Scientists crack 60-year-old mystery of Sun’s magnetic waves

Posted: December 3, 2019 by oldbrew in research
Tags: ,

The Sun from NASA’s SDO spacecraft


Making some progress anyway – and finding resonance is a key factor.

A Queen’s University Belfast scientist has led an international team to the ground-breaking discovery of why the Sun’s magnetic waves strengthen and grow as they emerge from its surface, which could help to solve the mystery of how the corona of the Sun maintains its multi-million degree temperatures, says Phys.org.

For more than 60 years observations of the Sun have shown that as the magnetic waves leave the interior of the Sun they grow in strength but until now there has been no solid observational evidence as to why this was the case.

The corona’s high temperatures have also always been a mystery. Usually the closer we are to a heat source, the warmer we feel.

However, this is the opposite of what seems to happen on the Sun—its outer layers are warmer than the heat source at its surface.

Scientists have accepted for a long time that magnetic waves channel energy from the Sun’s vast interior energy reservoir, which is powered by nuclear fusion, up into the outer regions of its atmosphere. Therefore, understanding how the wave motion is generated and spread throughout the Sun is of huge importance to researchers.
. . .
The experts formed a consortium called “Waves in the Lower Solar Atmosphere (WaLSA)” to carry out the research and used advanced high-resolution observations from the National Science Foundation’s Dunn Solar Telescope, New Mexico, to study the waves.

Dr. David Jess from the School of Mathematics and Physics at Queen’s led the team of experts. He explains: “This new understanding of wave motion may help scientists uncover the missing piece in the puzzle of why the outer layers of the Sun are hotter than its surface, despite being further from the heat source.

“By breaking the Sun’s light up into its basic colours, we were able to examine the behaviour of certain elements from the periodic table within its atmosphere, including silicon (formed close to the Sun’s surface), calcium and helium (formed in the chromosphere where the wave amplification is most apparent).

“The variations in the elements allowed the speeds of the Sun’s plasma to be uncovered. The timescales over which they evolve were benchmarked, which allowed the wave frequencies of the Sun to be recorded. This is similar to how a complex musical ensemble is deconstructed into basic notes and frequencies by visualising its musical score.”

The team then used super computers to analyse the data through simulations. They found that the wave amplification process can be attributed to the formation of an ‘acoustic resonator,’ where significant changes in temperature between the surface of the Sun and its outer corona create boundaries that are partially reflective and act to trap the waves, allowing them to intensify and dramatically grow in strength.

The experts also found that the thickness of the resonance cavity–the distance between the significant temperature changes–is one of the main factors governing the characteristics of the detected wave motion.

Full report here.
– – –
More information: David B. Jess et al. A chromospheric resonance cavity in a sunspot mapped with seismology, Nature Astronomy (2019). DOI: 10.1038/s41550-019-0945-2 , http://www.nature.com/articles/s41550-019-0945-2

Comments
  1. JB says:

    This millennium begins with an era of ubiquitous re-runs.
    Its now a decade less of a mystery than last year. Six more to go…

  2. Curious George says:

    What exactly is a magnetic wave?

  3. oldbrew says:

    Good question CG. Looks like Alfven waves, in the context of the Sun.
    Abstract: ‘the in situ amplification of magnetohydrodynamic waves’

    Wiki: In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines.

    https://en.wikipedia.org/wiki/Alfv%C3%A9n_wave

    See links in the paper re. waves here:
    https://www.nature.com/articles/s41550-019-0945-2

  4. gallopingcamel says:

    It is strange that photons generated in the core of our sun take many thousands of years to emerge from the photosphere while acoustic waves take only a few days to reach the surface.

    Sometimes the “Speed of Light” can be a snail’s pace.

  5. oldbrew says:

    Resonance again…

    NASA: Solar Wind Energy Source Discovered
    March 8, 2013

    “The source of the heating in the solar wind is ion cyclotron waves.”
    . . .
    “We have long wondered why heavier elements in the solar wind move faster and have higher temperatures than the lighter elements,” says Kasper. “This is completely counterintuitive.”

    The ion cyclotron theory explains it: Heavy ions resonate well with ion cyclotron waves. Compared to their lighter counterparts, they gain more energy and heat as they surf. [bold added]

    https://science.nasa.gov/science-news/science-at-nasa/2013/08mar_solarwind/
    – – –
    Synopsis: Why the Solar Wind Blows Hot and Cold
    February 28, 2013

    A new model shows that the nonuniform heating of ions in the solar wind may be explained by resonant interactions with a particular type of plasma wave. [bold added]

    https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.110.091102
    – – –
    https://en.wikipedia.org/wiki/Ion_cyclotron_resonance

  6. Phoenix44 says:

    I do wish they wouldn’t say the sun is “powered” by a fusion reactor. The sun is a fusion reactor. That’s what makes it a sun. No fusion, just a ball of gas.

  7. oldbrew says:

    DECEMBER 4, 2019
    Parker Solar Probe traces solar wind to its source on sun’s surface: coronal holes
    by University of California – Berkeley

    Thanks to extreme ultraviolet mapping of the sun by other spacecraft, such as STEREO, Bale and his colleagues were able to trace the wind and the magnetic fields back to a source—coronal holes—that strongly suggests that these holes are the source of the slow solar wind. Coronal holes, which are related to sun spots, are areas that are cooler and less dense than the surrounding corona.

    What was unexpected was a series of flips in the magnetic field as it streamed past the spacecraft. During these periods, the magnetic field suddenly reversed itself by 180 degrees and then, seconds to hours later, flipped back.

    “These switchbacks are probably associated with some kind of plasma jets,” Bale said. “My own feeling is that these switchbacks, or jets, are central to the solar wind heating problem.”

    https://phys.org/news/2019-12-parker-solar-probe-source-sun.html

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