Subscribe free to our newsletters via your
. 24/7 Space News .

SDO Spots Extra Energy in the Solar Corona
by Karen C. Fox for NASA's Goddard Space Flight Center
Greenbelt MD (SPX) Jul 28, 2011

These jets, known as spicules, were captured in an SDO image on April 25, 2010. Combined with the energy from ripples in the magnetic field, they may contain enough energy to power the solar wind that streams from the sun toward Earth at 1.5 million miles per hour. Credit: NASA/SDO/AIA - more captions, images and movies can be found here.

Like giant strands of seaweed some 32,000 miles high, material shooting up from the sun sways back and forth with the atmosphere. In the ocean, it's moving water that pulls the seaweed along for a ride; in the sun's corona, magnetic field ripples called Alfven waves cause the swaying.

For years these waves were too difficult to detect directly, but NASA's Solar Dynamics Observatory (SDO) is now able to track the movements of this solar "seaweed" and measure how much energy is carried by the Alfven waves.

The research shows that the waves carry more energy than previously thought, and possibly enough to drive two solar phenomena whose causes remain points of debate: the intense heating of the corona to some 20 times hotter than the sun's surface and solar winds that blast up to 1.5 million miles per hour.

"SDO has amazing resolution so you can actually see individual waves," says 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."

McIntosh published his research in a Nature article appearing on July 28. Alfven waves, he says, are actually fairly simple. They 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. SDO can see this material in motion and so can track the Alfven waves.

Alfven waves are part of a much more complex system of magnetic fields and plasma surrounding the sun. 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.

"We know there are mechanisms that supply a huge reservoir of energy at the sun's surface," says space scientist Vladimir Airapetian at NASA's Goddard Space Flight Center in Greenbelt, Md. "This energy is pumped into magnetic field energy, carried up into the sun's atmosphere and then released as heat."

But determining the details of this mechanism has long been debated. Airapetian points out that a study like this confirms Alfven waves may be part of that process, but that even with SDO we do not yet have the imaging resolution to prove it definitively.

When the waves were first observed in 2007 (more than six decades after being hypothesized by Hannes Alfven in 1942), it was clear that they could in theory carry energy up from the sun's surface to its atmosphere. However, the 2007 observations showed them to be too weak to contain the great amounts of energy needed to heat the corona so dramatically.

This study says that those original numbers may have been underestimated. 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,'" says McIntosh. "Because the movies really look like the sun was made of Jell-O wiggling back and forth everywhere. Clearly, these wiggles carry energy."

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 Alfven waves and found them to be a good match.

Going forward, they could analyze the shape, speed, and energy of the waves. 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 shortness of the repetition - known as the period of the wave - is also important. 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 Alfven 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.

"Knowing there may be enough energy in the waves is only one half of the problem," says Goddard's Airapetian. "The next question is to find out what fraction of that energy is converted into heat. It could be all of it, or it could be 20 percent of it - so we need to know the details of that conversion."

In practice, that means studying more about the waves to understand just how they impart their energy into the surrounding atmosphere.

"We still don't perfectly understand the process going on, but we're getting better and better observations," says McIntosh. "The next step is for people to improve the theories and models to really capture the essence of the physics that's happening."


Related Links
Solar Science News at SpaceDaily

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

New Ways to Measure Magnetism Around the Sun
Greenbelt MD (SPX) Jul 15, 2011
Those who study the sun face an unavoidable hurdle in their research - their observations must be done from afar. Relying on images and data collected from 90 million miles away, however, makes it tough to measure the invisible magnetic fields sweeping around the sun. Scientists must learn more about these fields because they are crucial to understanding how coronal mass ejections, or CMEs ... read more

Unique volcanic complex discovered on Lunar far side

Moon Express Announces Dr. Alan Stern as Chief Scientist

Northrop Grumman Honored by IEEE for Development of Lunar Module

Two NASA Probes Tackle New Mission: Studying The Moon

NASA's Next Mars Rover to Land at Gale Crater

Opportunity Closing In On Spirit Point At Endeavour Crater

MAVEN Mission Completes Major Milestone

NASA says Mars mountain will read like 'a great novel'

SwRI suborbital astronaut payload specialists move to flight planning phase, release mission patch

Graybiel Lab poised for next chapter of space exploration

Space Program Mavens Comment on the Future of Space Exploration

This Time It's Both Rocket Science AND Surgery

Spotlight Time for Tiangong

China launches new data relay satellite

Time Enough for Tiangong

China launches experimental satellite

New uses for Space Station

ISS to be sunk after 2020: Russian space agency

Certification for ISS onboard astronaut

NASA and International Partners Discuss New Uses for Space Station

Russia sends observation satellite into space

NASA inks agreement with maker of Atlas V rocket

Russia launches 2 foreign satellites into orbit

ILS Proton Successfully Launches the SES-3 Satellite for SES

Exoplanet Aurora Makes For An Out-of-this-World Sight

Distant planet aurorae modeled

Exoplanet Aurora: An Out-of-this-World Sight

Ten new distant planets detected

Turksat turns to GMV for control of its satellites

Lockheed Martin's Multi-Mission Signal Processor Completes Tracking Test

Sharper deeper faster 3D imaging

Rare Coupling of Magnetic and Electric Properties in a Single Material

The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement