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Sun's micro flares play major role in heating corona
Solar activity with a large coronal mass ejection. The effects of the solar flare are expected to cause interruptions in communications for several days.
THE SUN'S tiny numerous microflares may influence solar atmosphere more than the solar flares, according to new data from the University of California, Berkeley's (Reuven Ramaty High-Energy Solar Spectroscopic Imager) RHESSI satellite.
Solar flares propel energetic particles into space and are thought to be the main source of heat pumping the sun's outer atmosphere to about a few million degrees Celsius.
Now observations show that microflares a million times smaller are more frequent and may provide a major portion of the heat in the corona.
Since solar flares play a major role in space weather, RHESSI's discoveries could eventually help predict the big storms that interfere with radio communications on Earth.
Robert Lin, professor of physics at UC Berkeley presented data from RHESSI at the meeting of the International Astronomical Union in Sydney, Australia.
Microflares are identified by the hard X-rays they emit. Astronomers have also suggested that microflares may be mainly thermal events, heating the sun but not accelerating particles like larger flares.
If that were the case, they would produce more low-energy soft X-rays than high-energy hard X-rays. But they do not.
Interestingly, a subset of microflares are responsible for a type of radio burst from the sun studied intensively. These so-called Type III bursts are characterised by radio signals that decrease in frequency, like the whistle from a departing train.
Type III bursts appear to be associated with microflares that do very little heating of the solar atmosphere.
Instead, the stream of high-speed particles they produce seems to jet unchecked out of the sun at speeds up to one-third the speed of light, exciting radio oscillations at lower and lower frequencies as the particles pass through lower and lower density plasma.
"This probably has to do with the magnetic field in the region around the microflare, since particles are tied to the field lines and have to run along them," Lin said.
"We think that for normal microflares, the particle acceleration occurs in a closed magnetic region so the electrons can't get away; they do more heating that way.
In Type III bursts, the electrons are accelerated in an open magnetic field, and they have an easy way to escape, so they do some less of heating."
"When we look at the big and fast coronal mass ejections and extrapolate back to the sun, we find that at the very point where the coronal mass ejection is initiated, that is exactly where the flare energy release happened."
These largest of the mass ejections are the ones that have the greatest effect on Earth, exciting geomagnetic storms that can cause power outages and damage the communications satellites.
The shock wave from coronal mass ejections also produces energetic particles that pose a hazard to satellites and astronauts.
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