NASA's Solar Dynamics Observatory (SDO) has observed 'surfer'' waves just the size of the United States rolling through the atmosphere of the Sun.
The finding may hold clues as to how energy moves through Sun's atmosphere, known as the corona, and help solve an enduring mystery of why the corona is thousands of times hotter than originally expected.
"One of the biggest questions about the solar corona is the heating mechanism," said solar physicist Leon Ofman of NASA''s Goddard Space Flight Center, Greenbelt, Md. and Catholic University, Washington.
"The corona is a thousand times hotter than the sun''s visible surface, but what heats it up is not well-understood. People have suggested that waves like this might cause turbulence which cause heating, but now we have direct evidence of Kelvin-Helmholtz waves," he added.
Ofman and his colleague Barbara Thompson spotted these waves in images taken on April 8, 2010. These were some of the first images caught on camera by the SDO, a solar telescope with outstanding resolution.
"The waves we''re seeing in these images are so small," said Thompson. "But they''re only the size of the United States," she said.
Kelvin-Helmholtz instabilities usually occur when two fluids of different densities or different speeds flow by each other. In the case of the solar atmosphere, which is made of a very hot and electrically charged gas called plasma, the two flows come from an expanse of plasma erupting off the sun''s surface as it passes by plasma that is not erupting.
To confirm this description, the team developed a computer model to see what takes place in the region. Their model showed that these conditions could indeed lead to giant surfing waves rolling through the corona.
Ofman said that despite the fact that Kelvin-Helmholtz instabilities have been spotted in other places, there was no guarantee they''d be spotted in the sun''s corona, which is permeated with magnetic fields.
Seeing the big waves suggests they can cascade down to smaller forms of turbulence too.
Scientists believe that the friction created by turbulence – the simple rolling of material over and around itself – could help add heating energy to the corona.
The team''s results appeared online in Astrophysical Journal Letters on May 19, 2011 and will be published in the journal on June 10.
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