New discovery – 'magnetic cages' on the sun sometimes save us from massive solar eruptions

NASA’s SDO Reveals How Magnetic Cage on the Sun Stopped Solar Eruption

A dramatic magnetic power struggle at the Sun’s surface lies at the heart of solar eruptions, new research using NASA data shows. The work highlights the role of the Sun’s magnetic landscape, or topology, in the development of solar eruptions that can trigger space weather events around Earth.

The scientists, led by Tahar Amari, an astrophysicist at the Center for Theoretical Physics at the École Polytechnique in Palaiseau Cedex, France, considered solar flares, which are intense bursts of radiation and light. Many strong solar flares are followed by a coronal mass ejection, or CME, a massive, bubble-shaped eruption of solar material and magnetic field, but some are not — what differentiates the two situations is not clearly understood.

Using data from NASA’s Solar Dynamics Observatory, or SDO, the scientists examined an October 2014 Jupiter-sized sunspot group, an area of complex magnetic fields, often the site of solar activity. This was the biggest group in the past two solar cycles and a highly active region. Though conditions seemed ripe for an eruption, the region never produced a major CME on its journey across the Sun. It did, however, emit a powerful X-class flare, the most intense class of flares. What determines, the scientists wondered, whether a flare is associated with a CME?

On Oct. 24, 2014, NASA’s SDO observed an X-class solar flare erupt from a Jupiter-sized sunspot group.
Credits: Tahar Amari et al./Center for Theoretical Physics/École Polytechnique/NASA Goddard/Joy Ng

The team of scientists included SDO’s observations of magnetic fields at the Sun’s surface in powerful models that calculate the magnetic field of the Sun’s corona, or upper atmosphere, and examined how it evolved in the time just before the flare. The model reveals a battle between two key magnetic structures: a twisted magnetic rope — known to be associated with the onset of CMEs — and a dense cage of magnetic fields overlying the rope.

The scientists found that this magnetic cage physically prevented a CME from erupting that day. Just hours before the flare, the sunspot’s natural rotation contorted the magnetic rope and it grew increasingly twisted and unstable, like a tightly coiled rubber band. But the rope never erupted from the surface: Their model demonstrates it didn’t have enough energy to break through the cage. It was, however, volatile enough that it lashed through part of the cage, triggering the strong solar flare.

By changing the conditions of the cage in their model, the scientists found that if the cage were weaker that day, a major CME would have erupted on Oct. 24, 2014. The group is interested in further developing their model to study how the conflict between the magnetic cage and rope plays out in other eruptions. Their findings are summarized in a paper published in Nature on Feb. 8, 2018.

“We were able to follow the evolution of an active region, predict how likely it was to erupt, and calculate the maximum amount of energy the eruption can release,” Amari said. “This is a practical method that could become important in space weather forecasting as computational capabilities increase.”

In this series of images, the magnetic rope, in blue, grows increasingly twisted and unstable. But it never erupts from the Sun’s surface: The model demonstrates the rope didn’t have enough energy to break through the magnetic cage, in yellow. Credits: Tahar Amari et al./Center for Theoretical Physics/École Polytechnique/NASA Goddard/Joy Ng

31 thoughts on “New discovery – 'magnetic cages' on the sun sometimes save us from massive solar eruptions

    • In the solar atmosphere the stuff is a plasma [neutral mixture of positive and negative charged particles]. At the [large] length scales of interest, the magnetic field is ‘frozen’ into the plasma [as Alfven taught us] which simply means that the plasma movement that close to the sun is constrained by the magnetic field [further away from the Sun, the moving plasma – the solar wind – instead drags the magnetic field along]. We can see that constraint directly by the graceful arches of plasma outlining [or ‘illuminating’] the magnetic field lines. What we see is not the magnetic field [which is invisible] but the plasma bound to the field. So a strong magnetic field [the ‘canopy’] can prevent the plasma flowing away from the Sun, so no CME. It is the same mechanism that prevents the solar wind to reach the surface of the Earth: the Earth’s strong magnetic field prevents the penetration of the solar wind particles.

      • Very interesting and answered some other questions I had but I was thinking about quantum level where the photon, w and z bosons are the force carriers. You’ve answered one of my other questions as to what we see and how it works but do you know what the fields consist of, photons, w or z bosons?
        As always, thank you,

        • quantum level
          At the length scale we are talking about, quantum effects are not important. Good old maxwell’s equations suffice. The magentic field is maintained by electric currents generated by moving plasma across magnetic fields…

      • the Earth’s strong magnetic field prevents the penetration of the solar wind particles.

        Doesn’t the Earth’s magnetic field channel the solar wind into either pole?

      • Leif wrote, ” … the magnetic field is ‘frozen’ into the plasma [as Alfven taught us] …”
        Lief, respectfully, here is a counter-claim. Your thoughts?
        Real Properties of Electromagnetic Fields and Plasma in the Cosmos
        Astrophysicists often assume that plasmas are perfect conductors,
        and as such, any magnetic field in any plasma must be
        “frozen” inside it. (This rigid attachment is assumed in the magnetic
        reconnection mechanism that is discussed in Section IV.)
        Indeed, it was plasma pioneer Alfvén who first proposed this
        idea. It was based on the observation that, since plasmas were
        thought to be perfect conductors, they cannot sustain electric
        Alfvén’s original motivation for proposing “frozen-in” fields
        stemmed from another one of Maxwell’s equations, i.e.,
        ∇ × E = −dB/dt
        This implies that if the electric field in a region of plasma is
        identically zero valued (as it would have to be if the medium
        had zero resistance—perfect conductivity), then any magnetic
        field within that region must be time invariant (must be frozen).
        Thus, if all plasmas are ideal conductors (and thus cannot
        support electric fields), then any magnetic fields inside such
        plasmas must be frozen in, i.e., cannot move or change in any
        way with time.
        The electrical conductivity of any material, including plasma,
        is determined by two main factors, namely: 1) the density of the
        population of available charge carriers (free ions and electrons)
        in the medium and 2) the mobility of these carriers. Most,
        if not all, cosmic plasmas are magnetized (contain large and
        long internal magnetic fields). In any such plasma, the transverse
        (perpendicular to this field) mobility of charge carriers
        is severely restricted because of the spinning motion that is
        imposed on their momentum by Lorentz force (3). Mobility
        in the parallel (and antiparallel) direction, being unaffected by
        this transverse force, is extremely high because electrons and
        ions have long mean-free paths in such plasmas. However, the
        density (the number per unit volume) of these charge carriers
        may not be at all high, particularly, if the plasma is a very
        low pressure (diffused) one. Therefore, conductivity is less than
        ideal, even in the longitudinal direction, in cosmic plasma.
        Laboratory measurements demonstrate that a nonzero-valued
        electric field in the direction of the current (Eparallel > 0)
        is required to produce a nonzero current density within any
        plasma no matter what mode of operation the plasma is in.
        Negative-slope regions of the volt-ampere characteristic (negative
        dynamic resistance) of a plasma column reveal the cause
        of the filamentary properties of plasma, but all static resistance
        values are measured to be > 0.
        Thus, although plasmas are excellent conductors, they are not
        perfect conductors. Weak longitudinal electric fields can and do
        exist inside plasmas. Therefore, magnetic fields are not frozen
        inside them.
        When, in his acceptance speech of the 1970 Nobel Prize in
        physics, Alfvén pointed out that this frozen-in idea, which he
        had earlier endorsed, was false, many astrophysicists chose not
        to listen. In reality, magnetic fields do move with respect to
        cosmic plasma cells and, in doing so, induce electric currents.
        This mechanism (which generates electric current) is one cause
        of the phenomena that is described by what is now called
        plasma cosmology.
        Alfvén said, “I thought that the frozen-in concept was very
        good from a pedagogical point of view, and indeed it became
        very popular. In reality, however, it was not a good pedagogical
        concept but a dangerous ‘pseudo pedagogical concept.’
        By ‘pseudo pedagogical’ I mean a concept which makes you
        believe that you understand a phenomenon whereas in reality
        you have drastically misunderstood it.”
        Now, we know that there are slight voltage differences between
        different points in plasmas. Many astrophysicists are still
        unaware of this property of plasmas, and so, we often still
        read unqualified assertions such as “Once a plasma contains
        magnetic fields, they move with the plasma as if the magnetic
        field lines were frozen in [18].”
        In addition, “. . . plasmas and magnetic fields interact; they
        behave, approximately, as if they are ‘frozen’ together [19].”
        “. . . fields that are ‘stuck’ inside conductors take a long time
        to diffuse out (i.e., the magnetic flux is frozen into the moving

        • The problem with this ‘alternative’ explanation is that the length scales are vastly different.
          There is also a misconception about conductivity. The solar photosphere is not required to be a ‘perfect’ conductor. In fact, it is no more conductive than ordinary seawater. What matters is the very large scale of the field; something we cannot achieve in the laboratory [which is why laboratory plasma physics looks different].
          On Alfven: if magnetic fields and plasma are frozen in at all length scales nothing could ever happen [no electric fields]. The point is that as the lengh scale gets small enough [smaller than the gyro-radius] the plasma and the field can decouple: electric currents can [and do] flow and all kinds of interesting explosive phenomena can take place. This is what [my old friend] Hannes Alfven meant by ‘unfreezing’ the field.
          Your ‘alternative’ view is pseudo-science.

    • And what are the mechanisms that generate the magnetic fields with such asymmetry.
      BTW isn’t this merely “solar climate change”?

      • “Solar climate change”! Is there no end to the pernicious effect of man-made CO2!?! We’re doomed, I tell ye. Dooomed…

  1. Ropes, cages, twisting… are we talking a circus here, or something darker less family oriented? I do wish solar physicists would stop talking in metaphors and riddles.

    • What’s the ugliest
      Part of your body?
      What’s the ugliest
      Part of your body?
      Some say your nose
      Some say your toes
      (I think it’s your mind)
      F. Zappa 1968


  2. Our sun is somewhat of a interesting G-class star. It has the surface temperature of a G2V star (~5,800 C) but the mass of a cooler G4V. It also has not apparently have a Super Flare CME in at least 2 millennia, unlike what is seen on other G-class stars where the data suggests they occur about once a century.
    IOW, we are quite fortunate to have our seemingly special sun.
    For your inquisitive entertainment:
    Superflares on Ordinary Solar-Type Stars
    Bradley E. Schaefer, Jeremy R. King, and Constantine P. Deliyannis
    The Astrophysical Journal, Volume 529, Number 2

  3. At present is there a way to detect and measure or estimate the strength of a magnetic cage associated with an active sunspot region with enough accuracy to asses its ability to contain a CME?

    • detect and measure or estimate the strength of a magnetic cage
      Yes, the cage is rooted in the photosphere where we can measure its magnetic field. The field then ‘balloons’ into the [much] lower density corona where we can ‘see’ it because of the plasma stuck on it. We can compute the magnetic field around a source so can estimate its strength in the corona [we have not yet found a way of directly measuring it] using con-controversial physics.

  4. “Palaiseau Cedex, France”
    Cedex is for postal delivery. There is no location called “Palaiseau Cedex”!

  5. It’s the electrical fields that are twisting, the magnetic field lines are just indicative of that process.

    • You cannot separate the two.
      As the electric field depends on the reference frame [e.g. disappears in a frame moving with the plasma] we usually use the magnetic field [that does not depend on the frame] to show what is going on.

  6. Dr. S., can we say that sunspots, during the more active portion of the solar cycle, when more sunspots are present, that more ‘nearby each other’ active regions, would destabilize the magnetic cages (canopies) producing more CME’s from sunspots? And vice versa fewer nearby active regions, more stable magnetic cages?

    • You could say that. However, the sun is a messy place and things are never that simple.
      For example, when there are more sunspots, the ‘canopy’ and the cages are also more prevalent and stronger.

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