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VLF waves in the foreshockPlasma waves observed in the VLF range upstream of planetary bow shocks not only modify the particle distributions, but also provide important information about the acceleration processes that occur at the bow shock. Electron plasma oscillations observed near the tangent field line in the electron foreshock are generated by electrons reflected at the bow shock through a process that has been referred to as Fast Fermi acceleration. Fast Fermi acceleration is the same as shock-drift acceleration, which is one of the mechanisms by which ions are energized at the shock. We have generated maps of the VLF emissions upstream of the Venus bow shock, using these maps to infer properties of the shock energization processes. We find that the plasma oscillations extend along the field line up to a distance that appears to be controlled by the shock scale size, implying that shock curvature restricsts the flux and energy of reflected electrons. We also find that the ion acoustic waves are observed in the ion foreshock, but at Venus these emissions are not detected near the ULF forshock boundary. Through analogy with terrestrial ion observations, this implies that the ion acoustic waves are not generated by ion beams, but are instead generated by diffuse ion distributions found deep within the ion foreshock. However, since the shock is much smaller at Venus, and there is no magnetosphere, we might expect ion distributions within the ion foreshock to be different than at the Earth. Mapping studies of the terrestrial foreshock similar to those carried out at Venus appear to be necessary to determine if the inferences drawn from Venus data are applicable to other foreshocks.
Document ID
19950053617
Document Type
Reprint (Version printed in journal)
Authors
Strangeway, R. J. (UCLA, Los Angeles, CA US, United States)
Crawford, G. K. (Kyoto Univ. Kyoto, Japan)
Date Acquired
August 16, 2013
Publication Date
January 1, 1995
Publication Information
Publication: Advances in Space Research
Volume: 15
Issue: 9-Aug
ISSN: 0273-1177
Subject Category
ASTROPHYSICS
Funding Number(s)
CONTRACT_GRANT: NAGW-3497
CONTRACT_GRANT: NAG2-485
Distribution Limits
Public
Copyright
Other

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