Talk:Birkeland current

deleted solar image

I removed the solar EUV image of the Bastille Day post-flare arcade. It had been captioned as an example of a "solar Birkeland current", which it is not. Post-flare arcades are formed by line-tied boundary conditions at the photosphere, together with magnetic reconnection (collapse of a current sheet) during a flare. zowie 00:05, 3 October 2005 (UTC)[reply]

I removed an Hubble image of aurora on Jupiter and replaced it with a drawing of the field-aligned and ionospheric current system at high latitude. The new image is much more relevant to the topic. I intend on editing the text to connect the image to the text better. Richfj (talk) 16:41, 30 June 2011 (UTC)[reply]

too general?

The Most of my colleagues seem to use "Birkeland current" to refer only to the auroral-related electrojets around the Earth, specifically; the article seems to tie the term to the more general concept of field-aligned currents in any astrophysical plasma. Does anyone care to comment on this? If I haven't heard back in a few days, I'll try to get around to finding a more authoritative source. zowie 00:14, 3 October 2005 (UTC)[reply]

Indeed, Birkeland currents were originally applied to field-aligned currents in the ionosphere feeding the aurora, and I guesss they are most well-known here, and hence the use of the name here. But all field-aligned currents, no matter where they are, are also Birkeland currents. But field-aligned currents elsewhere are not generally recognised, and the use of the term is limited, but see for example, Synchrotron radiation spectrum for galactic-sized plasma filaments. Perhaps the article should be called Field-Align Currents, with Birkeland currents being the kind found in the ionosphere? --Iantresman 08:11, 3 October 2005 (UTC)[reply]

Hmmm.... Some sort of change sounds like maybe a good idea since it reflects current usage in the scientific community, notwithsanding the ADS link you gave. For example, a quick ADS search for "Birkeland current" in the abstract finds loads of references on the Earth, geospace, and planetary aurorae -- but in the first hundred or so references I found no other titles that refered to interstellar or intergalactic currents. Similarly for Google (aside from the Wikipedia entry! :-).

Since, on the large scale, all non-drift currents are field-aligned in the ideal MHD approximation, it doesn't seem to make sense to me to equate field-aligned currents and Birkeland currents. I'm not, myself, a space geophysicist, but many of my friends are :-). Is there any particular reference work or group of folks you polled to find current usage?

BTW, nice work on the history of Birkeland and on finding so many of the original references on space plasma physics. zowie 15:16, 3 October 2005 (UTC)[reply]

I have the same objection as Zowie. The name Birkeland currents in the professional world is only used for the Earth and planets, and then for specific currents. In all other cases the term field aligned currents is used. So at the beginning it would be better to state that usually the name field aligned currents is used.--Tusenfem 19:27, 2 April 2006 (UTC)[reply]

I wonder whether the article would be better named "field aligned current" (since this is the general term), and include a section on "Birkeland currents"? --Iantresman 20:49, 2 April 2006 (UTC)[reply]

I would object to the change, as the current scientific community tends to reject the idea of applying these types of plasma physics in space, simply because it is convenient to current contemporary theory. Large proponents, such as Hannes Alfven, of Birkeland current's propounded them to pervade all of space, and as such it is relevant to leave the article referring to them as it is. --OneRyt (talk) 11:46, 14 August 2009 (UTC)[reply]

upload

Image:Cygnus-loop.gif Image:Birkeland-anode-globe-fig259.jpg Image:Magnetic-rope.gif Image:Jupiter-aurora.jpg

Will you upload this image in Commons? It was expected that I wrote an article about Birkeland current in Wikipedia Japan. Please cooperate.

Can you upload the images yourself? All the images are in the public domain? --Iantresman 14:49, 31 October 2005 (UTC)[reply]

Characteristics: forces

The article currently states:

Pairs of parallel Birkeland currents can also interact; parallel Birkeland currents moving in the same direction will attract with an electromagnetic force inversely proportional to their distance apart (note that the gravitational force is inversely proportional to the square of the distance); parallel Birkeland currents moving in opposite directions will repel with an electromagnetic force inversely proportional to their distance apart. There is also a short-range circular component to the force between two Birkeland currents that is opposite to the longer-range parallel foreces. [Ref].

The gravitational attraction between two line masses also varies in inverse proportion to their separation, so what's the big deal? The reference is non-refereed and a mess on several fronts (e.g. calling the Earth's core a plasma). In particular, it offers no explanation for the claim of short-range repulsion. If this cannot be explained better or if a better reference cannot be found, I would strike it. --Art Carlson 19:50, 31 October 2005 (UTC)[reply]

If there was no Birkeland current flowing through a plasma, then there would be a number of electrons, ions and neutral particles whose mutual attraction would be electromagnetic (about up to the Debye sphere), and gravitational forces that varies as 1/r^2 because there is no line mass present. So the question is, can a Birkeland current in a plasma be considered a line mass from a gravitational perspective? And if so, is it significant since EM forces are 10^39 more powerful? I'm still checking.

As for the Earth's core being a plasma, this does sound rather contentious. On the other hand, the liquid core is often modelled with magnetohydrodynamics, so perhaps plasma-like is more accurate. --Iantresman 09:59, 8 November 2005 (UTC)[reply]

Characteristics: synchrotron radiation

The article currently states:

Electrons moving along a Birkeland current may be accelerated by a plasma double layer. If the resulting electrons approach relativistic velocities (ie. the speed of light) they may subsequently produce a Bennett pinch, which in a magnetic field will spiral and emit synchrotron radiation that includes radio, optical (ie. light), x-rays, and gamma rays.

A pinch just requires current. Whether the electron velocities are relativistic is irrelevant. The electrons might spiral (if they figure out how to become oblique to the magnetic field, but the pinch won't. Why go into details on the potential wavelength of synchrotron radiation in an article that isn't even about double layers? I'm not sure on cause and effect: does the double layer cause the current or the current cause the double layers? --Art Carlson 20:00, 31 October 2005 (UTC)[reply]

I think I kind of answered this one on another page. Your point about cause and effect I think is relevent, and not obvious. You may have read in Alfvén's Cosmic Plasma about "circuits", in which he considers several aspects to the source and cause of various plasma phenomenon.

My understanding is as follows. Birkeland currents are like electric cables in space, moving ions from one region to another. They do so in response to a load, in this case a double layer who's main features is the ability to accelerate ions. This will result in a beam of ions, which will pinch, and depending on various parameters, may result in a Bennett pinch. And then if the electrons are moving a relativistic velocities, then synchrotron radiation will be emited from the pinch, in the same way that synchrotron radiation is released in a laboratory z-pinch.

So perhaps Birkeland currents do not directly produce synchrotron radiation;, perhaps it's analogous to describing that a light bulb give off radiation, but not mentioning that it is connected to electric wires.

Again I would suggest Peratt's paper for detailed information, Evolution of the Plasma Universe: I. Double Radio Galaxies, Quasars, and Extragalactic Jets [PDF], and Alfvén's Cosmic Plasma.

--Iantresman 20:30, 1 November 2005 (UTC)[reply]

Inaccuracies and errors in the page

I read through the first part of the page, and there are a lot of inaccuracies that need to be changed.

They are sometimes referred to as field-aligned currents. IMHO, in science they are always called field-aligned currents and only in magnetospheric they are called Birkeland currents.
The current flows earthwards down the morning side of the Earth's ionosphere, around the polar regions, and spacewards up the evening side of the ionosphere. These Birkeland currents are now sometimes called auroral electrojets. Although the first part is okay, that the field aligned currents flow to the Earth at the dawn side, and away at the dusk side, I have trouble with stating that the electrojet is a Birkeland current. Birkeland currents are defined as field aligned currents, the electroject is perpendicular to the magnetic field and thus not a Birkeland current.
They can heat up the upper atmosphere which results in increased drag on low-altitude satellites. Is the drag on satellites truely caused by a heated up atmosphere? I would think that the increased magnetic field strength, caused by an active system in a magnetic storm would be the cause, because of stronger eddy currents in the spacecraft.
Birkeland currents are also one of a class of plasma phenonena called a z-pinch Here cause and result are switched around. A Birkeland current is not a z-pinch. A z-pinch may occur when a field aligned current exists. But there are certain restrictions to that, a pinch can only occur when the field strength increases above a certain level. I am not sure that z-pinches have been observed in the Earth's Birkeland currents.
This can also twist, producing a helical pinch that spirals like a twisted or braided rope, and this most closely corresponds to a Birkeland current. Why does this most closely correspond to a Birkeland current?
parallel Birkeland currents moving in opposite directions will repel with an electromagnetic force inversely proportional to their distance apart. But anti-parallel Birkeland currents will not occur, as the inflow is on the dawn side and the outflow is on the dusk side.
Electrons moving along a Birkeland current may be accelerated by a plasma double layer. Electrons are not moving along a Birkeland current, they 'are' the Birkeland current.
If the resulting electrons approach relativistic velocities (ie. the speed of light) they may subsequently produce a Bennett pinch No, this is not true, relativistic particles do not increase the current, so if the requirement for a Bennett pinch has not been fulfilled before, then making the electrons relativistic will not make any difference.

Well, I guess this is enough for a start. This page needs a big make-over.--Tusenfem 19:42, 20 May 2006 (UTC)[reply]

Please go ahead and make any changes you see fit. --Iantresman 23:36, 20 May 2006 (UTC)[reply]

I have started to make the changes to this page, based on the comments above. --Tusenfem (talk) 09:57, 13 August 2008 (UTC)[reply]

Most of the Characteristics section needs to be re-written. As it now stands, the article confuses field-aligned currents which are organized into lines or columns of current (i.e., the area of the current perpendicular to the field line is roughly a circle) with sheets of current (i.e., the area of the current perpendicular to the field line is much greater in one direction than a direction perpendicular to both the field line and the first direction). Birkeland currents are a pair of sheet currents. The following are my responses to the numbered comments above:

Agreed.
Agreed. I intend to re-write the Characteristics section to show how the Birkeland currents and the auroral electrojets are related but not the same thing.
I have already edited the article to explain that the increase drag is due to increased atmospheric density as the electric current in the ionospheric E-layer heat the atmosphere. I will look at this again to be sure that my explanation is clear.
I think the whole z-pinch discussion should be deleted. A z-pinch is related to a line of current and not a pair sheet currents.
The discussion of twist should be deleted. It is relevant to a line of current and not a sheet of current.
The electromagnetic attraction or repulsion due to the Birkeland currents is too small to be significant. The total currents are quite large but the current density is quite small.
Double layers in the ionosphere relate to the acceleration of electrons to create an auroral arc. This is a small scale phenomenon compared to the scale of the Birkeland currents. The existence Birkeland current system is a necessary condition for the double layers and arcs to exist but the Birkeland currents can exist without the double layers.
Electrons which carry the Birkeland currents have energies between ~1 eV and ~10 keV. Relativistic effects are not relevant.

Richfj (talk) 19:25, 21 July 2011 (UTC)[reply]

Added a paragraph to the history section.

Included a paragraph on last December's THEMIS observations with relevant NASA references. Should be non-controversial. Mgmirkin (talk) 18:15, 16 April 2008 (UTC)[reply]

Included NASA references:

See Birkeland's work [The Norwegian Aurora Polaris Expedition 1902-1903] Mgmirkin (talk) 04:51, 26 May 2008 (UTC)[reply]

Anonymous IP 69.86.169.166, please sign in and utilize the talk page before taking out valid edits or references. Thank you, Mgmirkin (talk) 05:58, 26 May 2008 (UTC)[reply]

I've added back in the two valid references you erroneously removed that deal directly with Birkeland current history (both NASA pages below specifically mention Birkeland currents, contrary to your inaccurate comment attached to the edit):

Electric Currents From Space (NASA educational page)

From the above link:

Birkeland Currents

...

When in 1973 the navy satellite Triad (see history) flew through this region in a low-altitude orbit, its magnetometer indeed detected the signatures of two large sheets of electric current, one coming down on the morning side of the auroral zone, one going up on the evening side, as expected. Because Kristian Birkeland had proposed long before currents which linked Earth and space in this fashion, they were named Birkeland currents (by Schield, Dessler and Freeman, in a 1969 article predicting some of the features observed by Triad). Typically, each sheet carries a million amperes or more.

Mgmirkin (talk) 06:11, 26 May 2008 (UTC)[reply]

Electric Currents From Space - History (NASA educational page)

From the above link:

Although signs of currents flowing from space along magnetic field lines were occasionally detected by earlier satellites, it was the US Navy's Triad, carrying the instrument of Alfred Zmuda and James Armstrong, that in 1973 traced their full pattern. Triad was an experimental navigation satellite, and it circled the Earth in a low altitude orbit which went from pole to pole, while the Earth rotated beneath it. Zmuda and Armstrong were allowed to place on it a magnetometer as an extra "piggyback experiment," and it continued to return scientific data for many years after the Navy's experiment had ended.

When Triad crossed a current sheet, a characteristic "signature" was generally noted: the direction of the magnetic field rotated fairly abruptly, while its strength stayed practically the same. From such rotations a wealth of information was extracted about the structure and variation of the currents. Tragically, both experimenters had died by the time their article on "Birkeland currents" appeared in 1974.

Mgmirkin (talk) 06:11, 26 May 2008 (UTC)[reply]

Both pages specifically deal with and reference Birkeland currents. Mgmirkin (talk) 06:03, 26 May 2008 (UTC)[reply]

Anonymous IP 69.86.169.166, let us also not play semantic word games. The fact that the articles do not use the two words "Birkeland current" does not negate the fact that they precisely fit the description given in the opening paragraph of the Birkeland current article (IE, "field-aligned currents").

According to the Birkeland current article:

A Birkeland current generally refers to any electric current in a space plasma, but more specifically when charged particles in the current follow magnetic field lines (hence, Birkeland currents are also known as field-aligned currents).

You will notice that that has been changed now, because it does not refer to any electric current in a plasma. If at all extended to general space plasma physics, the current have to be at least parallel to the magnetic field. If they are perpendicular, e.g. they can be Hall currents, etc. --Tusenfem (talk) 10:02, 13 August 2008 (UTC)[reply]

Birkeland currents often show filamentary, or twisted "rope-like" magnetic structure.

Mgmirkin (talk) 07:02, 26 May 2008 (UTC)[reply]

With respect to the two articles on the THEMIS discovery:

According to the first NASA press release on the THEMIS discovery:

"The satellites have found evidence of magnetic ropes connecting Earth's upper atmosphere directly to the sun," said David Sibeck, project scientist for the mission at NASA's Goddard Space Flight Center, Greenbelt, Md. "We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras."
A magnetic rope is a twisted bundle of magnetic fields organized much like the twisted hemp of a mariner's rope.

Charged particles from the solar wind flow along magnetic field lines. This fits the description of "field-aligned currents" mentioned in the opening paragraph of the Birkeland current article.

Mgmirkin (talk) 07:02, 26 May 2008 (UTC)[reply]

According to the second NASA press release on the THEMIS discovery:

THEMIS observed [a magnetic flux rope] recently with a total energy of five hundred thousand billion (5 x 1014) Joules. "That's approximately equivalent to the energy of a magnitude 5 earthquake,"
"The satellites have detected magnetic 'ropes' connecting Earth's upper atmosphere directly to the Sun," says Dave Sibeck, project scientist for the mission at the Goddard Space Flight Center. "We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras."

Again, this press release mirrors the first. Charged particles from the solar wind follow magnetic field lines, delivering five hundred trillion Joules of energy to the arctic region. This again fits the definition of "field-aligned currents" used in the opening paragraph of the Birkeland current article.

Mgmirkin (talk) 07:02, 26 May 2008 (UTC)[reply]

If you, for some reason, feel the above descriptions do not fit the description of field-aligned currents (or, currents in general), please see the multimedia from the THEMIS press release. Specifically the image wherein they state:

Flux Ropes Power the Magnetosphere!
Flux ropes pump 650,000 Amp current into the Arctic!
They then liken the interaction to a "30 kiloVolt battery in space."

If the prior two articles were insufficient support, NASA's explanation of the interaction in terms of a current of 650,000 Amps leave little to the imagination. These are clearly identified in the NASA press release as electric currents flowing along magnetic fields ("field-aligned currents," AKA Birkeland currents).

As such I am reinstating the removed content. Please leave it there unless you can provide a concrete reason not to.

Mgmirkin (talk) 07:02, 26 May 2008 (UTC)[reply]

Thank you for pointing out the possible confusion. Hopefully the above information sufficiently resolves the issue. If not, feel free to explain why. Mgmirkin (talk) 07:02, 26 May 2008 (UTC)[reply]

I removed this post from the history section of the article page by the IP 146.5.17.92 because it is not the place for it: "This is argumentative. To substantiate the statement it must be explained how ion cyclotron waves in the solar wind [ref cited] relate to field aligned currents in the magnetosphere or even in the solar magnetic field." Aarghdvaark (talk) 08:18, 30 April 2013 (UTC)[reply]

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Field-aligned vs Vertical

Brikeland's original work said that the currents were vertical, not field-aligned. The realisation that they were field-aligned only came later. It would be advisable to make this distinction in the original text to avoid confusion.

200 NOK

The "Fig.50" diagram shown in this article is the same as the one that appears on the old (1994-2017) 200 Norwegian Krøner banknote https://wiki.riteme.site/wiki/Banknotes_of_the_Norwegian_krone#Series_VII_notes_.281994-2020.29.

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"This view was scorned by other researchers"

This assertion has as its "support" The Origin of Magnetic Storms. Rather than "scorn," the final sentence is "The view that the impact of the projected particles causes luminosity remains allowable, so that Prof. Birkeland’s theory of the aurora borealis is still tenable."

Schuster's grave seems like an odd place to plant a flag.

2600:1702:2670:D6A0:2805:953B:859F:D02A (talk) 07:30, 18 December 2021 (UTC)[reply]