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ULF waves in the Io torus: Ulysses observationsThroughout the Io torus, Ulysses has observed intense ultralow frequency (ULF) wave activity in both electric and magnetic components. Such ULF waves have been previously suggested as the source of ion precipitation leading to Jovian aurorae. The peaks of the wave spectra are closely related to the ion cyclotron frequencies, which is evidence of the waves being ion cyclotron waves (ICWs). Analysis of the dispersion relation using a multicomponent density model shows that at high latitudes (approximately 30 deg), peak frequencies of the waves fall into L mode branches of guided or unguided ICWs. Near the equator, in addition to the ICWs below f(sub cO(2+)), there are strong signals at approximately 10 Hz which require an unexpectedly large energetic ion temperature anistropy to be explained by the excitation of either convective or nonconvective ion cyclotron instabilities. Their generation mechanism remains open for the future study. Evaluation of the Poynting vector and the dispersion relation analysis suggest that the waves near the equator had a small wave angle relative to the magnetic field, while those observed at high latitudes were more oblique. The polarization of the waves below f(sub cH(+)) is more random than that of the whistler mode waves, but left-hand-polarized components of the waves can still be seen. The intensity of the ICWs both near the equator and at high latitudes are strong enough to meet the requirement for producing strong pitch angle scattering of energetic ions.
Document ID
19950046644
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Lin, Naiguo
(Minnesota Univ. Minneapolis, MN, United States)
Kellogg, P. J.
(Minnesota Univ. Minneapolis, MN, United States)
Macdowell, R. J.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Mei, Y.
(California Univ. Los Angeles, CA, United States)
Cornilleau-Wehrlin, N.
(Centre de Recherche en Physique de l'Environment Issy les Moulineaux, Fra, United States)
Canu, P.
(Centre de Recherche en Physique de l'Environment Issy les Moulineaux, Fra, United States)
De Villedary, C.
(Centre de Recherche en Physique de l'Environment Issy les Moulineaux, Fra, United States)
Rezeau, L.
(Centre de Recherche en Physique de l'Environment Issy les Moulineaux, Fra, United States)
Balogh, L.
(Imperial Coll. of Science and Technology London, United Kingdom)
Forsyth, R. J.
(Imperial Coll. of Science and Technology London, United Kingdom)
Date Acquired
August 16, 2013
Publication Date
December 1, 1993
Publication Information
Publication: Journal of Geophysical Research
Volume: 98
Issue: A12
ISSN: 0148-0227
Subject Category
Astrophysics
Accession Number
95A78243
Funding Number(s)
CONTRACT_GRANT: NAS5-31219
Distribution Limits
Public
Copyright
Other

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