Magnetic reconnection and physical processes

[Zeuzzz]

Has anyone ever claimed differently?
The field lines are just a very useful tool.

So "a magnetic field is a continuum, not a set of discrete lines." .. "The field lines are just a very useful tool"

So then basing an energy releasing process on the properties of these tools, and not the actual magnetic fields continuum, would seem rather dubious, would it not?

 

[tusenfem]

So "a magnetic field is a continuum, not a set of discrete lines." .. "The field lines are just a very useful tool"

So then basing an energy releasing process on the properties of these tools, and not the actual magnetic fields continuum, would seem rather dubious, would it not?

No, as usual you don't understand anything.

Even though the field is a continuum, the field lines are a very useful tool to show you where the magnetic tension (curved/bended field lines) and magnetic pressure (comparable to dense field lines) are.

Naturally, we could run a PIC code for reconnection and then plot "all" field lines, the thing is, the figure would be black, and you would not see anything anymore. THAT is why one plots only a limited number of field lines, to know what the field, in general, looks like globally.

 

[tusenfem]

Does magnetic reconnection require plasma to function??

What does that even mean: the plasma to function??????????

 

[sol invictus]

So "a magnetic field is a continuum, not a set of discrete lines." .. "The field lines are just a very useful tool"

So then basing an energy releasing process on the properties of these tools, and not the actual magnetic fields continuum, would seem rather dubious, would it not?

Snow/rockslides only occur on sufficiently steep slopes. So suppose I look at a contour map of some hills and find a spot where the contour lines are close together. I point at that spot and say "here's a spot where there's a high risk for a dangerous avalanche". Sound reasonable?

Not according to Zeuzzz. After all, slopes are continuous, they're not composed of discrete lines. So, says Zeuzzz, isn't it dubious to base an energy releasing process like an avalanche on the properties of these lines, rather than the actual slope?

I really can't figure out what the mental block is. Magnetic field lines are a representation of the field. In the limit you draw more and more lines, they become a more and more precise and accurate depiction of it. When the lines reconnect, that indicates that a specific type of behavior is occurring in the field.

When magnetic field lines are tangled or bent rather than straight, there is excess energy stored that could be released by a reconnection that allows them to straighten (similar to how when contour lines are close together, energetic avalanches can occur). And in fact when B lines reconnect in plasma, lots of energy gets released and goes into accelerating the plasma.

All of those statements are facts, and just about as indisputable as facts can get. They're supported by theory, simulations, and experiments. There are open questions about (for example) which astrophysical phenomena are caused or strongly affected by this and which aren't, but there is no debate at all about the basics.

 

[Tim Thompson]

Reconnection vs Circuit

The Hall parameter is a term in the generalized Ohm's law for the resistivity of the plasma ...

See the problem yet folks, especially you RC? You've got a discharge process going on inside the filaments, and between the filaments, and the resistivity of the current flow through the plasma is what heats the loops. Whether they "reconnect" or not, each loop can reach millions, sometimes tens of millions of degrees Kelvin. That's a "discharge" folks and can be expressed more effectively in terms of circuits and resistance to current flow.

There is no problem to see, there is no discharge, and the resistivity alone cannot explain coronal loop heating. You keep repeating your circuit mantra, but you have never even once provided any reason, based on real physics, to believe anything you say about the sun. Until you actually show us some real physics, it's nothing but empty claims.

I'd really like to hear your explain how a single coronal loops reaches millions, sometimes tens of millions of degrees Kelvin over a 6000 K photosphere. The "circuit/resistor" approach explain that heating process quite nicely, but you seem to have no way to explains that heating process via "magnetic reconnection', unless you've claiming the loop is "magnetically reconnecting" within itself!

The resistivity alone is too low to heat the coronal loop simply by resisting the current flow, as in a normal circuit. Something else has to join in the heating process. Energy can be injected into the coronal loop, in the form of a fast current, by virtue of magnetic reconnection at the loop footpoints (e.g., Kittinaradorn, Ruffolo & Matthaeus, 2009). There is a definite correlation between energy generated at the footpoints of a coronal loop and the photospheric magnetic field, indicating that reconnection at the base of the corona is responsible for heating coronal loops (e.g., Katsukawa, 2007). A coronal loop can be heated by magnetic reconnection throughout the loop (e.g., Hood, Browning & van der Linden, 2009). While resistivity by itself can't heat a coronal loop, resistivity can play a role in coronal loop heating by damping of Alfven or magnetosonic waves (e.g., Van Doorsselaere, Andries & Poedts, 2007). Obviously resistivity must play a role in the loop heating, since resistive MHD is so much more amenable to such things than is ideal MHD. But idea that one and only one mechanism heats coronal loops is far too simplistic. I think a combination of wave heating and magnetic reconnection at the loop footpoints are the primary sources of loop heating (e.g., the papers above plus Diaz, Oliver & Ballester, 2006; Taroyan, Bradshaw & Doyle, 2006; O'Neill & Li, 2005; Schmeider, et al., 2004 & etc.).

The "circuit/resistor" approach is no more literally physically true than is the field line approach to understanding magnetic fields, although the latter is superior in explanatory power. The "circuit/resistor" approach allows us to organize our understanding by analogy in the same way the field lines allows us to organize our understanding of magnetic fields. As I have said before (Magnetic Reconnection Redux VII; Fields: Points & Lines; Fields: Points & Lines II), the physical reality of field lines is not relevant to the physical reality of magnetic reconnection. Likewise, the physical reality of the circuit elements is not relevant to a circuit model for coronal loops or solar flares.

The circuit paradigm for understanding coronal loops and solar flares is an analogy, not a literal physical picture of what is happening. It's just another rhetorical trick for making the physics easier to grasp at some building block, flowchart level, whereby we can avoid the details of the physics. Mozina's big mistake here is assuming without any physical justification that the details of the circuit paradigm correspond exactly to the details on the real physical process in a one to one fashion. But a detailed study of the actual physics, such as found in the papers cited here, demonstrates with clarity that it simply is not so. The circuit paradigm can "explain the heating process quite nicely" only as a flowchart can "explain quite nicely" the functional intent of software. But just because you can read the flowchart does not mean you can write the code that does the job.

 

[brantc]

Have you read any of the posts in this thread?
Magnetic reconnection is a change in topology of the magnetic field that can be done with bar magnets.
It gets much more scientifically interesting and challenging when it happens in a magnetic field that contains plasma.

What?????

The experiment with iron filings????

Baloney!!!!!

If you measure a magnetic field with a Hall Probe or magnetometer it is a continuous function. No field lines, no bundles of flux tubes, all you see is the field strength ramp up and down at any one spot.
I have a box full of magnets and a magnetometer!!
I have measured all kinds of stuff.... I could even hook it up to Igor Pro and log/graph the field if I had to.

What you are seeing is the effect of the magnetic field going through the filings..... The filings move. The magnetic field does not change.

That is not reconnection. Unless you want to say by virtue of lower energy configuration it is..... So then each iron filing is reconnecting....

Reconnection in a flux tube is a change in magnetic field strength as the plasma changes.

Nothing to see here.... Move along!!!!

 

[brantc]

Originally Posted by brantc View Post
Does magnetic reconnection require plasma to function??

What does that even mean: the plasma to function??????????

You have maintained that a flux tube is a magnetic tube. And it does not come from the plasma flowing through it.

So can you have a flux tube without the plasma? Does a flux tube need the plasma to form?

And you have said that reconnection can happen in permanent magnets.

So show me an example of reconnection happening in space with no plasma.

 

[brantc]

I think a combination of wave heating and magnetic reconnection at the loop footpoints are the primary sources of loop heating (e.g., the papers above plus Diaz, Oliver & Ballester, 2006; Taroyan, Bradshaw & Doyle, 2006; O'Neill & Li, 2005; Schmeider, et al., 2004 & etc.).

Heating in a loop is really just the acceleration of the particles and if we are viewing it at 171 to 192nnm then it is about 1 to 2 million degrees or 100 to 200eV.

This acceleration is most efficiently performed by electric fields.
Reconnection needs to be separated out from the actual heating as an effect of the motion of the particles. Reconnection does not cause the initial acceleration of the particles in the loop.
Jets(particle acceleration) are a result of the reconnection but this is after the initial particle motion from the electric fields, which is the steady state condition as the loop is feed from the solar surface.
It seems as though there should be an impulsive component, as well as a steady state component that lasts as long as the loop.

Looking at the base of the loops, you can see from the magnetogram that there are different polarities at the ends of the loops.

Generally speaking if you have different polarities of magnetic fields then there are different polarities of electric fields. So since you have different polarities of electric field across a flux tube then it will accelerate the respective polarity particles.
I think the electric field came first then the flux tube.

And you know about Coronal Rain???

"Glowing brightly in extreme ultraviolet light, the hot plasma entrained above the Sun along arching magnetic fields is cooling and raining back down on the solar surface."
http://apod.nasa.gov/apod/ap001115.html


Interesting paper I found concerning the helical flux tubes observed on the solar surface.

ERUPTION OF A MULTIPLE-TURN HELICAL MAGNETIC FLUX
TUBE IN A LARGE FLARE: EVIDENCE FOR EXTERNAL AND
INTERNAL RECONNECTION THAT FITS THE BREAKOUT MODEL
OF SOLAR MAGNETIC ERUPTIONS
http://solarscience.msfc.nasa.gov/papers/garyga/HelixPaper.html

 

[Reality Check]

What?????

The experiment with iron filings????

Baloney!!!!!

If you measure a magnetic field with a Hall Probe or magnetometer it is a continuous function. No field lines, no bundles of flux tubes, all you see is the field strength ramp up and down at any one spot.
I have a box full of magnets and a magnetometer!!
I have measured all kinds of stuff.... I could even hook it up to Igor Pro and log/graph the field if I had to.

What you are seeing is the effect of the magnetic field going through the filings..... The filings move. The magnetic field does not change.

That is not reconnection. Unless you want to say by virtue of lower energy configuration it is..... So then each iron filing is reconnecting....

Reconnection in a flux tube is a change in magnetic field strength as the plasma changes.

Nothing to see here.... Move along!!!!

What?????

Not the experiment with iron filings!!!!

Not Baloney!!!!!

I do hope that you are not dumb enough to try to measure magnetic field lines with a Hall Probe or magnetometer. A magnetic field is a continuous vector field. Magnetic field lines are a representation of the magnetic vector field. Magnetic field lines can be displayed directly by looking at the effect of the magnetic field on iron filings.

Magnetic reconnection is a change in topology of the magnetic field.

This is a semantic complaint. Consider the field

If we vary a and b, we change the magnetic field. For ALL a < b, the points (-1,1) and (1,1) are connected by a magnetic field line. For ALL a > b, the points (-1,1) and (-1,-1) are connected by a magnetic field line. Whether or not you consider that line real is irrelevant: the field is real, and the rules for drawing the line are unambiguous. So we can call this as magnetic reconnection. You may object to the label, but your objection is purely semantic: what's happening (the change in the magnetic field) is real, and the rules for determining whether or not what's happening fits our definition of the term are clear and consistent.

This can be demonstarted with refrigerator magnets as The Man posted in another thread and mentioned in this thread.

Originally Posted by The Man
MM, take a couple of refrigerator magnets (the flat rectangular business card or credit card company types), they have alternating north south stripes (generally running vertically). If you place two back to back and slide them across each other you will feel those magnetic stripes alternately repelling and attracting each other. When you feel it switching from resisting the sliding to that sliding being easier (and being pulled in that direction) that is magnetic reconnection as field lines from the stripes on one refrigerator magnet reconnect to the next stripes on the other refrigerator magnet. No “magic magnets”, just what magnets do and reconnection that you can experience in your own kitchen or home. You could do the same thing with a compass and a magnet, the compass needle being itself a small magnet. When the magnet is far from the compass the needle is connected to the earths magnetic field as you bring the magnet closer to the compass at some point the felid of the needle reconnects to that of the magnet and the compass points at the magnet. Move the magnet away from the compass and the field of the needle will reconnect to the magnetic field of the earth. Repeat as many times as you feel necessary until you stop believing in "magic magnets".

 

[Zeuzzz]

Snow/rockslides only occur on sufficiently steep slopes. So suppose I look at a contour map of some hills and find a spot where the contour lines are close together. I point at that spot and say "here's a spot where there's a high risk for a dangerous avalanche". Sound reasonable?

Of course it sounds reasonable, avalanches have been studied for years and its well known the steeper the gradient the more chance of an avalanche.

With magnetic reconnection we had no previous examples of field line topologies creating energy effects. Before then wave lines simple did what they are meant to do.

When the lines reconnect, that indicates that a specific type of behavior is occurring in the field.

When magnetic field lines are tangled or bent(how? Maths of field line bends and tangles please) rather than straight, there is excess energy stored that could be released by a reconnection (of what? what λ is used between lines in your example?) that allows them to straighten

Could you please elaborate on the three bolded statements.

 

[tusenfem]

You have maintained that a flux tube is a magnetic tube. And it does not come from the plasma flowing through it.

So can you have a flux tube without the plasma? Does a flux tube need the plasma to form?

And you have said that reconnection can happen in permanent magnets.

So show me an example of reconnection happening in space with no plasma.

A magnetic flux tube, in principle, is just a bundle of field lines, for which the magnetic flux through the start and end surface is the same, period, end, no further, that's it, final, nothing more to write down.

Now, naturally, we have to chose a surface, for example the cross section of Io, which then creates the Io flux tube. Note, that here the situation is different as in this definition the magnetic field lines are moving along the surface, entering and exiting, but in the end, as it is quasi-stationary, the flux "through Io" remains relatively constant.

Now, take a foot point on the sun for a coronal loop or a prominence. There the field is rather well anchored in the photosphere and not such motion is happening with the field lines, but they can move as a collective, which they do. They shear the field, generating a EMF.

In all, we still don't need any plasma whatsoever, as magnetic fields can quite easily exist in vacuum or in neutral gas. Indeed, before I switched on the plasma in the double plasma machine, the magnetic field generated by the coils around the tube was quite well in existence, as I usually noted when I forgot to take off my watch trying to adjust stuff. Measurements showed that the field was rather constant in the region where the plasma tube would be located (see my paper about this double layer experiment, some pages back). I can define a flux tube that has the size of either the glass tube or of the cathode in the tube (more useful).

Reconnection does not happen in permanent magnets, but in the region between the magnets. That this needs to happen is quite easily seen, when you draw a set of field lines for two magnets side by side and then move them apart. Then you find that in between the field will be less strong (with the stronger field closer to the magnet on either side of the middle line) and thus field lines had to be reconnected. How this exactly works, I don't know, that is still a question to be solved, for example by the upcoming space mission MMS, but there will be plasma involved there which makes it more complicated. In the case of no plasma it is most likely already solved as just moving magnetic fields in vacuum, take a vector potential description of it all etc. This is probably even in Jackson, but I am at home, so I cannot check that. (However, as nothing really happens in that case, it is not very interesting.)

Now as soon as plasma is present, then there can be extra currents, e.g. driven by the EMF of the shearing footpoint motions of the flux tube, and these currents create a flux rope structure.

It is possible very unlikely that examples of reconnection in space with no plasma present can be given, as there is plasma plasma everywhere.

 

[tusenfem]

Heating in a loop is really just the acceleration of the particles and if we are viewing it at 171 to 192nnm then it is about 1 to 2 million degrees or 100 to 200eV.

Just acceleration is NOT heating. Mainly the electrons will be accelerated by the EMF in a loop. These will NOT emit these emissions, but the ions will that are hit by the accelerated electrons. If all particles would be accelerated you would not see zilch, there have to be coulomb collisions in order to transport the energy of the electrons (the ions can usually be taken as a neutralizing background) to the ions.

This acceleration is most efficiently performed by electric fields.
Reconnection needs to be separated out from the actual heating as an effect of the motion of the particles. Reconnection does not cause the initial acceleration of the particles in the loop.
Jets(particle acceleration) are a result of the reconnection but this is after the initial particle motion from the electric fields, which is the steady state condition as the loop is feed from the solar surface.
It seems as though there should be an impulsive component, as well as a steady state component that lasts as long as the loop.

Acceleration of charged particles is, indeed easiest by electric fields.

Shearing motion of the foot points generates currents in the loops.

But you are forgetting a lot of stuff in the reconnection part here. I would advise to take a look at the simplest models of a reconnecting loop by Kuperus & van Tend for example to fully understand the basics of what is happening, and which electric fields are created and which field aligned currents are created around the reconnection region. Your view of this process is way to simplistic.
Looking at the base of the loops, you can see from the magnetogram that there are different polarities at the ends of the loops.

Generally speaking if you have different polarities of magnetic fields then there are different polarities of electric fields. So since you have different polarities of electric field across a flux tube then it will accelerate the respective polarity particles.
I think the electric field came first then the flux tube.

And you would be wrong about the different polarities, they will only generate different polarities of electric field when they have the same motion. The electric field that is created in the loop, the EMF, is given by the cross product vxB, so you cannot say that "generally speaking ... opposite ... opposite."

And you know about Coronal Rain???

"Glowing brightly in extreme ultraviolet light, the hot plasma entrained above the Sun along arching magnetic fields is cooling and raining back down on the solar surface."
http://apod.nasa.gov/apod/ap001115.html

Let's first keep to the heating and stuff, then we can come back to the cooling.

Interesting paper I found concerning the helical flux tubes observed on the solar surface.

ERUPTION OF A MULTIPLE-TURN HELICAL MAGNETIC FLUX
TUBE IN A LARGE FLARE: EVIDENCE FOR EXTERNAL AND
INTERNAL RECONNECTION THAT FITS THE BREAKOUT MODEL
OF SOLAR MAGNETIC ERUPTIONS
http://solarscience.msfc.nasa.gov/papers/garyga/HelixPaper.html

And ..........

 

[sol invictus]

Of course it sounds reasonable, avalanches have been studied for years and its well known the steeper the gradient the more chance of an avalanche.

Magnetic fields have been studied for more than 150 years. So.... what's your point?

With magnetic reconnection we had no previous examples of field line topologies creating energy effects. Before then wave lines simple did what they are meant to do.

What are you talking about? Previous to what? "Meant to do"?? We're talking about solutions to Maxwell's equations, which Maxwell and others discovered in the mid-late 1800s.

Could you please elaborate on the three bolded statements.

"When the lines reconnect, that indicates that a specific type of behavior is occurring in the field. "

It's called "magnetic reconnection". If you want to know more, you'll have to ask more specific questions.

"When magnetic field lines are tangled or bent(how? Maths of field line bends and tangles please) rather than straight, there is excess energy stored"

It's fairly simple. The energy density in the field scales with the density of lines (similar to how a slope's gradient does with its contour lines). That means there's a lot of energy in regions where the lines are tightly knotted or kinked. But if the lines can't reconnect and at the same time are stuck to a fluid (as happens in a plasma in the approximation that the conductivity is infinite), and if the plasma moves around due to currents for a while, it should be very easy to picture how the lines get very tangled. Then when they do reconnect, lots of magnetic field energy is rapidly released.

As for math I can give you far more than you can handle, but the basic equation is that the energy density in an electromagnetic field is proportional to the field strength squared.

that could be released by a reconnection (of what? what λ is used between lines in your example?) that allows them to straighten"

What's λ? As for "between the lines", the field is continuous, so I don't know what you're asking. I have a suggestion for you - translate your questions into the contour line example before asking them. If they don't make sense, they probably don't make sense here either.

 

[Michael Mozina]

A magnetic flux tube, in principle, is just a bundle of field lines, for which the magnetic flux through the start and end surface is the same, period, end, no further, that's it, final, nothing more to write down.

You mean: "No explanation offered". The magnetic lines don't "bundle themselves" into tight little spirals. Electrical currents cause that behavior in plasmas. You're ignoring the "cause" of the bundling process that creates those "flux tubes". It's called "current flow".

This has become nothing but a renaming of known processes convention. You've renamed "magnetic attraction", "magnetic reconnection". You've renamed "magnetic repulsion", "magnetic disconnection/reconnection". You've renamed "induction", "magnetic reconnection". You've renamed a "circuit reconnection", "magnetic reconnection". All you've done is turn electrical theory on it's head.

 

[tusenfem]

You mean: "No explanation offered". The magnetic lines don't "bundle themselves" into tight little spirals. Electrical currents cause that behavior in plasmas. You're ignoring the "cause" of the bundling process that creates those "flux tubes". It's called "current flow".

Oh for goodness sake MM, even Alfvén uses this kind of definition for a magnetic flux tube in Cosmical Electrodynamics.

This has become nothing but a renaming of known processes convention. You've renamed "magnetic attraction", "magnetic reconnection". You've renamed "magnetic repulsion", "magnetic disconnection/reconnection". You've renamed "induction", "magnetic reconnection". You've renamed a "circuit reconnection", "magnetic reconnection". All you've done is turn electrical theory on it's head.

That is all YOUR work, the renaming, because you willfully misunderstand what SI and others are writing. They never said that magnetic attraction is magnetic reconnection and the other rubbish that you write above.

When are you going to come up with REAL answers, REAL models of your circuits reconnection, of the particles reconnecting, etc. etc. I know when, probably when easter and pentecost fall on the same day, as we say in the Netherland.

You just are a bigbmouth and a fraud without any substance whatsover then moan and bitch about mainstream physics in which you have (astonishingly) failed magnificently.

 

[Michael Mozina]

You just are a bigbmouth and a fraud without any substance whatsover then moan and bitch about mainstream physics in which you have (astonishingly) failed magnificently.

Er, people who live in glass houses.....

In all, we still don't need any plasma whatsoever, as magnetic fields can quite easily exist in vacuum or in neutral gas.

Let's see an empirical demonstration of "flux tubes" with magnetic field lines curled into little flux tubes in a 'vacuum', and show me how they "reconnect", and then talk to me about who's a "fraud without any substance whatsoever." Oh the irony of that comment. You pegged the meter again.

 

[Michael Mozina]

Oh for goodness sake MM, even Alfvén uses this kind of definition for a magnetic flux tube in Cosmical Electrodynamics.

In what context, heavy, dense, non current carrying plasma, or light plasma like we find in the solar atmosphere? Quote please...(yes, I have the book).

 

[GeeMack]

You mean: "No explanation offered".

No explanation offered? You mean like this...

The "circuit/resistor" approach explain that heating process quite nicely, but you seem to have no way to explains that heating process via "magnetic reconnection', unless you've claiming the loop is "magnetically reconnecting" within itself!

Okay. Go for it. Do something you've never done in all your years. Explain it quite nicely using the "circuit/resistor" approach, quantitative, like real science. No pretty pictures allowed. You have an opportunity here to show people that you're not in grade school anymore. Show your work.

Waiting and waiting...

So are you going to just let this claim become another one of your lies? Or another demonstration of your ignorance? Or will you explain quite nicely, using the "circuit/resistor" approach, how a single coronal loop reaches millions, sometimes tens of millions of degrees?

... and waiting.

Again, your ignorance is one Hell of a useful argument when you can't really do what you claim you can do, isn't it, Michael?

And again, what's that word that means you've said something you know is not true?

 

[tusenfem]

Let's see an empirical demonstration of "flux tubes" with magnetic field lines curled into little flux tubes in a 'vacuum', and show me how they "reconnect", and then talk to me about who's a "fraud without any substance whatsoever." Oh the irony of that comment. You pegged the meter again.

Do you even READ what is written or do you just immediately start dishing out tripe? Nowhere have I said that there are "field lines curled into little flux tubes" in vacuum. The idea is preposterous.

But I guess the fact that you have nothing of substance to offer, you just come up with your own misinterpretation of what other people are saying.

 

[tusenfem]

In what context, heavy, dense, non current carrying plasma, or light plasma like we find in the solar atmosphere? Quote please...(yes, I have the book).

What is a "light" plasma, a plasma made of photons?

I guess we are back at post 381, in an indirect way referring to post 342 where I wrote (so you don't have to klick back, god forbid you would do something yourself, like answering loads of questions). Something you COMPLETELY ignored, but now suddenly are in need of the reference. Clearly, you only read what you want, and discard what is unwanted.

If you look at Cosmic Electrodynamics by Alfven and Falthammar you will see what a flux tube is in 3.13.1 figure 3.18 (a). That is just a collection of field lines, they write: Consider a cylindrical flux tube (Fig . 3 .18 (a)) with length l and radius R << l. Now this field B = Bz, the z-component of this field is curl free and thus there is no current in along the field. Also it can easily be that the tube is empty and there is only magnetic field. Then they start to twist one of the footpoints, and then something happens and currents will be set up to facilitate the twist of the field. However, NOTE that ALFVEN and Falthammar do not discuss any current or plasma *AT ALL* when calculating the magnetic energy created by the twisting in Eq. 4 on page 117. The only place where gas starts to play a role is on page 118 where they write: The magnetic force is radial and in equilibrium it is balanced by a radial pressure gradient.