Coupling of Birkeland Current Rings

  1. Thomas A. Potemra
  1. G. L. Siscoe and
  2. N. U. Crooker

Published Online: 21 MAR 2013

DOI: 10.1029/GM028p0260

Magnetospheric Currents

Magnetospheric Currents

How to Cite

Siscoe, G. L. and Crooker, N. U. (1984) Coupling of Birkeland Current Rings, in Magnetospheric Currents (ed T. A. Potemra), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM028p0260

Author Information

  1. Department of Atmospheric Sciences, University of California, Los Angeles, CA 90024

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1984

ISBN Information

Print ISBN: 9780875900551

Online ISBN: 9781118664131



  • Magnetospheric currents—Congresses;
  • Plasma instabilities—Congresses


The Regions 1 and 2 Birkeland current patterns in the ionosphere can be idealized as two nearly concentric, bipolar circles or rings. The Region 1 ring is electrically connected to the outer (or poleward) boundary of the plasma sheet and the Region 2 ring to its inner (or equatorward) boundary. The physics governing the radii of these two rings are therefore different. In particular, in the absence of substorms the rate of change of the radius of the Region 1 ring is proportional to the polar cap potential, but the rate of change of the radius of the Region 2 ring is proportional to the rate of change of the polar cap potential. Thus, the rates of growth and decay of the radii of these rings will in general be different. Calculation shows that during dayside merging intervals, Ring 1 expands about 16 times faster than Ring 2. Under typical merging potentials, Ring 1 will cross the initial ring separation in about 1 hour. We identify situations in which the circles approach very near to each other (or actually attempt to cross each other) as necessitating the onset of a substorm to cause a sudden reduction in the radius of the inner ring. Thus, the behavior of the rings, which would otherwise be nearly independent of each other, are instead strongly coupled by the substorm process. The theory predicts the common radius of the coupled ring system (∼ 19° to 22°) and its dependence on the cross- polar-cap potential (∼ Φ 0.2).