Illustration of Birkeland current

1908 Birkeland current

The book of science

Tom Sharp

Kristian Birkeland electromagnetism Illustration of Birkeland current

Birkeland current

On an expedition to study the aurora north of the Arctic Circle, Kristian Birkeland observed that when the aurora appeared needles of magnetometers changed direction, and he realized that the solar wind passing through the earth’s magnetic field created electric currents responsible for the aurora.

Auroral electrojets

Plasma moves through the ionosphere driven by the solar wind guided by the magnetosphere. In the upper lattitudes of earth’s atmosphere, auroral electrojects circulate.


Birkeland currents produce azimuthal magnetic fields that pinch the current into filamentary cables twisting in spirals. Watch me twist, subject to forces I cannot feel, as I try to defend my narrow beliefs.

Birkeland currents are carried by electrons freed from oxygen, helium, and hydrogen nuclei, that is, by ionospheric plasmas.

Birkeland was not the first scientist to propose the existence of electrically conducting regions of the atmosphere. Around 1839, Carl Friedrich Gauss had proposed that these could account for observed variations of the earth’s magnetic field.

See also in The book of science:

Readings in wikipedia: