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Linear and nonlinear properties of the ULF waves driven by ring-beam distribution functionsThe problem of the exitation of obliquely propagating magnetosonic waves which can steepen up (also known as shocklets) is considered. Shocklets have been observed upstream of the Earth's bow shock and at comets Giacobini-Zinner and Grigg-Skjellerup. Linear theory as well as two-dimensional (2-D) hybrid (fluid electrons, particle ions) simulations are used to determine the properties of waves generated by ring-beam velocity distributions in great detail. The effects of both proton and oxygen ring-beams are considered. The study of instabilities excited by a proton ring-beam is relevant to the region upstream of the Earth's bow shock, whereas the oxygen ring-beam corresponds to cometary ions picked up by the solar wind. Linear theory has shown that for a ring-beam, four instabilities are found, one on the nonresonant mode, one on the Alfven mode, and two along the magnetosonic/whistler branch. The relative growth rate of these instabilities is a sensitive function of parameters. Although one of the magnetosonic instabilities has maximum growth along the magnetic field, the other has maximum growth in oblique directions. We have studied the competition of these instabilities in the nonlinear regime using 2-D simulations. As in the linear limit, the nonlinear results are a function of beam density and distribution function. By performing the simulations as both initial value and driven systems, we have found that the outcome of the simulations can vary, suggesting that the latter type simulations is needed to address the observations. A general conclusion of the simulation results is that field-aligned beams do not result in the formation of shocklets, whereas ring-beam distributions can.
Document ID
19950056460
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Killen, K.
(University of California, La Jolla, CA United States)
Omidi, N.
(University of California, La Jolla, CA United States)
Krauss-Varban, D.
(University of California, La Jolla, CA United States)
Karimabadi, H.
(University of California, La Jolla, CA United States)
Date Acquired
August 16, 2013
Publication Date
April 1, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: A4
ISSN: 0148-0227
Subject Category
Geophysics
Accession Number
95A88059
Funding Number(s)
CONTRACT_GRANT: NAG5-1492
CONTRACT_GRANT: NAGW-1806
Distribution Limits
Public
Copyright
Other

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