Alfven Wave Propagation in the Presence of Auroral Density Cavities

Details Alfven Wave Propagation in the Presence of Auroral Density Cavities Alfven Wave Propagation in the Presence of Auroral Density Cavities

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm53d..03l&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM53D-03

Physics

2704 Auroral Phenomena (2407), 2712 Electric Fields (2411), 2736 Magnetosphere/Ionosphere Interactions (2431), 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 7836 Mhd Waves And Instabilities (2149, 2752, 6050)

Scientific paper

Observations in the auroral zone from, for example, the FAST satellite have indicated that deep density cavities exist. These cavities imply a large perpendicular gradient to the Alfvén speed, which can lead to phase mixing and the formation of narrow-scale electric and magnetic field structures. Such cavities can modify the mode structure of the Alfvén waves leading to the possibility of discrete cavity modes trapped within the cavity, especially in the case where the plasma inside the cavity is warm (i.e., that the electron thermal speed is greater than the local Alfvén speed) and the outside plasma is cold. In the auroral zone, the situation is complicated by the fact that there are strong parallel gradients in the Alfvén speed (the so-called ionospheric Alfvén resonator) in addition to the perpendicular gradients. Coupling to the Pedersen and Hall conductances of the ionosphere also affects the propagation of these waves. Numerical modeling of this situation has been carried out, indicating that such waves have outward phase motions but inward Poynting flux, consistent with the Alfvén wave dispersion relation modified by electron inertia as well as with FAST observations.

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