Physics – Space Physics
Scientific paper
Aug 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1160l&link_type=abstract
Journal of Geophysical Research (Space Physics), Volume 107, Issue A8, pp. SIA 6-1, CiteID 1160, DOI 10.1029/2001JA000308
Physics
Space Physics
44
Ionosphere: Auroral Ionosphere (2704), Ionosphere: Current Systems (2708), Ionosphere: Electric Fields (2712), Ionosphere: Ionosphere/Magnetosphere Interactions (2736)
Scientific paper
The ionospheric feedback instability has been invoked as a possible mechanism for the formation of narrow auroral arcs. This instability can excite eigenmodes of both field line resonances and the ionospheric Alfvén resonator, producing narrow-scale structures. Although the basic dispersion relation of this instability has been discussed for both of these cases, the energetics of this instability has not been discussed quantitatively and questions remain as to the nonlinear evolution of this instability. The free energy for this instability comes from the reduction of Joule heating due to the preexisting convection caused by the self-consistent changes in ionization and conductivity due to Alfvénic perturbations on the ionosphere. In an active ionosphere, narrow-scale Alfvén waves can be overreflected; i.e., the reflected wave can have a larger amplitude than the incident wave, with the extra energy coming from a local reduction of Joule heating. Recombination produces a damping of this instability, particularly for high background conductivity, indicating that this instability operates best in a dark background ionosphere. This feedback interaction produces narrow-scale currents when strong gradients in the conductivity are produced, and effects from parallel resistivity or possibly kinetic effects will become important in its evolution. Theoretical constraints on low-spatial resolution observations of the energy dissipated by precipitation as opposed to Joule heating will be discussed.
Lysak Robert L.
Song Yan
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