The visual aurora is a manifestation of a system of field-aligned currents that couple the magnetosphere and ionosphere. Changes in these currents are mediated by the propagation of shear mode Alfvén waves along auroral field lines. The development of parallel electric fields on these field lines is considered in terms of the propagation characteristics of Alfvén waves. Auroral parallel electric fields occur in low-density regions where the ratio Bln maximizes. On the scale of individual auroral arcs, the electron inertial effect becomes critically important, and inhomogeneities in the Alfvén speed both parallel and perpendicular to the field must be considered to develop a complete theory of the formation of auroral arcs. Mechanisms such as nonlinear effects, ionospheric feedback or phase mixing at horizontal gradients in the Alfvén speed can act to produce the narrow scales observed in auroral arcs.
|Original language||English (US)|
|Title of host publication||Magnetospheric Current Systems, 2000|
|Editors||Ryoichi Fujii, Shin-Ichi Ohtani, Michael Hesse, Robert L. Lysak|
|Publisher||Blackwell Publishing Ltd|
|Number of pages||9|
|State||Published - 2000|
|Name||Geophysical Monograph Series|
Bibliographical noteFunding Information:
AcknowledgmentsT. his work was supportedb y NASA grant NAG5-4466 and NSF grant ATM-9502907. Supercomputer resources were provided by the Minnesota Supercomputing
© 2000 by the American Geophysical Union.