Electric Fields, Birkeland Currents and Electron Precipitation in the Vicinity of Discrete Auroral Arcs
- S.-I. Akasofu and
- J.R. Kan
Published Online: 26 MAR 2013
Copyright 1981 by the American Geophysical Union.
Physics of Auroral Arc Formation
How to Cite
Burke, W. J. (1981) Electric Fields, Birkeland Currents and Electron Precipitation in the Vicinity of Discrete Auroral Arcs, in Physics of Auroral Arc Formation (eds S.-I. Akasofu and J.R. Kan), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM025p0164
- Published Online: 26 MAR 2013
- Published Print: 1 JAN 1981
Print ISBN: 9780875900506
Online ISBN: 9781118664360
- Auroras—Addresses, essays, lectures
Simultaneous measurements of electric fields, Birkeland currents and electron fluxes are presented from one winter, polar-cap and two auroral zone passes, of the USAF satellite S3-2. At the time of the polar-cap pass the IMF had a 7.1 nT northward component. The large-scale electric field was highly irregular. Five upward Birkeland current sheets accompanied by enhanced electron precipitation are taken as signatures of sun-aligned arcs in the polar cap. These current sheets were all embedded in regions of negative space charge. The precipitating electrons had average energies <2keV, and carried energy fluxes up to 3 ergs/(cm2-sec-ster).
During a substorm period “electrostatic shock” like structures were observed at altitudes of 1050 and 1350 km, on the dawn and dusk sides of the auroral oval. In the dawn (dusk) side event the transverse magnetic field component deflected by 100 (300) nT and recovered in 4 (7) seconds. In both cases the satellite traversed an upward current sheet in 1/4 seconds corresponding to average current densities of 45 and 135 μ A/m2 contained in latitudinal widths of <2 km. Between the current sheets where JII ≈ 0 the electric field rotated and returned to its original configuration. Spatial aliasing of electron measurements precludes a positive identification of the energy distribution of the current carriers. Return current sheets were more spatially spread out, having maximum intensities of 10 to 15 μ A/m2.
As a whole, the data support a magnetospheric rather than an ionospheric generator model of discrete arcs.