Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm11a0795d&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM11A-0795
Physics
2720 Energetic Particles, Trapped, 2730 Magnetosphere: Inner, 2752 Mhd Waves And Instabilities, 7827 Kinetic And Mhd Theory
Scientific paper
The poloidal mode is most often observed at the outer edge of the ring current during stormtime enhancements. It is usually thought to be driven by the gradient in the hot particle pressure and/or pressure anisotropy (parallel and perpendicular to the magnetic field). Besides large azimuthal mode number m ( ~ 100), these waves have period >= 100 s (Pc 4 and 5), dominant magnetic fluctuations in the radial (hence the name ``poloidal'') or parallel direction, and second harmonic structure (single node at equator) for the azimuthal component of the electric field. One crucial question is what determines the radial extent of the mode. Zero temperature MHD predicts that the mode structure will be singular about the mode resonant surface. Vetoulis and Chen [1994,1996] examined the finite pressure poloidal mode using a WKB expansion in the radial direction. They proposed that a finite width poloidal mode might exist in a region where there is a dip in the square of the poloidal frequency f pol. The energy may leak out of the region of localization to be absorbed at a toroidal (magnetic fluctuations in the azimuthal direction) resonance, but if the dip in f pol2 is large enough, the rate of leakage may be slow [Denton and Vetoulis, 1998]. A special kind of pressure profile is required, one having a large second derivative with respect to L shell. Although the theory provides a pleasing explanation of the radial structure of the mode, it has never been demonstrated for any wave event whether the pressure profile in the vicinity of the mode is consistent with the theory. In this paper, we examine data from the Scatha and AMPTE/IRM spacecraft during times for which poloidal waves are observed. Using the observed radial pressure variation, we calculate the poloidal mode frequency versus radius using MHD and compare the results to the predications of the Vetoulis and Chen theory. Denton, R.E., and G. Vetoulis, J. Geophys. Res., 103, 6729, 1998. Vetoulis, G., and L. Chen, Geophys. Res. Lett., 21, 2091, 1994; J. Geophys. Res., 101, 15,441, 1996.
Denton Richard E.
Hudson Mary K.
Lessard Marc R.
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