http://www.cosmosmagazine.com/node/3356/full
Be Well.
David
Solar storms create 'killer electrons'
A stream of charged particles from the Sun hits Earth's magnetosphere.
Credit: NASASYDNEY: 'Killer electrons' - electrons circling Earth that wreck satellites and can cause cancer in astronauts - are created when Solar storms create shockwaves in the Earth's protective magnetic bubble, scientists said.
The Earth's magnetic field abounds with charged, fast moving particles that orbit up to 64,000 km above the surface. When a severe solar storm - a stream of energetic particles emanating from the Sun - hits the Earth's magnetic field, it creates a shockwave that boosts the number of particles by up to ten times as much.
These highly energetic negative particles, which scientists have dubbed 'killer' electrons, can penetrate satellites and spacecraft and cause miniature lightning storms within the electronics. They also pose a health risk to astronauts.
Particle energy amplified
Until now, scientists were unsure what was causing the electrons to accelerate to such high speeds. An international team led by space physicist Qiugang Zong from Peking University in China and the University of Massachusetts Lowell in the U.S. says waves within the magnetic field itself amplify the energy of the particles to the point where they become a serious hazard.
As the waves travel through Earth's magnetic field, it causes the charged particles to accelerate - first in one direction, then in the opposite direction.
Because the particles are oscillating in phase with the waves they begin to speed up - this is like sloshing back and forth in the bath in time with the reflected waves, causing them to get bigger.
Different frequencies accelerate electrons
"A killer electron storm is the most dangerous phenomena in the space environment," Zong said. When these storms occur, satellites should be switched to safe mode or turned off, launches delayed and astronauts should avoid spacewalks, he said.
The researchers used data from the European Space Agency's four Cluster satellites on two solar storm events, a big one in November 2004 and another, smaller event in 2001.
They then analysed the data to examine the role played by different frequency 'pulses' in the magnetic field, including two sets of waves: ultra low frequency waves (ULF, 0.001-1 Hertz waves) and very low frequency waves (VLF waves, 3-30 kHz). The results were published last year in the Journal of Geophysical Research.
While the VLF waves accelerate the particles over longer timescales, it is the lower frequency ULF waves that give the initial kick start, says Zong.
Space weather scientist Murray Parkinson, from the IPS Radio and Space Services at the Bureau of Meteorology in Sydney likened the effect to a ringing bell.
Shockwaves around Earth
A bell hit by a rod rings with soundwaves. Similarly, as the shockwave from the solar storm hits the Earth's magnetosphere, the pressure rises and the system begins to 'ring' with these ultra low frequency waves.
The ULF waves cause the particles to accelerate back and forth, and you would expect there would be no net acceleration, he says.
"But there are certain resonances where particles are drifting in phase with the waves and it produces a net acceleration," he says. The VLF waves continue this acceleration, but on a longer timescale.
"There's been a question mark about the physics that leads to the acceleration of these particles and how they are boosted to these lethal relativistic energies," he says. "We've lost many spacecraft due to hazardous radiation environments - I think this is quite a significant result."
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