August 17, 2012
Researchers Track And Measure Electron Beams From The Sun
April Flowers for redOrbit.com - Your Universe Online
Understanding weather patterns here on Earth is a complicated process, with scientists teasing apart different kinds of atmospheric movements, such as the great jet streams that can move across a whole hemisphere versus more localized, intricate flows, to create a whole picture.
Those same methods and processes are used to understand the flows of the space weather system that links the Sun and the Earth as the Sun shoots material out in all directions, creating its own version of a particle sea to fill up the solar system.
"People think of the sun as giving out light and heat," says Ruth Skoug, a space scientist at Los Alamos National Laboratory in Los Alamos, N.M. "But it is also always losing particles, losing mass."
The sun sends out a steady outflow of solar particles called the solar wind. There are also giant, sudden explosions of material called coronal mass ejections, or CME's. Skoug studies yet a third type of solar particle flow jets of high-energy electrons streaming from the sun known as electron strahl.
Skoug and her colleagues, through a five-year study of the strahl, have researched another piece of the giant space weather puzzle.
Skoug contends that each fast moving electron is constrained to move along magnetic field lines that flow out from the Sun, some of which loop back to touch the Sun again while others extend out to the edges of the solar system. The electron's charge interacts with the field lines such that each particle sticks close to the line, like a bead on an abacus — but it also gyrates in circles around the field lines at the same time.
Magnetic fields get weaker as they move further away from the sun. A physical law that applies in those cases in which electrons are not pushed off course, or "scattered," demands that the electron gyrations get smaller and more stretched out along the field line. One would expect the electron strahl to become a more focused, pencil-thin beam when measured near Earth, given this physical law.
Skoug and colleagues use NASA's Advanced Composition Explorer (ACE) mission to measure the electrons, but the results were not quite what was expected.
"Wherever we look, the electron strahl is much wider than we would have expected," says Eric Christian, the NASA's deputy project scientist for ACE at NASA Goddard Space Flight Center in Greenbelt, Md. "So there must be some process that helps scatter the electrons into a wider beam."
Strahls come in a variety of sizes, so Skoug and her team sifted through five years´ worth of ACE data looking for patterns. While they spotted strahls of all widths, they found that certain sizes showed up more frequently. They also found different characteristics in strahls along open field lines that did not return to the sun than from strahls on closed lines that loops back. On open lines, the most common width by far is about ten times the size of the thin beam of electrons expected if there had been no extra scattering. The closed lines, however, showed a nearly equal number of strahls at that width and at a width some four times even larger.
An additional pattern showed up in the strahls on closed lines. While the strahls varied in width, they did not tend to differ in the total number of electrons passing by. This suggests the different shaped strahls, which come from similar places on the sun, may have been the same in composition when they left the sun but were altered by their path and the scattering they encountered.
"We don't yet know how the electrons get scattered into these different widths," says Skoug. "The electrons are so spread out that they rarely bump into each other to get pushed off course, so instead we think that electromagnetic waves add energy, and therefore speed, to the particles."
There are numerous types of these waves, however, traveling at different speeds, in different sizes and in different directions, and no one yet knows which kinds of waves might be at work. Research like this helps start the process of eliminating certain scattering options, since the correct version must, of course, cause the specific variations seen by Skoug and her colleagues.