Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11c..04l&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM11C-04
Physics
2407 Auroral Ionosphere (2704), 2431 Ionosphere/Magnetosphere Interactions (2736), 2708 Current Systems (2409), 2712 Electric Fields (2411), 2736 Magnetosphere/Ionosphere Interactions
Scientific paper
John Winckler provided perhaps the first evidence of the ionospheric Alfvén resonator when he discovered 0.8 s and 1.6 s periodicities in the X-ray emissions from an auroral arc. Such frequencies in the ionospheric Alfvén resonator can be excited by the ionospheric feedback instability. 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 pre-existing convection caused by the self-consistent changes in ionization and conductivity due to Alfvénic perturbations on the ionosphere. Narrow-scale Alfvén waves can be over-reflected, i.e., the reflected wave can have a larger amplitude than the incident wave, in an active ionosphere, 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 Yushu
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