View Full Version : Why the Sun's atmosphere is hotter than its surface

2015-Jun-22, 12:48 AM
This one sort of made my head explode.

By simulating the evolution of part of the Sun's interior and exterior, researchers from the Centre de Physique Théorique (CNRS/École polytechnique) and the Laboratoire Astrophysique, Interprétation -- Modélisation (CNRS/CEA/Université Paris Diderot) have identified the mechanisms that provide sufficient energy to heat the solar atmosphere. A layer beneath the Sun's surface, acting as a pan of boiling water, is thought to generate a small-scale magnetic field as an energy reserve which, once it emerges from the star, heats the successive layers of the solar atmosphere via networks of mangrove-like magnetic roots and branches[1].

All fine and well, until I read this part.

The scientists also discovered that a structure resembling a mangrove forest appears around the solar mesospots: tangled 'chromospheric roots' dive into the spaces between the granules, surrounding 'magnetic tree trunks' that rise up towards the corona and are associated with the larger-scale magnetic field.

The researchers' calculations show that, in the chromosphere, heating of the atmosphere results from multiple micro-eruptions in the mangrove roots that carry intense electric current, in pace with the 'bubbles' from the boiling plasma.

Mind blown.

Reality Check
2015-Jun-22, 01:14 AM
Back on 29 April 2015 there was this report: Sun's blistering heat: Strong evidence for coronal heating theory (http://www.sciencedaily.com/releases/2015/04/150429094830.htm)

Clear evidence now suggests that the heating mechanism depends on regular, but intermittent explosive bursts of heat, rather than on continuous gradual heating. This solution to the coronal heating mystery was presented in a media briefing on April 28, 2015, at the Triennial Earth-Sun Summit, or TESS, meeting in Indianapolis, Indiana.
The "multiple micro-eruptions" in the computer simulation sound like the nanoflares that the EUNIS sounding rocket mission has found evidence for.

John Mendenhall
2015-Jun-22, 03:28 PM
Hey, The Sun is a raging thermonuclear furnace. We are lucky it behaves as well as it does.

Ken G
2015-Jun-26, 12:46 PM
With all the mangrove imagery, it's hard to tell what is new about the claims being made. Honestly they sound like arguments I heard about 20 years ago! So somehow, the new evidence has not percolated through the pop-sci translation of this. It has long been known that magnetic fields permeate the atmosphere in complex ways, one might even go so far as to imagine a twisted mangrove forest. 20 years ago. It was also clear that this would lead to a considerable storage of "free energy", energy available to be downgraded into heat by various processes. What was not so clear was only what those processes were, and how they competed with nonmagnetic heating sources.

In particular, what was not clear was whether the free energy got dissipated into heat via great reconfigurations that produced solar flares, with the rest of the coronal heating coming from nonmagnetic sources (like waves from the photosphere "breaking" on the shore of the atmosphere, among the mangrove trees), or if it got dissipated in a spectrum of lots and lots of micro events forming a distribution that includes the monsters (so, via nanoflares). It seems they are finding evidence the latter explanation is more valid. But the pop-sci writer liked the mangrove tree analogy, so that's what we hear is the new finding, even though it doesn't sound new to me at all-- it just sounds like the expected result that when you look at smaller scale details of the magnetic field, you see smaller scale details of the field! Is the fault with the scientists for not being clear what they were really discovering, or with the pop-sci writer for pouncing on the only part they understood? Who knows. Popular science is the worst way to bring scientific concepts to the public, except that it's the only way.

2015-Jun-30, 08:50 PM
With all the mangrove imagery, it's hard to tell what is new about the claims being made. It is the "electric current" part that blows my mind.

Ken G
2015-Jul-01, 02:15 AM
Electric currents are normal in complex magnetic environments. Electric currents must run along the field lines in the common approximation, because currents trying to cross field lines would be deflected by the Lorentz force. However, currents running along the fields produce their own magnetic fields, which tend to wrap the field around, "twisting" it. The energy related to the currents and the twisted fields is "free" energy, in the sense that it can be extracted by any mechanism that causes the fields to relax to a less tortured state, or less "mangrove-like" state. The question that has been kicking around for a long time is just how that relaxation occurs-- what are the details of it, what can be predicted about it. I don't think anyone who has been working on it for all these years would suddenly say, "aha, mangrove trees, that explains everything-- why didn't I see it before?" But saying that there is evidence the energy is released in a broad spectrum of micro-events, rather than in bifurcations that cause more global rearrangements as the field loses its equilibrium and has to find a new one, is indeed progress toward understanding. Without reading the article, I can't tell how much really fundamental new information has been learned since 20 years ago, that part just doesn't percolate through the pop-sci translation. I'd say this is a common problem-- someone discovers something fundamentally new about black holes, for example, and the interviewer asks "you mean light can't escape from these things, the gravity is too strong?", and then the article ends up being about this great discovery that there are astrophysical objects that light cannot escape! It must be hard to communicate what is really new in the discovery, without taking all those intermediate steps that led there.