Why am I not surprised that you did not know that?
Oh, please stop this double layer stuff, have you ever really studied double layers?
Yep. Although in my spare time, not in any education.
I happen to have done my PhD research on double layers. A current disruption is not the same as a double layer. The Ej approach, sounds very scientivid, unfortunately meaningless. Yes, if you want to do it the hard way, you can try to describe reconnection in the Ej view, but it is a hell of a lot simpler to do it in Bv. And the latter does absolutely not mean that we do not care about currents that NEED to flow in reconnection regions.
I didn't say that a current disruption is the same as a double layer. I was referring to
Alfvens exploding double layer model, a variant of current disruption that includes the formation of a double layer.
Do you know the differences between Bv and Ej?
I'll post some of my other posts from elsewhere here, saves me writing it out again.
They are not equivalent, there are differences. Magnetic reconnection does not encompass automatically all current-driven processes because an electric current based on the Ampere’s law is associated with a non-zero curl B and thus can be cast into a magnetic reconnection configuration when the background field is removed. [....]
Let’s outline my points in a more coherent manner then. And maybe some of the differences between the Ej approach and the Bu approach would be a good idea.
- The standard description of Magnetic reconnection in plasma is the process by which magnetic field energy is converted into kinetic energy.
- The field configuration of the neutral point involved in magnetic reconnection configuration obeys Maxwell’s laws.
- None of the above are a physical description of how the magnetic energy is liberated from the field; there is no mention of the physical object that has to be receiving the kinetic energy, or any of the magnitudes involved.
- Hannes Alfvén, the founder of the concept “frozen-in magnetic field lines” (which he later spoke critically of), was severely opposed to the concept of magnetic reconnection and preferred to use plasma physics and the current disruption model, the “Ej approach” which utilizes the electric field and current density instead of the magnetic field and bulk plasma flow model magnetic reconnection is currently based on.
- Alfven also proposed that the E-fields resulting from double layers in the plasma may play a role in particles gaining their kinetic energy.
- The Ej Aprroach (Current disruption) and the Bu approach (magnetic reconnection) have several differences, however they are similar in the sense that they are both phenomena that involve the breakdown of the ideal MHD condition and both can arrise from the same magnetic field neutral point setup.
- One major characteristic of current disruption is the large magnetic fluctuations and time-varying electric currents. No large magnetic fluctuations are expected for the “dissipation” region in Magnetic reconnection.
- A magnetic neutral line is essential for magnetic reconnection, but not for current disruption, which can occur in various other field conditions, and is well known for releasing energy from solar flares and other phenomenon (one of the few areas where this idea has gained some acceptance, mainly due to Alfvens persistence of pursuing the electrical current theory as opposed to the magnetic one) (ref ref)
- Local current is reduced and breaks up into filaments in current disruption, but not so in magnetic reconnection.
- The plasma instabilities invoked for their onsets are different. For magnetic reconnection, the tearing instability is thought to be the main mechanism (ref), and instead KBI and CCI instabilities are used for current disruption. (ref)(ref)
- The plasma flow pattern associated with current disruption is not ordered by the magnetic field configuration, and the change in magnetic field topology is not essential (although it may occur)
- Reduction and filamentation of local current is a characteristic of the Ej approach that is not manifested in magnetic reconnection theory.
- The Ej approach, although very similar, is not equivalent to the Bu approach for magnetic reconnection.
Have you read the papers by Parker and Lui, who discuss the two paradigms and show that they are the same? (They have to be the same because the BOTH come from the same Maxwell equations)
No, they are not the same. And yes, Lui's papers have been my main sources. He tends to prefer the current disruption method, and this area still causes heated debate, with many people strongly disagreeing with Lui, but some endorsing him and his colleagues. I would recommend the series of publications here, they act as a really good reference;
Proceedings of the Magnetic Reconnection Meeting, and many of the authors are sceptical of magnetic reconnection, point out Alfvens valid criticism of it, the Ej paradigm, the current disruption model, the (now pretty much falsified) parker model, and discuss what exactly the physical process behind magnetic reconnection is supposed to be (which is the most interesting paper [page 26 of 72])
Heres A few more of lui's publications relevant to this that I've used before, if you want to check them out;
http://cat.inist.fr/?aModele=afficheN&cpsidt=911153
http://www.cosis.net/abstracts/EGU06/01545/EGU06-J-01545.pdf
http://www.agu.org/eos_elec/010093e.html
http://www.sciencedirect.com/scienc...serid=10&md5=932a7cc1bd52eba9871d7ef3d03f9917
Ej and Bu approaches are not exactly equivalent, for the reasons I listed above. They do arise from the same conditions, and are equivalent in terms of maxwells equations which they are derived from, but there are very subtle differences. I feel that magnetic reconnection is a bit dated now, it lacks a detailed physical description for the energy release between each line, the reconnection rate is always arbitrarily set, positive ions are likely to be unmagnetized in the central part of the plasma sheet (indicating that the frozen-in-field concept is not valid there), the Bu approach does not include all current driven process's as Amperes law is associated with a non zero curl, there are problems when converting the old 2D reconnection model into 3D, and other reasons, mainly that I find the interaction of two lines that are arbitrarily put in by us somewhat meaningless.
Although there exists a kinetic approach to magnetic reconnection (see
Hills model, or
Galeevs model), most of the reconnection models are based on the concept that space plasmas behave like regular fluids and are well described under the Magneto-Fluid-Dynamic approximation. In this
approximation the state of the plasma is represented by local macroscopic properties, which depend on position in space r, and on time, t. Magnetic reconnection also relies on the concept of magnetic field lines, and its probaly a good idea to recall that field lines were used by Faraday to assist visualization of the magnetic force on small magnets (often inproperly called magnetic lines of force). In space plasmas the mathematical concept of field line motion relies on its association with a flow field (see
Newcombs work for the origin of this idea).
There is however the alternative interpretation of what is creating this energy release, the Current disruption approach that Alfven and others have endorsed.
Current sheets are ubiquitous and well recognized to exhibit dynamic activity in particle acceleration, intense wave generation, and plasma turbulence. Current disruption is basically caused by Intense current densities in current sheets. Current disruption and magnetic reconnection, arise from two different approaches in treating space plasma problems. The “Ej approach” considers electric field and current density as primary quantities while the “Bu approach” considers magnetic field and plasma flow as primary quantities. Current disruption is used in the former approach while magnetic reconnection in the latter.
There are many limitations of the B-u paradigm and merits of the E-j paradigm However, my main objection to the B-u paradigm is its reliance on magnetohydrodynamics, when many of the processes occurring in magnetic reconnection are inherently kinetic, requiring an approach that can better be summed up as the E-j paradigm that Alfven endorsed. However astronomers who prefer to avoid mentioning electric currents as a primary source of cosmic energy releases fall back on magnetic reconnection as an explanation.
And this publication in the most recent PC journal by ex director of the geophysical institute, Syun-Ichi Akasofu, pretty much sums up the state of magnetic reconnection theory today, and proposes an array of perfectly valid electrical alternatives to many MR process';
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/27/4287017/04287018.pdf?temp=x
Many theorists and observers are trying to explain these four facts, sometimes including the acceleration of auroral electrons, in terms of magnetic reconnection and the X-line formation.
In the past, much effort has been made in interpreting plasma flows and magnetic field changes in the magnetotail in an attempt to validate magnetic reconnection. In fact, hundreds of papers have been published in this regard.
In this paper, however, it is shown that the four facts can be explained by a simultaneous and sudden growth of two electric current systems (Fig. 9) that can be explained by a single process, namely, the growth of an Earthward-directed electric field Er in the plasma sheet, which will be explained shortly. This is because it drives the meridional loop currents, and the electrons carrying the field-aligned current (the upward portion of the current) cause the aurora. At the same time, the electric field Er transmitted to the ionosphere is directed southward, driving the westward electrojet. The westward electrojet generated forms the azimuthal loop. [....]
We also know that successive substorms occur when a large magnitude of the IMF Bz component is steadily directed southward for 10–20 h. This suggests that, when the magnetosphere is continuously driven, the cross-tail current is intermittently reduced, as Lui [25] suggested.
If the return current from the westward electrojet becomes stronger than the cross-tail current, the magnetic X-line might form, and “over-dipolarization,” in which the magnetic field in the magnetosphere becomes greater than that of the Earth’s dipole field, can occur. However, like solar flare cases, magnetic reconnection or the X-line does not play the role of initiating substorm onset as the magnetic reconnection theories propose. The MHD formalism cannot properly deal with both the plasma instability process and the growth of Er. [.....]
Conclusion.
What we consider to be the basic concepts in guiding solar and magnetospheric physics may not really be well founded. I demonstrated this conclusion by choosing the simplest cases in sunspots, solar flares, and magnetospheric substorms, yet they contain all the essential features: sunspots single spots; solar flares an antiparallel flow in a magnetic arcade; solar ejecta magnetic flux ropes; substorm Boström’s current system. The simplest qualitative discussions can be more useful than elaborate MHD simulations based on unsubstantiated guiding concepts. History tells us that some of what is thought to be “truth” in science is often only an agreement or understanding, which is either right or wrong, among contemporary scientists. Changes in “truth” make science progress, although not always.
I think that there are distinct advantages to treating the current as primary in every case. Magnetic reconnection seems to have fallen short of being able to describe many processes in space despite its popularity since the original proposal all those years ago (1950's). I think alternatives should be considered in all magnetic reconnection senarios, as MHD simulations based on an array of assumptions often give erroneous results.
No, I do not have the paper, maybe I can get it at the office. But if you had read the abstract you would have seen that they say when the plasma tail appears disconnected from the cometary head so it is clear they mean the ion/plasma tail and not the dust tail.
Your quite right
Thanks, I'll try to get hold of it myself meanwhile, and i'll see if an alternative electrical approach can be applied in this situation, like most other areas that use MR....
