London, July 28 (ANI): Why the sun's outer atmosphere, or corona, is 20 times hotter than its surface and how the solar wind is accelerated up to 1.5 million miles per hour have deceived scientists for decades, but it seems they are now one step closer to solving the mystery.
An international team of scientists has discovered that powerful magnetic field ripples, called Alfven waves, might be driving the solar wind and heating much of the corona.
Using NASA's Solar Dynamics Observatory (SDO) satellite, they traced the movements of this solar 'seaweed' and measured how much energy is being carried by the Alfven waves.
The scientists found that the waves carry more energy than previously thought.
"SDO has amazing resolution so you can actually see individual waves," said Scott McIntosh at the National Center for Atmospheric Research in Boulder, Colo.
"Now we can see that instead of these waves having about 1000th the energy needed as we previously thought, it has the equivalent of about 1100W light bulb for every 11 square feet of the sun's surface, which is enough to heat the sun's atmosphere and drive the solar wind," he added.
McIntosh said Alfven waves are waves that travel up and down a magnetic field line much the way a wave travels up and down a plucked string.
The material surrounding the sun-electrified gas called plasma - moves in concert with magnetic fields.
Understanding that system could help answer general questions such as what initiates geomagnetic storms near Earth and more focused questions such as what causes coronal heating and speeds of the solar wind - a field of inquiry in which there are few agreed-upon answers.
McIntosh, in collaboration with a team from Lockheed Martin, Norway's University of Oslo, and Belgium's Catholic University of Leuven, analyzed the great oscillations in movies from SDO's Atmospheric Imagine Assembly (AIA) instrument captured on April 25, 2010.
"Our code name for this research was 'The Wiggles'. Because the movies really look like the sun was made of Jell-O wiggling back and forth everywhere. Clearly, these wiggles carry energy," said McIntosh.
The team tracked the motions of this wiggly material spewing up-in great jets known as spicules - as well as how much the spicules sway back and forth. They compared these observations to models of how such material would behave if undergoing motion from the Alfv?n waves and found them to be a good match.
The sinusoidal curves deviated outward at speeds of over 30 miles per second and repeated themselves every 150 to 550 seconds. These speeds mean the waves would be energetic enough to accelerate the fast solar wind and heat the quiet corona.
The shorter the period, the easier it is for the wave to release its energy into the coronal atmosphere, a crucial step in the process.
Earlier work with this same data also showed that the spicules achieved coronal temperatures of at least 1.8 million degrees Fahrenheit.
Together the heat and Alfv?n waves do seem to have enough energy to keep the roiling corona so hot. The energy is not quite enough to account for the largest bursts of radiation in the corona, however.
The study appears in the July 28 issue of Nature. (ANI)
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