Magnetic reconnection and physical processes

[Zeuzzz]

My oh my it seems that the reconnection rate is indeed set arbitrarily! Would you have that the rate and thus position of the magnetic field lines is arbitrarily set. Making any energy release from the randomly specified rate and position completely moot in the real world.

http://www.sciencedirect.com/scienc...serid=10&md5=5ca057794c1cf90b0b72096301bf8937

Abstract

Magnetic reconnection is one of the most important energy conversion processes in space plasmas. Theoretical models of magnetic reconnection have been traditionally developed within the framework of magnetohydrodynamics (MHD). However, in low density astrophysical plasmas as those found in the magnetopause and the magnetotail, the current sheet thickness can be comparable to the ion inertial scale and therefore the Hall electric field becomes non-negligible. The role of the Hall current is to increase the reconnection rate with respect to MHD predictions, which therefore poses a promising mechanism for fast reconnection. We present results from parallel simulations of the incompressible Hall MHD equations in View the MathML source dimensions. We quantitatively evaluate the relevance of the Hall current in the reconnection process by performing a set of simulations with different values of the Hall parameter. We compute the corresponding reconnection rates as a function of time, and explore the spatial structure of the fields in the surroundings of the diffusion region. We quantify the increase of the reconnection rate as a function of the Hall parameter, and confirm the presence of a quadrupolar structure for the out-of-plane magnetic field.

What a muddle these constructs can put us in. When he says

"We quantitatively evaluate the relevance of the Hall current in the reconnection process"

Its a completely faulty premise, as the hall currents are not one of the things relevant to magnetic reconnection, they are producing what they are calling 'magnetic reconnection'. They are instead trying to prove the existance of a hypostatized abstraction (which they never will) by using a real measurable phenomenon.

 

[Tim Thompson]

Reconnection Rate Not Arbitrarily Set

My oh my it seems that the reconnection rate is indeed set arbitrarily!

No it isn't. Back to English 101 for you my friend!
Abstract
Magnetic reconnection is one of the most important energy conversion processes in space plasmas. Theoretical models of magnetic reconnection have been traditionally developed within the framework of magnetohydrodynamics (MHD). However, in low density astrophysical plasmas as those found in the magnetopause and the magnetotail, the current sheet thickness can be comparable to the ion inertial scale and therefore the Hall electric field becomes non-negligible. The role of the Hall current is to increase the reconnection rate with respect to MHD predictions, which therefore poses a promising mechanism for fast reconnection. We present results from parallel simulations of the incompressible Hall MHD equations in 2 1/2 dimensions. We quantitatively evaluate the relevance of the Hall current in the reconnection process by performing a set of simulations with different values of the Hall parameter. We compute the corresponding reconnection rates as a function of time, and explore the spatial structure of the fields in the surroundings of the diffusion region. We quantify the increase of the reconnection rate as a function of the Hall parameter, and confirm the presence of a quadrupolar structure for the out-of-plane magnetic field.

The reconnection rate was not set arbitrarily, the Hall parameter was. The reconnection rate is calculated (not set arbitrarily) as a function of time, and because the Hall parameter was fixed for each simulation, it should be obvious that the authors can now ... "quantify the increase of the reconnection rate as a function of the Hall parameter".

 

[Zeuzzz]

No it isn't. Back to English 101 for you my friend!
Abstract
Magnetic reconnection is one of the most important energy conversion processes in space plasmas. Theoretical models of magnetic reconnection have been traditionally developed within the framework of magnetohydrodynamics (MHD). However, in low density astrophysical plasmas as those found in the magnetopause and the magnetotail, the current sheet thickness can be comparable to the ion inertial scale and therefore the Hall electric field becomes non-negligible. The role of the Hall current is to increase the reconnection rate with respect to MHD predictions, which therefore poses a promising mechanism for fast reconnection. We present results from parallel simulations of the incompressible Hall MHD equations in 2 1/2 dimensions. We quantitatively evaluate the relevance of the Hall current in the reconnection process by performing a set of simulations with different values of the Hall parameter. We compute the corresponding reconnection rates as a function of time, and explore the spatial structure of the fields in the surroundings of the diffusion region. We quantify the increase of the reconnection rate as a function of the Hall parameter, and confirm the presence of a quadrupolar structure for the out-of-plane magnetic field.

The reconnection rate was not set arbitrarily, the Hall parameter was. The reconnection rate is calculated (not set arbitrarily) as a function of time, and because the Hall parameter was fixed for each simulation, it should be obvious that the authors can now ... "quantify the increase of the reconnection rate as a function of the Hall parameter".

Ok, the reconnection rate is defined as whatever the the Hall parameter is, and "the Hall parameter was [is arbitrarily set]"

2Q's:

1) Why is the Hall parameter arbitrarily set?
2) What in that case does it represent?

I've found this in another;

http://journals.cambridge.org/actio...60465FF87.tomcat1?fromPage=online&aid=5479148

Our main goal is to find the dependencies of reconnection rate on different properties of turbulence.

Seems that whatever sets the reconnection rate is still being investigated and dependencies sought out. Gee, I wonder if they ever thought that the rate is set only in our heads when we decide the arbitrary wavelengths of the field lines.

 

[brantc]

Nice story.
Better known as nothing to do with magnetic reconnection in solar flares until you produce a mathematical model from your story and thus predictions that match observations.
But a few questions about this theory of yours:

• If it is not your theory then what textbook did you get it from?
• Where does the electric field come from?
• How does the electric field constrict the plasma into a pair of flux tubes?
• How strong does the electric field need to be to constrict the plasma into a pair of flux tubes?
• Why a pair of flux tubes (why not 1, 3, 4, etc.)?
• What directions are the electric currents going in each flux tube.
• What observational evidence do you have for this theory?
• What experimental evidence do you have for this theory?

If you had said electric field once then maybe it was a mistake but you said it twice so it has to be a lack up understanding.

We are talking about basically the z-pinch and variations thereof using the Bennett relation better known as a flux tube. The right hand rule.

Here is a good resource.
http://www.plasma-universe.com/Pinch_(plasma_physics)

Actually, Anthony Peratt did PIC simulations on plasma filament forces.
Section D.
http://plasmascience.net/tpu/downloadsCosmo/Peratt86TPS-I.pdf

So its not my theory, its just a description of a flux tube using known laboratory physics.

 

[Reality Check]

If you had said electric field once then maybe it was a mistake but you said it twice so it has to be a lack up understanding.

We are talking about basically the z-pinch and variations thereof using the Bennett relation better known as a flux tube. The right hand rule.

Here is a good resource.
http://www.plasma-universe.com/Pinch_(plasma_physics)

Actually, Anthony Peratt did PIC simulations on plasma filament forces.
Section D.
http://plasmascience.net/tpu/downloadsCosmo/Peratt86TPS-I.pdf

So its not my theory, its just a description of a flux tube using known laboratory physics.

No we are not.
I am talking about magnetic reconection which is the topic of this thread.
You are talking about the z-pinch, etc. It up to you to show that this is exactly the same as a flux tube or sumething to do with magnetic reconection.

The Bennett relation is not a flux tube. A z-pinch is not a flux tube.

I know that PIC simulations have been done in plasma physics for decades. Why are you surprised about it?

Citing that paper of Anthony Peratt though is not wise since it is about his invalid plasma theory of galaxy formation.

 

[Reality Check]

What is your source for reconnection rate are set arbitarily in MHD simulations

I will emphasis that the question is about the OP, not about a paper that you just found and misinterpreted:
First asked 27 January 2010
Zeuzzz,
What is your source for your assertion in the OP that the reconnection rate is set arbitarily in MHD simulations?

Or can we take it that you are satisfied that the reconnection rate is measured in MHD simulations, not a parameter input to the simulations?

Ok, the reconnection rate is defined as whatever the the Hall parameter is, and "the Hall parameter was [is arbitrarily set]"

2Q's:

1) Why is the Hall parameter arbitrarily set?
2) What in that case does it represent?

Still not quite understanding the abstract Zeuzzz.
The role of Hall currents on incompressible magnetic reconnection is strangely enough about the role of Hall currents on incompressible magnetic reconnection.
The reconnection rate comes out from the simulation. It looks like a simple count of the number of reconnections per unit time.
A parameter input to the simulation for Hall MHD is the Hall parameter.
Varying the Hall parameter varies the reconnection rate.
The Hall parameter is not arbitrarily set. It is set to a range of values to see what is the role of Hall currents on incompressible magnetic reconnection. It looks like one role is to vary magnetic reconnection rates.

I've found this in another;
http://journals.cambridge.org/actio...60465FF87.tomcat1?fromPage=online&aid=5479148

Seems that whatever sets the reconnection rate is still being investigated and dependencies sought out.

That is right - that is how science works.
The reconnection rate in magnetic reconection looks like a complex issue.

 

[Zeuzzz]

The reconnection rate in magnetic reconection looks like a complex issue.

Odd that what one would consider the most basic attribute to study of any phenomena (the time/rate it occurs) seems to be such a tricky subject. Maybe this fundamental lack of explanation for one of the most basic properties of MR is just a wider symptom of misusing magnetic field lines, and not currents and circuits.

 

[Tubbythin]

Odd that what one would consider the most basic attribute to study of any phenomena (the time/rate it occurs) seems to be such a tricky subject. Maybe this fundamental lack of explanation for one of the most basic properties of MR is just a wider symptom of misusing magnetic field lines, and not currents and circuits.

Or maybe MR can just be complicated.

 

[Zeuzzz]

Or maybe MR can just be complicated.

Explain then why this is. I'm all ears.

Sol and everyone seem adament that its all incredibly straightforward and everyone who is not sure are fools.

 

[Tubbythin]

Explain then why this is. I'm all ears.

Sol and everyone seem adament that its all incredibly straightforward and everyone who is not sure are fools.

The basic principles can be simple whilst having detailed minutiae.

 

[Reality Check]

Odd that what one would consider the most basic attribute to study of any phenomena (the time/rate it occurs) seems to be such a tricky subject. Maybe this fundamental lack of explanation for one of the most basic properties of MR is just a wider symptom of misusing magnetic field lines, and not currents and circuits.

There is no fundamental lack of explanation for the reconection rate.
It is merely a complex and basic property of magnetic reconnection that depends on many factors.
Basic does not mean simple.

 

[Reality Check]

What is your source for reconnection rate are set arbitarily in MHD simulations

You forgot the question:
I will emphasis that the question is about the OP, not about a paper that you just found and misinterpreted:
First asked 27 January 2010
Zeuzzz,
What is your source for your assertion in the OP that the reconnection rate is set arbitarily in MHD simulations?

Or can we take it that you are satisfied that the reconnection rate is measured in MHD simulations, not a parameter input to the simulations?

 

[Zeuzzz]

You forgot the question:
I will emphasis that the question is about the OP, not about a paper that you just found and misinterpreted:
First asked 27 January 2010
Zeuzzz,
What is your source for your assertion in the OP that the reconnection rate is set arbitarily in MHD simulations?

Or can we take it that you are satisfied that the reconnection rate is measured in MHD simulations, not a parameter input to the simulations?

My source was the paper fom the ex-director of the geophysical institute, go back if you want and check I quoted it.

Even said, if the connection rate is set on various different criteria in each situation are these criteria constant? Or does a MR theorist have a collection of measured variables they can try to make significant by correlating it to the rate consistantly?

 

[Reality Check]

I'd like to know from this publication where the energy was localized;

http://sprg.ssl.berkeley.edu/adminstuff/webpubs/2007_np_236.pdf

What do you mean by "localized"?
Where in the In situ evidence of magnetic reconnection in turbulent plasma paper do they say that the energy release was "localized"?
I suspect that the energy was "localized" where the increased kinetic and thermal energy of the plasma was measured by the Cluster spacecraft.

 

[Reality Check]

My source was the paper fom the ex-director of the geophysical institute, go back if you want and check I quoted it.

Found the post (got lost when I skipped the the field/lines are physical or not derail).
He is obvioulsy wrong or misinterpreted (maybe English is not his first language?).
Reconnection rates in MHD simulations are not set. They are a result of the input parameters as the papers you have cited lately show.

 

[Zeuzzz]

I suspect that the energy was "localized" where the increased kinetic and thermal energy of the plasma was measured by the Cluster spacecraft.

You suspect but proof would be appreciated.

 

[tusenfem]

What do you mean by "localized"?
Where in the In situ evidence of magnetic reconnection in turbulent plasma paper do they say that the energy release was "localized"?
I suspect that the energy was "localized" where the increased kinetic and thermal energy of the plasma was measured by the Cluster spacecraft.

Hey, that paper is by my colleague and friend Alessandro, four doors down from my office.

Maybe read the paper Zeuzzz, and you might find out.

 

[Reality Check]

You suspect but proof would be appreciated.

Then the energy was "localized". The proof is that the letter contains the word "localized".

However, high-energy electrons have been found in the terrestrial
magnetotail²⁸, where reconnection is often localized within many small-scale magnetic islands. We speculate that in a turbulent plasma, magnetic reconnection does not develop large-scale X-lines such as those at the terrestrial magnetopause³¹ or in the solar wind⁵, but instead it is most likely localized. If the production of high-energy particles occurs during localized small-scale reconnection, then particle acceleration to high energies should be common during turbulent reconnection.

(emphasis added)

So the answer to your question:

I'd like to know from this publication where the energy was localized?
​

is

small-scale magnetic islands
​

which you should have been able to read for yourself.

 

[Reality Check]

Found the post (got lost when I skipped the the field/lines are physical or not derail).
He is obvioulsy wrong or misinterpreted (maybe English is not his first language?).
Reconnection rates in MHD simulations are not set. They are a result of the input parameters as the papers you have cited lately show.

Another possibility:
He may not be talking about MHD simulations of magnetic reconnections at all.
He may be talking about MHD simulations of substorms where maybe magnetic reconnection is assumed and a value for the rate has to be supplied.

 

[Tim Thompson]

Reconnection Rates and the Hall Parameter

Ok, the reconnection rate is defined as whatever the the Hall parameter is, ...

Where do you dig up this garbage? The Hall parameter is a term in the generalized Ohm's law for the resistivity of the plasma ...

[latex] \boldsymbol E + \boldsymbol U \times \boldsymbol B - (1/ne)\boldsymbol J \times \boldsymbol B + (1/ne)\nabla(nkT) = \eta \boldsymbol J[/latex]

Here the Hall parameter is [latex](1/ne)\boldsymbol J \times \boldsymbol B[/latex]

The Hall parameter can be neglected if the MHD pressure is negligible, since the JxB term becomes negligible compared to the UxB term, and it can also be neglected if the electron-ion collision frequency is large compared to the electron cyclotron frequency because the JxB term is then small compared to [latex]\eta \boldsymbol J[/latex] (see Fundamentals of Plasma Physics, Paul M. Bellan, section 2.6.3 "MHD Ohm's law")

On the other hand, the reconnection rate comes straight out of Maxwell's equations, specifically Faraday's Law ...

[latex] \boldsymbol E = - \partial \boldsymbol A / \partial t - \nabla \phi [/latex]

where E is the electric field, A is the vector potential of the magnetic field and [latex]\phi[/latex] is the scalar potential of the magnetic field. The reconnection rate is basically the scalar [latex]\partial A / \partial t[/latex] (see Magnetic Reconnection: MHD Theory and Application, Priest & Forbes, section 1.6 "Classification of Two-Dimensional Reconnection").

Magnetic reconnection happens only in resistive plasmas and is a function of the resistivity, which includes the Hall parameter. Therefore, it is a perfectly legitimate scientific exercise to make the Hall parameter the only variable parameter in the generalized Ohm's law for the plasma, in order to understand how the reconnection rate depends on the Hall effect (which basically says that there can be no scalar relationship between J and the E + UxB terms; the details are a bit more complicated, see The Physics of Plasmas, Boyd & Sanderson, page 65 for gory details).

So the notion that the reconnection rate is in any way arbitrarily set is simply rubbish from the start.

1) Why is the Hall parameter arbitrarily set?

Answered above: "Therefore, it is a perfectly legitimate scientific exercise to make the Hall parameter the only variable parameter in the generalized Ohm's law for the plasma, in order to understand how the reconnection rate depends on the Hall effect."

2) What in that case does it represent?

I am not sure what "it" is supposed to be, the Hall parameter, or the fact that the Hall parameter is arbitrarily set. But I think the discussion above answers this question well enough in all cases.

Seems that whatever sets the reconnection rate is still being investigated and dependencies sought out.

So what? Magnetic reconnection has no privileged spot in the scientific hierarchy; much is known, but also much is not known. That's what scientific research is supposed to do, explore the unknown based on the known.

Gee, I wonder if they ever thought that the rate is set only in our heads when we decide the arbitrary wavelengths of the field lines.

I have no idea what you are talking about. What wavelengths? Nobody is setting any wavelengths, nobody is using any wavelengths, and I don't see any waves in the equations above.