Hinode, IRIS, and ATERUI cooperate on 70 year old solar mystery

August 23, 2015, National Astronomical Observatory of Japan
Signs of resonant absorption are shown. Alfvénic waves propagating in the prominence produce transverse oscillations of the threads. On a graph plotting displacement vs. time, this motion appears as a wavy structure (shown in yellow in the top left panel). The waves resonate and produce a characteristic torsional flow which was observed by IRIS (purple dots in the panel). This flow becomes turbulent and heats the plasma. 3D numerical simulations of an oscillating prominence thread (top-right panel) successfully reproduce this process. The schematic diagram on the bottom shows the evolution of the thread's cross-section. Credit: JAXA/NAOJ

Solar physicists have captured the first direct observational signatures of resonant absorption, thought to play an important role in solving the "coronal heating problem" which has defied explanation for over 70 years.

An international research team from Japan, US, and Europe led by Drs. Joten Okamoto and Patrick Antolin combined high resolution observations from JAXA's Hinode mission and NASA's IRIS (Interface Region Imaging Spectrograph) mission, together with state-of-the-art numerical simulations and modeling from NAOJ's ATERUI supercomputer. In the combined data, they were able to detect and identify the observational signatures of resonant absorption.

Resonant absorption is a process where two different types of magnetically driven waves resonate, strengthening one of them. In particular this research looked at a type of magnetic waves known as Alfvénic waves which can propagate through a prominence (a filamentary structure of cool, dense gas floating in the ). Here, for the first time, researchers were able to directly observe resonant absorption between transverse waves and torsional waves, leading to a turbulent flow which heats the prominence. Hinode observed the transverse motion and IRIS observed the torsional motion; these results would not have been possible without both satellites.

This new information can help explain how the solar corona reaches temperatures of 1,000,000 degrees Celsius; the so called "coronal heating problem."

The solar corona, the outer layer of the Sun's atmosphere, is composed of extreme high temperature gas, known as plasma, with temperatures reaching millions of degrees Celsius. As the outer layer of the Sun, the part farthest from the core where the nuclear reactions powering the Sun occur, it would logically be expected to be the coolest part of the Sun. But in fact, it is 200 times hotter than the photosphere, the layer beneath it. This contradiction, dubbed "the coronal heating problem" has puzzled astrophysicists ever since the temperature of the corona was first measured over 70 years ago.

Space-borne missions to observe the Sun and other technological advances have revealed that the magnetic field of the Sun plays an essential role in this riddle. But the key to solving the "" is understanding how magnetic energy can be converted efficiently into heat in the corona. There have been two competing theories.

The first theory involves solar flares. Although each flare converts large amounts of magnetic energy into thermal energy, the overall frequency of solar flares is not high enough to account for all of the energy needed to heat and maintain the . To solve this discrepancy, the idea of "nanoflares" was introduced. It is thought that nanoflares, miniature solar flares, occur continuously throughout the corona and that the sum of their actions convert enough magnetic energy into heat to make up the difference. Unfortunately, such nanoflares have yet to be detected.

(Top) Numerical simulations by ATERUI show how resonant absorption can explain the relationship observed between the resonant flow (purple) and the transverse motion (green). The simulations also show that turbulence appears. (Bottom) A time sequence showing one complete cycle of the resonant flow in relation to the transverse motion. Credit: NAOJ

The second hypothesis is based on magnetically driven waves. Thanks to space missions such as the Japanese "Hinode" mission (launched in 2006), we now know that the solar atmosphere is permeated with "Alfvénic" waves. These magnetically driven waves can carry significant amounts of energy along the , enough energy in fact to heat and maintain the corona. But for this theory to work, there needs to be a mechanism through which this energy can be converted into heat.

To look for this conversion mechanism, the research team combined data from two state-of-the-art missions: Hinode and the IRIS imaging and spectroscopic satellite (the newest NASA solar mission, launched in 2013).

Both instruments targeted the same solar prominence. A prominence is a filamentary bundle of cool, dense gas floating in the corona. Here, 'cool' is a relative term; a prominence is typically about 10,000 degrees. Although denser than the rest of the corona, a prominence doesn't sink because magnetic field lines act like a net to hold it aloft. The individual filaments composing the prominence, called threads, follow the magnetic field lines.

Hinode's very high spatial and temporal resolution allowed researchers to detect small motions in the 2-dimensional plane of the image (up/down and left/right). To understand the complete 3-dimensional phenomenon, researchers used IRIS to measure the Doppler velocity (i.e. velocity along the line of sight, in-to/out-of the picture). The IRIS spectral data also provided vital information about the temperature of the prominence.

These different instruments allow the satellites to detect different varieties of Alfvénic waves: Hinode can detect transverse waves while IRIS can detect torsional waves. Comparing the two data sets shows that these two types of waves are indeed synchronized, and that at the same time there is a temperature increase in the prominence from 10,000 degrees to more than 100,000 degrees. This is the first time that such a close relationship has been established between Alfvénic waves and prominence heating.

But the waves are not synchronized in the way scientists expected. Think of moving a spoon back-and-forth in a cup of coffee: the half-circular torsional flows around the edges of the spoon appear instantly as the spoon moves. But in the case of the prominence threads, the torsional motion is half-a-beat out of sync with the transverse motion driving it: there is a delay between the of the transverse motions and the maximum speed of the torsional motion, like the delay between the motion of the hips of a dancer in a long skirt and the motions of the skirt hem.

(Left) For reference, this is an image of the entire Sun taken by SDO/AIA in extreme ultra-violet light (false color). (Right) An image of a solarprominence at the limb of the Sun was taken by Hinode/SOT in visiblelight (Ca II H line, false color). As shown in the image, a prominenceis composed of long, thin structures called threads. A scale model ofthe Earth is shown on the right for reference. Credit: NASA/JAXA/NAOJ

To understand this unexpected pattern the team used NAOJ's ATERUI supercomputer to conduct 3D numerical simulations of an oscillating prominence thread. Of the theoretical models they tested, one involving resonant absorption provides the best match to the observed data. In this model, transverse waves resonate with torsional waves, strengthening the torsional ; similar to how a child on a swing can add energy to the swing, causing it to swing higher and faster, by moving his body in time with the motion. The simulations show that this resonance occurs within a specific layer of the prominence thread close to its surface. When this happens, a half-circular torsional flow around the boundary is generated and amplified. This is known as the resonant flow. Because of its location close to the boundary, the maximum speed of this flow is delayed by half-a-beat from the maximum speed of the , just like the pattern actually observed.

The simulations further reveal that this resonant flow along the surface of a thread can become turbulent. The appearance of turbulence is of great importance since it is effective at converting wave energy into heat energy. Another important effect of this turbulence is to enlarge the resonant flow predicted in the models to the size actually observed.

This model can explain the main features of the observations as the results of a two-step process. First resonant absorption transfers energy to the torsional motions, producing a resonant flow along the surface of the prominence thread. Then turbulence in this strengthened resonant flow converts the energy into heat.

This work shows how the power of multiple satellites, such as Hinode and IRIS, can be combined to investigate long-standing astrophysical problems and will serve as an example for other research looking for similar heating in other solar observations.

These results were published in The Astrophysical Journal, Vol 809 in August, 2015.

Explore further: IRIS celebrates year two with ongoing scientific discoveries

More information: "Resonant Absorption of Transverse Oscillations and Associated Heating in a Solar Prominence. I. Observational Aspects" T. J. Okamoto, P. Antolin, B. De Pontieu, H. Uitenbroek, T. Van Doorsselaere, T. Yokoyama 2015, The Astrophysical Journal, 809, 71

"Resonant Absorption of Transverse Oscillations and Associated Heating in a Solar Prominence. II. Numerical Aspects" P. Antolin, T. J. Okamoto, B. De Pontieu, H. Uitenbroek, T. Van Doorsselaere, T. Yokoyama 2015, The Astrophysical Journal, 809, 72

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Egleton
5 / 5 (2) Aug 24, 2015
Oh no. Electric universe.
Don't you just hate it when your favorite radical hypothesis just bites the dust?
Lesson to one and all.
Your favorite hypothesis is not tied up to your Ego. Just let it go. You will survive the trauma.
carlo_piantini
1 / 5 (7) Aug 24, 2015
Exactly how has demonstrated magnetic activity "hurt" an electric model of stars? Unless you think that all of this magnetic activity occurs entirely without the presence of electricity, which is completely absurd. This entire article is about how the electromagnetic aspects of the Sun's character help to heat the solar corona, and the chief mechanism involved electrically conducting filaments that flow parallel along the magnetic field lines and a resonant circuit of energy transfer. No part of that is mutually exclusive to an anodic/cathodic model of Sun, and in fact, this is *awesome*. If the same kind of solar prominences and resonant activity can be found with SAFIRE, all the better.

Plus, have you ever read anything about Tesla's ideas on spherical electrical oscillators, or resonantly coupled circuits? I'd clearly think that information could usefully be applied in this situation.
carlo_piantini
1 / 5 (5) Aug 24, 2015
That's the problem: our "favorite radical hypothesis" (a) hasn't bitten the dust with this and (b) can actually be tested in a lab, to which point it's been fairly successful. I don't know when scientists stopped being interested in lab-driven empirical science, but SAFIRE is an incredible extension to Birkeland's original solar system modeling and it "likewise" produced very nice results of a significantly increased temperature in the corona of the "sollelus" - the mini sun. It also produced anode tufting, a solar minimum and maximum in "sunspots" as a produce of voltage, if I'm not mistaken, and super rotation of the plasma in the equatorial.

I don't see what I've read above to be mutual exclusive in any way with those lab results. You can read them here: https://community...DOC-6676

Not sure where the idea is coming from that all this magnetic activity is somehow free from the presence of electric currents and fields.
docile
Aug 24, 2015
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docile
Aug 24, 2015
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carlo_piantini
1 / 5 (6) Aug 24, 2015
You can also couple this news with the recent discovery that emergent magnetic flux is *not* responsible for the explosive jets in coronal holes, but is instead actually due to erupting double layers that form in the filaments of the corona: https://www.nasa....ure.html

The astronomers don't seem to make any mention of Alfven though, despite his insistence that exploding double layers in electrical filaments is essentially one of the biggest aspects of his solar program. The electric star model is doing really well right now, as it turns out.
plasmasrevenge
2.3 / 5 (6) Aug 24, 2015
I think it's really sad that people still make the mistake of pointing to an analysis which is couched in one particular paradigm as "proof" that another paradigm which bases on a completely different hypothesis is somehow incorrect. The complexity of these observations will NEVER be unraveled if the scientific community is simply unable to pursue more than one paradigm at a time. The path to knowledge does not go through decisions to remain ignorant. Treating science like it's a sport is really an invitation for bias and politics.
carlo_piantini
1 / 5 (4) Aug 24, 2015
@bschott: That's not something I'm sure, but the link I posted has a video and pdf explaining the experimental setup, although its fairly basic. The SAFIRE team, which happens to work independently from the main EU community, is working on building the full-scale demonstration setup. Monty Childs, the head of the experiment, gave a talk at the EU conference this year, which, at some point will probably be up on their channel. *Very* promising early results, and their experimental design is fantastic. I'll email it to you when its up.

@plasmasrevenge: It can't for the life of me understand why astrophysics has essential become a monopolistic industry. On both sides! It comes from people in the EU community just as aggressively as from the mainstream community. Multiple theories can exist at one time, compete with one another, *work together*, and discover new things.
carlo_piantini
1 / 5 (6) Aug 24, 2015
I'm not understanding the issue you have with the Sun setup as an anode.
carlo_piantini
1 / 5 (6) Aug 25, 2015
I think the problem you have though is an issue with approximation. The magnet inside the sollelus stands as an approximation of the magnetic field within the Sun as it exists already, because it is not *yet* possible to form an actual star from the plasma itself - regardless of whatever model you want to use. The entire point of the sollelus/SAFIRE experiment is not - at this point - to discuss how stars form. It is to discern whether stars, after their formation, behave as either anodes or cathodes in the solar circuit.

We're trying to study the behavior of the Sun in the present circuit of the solar system, not how stars form in the first place. Yet. So approximating the existing magnetic field of the Sun by placing a magnet inside the sollelus is no different than Birkeland placing a magnetic inside his terella to replicate the existing magnetic field of the Earth.
carlo_piantini
1 / 5 (6) Aug 25, 2015
I love the 1-star ratings on this site, as I'm discussing a completely empirical piece of laboratory equipment. The SAFIRE project is a piece of electrical equipment - it is "literally" an extension of Birkeland's terella work, which any unbiased scientific mind has to acknowledge as a critical scientific achievement - he was able to build the first accurate model of the aurora fifty years before anyone else, and likewise, from an article clipping I found entitled "Electricity in World's Creation" he was able to predict what seems like Alfven's idea of critical ionization velocity.

Birkeland gathered an enormous amount of data, built a laboratory model, and confirmed his theory. The exact same thing is being done with the SAFIRE project. And so far, for a very preliminary setup, it's been fairly successful - anode tufting, non-visible surface ejections (think nano flares), the development of a significantly hotter corona, a min/max sun-spot cycle, etc.
carlo_piantini
1 / 5 (5) Aug 25, 2015
Any magnet used in any experiment by the EU is proof that the plasma needs it to form anything.


No it's not, because the experiment isn't trying to form anything at all. The experiment isn't a model of stellar formation, it's a model of stellar behavior. You're confusing the idea of Thornhill's electric star model, where galactic scale Birkeland currents form massive z-pinches which condense into the stars - which *is* a product of current density - with the idea of the Sun existing *already* in space, with its associated magnetic field. There experiment isn't trying to 'create a sun out of plasma', it's approximating the Sun as it already exists with sollelus.

It was done 2 years ago.


Where was this done two years ago, and what solar features/phenomena were replicated?
carlo_piantini
1 / 5 (3) Aug 25, 2015
I think that something is certainly getting lost in translation here. The formations that you quoted are all are due to (a) the presence of the magnetic field intended to approximate the magnetic field of the Sun and (b) the discharge of electric current through the plasma from the anode. No one is debating that you need a magnetic field to direct the flow of the plasma to form the currents. Birkeland's entire experiment proved that the cathode rays emitted into his vacuum chamber cause the aurora explicitly because the electrons follow the magnetic field lines down into the polar regions of the terella.

The sollelus experiment is setup in the similar fashion, where the solenoid (I believe) is housed inside the anode, which is discharging into the surrounding plasma. This is to mimic the magnetic field of the Sun.
carlo_piantini
1 / 5 (3) Aug 25, 2015
I think the miscommunication is coming from this?

The EU theory is that electric currents are responsible for all we observe, including the magnetic fields that permeate space.


This is not my understanding of Alfven's ideas or Birkeland's. If they're being suggested by people like Thornhill then that's his idea, but it's not - at least to my knowledge - what they said. Even in terms of Bostick's experiments, the plasmoids were shot into pre-existing magnetic fields, and it was their interactions within said fields that caused them to form their spiral morphology. Magnetic fields are definitely necessary.
carlo_piantini
1 / 5 (3) Aug 25, 2015
No problem at all, and I was positive that we were simply confusing one another. I stand firmly in the belief that all of Alfven's work should be read, simultaneously, along side the primary astrophysical literature. The main issue is that his work exists primarily in the plasma/electrical engineering literature, mostly the IEEE, and so I *seriously* doubt that any student coming up today in an astrophysics program is going to have any contact with it, other than maybe being exposed to his primary work on magnetohydrodynamics. But, there are plenty of astrophysicists here apparently, so, they can be the judge of that.

You can find a *really* big portion of his work here, for free: http://www.diva-p...wid=5845
carlo_piantini
2 / 5 (4) Aug 25, 2015
No problem! Just remember, and I insist on this: it's not clear whether Alfven's criticism of the astrophysics community is valid - regarding the underutilization of electric double layers, the consideration of space plasmas as infinitely conductive so as to allow the magnetic field lines to be "frozen-in", etc. You can read that criticism here: http://www.nobelp...ture.pdf

Anyone entering into astrophysics as a legitimate student, like I am, owes it to *themselves* to read his criticism, read the rest of his work, and directly compare it to the history of cosmic plasma physics as recorded in the primary astrophysical literature, starting probably anywhere ~1940+. This should be done simultaneously with a comparative reading of laboratory plasma physics literature. Both domains should be studied up to the present day, in conjunction with lab work, if possible.
vidyunmaya
1 / 5 (3) Aug 30, 2015
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jljenkins
2.6 / 5 (5) Sep 19, 2015
Oh no. Electric universe.
Don't you just hate it when your favorite radical hypothesis just bites the dust?
Lesson to one and all.
Your favorite hypothesis is not tied up to your Ego. Just let it go. You will survive the trauma.

Oh, but it is. That's the whole problem. That's why the aether crowd and the weird magnetism crowd and the AGW deniers cannot be influenced by evidence or debate. Those groups provide ego identity. lol It's like the girl I saw the other day with the "Conspiracy Theorist" tee. I'll bet she's really objective in weighing facts! Probably never gets laid either. Just like the aforementioned groups.

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