the first time.
The evolution of a coronal mass
ejection, or CME (an explosive event associated with solar flares) has been followed
all the way from the Sun's surface to the point at which the charged particles impact
on the terrestrial magnetosphere.
Though the CME phenomenon is well known, until now it has only be possible to follow
them directly during the first few hours of their development, while the plasma
ejected from the Sun is still sufficiently dense, and therefore luminous, to be
detected optically.
A few hours after the eruption the density and surface brightness
have fallen so much that the particle flux is only a slight brightness enhancement
over the zodiacal light, that is, almost as transparent as interplanetary space. In
other words, after a CME, although it was known that a solar storm was about to hit
our planet its time of arrival could only be estimated with an accuracy of about 4
hours, an uncomfortably large error, especially for the planning of the orbital
activities of astronauts.
But thanks to the images obtained by STEREO-A (one of the twin probes launched in
2006 in order to follow solar activity) DeForest and colleagues have developed a new
technique that allows a CME to be followed from its emergence from the solar
atmosphere all the way to Earth.
The first demonstration of this new capability used
archival images from a CME that occurred in December 2008 to produce a film of its
evolution, some frames from which are shown above (the full version can be seen at
http://svs.gsfcnasa.gov/vis/a010000/a010800/a010809/index.html).
The new technique also gives an accurate value for the density of the flux of
particles arriving from the Sun, allowing for a better and faster estimate of the
effects on our space activities.
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