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Solar Sigmoids Explained

This figure shows the time evolution and final eruption of the sigmoid. Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)

This figure shows the time evolution and final eruption of the sigmoid. Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)

S-shaped structures called ‘Sigmoids’ have been found in the outer atmosphere of the Sun — the corona. Sigmoids are thought to be a crucial part of explosive events like solar flares. Now a group of astronomers have developed the first model to reproduce and explain the nature of the different stages of a sigmoid’s life. Recently, the X-Ray Telescope (XRT) on board the Hinode space mission was used to obtain the first images of the formation and eruption phase of a sigmoid at high resolution. These observations revealed sigmoids have very complex structures.

Professor Alan Hood and Dr. Vasilis Archontis, both from the Mathematical Institute at St. Andrews University, Scotland, presented their team’s findings today at the European Week of Astronomy and Space Science conference at the University of Hertfordshire.
Over the years a series of theoretical and numerical models have been proposed to explain the nature of sigmoids but until now there was no explanation on how such complex structures form, erupt and fade away. The new model describes how sigmoids consist of many thin and twisted layers (or ribbons) of strong electric current. When these layers interact it leads to the formation of the observed powerful flares and the eruption of strong magnetic fields which carry highly energetic particles into interplanetary space. The team also found that as the sigmoids die out, they produce a ‘flare’ eruption.

Dr. Archontis sees the connection between the two astronomers’ model and work on predicting solar flares. He remarks, “Sigmoids work as ‘mangers’ or ‘cocoons’ for solar eruptions. There is a high probability that they will result in powerful eruptions and other explosive events. Our model helps scientists understand how this happens.”

Prof. Hood adds that these events have real significance for life on Earth, “Sigmoids are among the most interesting features for scientists trying to forecast the solar eruptions – events that can disrupt telecommunications, damage satellites and affect the way navigation systems are operated’.

Explanation of image: This figure shows the time evolution and final eruption of the sigmoid. It consists of three columns (time is running from top to bottom). Columns 1 and 2 show results from numerical experiments. The yellow isosurfaces are surfaces of electric current (left panels). Column 2 (middle panels) shows temperature. Column 3 shows ‘temperature’ (intensity) as it is recorded by the observations (Hinode mission). Notice that the agreement on the shape of the sigmoid, internal structure and thermal distribution along the sigmoid, between numerical experiments and observations is very good and fairly balanced. Notice, that even the ‘flaring’ episode (flashing) at the middle of the sigmoid at the down-right snapshot from observations is reproduced exceptionally well by our numerical experiments (down-middle). Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)

Source: RAS


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Angry Taxpayer April 21, 2009, 9:17 PM

    I’m sure glad that I don’t watch TV, if I did I wouldn’t have time to read these posts, this is more fun. I don’t understand much of what any of you are saying or talking about, but that doesn’t seem to matter as i don’t think any of you do either.

    I love the comments the Oiils (?) mastery makes about how intelligent he is and has to educate the rest of us, reminds me of my neighbor in a Home Owners Association i used to live in, she knew far better than me how I should live and manage my life. Lots of those kind of people around. I sold that house and moved out of any HOA, me thinks Oiils should be ignored, but then where would the fun be? I would have to get TV :(

  • IVAN3MAN April 22, 2009, 5:25 AM

    RE: OilIsMastery and the alleged impostor.

    Poe’s Law states:

    Without a winking smiley or other blatant display of humor, it is impossible to create a parody of Fundamentalism that SOMEONE won’t mistake for the real thing.

  • OilIsMastery April 22, 2009, 12:34 AM

    Angry Taxpayer,

    I never said I was intelligent. That is a crackpot impersonating me in order to make you reject science in favor of pseudoscience.

  • Jon Hanford April 22, 2009, 9:22 AM

    @ solrey, if you are going to link me to peer-reviewed papers, then start changing crucial wording to fit your theories, why not tell me of these substitutions in the same post with the link to the paper? Then you chastise me for not “knowing” : “The plasma physics/maths are the same, the primary difference is in the written description, so just substitute terminology:
    Flux Rope = Birkeland current/axial jet from the central plasmoid
    Cusped Arcade = the plasmoid formed within the z-pinch
    Sigmoid (two J-like bundle of fieldlines) = two S-plasmoids” And why should I take your word for these ‘definitions’. It’s like saying “the sun is powered by fusion and gravity is the dominant force in the universe…..Oh, and by the way, for fusion, read electromagnetism and for gravity read plasma. Taking published papers and inserting your illogical terminology is not only confusing, it is deceptive and incorrect. So I won’t be asking for peer-reviewed published papers from you since you’re now prone to pick and choose which one of your favorite terms can be substituted for anything in the paper. It’s no longer peer-reviewed after you’ve gone and changed parts of the accepted manuscript! And you still have not replied to Olaf’s observation on this paper: “What is worse, they use real gravity AND magnetic reconnection, 2 things that is not allowed in the EU theory!”

  • Anaconda April 23, 2009, 9:25 AM

    @ Jon Hanford:

    I agree with you, if solrey is going to cite a peer-reviewed paper and rely on substitution of terms, then he should notify readers in advance what those substitution of terms are.

    (Then the readers know what to look for when reading — it helps solrey’s ideas get across.)

    But once solrey has so notified readers of the substitution of terms he is on solid ground scientifically.

    Observation & measurement is one step in the scientific process — analysis & interpretation is another.

    It is perfectly reasonable and respected to draw a different conclusion from a scientific paper based on a different interpretation of that scientific paper.

    Clearly, electric current is present and a driving force at the surface of the Sun.

    The questions which remains to be answered are thus: Is the energy at the surface of the Sun and above in the corona generated in an unobserved process inside the Sun, or is the energy transmitted to the Sun’s surface and corona from an unobserved process outside the Sun?

    Whether this energy is expressed as electromagnetic current s has been answered.

    Yes, the Sun’s energy is expressed as electromagnetic energy.

    Oh and by the way, Jon Hanford, besides grousing about solrey’s lack of notification of substitution of terms, you never did refute his analysis & interpretation of the paper he presented.

    solrey’s presentation was…well…Stellar!

    Read the thread — notice who got the work done and presented analysis & interpretation of the post and paper and who spent all their time grousing about this and that.

    solrey got the work done. His opponents were left to complain and grumble.

    Congrats, solrey.

  • Anaconda April 23, 2009, 9:47 AM

    @ Jon Hanford:

    Hanford states: “Taking published papers and inserting your illogical terminology is not only confusing, it is deceptive and incorrect.”

    As I stated, above, once you have announced your substitution of terms, and I will add, here, explanations for why the substitution is appropriate, then the analysis & interpretation is fine.

    Jon Hanford, you must be unfamiliar with scientific process & practice for you not to know about the accepted practice of re-interpretation of observation & measurement in scientific papers.

    But perhaps, “modern” astronomy is unused to this basic practice of modern science.

    I got news for you — get used to it.

    And some advice for astrophysicists — actively consider electromagnetism in both your observation & measurement and perhaps, more important, your analysis & interpretation — or expect to have somebody else do it for you.

    First up gives you all the options.

    Clean up gives you all the glory.

    Solrey hit a grand slam home run.

    And the authors of the paper?

    Just men on base for the clean up batter.

  • Hon. Salacious B. Crumb April 23, 2009, 2:47 PM

    Anaconda said;
    “solrey’s presentation was…well…Stellar!”
    Solrey hit a grand slam home run.”

    What? Here we have the delusion jackass supports a half-blind fool. One “peer-reviewed paper” does mean the whole has of cards. Where is all the observation support? No where.
    Get real, gravitation is the principle force driving most of the behaviour, only rare exotic phenomena is useful enough where electromagnetic is significant – and still it takes a gravitation source to drive it!
    Dingbats rarely will be accepted if they have a pre-existing agenda. When they have been proven as deceptive and expressing falsehood, why should anyone believe you!

  • Will April 24, 2009, 6:48 AM

    Nancy and Fraser,

    Don’t know if it’s doable however, some attempt at verifying the posters name with their Mail address may add to the integrity of this forum.

    For instance (and this assumes you keep our Mail address on your data base and you verify that it is a valid address), I post as Will and my e-mail address is xxxx@gmail.com. Later on I submit another post as Wilma with my same e-mail address, your web s/w catches this and the later post added would read:

    Wilma (aka Will) says:
    April 23, 2009 at 2:45pm
    My message………..

    Something has to be done to eliminate the childish trash talk and impostor accusations and maybe get this forum back to respectability,