The Sun’s coronal tail wags its photospheric dog


High-resolution images captured by NJIT's New Solar Telescope at Big Bear Solar Observatory show solar flares speeding up the rotation of sunspots. CREDIT NJIT

High-resolution images captured by NJIT’s New Solar Telescope at Big Bear Solar Observatory show solar flares speeding up the rotation of sunspots. CREDIT NJIT

Solar physicists have long viewed the rotation of sunspots as a primary generator of solar flares – the sudden, powerful blasts of electromagnetic radiation and charged particles that burst into space during explosions on the sun’s surface. Their turning motion causes energy to build up that is released in the form of flares.

But a team of NJIT scientists now claims that flares in turn have a powerful impact on sunspots, the visible concentrations of magnetic fields on the sun’s surface, or photosphere. In a paper published in Nature Communications this week, the researchers argue that flares cause sunspots to rotate at much faster speeds than are usually observed before they erupt.

Their observations, based on high-resolution images captured through NJIT’s 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO), come as something of a surprise. The sun’s outer layer, or corona, where flares are released, has a plasma density about a hundred million times smaller than that of the photosphere.

“It’s analogous to the tail wagging the dog. The lower-density regions are much less energetic and forceful,” said Chang Liu, a research professor of physics at NJIT and the principal author of the study, “Flare differentially rotates sunspot on Sun’s surface.”

“We do think the rotation of sunspots builds up magnetic energy that is released in form of solar flares, but we have also observed conclusively that flares can cause sunspots to rotate about 10 times faster,” he added. “This highlights the powerful, magnetic nature of solar flares.”

Previous images captured by space solar missions at lower resolutions hinted at this phenomenon, the researchers said, but were inconclusive.

“Our new images allow us to not only confirm it, but to also characterize the time-spatial dimension of the sunspot’s rotation – to describe its progressive, non-uniform rotation – as the flare travels through it,” Liu said.

Haimin Wang, a distinguished professor of physics at NJIT and a co-author of the paper, said the observations will prompt scientists to revisit the mechanisms of flares – and the basic physics of the Sun – in a fundamental way.

“We used to think that the surface’s magnetic evolution drives solar eruptions. Our new observations suggest that disturbances created in the solar outer atmosphere can also cause direct and significant perturbations on the surface through magnetic fields, a phenomenon not envisioned by any major contemporary solar eruption models. This has immediate and far-reaching implications in understanding energy and momentum transportation in eruptions on the Sun and other stars,” Wang said. “We will continue to study, and possibly re-interpret, the relationship between the different layers of the Sun.”

Images captured by NST, the world’s largest ground-based solar telescope, are providing an unprecedented glimpse into the complex dynamics of the Sun’s many layers, as well as insights into the massive eruptions originating in the solar atmosphere that are responsible for space weather.

Last year, scientists at BBSO captured the first high-resolution images of magnetic fields and plasma flows originating deep below the Sun’s surface, tracing the evolution of sunspots and magnetic flux ropes through the chromosphere before their dramatic appearance in the corona as flaring loops.

Another recent set of images give a first-ever detailed view of the interior structure of umbrae – the dark patches in the center of sunspots – revealing dynamic magnetic fields responsible for the plumes of plasma that emerge as bright dots interrupting their darkness. The high-resolution images show the atmosphere above the umbrae to be finely structured, consisting of hot plasma intermixed with cool plasma jets as wide as 100 kilometers.


The paper:

Flare differentially rotates sunspot on Sun’s surface


Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to 50° h−1) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related phenomena. (open access paper)



25 thoughts on “The Sun’s coronal tail wags its photospheric dog

  1. What about Hyder flares from collapsing filaments? do they also feed back energy to rotate the place where they originated from?

  2. ..””Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory.””..

    Well Dr. S., the above, should be of interest to you..and cycle progression.

    Magnetic reconnection occurring in the outer solar atmosphere, are we having fun now. Models of other stars indicate reconnection out to 6 or more solar radii.. with some interstellar inflow contributions..but we don’t talk about that.

    good stuff.

    This was pretty cool too.. we and scary..

    Goodness gracious great balls of fire…

    Hubble detects giant ‘cannonballs’ shooting from star
    October 6, 2016 by Karl Hille

    This four-panel graphic illustrates how the binary-star system V Hydrae is launching balls of plasma into space. Panel 1 shows the two stars orbiting each other. One of the stars is nearing the end of its life and has swelled in size, becoming a red giant. In panel 2, the smaller star’s orbit carries the star into the red giant’s expanded atmosphere. As the star moves through the atmosphere, it gobbles up material from the red giant, which settles into a disk around the star. The buildup of material reaches a tipping point and is eventually ejected as blobs of hot plasma along the star’s spin axis, shown in panel 3. This ejection process is repeated every eight years, the time it takes for the orbiting star to make another pass through the bloated red giant’s envelope, shown in panel 4. Credit: NASA, ESA, and A. Feild (STScI)

    Read more at:

  3. This sounds like the usual hype [fundamental change, etc].
    Reconnection has been the favorite mechanism for more than half a century, so nothing new there.
    It seems to me that the paper has things backwards. A rotating sunspot twists its magnetic field, feeding energy into the configuration. The release of that energy is the flare [or the CME] and is caused by instability [with subsequent reconnection and electric currents being generated]. It seems to me that a sudden increase of the rotation rate would feed more energy into the field and hence trigger the flare in short order. The tail does not wag the dog.

    • ” A rotating sunspot twists its magnetic field, ”

      which leads to the question why is the sunspot rotating? Because there is a twisted magnetic field?

    • From the paper: “Taken together, the exceptionally high-resolution observations from BBSO/NST make it possible to witness, for the first time, a sudden sunspot differential rotation that exhibits an intrinsic spatiotemporal relationship with the coronal energy release process, manifested as flare ribbon propagation and HXR emission profile. The measured angular velocity of rotation amounts up to ∼50° h−1, which is much higher than that of the reported pre-flare rotating sunspots. These strongly indicate that the observed sunspot rotation on the photosphere is a result, not a cause, of the flare magnetic reconnection in the corona, which challenges the conventional view of the photosphere-corona coupling.” (emphasis mine)

      Dr. Svalgaard, are you specifically disagreeing with this finding, or with their work in general? If so, why specifically do you call it into question? Please note that in the introduction they indicate that the opposite relationship is in fact well established, and that this simply is the first time they’ve been able to conclusively observe that it is possible for flares to influence sunspots rather than sunspots being the sole influence on solar flaring. In other words, I understand their findings (regardless of the authors’ editorialism) to indicate simply that the current understanding is “incomplete,” rather than “incorrect;” what say you?

      • It is hard to generalize from this one case as things are messy. Let us see what the next flare gives us. If the dog-wagging is a general feature of the flare, every flare should show this effect.

    • So all the billions of stars in trillions of galaxies are being fuelled externally. Where is ‘outside’ and where does ‘outside’ get His energy from?

  4. This seems to be money graph:

    That looks like two concurrent changes, with not obvious causation.

    In fact the angle as plotted is a cumulative observation, it would be more informative if they plotted d/dt(angle) , the graphs would then be seem to have similar form and we may be able to read more from it.

    It’s like atmospheric CO2, as a cumulative time series it’s pretty straight and uninformative. It’s when you look at d/dt(CO2) that you start to be able see what may be causing the changes because you can actually see them.

    • IMO by the time SXR flux peaks the dθ/dt has already dropped to half its peak value. It also goes to zero and negative within the scope of the graph whilst flux is still declining.

      Not really that good for tail wagging dog hypothesis.

  5. Poynting’s theorem

    In electrodynamics, Poynting’s theorem is a statement of conservation of energy for the electromagnetic field

    a game changer?

    In the end the paper discusses conservation of energy; not generation of energy.

  6. It seems to me there is another matter that is related to the unexpectedness of this dog wagging. It is the matter of the huge increase in temperature and energy of particles leaving the sun’s surface when they rise to the chromosphere. I hope I have described that correctly.

    For years it simply made no sense that particles leaving the surface at 6000 degrees would heat up dramatically as the moved farther away. And where does the acceleration and energy come from?

    So an explanation offered that supported the standard model was hailed, if you all remember discussing it here. But that rather convenient explanation is somewhat contradicted by this new paper. If there is enough accumulated charge in the ‘weak’ zone to spin the sunspot by, perhaps, opening a magnetic ‘drain’, there may be a directly related mechanism that accounts for the acceleration of particles away from the surface. Clearly there is a lot of energy moving up and down. Perhaps it is an indication of the presence of Dark Matter, or the postulated Darker Matter that surrounds all celestial bodies.

    Obviously the EU promoters have their model for this but discussion is not permitted here. The omnivores will continue watching this most interesting topic from all sides. I am sure many surprises remain.

  7. As I browse the comments, I am reminded of why this site should be on everyone’s short list of climate blogs: the spirit of science is alive and well, here. Mr. Watts can be proud of what he (and his compadres) have built. In particular, I sense a disturbance in the The Force caused by the proximity of electrical engineers.

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