Formation of Auroral Arcs by Plasma Sheet Processes

  1. S.-I. Akasofu and
  2. J.R. Kan
  1. W. J. Heikkila

Published Online: 26 MAR 2013

DOI: 10.1029/GM025p0266

Physics of Auroral Arc Formation

Physics of Auroral Arc Formation

How to Cite

Heikkila, W. J. (1981) Formation of Auroral Arcs by Plasma Sheet Processes, in Physics of Auroral Arc Formation (eds S.-I. Akasofu and J.R. Kan), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM025p0266

Author Information

  1. University of Texas at Dallas, Richardson, Texas 75080

Publication History

  1. Published Online: 26 MAR 2013
  2. Published Print: 1 JAN 1981

ISBN Information

Print ISBN: 9780875900506

Online ISBN: 9781118664360



  • Auroras—Addresses, essays, lectures


There is a cross-tail electric field, and a neutral sheet current in the plasma sheet, both in the dawn-dusk direction; thus E.J. is positive, and there is particle energization. This corresponds to a power dissipation of about 1012 watts out to lunar orbit under average conditions. If the first adiabatic invariant is conserved, the mirror points of all particles will be lowered as they are energized, by any mechanism. Particles which already mirror at low altitudes will be precipitated. In the distant plasma sheet, it is likely that curvature drift is the most important source of drift parallel to the electric field, leading to what is commonly called Fermi acceleration of the particles. This energization mechanism is proportional to the neutral sheet current density. It is a form of field-aligned acceleration, with rapid lowering of mirror points, due to the transverse electric field in the plasma sheet. The process will work for both negative and positive particles. We now postulate a filamentation of the neutral sheet current. The maximum energization by curvature drift, and the accompanying intense precipitation, will form an auroral band or arc along the sheet of magnetic field lines that maps out to the local enhancement of the crosstail current, explaining inverted V events. It seems possible that acceleration by a parallel component of the electric field at low altitudes may be a minor effect under normal conditions, but may take on increased importance with intense arcs, or during substorms.