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Alfven Waves Drive Coronal Heat + Solar Wind

  1. Jul 28, 2011 #1

    Dotini

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    Gold Member

    One of the all-time great science mysteries is now a step closer to explanation. The surface of the sun, known as the photosphere, can reach temperatures of 5,000 degrees. To many it would seem logical that the temperature would lower further away from the sun. But, the outer atmosphere, known as the corona, has been shown to reach temperatures of over a million degrees.

    http://www.physorg.com/news/2011-07-power-sun-intense.html
    The study uses satellite observations to reveal that magnetic oscillations carrying energy from the Sun's surface into its corona are far more vigorous than previously thought. These waves are energetic enough to heat the corona and drive the solar wind, a stream of charged particles ejected from the Sun that affects the entire solar system.

    Alfven waves were directly observed for the first time in 2007. Scientists recognized them as a mechanism for transporting energy upward along the Sun's magnetic field into the corona. But the 2007 observations showed amplitudes on the order of about 1,600 feet (0.5 kilometers) per second, far too small to heat the corona to its high levels or to drive the solar wind. http://www.sciencemag.org/content/317/5842/1192.abstract

    General info on Alfven waves: http://en.wikipedia.org/wiki/Alfvén_wave

    Respectfully submitted,
    Steve
     
  2. jcsd
  3. Jul 28, 2011 #2

    Drakkith

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    Staff: Mentor

    Interesting!
     
  4. Jul 31, 2011 #3

    Dotini

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    Yes, interesting from an intellectual point of, but possibly important, too.

    Not only has this question been at the forefront of astrophysics for 50 years, but now Dr Richard Fisher, the director of NASA’s Heliophysics division, warned in an interview of a once-in-a-lifetime ‘space storm’ after the sun wakes ‘from a deep slumber’ sometime around 2013, causing ‘20 times more economic damage than Hurricane Katrina’.

    http://www.sciencedaily.com/releases/2011/07/110727131404.htm
    http://www.thehindu.com/sci-tech/article2296011.ece

    "Alfven waves were directly observed for the first time in 2007. Scientists recognized them as a mechanism for transporting energy upward along the Sun's magnetic field into the corona. But the 2007 observations showed amplitudes on the order of about 1,600 feet (0.5 kilometers) per second, far too small to heat the corona to its high levels or to drive the solar wind.

    The new satellite observations used in the current study reveal Alfven waves that are over a hundred times stronger than previously measured, with amplitudes on the order of 12 miles (20 km) per second -- enough to heat the Sun's outer atmosphere to millions of degrees and drive the solar wind. The waves are easily seen in high-resolution images of the outer atmosphere as they cause high-speed jets of hot material, called spicules, to sway.

    Now that the real power of the waves has been revealed in the corona, the next step in unraveling the mystery of its extreme heat is to study how the waves lose their energy, which is transferred to plasma. To do that, scientists will need to develop computer models that are fine enough in detail to capture how the jets and waves work together to power the atmosphere. By studying the Sun's underlying physics with these tools, scientists could better understand the Sun's 11-year sunspot cycle and its impacts on Earth."


    Respectfully submitted,
    Steve
     
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