File:420px-Magnetic-rope.png

Summary[edit]

The self-constricting magnetic field lines and current paths in a Birkeland current (or magnetic rope). The current is strongest at the axis and becomes weaker further away. Currents flow parallel to the magnetic field, and derives partly from an external axial field and partly from the toroidal field produced by the current itself.

Image credit: http://history.nasa.gov/SP-345/ch15.htm#250 (and arrows coloured by myself)

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