HR: 17:40h
AN: SM44A-07    [Abstracts]
TI: BBELF and Electromagnetic VLF Wave Cavities in the Auroral Ionosphere
AU: * Knudsen, D J
EM: knudsen@phys.ucalgary.ca
AF: Department of Physics and Astronomy University of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4 Canada
AU: Wallis, D D
EM: wallis@sp-agency.ca
AF: Department of Physics and Astronomy University of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4 Canada
AU: Pfaff, R F
EM: robert.f.pfaff@nasa.gov
AF: NASA GSFC, Mail Code 696, Greenbelt, MD 20771 United States
AU: Bock, B J
EM: bock@phys.ucalgary.ca
AF: Department of Physics and Astronomy University of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4 Canada
AU: Bounds, S R
EM: srb@gamma.physics.uiowa.edu
AF: Department of Physics and Astronomy , University of Iowa, Iowa City, IA 52242 United States
AU: Burchill, J K
EM: burchill@phys.ucalgary.ca
AF: Department of Physics and Astronomy University of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4 Canada
AU: Clemmons, J H
EM: james.h.clemmons@aero.org
AF: The Aerospace Corporation, Mail Stop M2/260, PO Box 92957, Los Angeles, CA 90009-2957 United States
AU: Pincon, J
EM: jlpincon@cnrs-orleans.fr
AF: LPCE/CNRS, 3A ave. de la Recherche Scientifique, Orleans, 45071 France
AB: The GEODESIC sounding rocket (February 26, 2000) encountered dozens of VLF wave-filled density depletions in the auroral ionosphere at the time of a substorm onset. These cavities were similar to lower-hybrid cavities observed by many previous sounding rockets and by the Freja satellite, but with several striking differences: 1) VLF waves (near and above the lower-hybrid cutoff frequency $f_{LH}$) inside the cavities had a strong magnetic component. In fact the magnetic fields were enhanced more strongly, relative to fields outside cavities, than were VLF electric fields. 2) The cavities were found primarily in a return (downward) current region. 3) Cavity waves show no indication of counter-rotating eigenmodes that have been demonstrated previously to indicate passive scattering of externally incident VLF hiss. These points lead us to conclude that the waves were generated inside the cavities, presumably by unstable filaments of upward-drifting thermal ionospheric electrons. Broad-band electrostatic ELF waves were also strongly enhanced inside cavities, and extended up to $f_{LH}$. These waves also appear to have a geophysical origin, and likely contributed to observed ion heating up 10 eV observed in and near cavities.
DE: 2471 Plasma waves and instabilities
DE: 2704 Auroral phenomena (2407)
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting