Massive Plasma Waves Sweep The Sun

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This still from a NASA and Helioviewer.org video shows the huge solar flare and coronal mass ejection (lower right) that erupted from the sun June 7, 2011, as seen by the Solar Dynamics Observatory. CREDIT: NASA/GSFC/Heliovewer.org

SOLAR PROMINENCE: NASA's Solar Dynamics Observatory captured this view of a powerful M3.6 Class solar flare on Feb. 24, 2011 during a 90-minute sun storm. NASA scientists called the display a "monster prominence" that kicked up a huge plasma wave. (Photo: NASA)

"We're Seeing Things We've Never Seen Before"
(NASA)       11 June 2011  

A huge storm on the sun this past week unleashed what some have called the most massive eruption of solar plasma ever seen. NASA astronomers said the huge June 7 solar eruption, called a coronal mass ejection, probably wasn't the biggest ever, but it is notable both for its size and its odd behavior, as massive waves of plasma roared off the sun only to rain back down on the solar surface.

 "We're seeing things we've never seen before," said Phillip Chamberlin, an astrophysicist at NASA's Goddard Spaceflight Center and a deputy project scientist on the agency's Solar Dynamics Observatory (SDO) satellite. "It's a really exciting event. There are a lot of exceptions to it."

Since scientists know how these waves initiated by a Kelvin-Helmholtz instability they can use this information to 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," says solar physicist Leon Ofman of NASA's Goddard Space Flight Center and Catholic University. "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."

Ofman and his Goddard 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 Solar Dynamics Observatory (SDO), a solar telescope with outstanding resolution that launched on February 11, 2010 and began capturing data on March 24 of that year.  That these "surfer" waves exist in the sun at all is not necessarily a surprise, since they do appear in so many places in nature including, for example, clouds on Earth and between the bands of Saturn.

"The waves we're seeing in these images are so small," says Thompson, the deputy project scientist for SDO. "They're only the size of the United States."

Kelvin-Helmholtz instabilities occur when two fluids of different densities or different speeds flow by each other. In the case of ocean waves, that's the dense water and the lighter air. As they flow past each other, slight ripples can be quickly amplified into the giant waves loved by surfers. 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. The difference in flow speeds and densities across this boundary sparks the instability that builds into the waves.

In order 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 says 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.  "I wasn't sure that this instability could evolve on the sun, since magnetic fields can have a stabilizing effect," he says. "Now we know that this instability can appear even though the solar plasma is magnetized."

Seeing the massive 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.

Hammering out the exact mechanism for heating the corona will continue to intrigue researchers for some time but, says Thompson, SDO's ability to capture images of the entire sun every 12 seconds with such precise detail will be a great boon.

"SDO is not the first solar observatory with high enough visual resolution to be able to see something like this," she says. "But for some reason Kelvin-Helmholtz features are rare. The fact that we spotted something so interesting in some of the first images really shows the strength of SDO."

The Daily Galaxy via NASA/Goddard Space Flight Center

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Humongous plasma waves speed across the sun
They are so huge it would take up to 16 Earths, end-to-end, to match them

Humongous waves of hot plasma roiling on the surface of the sun appear to be moving at speeds as high as 4.5 million miles per hour, a new study has found. The waves are so huge it would take up to 16 Earths, end-to-end, to match them. It's the first unambiguous evidence that the sun's lower atmosphere contains such superfast "magnetosonic waves," scientists said.

The fast waves have velocities of 2.3 million to 4.5 million mph, periods in the range of 30 to 200 seconds, and wavelengths of 62,000 to 124,000 miles, equivalent to stacking between eight to 16 Earths on top of one another. Scientists discovered the waves with the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory (SDO), dedicated to observing the sun from orbit around Earth.

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Ripples in a pond
Waves on the sun are produced when a flare or eruption on the solar surface kicks up hot plasma, similar to ripples in water produced when a rock is dropped into a still pond.

Scientists have observed slow-moving waves on the sun, but fast-moving waves, which were also predicted by theory, had so far gone undetected because previous space telescopes could not take pictures rapidly enough to image these fast waves.

"They seem to be a common phenomenon," said Karel Schrijver, principal physicist at the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif., in a statement. "During the first year of the SDO mission, despite the sun being relatively quiet, we have seen about a dozen such waves. Although their exact trigger mechanism is currently under investigation, they appear to be intimately related to flares that sometimes exhibit pulsations at similar frequencies." 

Enigmatic processes
Waves such as these are believed to be responsible for many fundamental yet enigmatic processes on the sun, such as heating the corona to millions of degrees, accelerating the solar wind, triggering remote eruptions and delivering energy and information between different parts of the atmosphere.

By observing these waves, scientists hope to better understand the solar physics of such processes and their consequences on near-Earth space and the terrestrial environment.  

"This discovery and analysis is very significant because we are witnessing phenomena of which we were previously unaware," said Alan Title, principal investigator of the Atmospheric Imaging Assembly at the Lockheed Martin lab, who first noticed the fast propagating waves in routine SDO movies. "In light of this discovery, the more we look at solar flares, the more of these waves we see, and as observation and analysis lead to insight, the better we will understand the processes involved."

Stanford University scientist Wei Liu, a research associate at the Lockheed Martin laboratory, presented the findings Wednesday at the annual meeting of the Solar Physics Division of the American Astronomical Society in Las Cruces, N.M. The researchers also detail their discovery in a paper to be published in The Astrophysical Journal Letters.

Surfer waves on the sun?
Another recent study of waves on the sun found "surfer" waves the size of the United States in the solar corona.  These so-called Kelvin-Helmholtz waves, also discovered using data from SDO, could help astronomers understand how energy moves through the solar atmosphere.

"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 in 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."  That research was published online on May 19 in the Astrophysical Journal Letters.

http://www.msnbc.msn.com/id/43441928/ns/technology_and_science-space/