The aurora on Jupiter, powered by Jovian Birkeland currents [Ref.]

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. They are caused by the movement of a plasma perpendicular to a magnetic field. Birkeland currents often show filamentary, or twisted "rope-like" magnetic structure. They are sometimes referred to as field-aligned currents. Jump to: navigation, search Image File history File links Jupiter-aurora. ... Jump to: navigation, search Image File history File links Jupiter-aurora. ... The word plasma has a Greek root which means to be formed or molded (the word plastic shares this root). ...

Originally Birkeland currents referred to electric currents that contribute to the aurora, caused by the interaction of the plasma in the Solar Wind with the Earth's magnetosphere. 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. The currents were predicted in 1903 by Norwegian explorer and physicist Kristian Birkeland, who undertook expeditions into the Arctic Circle to study the aurora. Aurora is the Latin word for dawn. It can refer to: Aurora was the ancient Roman equivalent of Eos, the ancient Greek goddess of the dawn. ... The word plasma has a Greek root which means to be formed or molded (the word plastic shares this root). ... A solar wind is a stream of charged particles (i. ... A magnetosphere is the region around an astronomical object, in which phenomena are dominated by its magnetic field. ... The ionosphere is the part of the atmosphere that is ionized by solar radiation. ... Kristian Birkeland Kristian Birkeland (December 13, 1867 - June 15, 1917) was born in Christiania (Oslo today) and wrote his first scientific paper at the age of 18. ...

Professor Emeritus of the Alfvén Laboratory in Sweden, Carl-Gunn Fälthammar wrote (1986): "A reason why Birkeland currents are particularly interesting is that, in the plasma forced to carry them, they cause a number of plasma physical processes to occur (waves, instabilities, fine structure formation). These in turn lead to consequences such as acceleration of charged particles, both positive and negative, and element separation (such as preferential ejection of oxygen ions). Both of these classes of phenomena should have a general astrophysical interest far beyond that of understanding the space environment of our own Earth." A plasma is a quasineutral, electrically conductive fluid. ... Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. ... Plasma acceleration is a technique for accelerating charged particles, such as electrons and ions, using an electric field associated with an electron plasma wave. ...

Auroral-like Birkeland currents created by scientist Kristian Birkeland in his terrella, featuring a magnetised anode globe in an evacutated chamber.

Jump to: navigation, search Image File history File links Birkeland-anode-globe-fig259. ... Jump to: navigation, search Image File history File links Birkeland-anode-globe-fig259. ... Kristian Birkeland Kristian Birkeland (December 13, 1867 - June 15, 1917) was born in Christiania (Oslo today) and wrote his first scientific paper at the age of 18. ... Categories: Stub ...

Characteristics

Auroral Birkeland currents can carry about 1 million amps [Ref.]. They can heat up the upper atmosphere which results in increased drag on low altitude satellites.

Birkeland currents can also be created in the laboratory with multi-terra watt pulse power generators. The resulting cross-section pattern indicates a hollow beam of electron in the form of a circle of vortices, a formation called the diocotron instability (similar, but different to the Kelvin-Helmholtz instability), that subsequently leads to filamentation. Such vortices can be seen in aurora as "auroral curls". This is an article on the real vortex phenomena. ... Categories: Physics stubs | Fluid dynamics ...

Birkeland currents are also one of a class of plasma phenonena called a z-pinch, so named because the azimuthal magnetic fields produced by the current pinches the current into a filamentary cable. 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. 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]. Jump to: navigation, search The Z machine at Sandia National Laboratories in Albuquerque, New Mexico. ... This article covers the physics of gravitation. ...

Electrons moving along a Birkeland current will also spiral around magnetic field lines. If the electrons approach relativistic velocities (ie. the speed of light), they will emit synchrotron radiation that includes radio, optical (ie. light), x-rays, and gamma rays. Synchrotron radiation is electromagnetic radiation, similar to cyclotron radiation, but generated by the acceleration of relativistic electrons (i. ... See also list of optical topics. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... This article is about electromagnetic radiation. ...

Cosmic Birkeland Currents

The Cygnus Loop has characteristics of an interstellar Birkeland current: (1) A plasma medium (2) Filamentation (3) Braiding, twisted "rope-like" structure. [Ref.]

Plasma physicists suggest that many structures in the universe exhibiting filamentation are due to Birkeland currents. Peratt (1992) notes that "Regardless of scale, the motion of charged particles produces a self-magnetic field that can act on other collections of charged particles, internally or externally. Plasmas in relative motion are coupled via currents that they drive though each other". (See Plasma scaling). Examples include: Jump to: navigation, search Image File history File links Cygnus-loop. ... Jump to: navigation, search Image File history File links Cygnus-loop. ... The parameters of plasmas, including their spatial and temporal extent, vary by many orders of magnitude. ...

History

Kristian Birkeland predicted auroral electrojets in 1908. He wrote: "[p.95 ..] the currents there are imagined as having come into existence mainly as a secondary effect of the electric corpuscles from the sun drawn in out of space, and thus far come under the second of the possibilities mentioned above. [p.105 ..] Fig. 50a represents those in which the current-directions at the storm-centre are directed westwards, and 50b those in which the currents move eastwards."

The history of Birekland Currents appears to mired in politics, and is summarised by Stephen G. Brush in his article "Alfvén's Programme in Solar System Physics" (IEEE Trans. Plasma Science, Vol. 20 No. 6, Dec 1992). Jump to: navigation, search Image File history File links Download high resolution version (878x632, 53 KB) Summary Kristian Birkeland predicted auroral electrojets in 1908. ... Jump to: navigation, search Image File history File links Download high resolution version (878x632, 53 KB) Summary Kristian Birkeland predicted auroral electrojets in 1908. ...

After Kristian Birkeland suggested "currents there are imagined as having come into existence mainly as a secondary effect of the electric corpuscles from the sun drawn in out of space," (1908), his ideas were generally ignored in favour of an alternative theory from British mathematician Sydney Chapman. Sydney Chapman (January 29, 1888 – June 16, 1970) was a British astronomer and geophysicist. ...

In 1939, the Swedish Engineer and plasma physicist Hannes Alfvén promoted Birkeland's ideas in a paper published on the generation of the current from the Solar Wind. One of Alfvén's colleagues, Rolf Boström, also used field-aligned currents in a new model of auroral electrojets (1964). Hannes Olof Gösta Alfvén (May 30, 1908; Norrköping, Sweden - April 2, 1995; Djursholm, Sweden) was a Swedish electrical power engineer. ...

In 1966 Alfred Zmuda, J.H. Martin, and F.T.Heuring reported their findings of magnetic disturbance in the aurora, using a satellite magnetometer, but did not mention Alfvén, Birkeland, or field-aligned currents, even after it was brought to their attention by editor of the space physics section of the journal, Alex Dressler.

In 1967 Alex Dessler and one of his graduates students, David Cummings, wrote an article arguing that Zmuda et al had indeed detected field align-currents. Even Alfvén subsequently credited (1986) that Dessler "discovered the currents that Birkeland had predicted" and should be called Birkeland-Dessler currents.

In 1969 Milo Schield, Alex Dessler and John Freeman, used the name "Birkeland currents" for the first time. In 1970, Zmuda, Armstrong and Heuring wrote another paper agreeing that their observations were compatible with field-aligned currents as suggested by Cummings and Dessler, and by Bostrom, but again made no mention of Alfvén and Birkeland.

1n 1970, a group from Rice University also suggested that the results of an earlier rocket experiment was consistent with field-aligned currents, and credited the idea to Boström, and Dessler and his colleagues, rather than Alfvén and Birkeland. In the same year, Zmudu and Amstrong did credit Alfvén and Birkeland, but felt that they ".. cannot definitely identify the particles constituting the field-aligned currents."

It wasn't until 1973 that the navy satellite Triad, carrying equipment from Zmuda and James Armstrong, detected the magnetic signatures of two large sheets of electric current. Their papers (1973, 1974) reported "more conclusive evidence" of field-aligned currents, citing Cummings and Dessler but not mentioning Birkeland or Alfven.

It had taken 65 years to confirm Birkeland's original predictions.

References

The complex self-constricting magnetic field lines and current paths in a Birkeland current that may develop in a plasma [Ref]

• Alfvén, Hannes (1939), Theory of Magnetic Storms and of the Aurorae, K. Sven. Vetenskapsakad. Handl., ser. 3, vol. 18, no. 3, p. 1, 1939. Reprinted in part, with comments by A. J. Dessler and J. Wilcox, in Eos, Trans. Am. Geophys. Un., vol. 51, p. 180, 1970.
• Alfvén, Hannes, "Double layers and circuits in astrophysics," IEEE Trans. Plasma Sci., vol. 14, p. 779, 1986 (on p. 787).
• Armstrong J. C.; Zmuda, A. J.; "Field-aligned current at 1100km in the auroral region measured by satellite," J. Geophys. Res., vol. 75, p. 7122, 1970.
• Armstrong J. C.; Zmuda, A. J.; "Triaxial magnetic measurements of field-aligned currents at 800 kilometers in the auroral region: Initial results," J. Geophys. Res., vol. 78, p. 6802, 1973; Zmuda A. J.; Armstrong J. C.; "The diurnal flow pattern of field-aligned currents," J. Geophys. Res., vol. 79, p. 4611, 1974.
• Birkeland, Kristian (1908), The Norwegian Aurora Polaris Expedition 1902-1903
• Bostrom, R., "A model of the auroral electrojets," J. Geophys. Res., vol. 69, p. 4983, 1964.
• Cummings, W. D.; Dessler, A. J.; "Field-aligned currents in the magnetosphere," J. Geophys. Res., vol. 72, p. 1007, 1967.
• Peratt, Anthony (1992), Physics of the Plasma Universe, "Birkeland Currents in Cosmic Plasma" (p.43-92)
• Rostoker, G.; Armstrong, J. C.; Zmuda, A. J. (1975), "Field-aligned current flow associated with intrusion of the substorm-intensified westward electrojet into the evening sector", Journal of Geophysical Research, vol. 80, Sept. 1, 1975, p. 3571-3579
• Schield, M. A.; Freeman, J. W.; Dessler, A. J., (1969) "A Source for Field-Aligned Currents at Auroral Latitudes", Journal of Geophysical Research, Vol. 74, p.247
• Zmuda, A. J.; Martin, J. H.; Heuring, F. T. "Transverse magnetic disturbances at 1100 kilometers in the auroral region," J . Geophys. Res., vol. 71, p. 5033, 1966.
• Zmuda, A. J.; Armstrong, J. C.; Heuring, F. T. "Characteristics of transverse magnetic disturbances observed at 1100 km in the auroral oval", J. Geophys. Res., vol. 75, p. 4757, 1970.

Image File history File links Download high resolution version (560x800, 33 KB) Summary The self-constricting magnetic field lines and current paths in a Birkeland current (or magnetic rope). ... Image File history File links Download high resolution version (560x800, 33 KB) Summary The self-constricting magnetic field lines and current paths in a Birkeland current (or magnetic rope). ... The word plasma has a Greek root which means to be formed or molded (the word plastic shares this root). ...

See also

(Peer-reviewed online in full)

• Potemra, T. A. "Birkeland currents in the earth's magnetosphere", from a Special Issue of Astrophysics and Space Science" Dedicated to Hannes Alfvén on 80th Birthday

• Alfvén, Hannes, On the Filamentary Structure of the Solar Corona (1963)

• Alfvén, Hannes, Currents in the Solar Atmosphere and a Theory of Solar Flares (1967)

• Alfvén, Hannes, On the Importance of Electric Fields in the Magnetosphere and Interplanetary Space (1967)

• Cloutier, P. A.; Anderson, H. R. Observations of Birkeland currents (1975)

• Potemra, T. A. Observation of Birkeland currents with the TRIAD satellite (1978)

Web site links

• Plasma fibres and Walls
• Electric Currents from Space
• Electric Currents from Space--History
• Electric Currents and Transmission Lines in Space
• HU/APL Global Birkeland Currents