Birkeland current

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.

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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.

Related Topics:
Aurora - Plasma - Solar Wind - Magnetosphere - Ionosphere - Kristian Birkeland

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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."

Related Topics:
Waves - Instabilities - Acceleration of charged particles

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