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Kilometer-sized waves in electron density in the Venusian nightside ionosphereAs periapsis of the Pioneer Venus Orbiter (PVO) descended into the lower nightside ionosphere of Venus in the Fall of 1992, wave-like ionospheric density strucutures began to appear on some of the volt-ampere characteristics of the Orbiter Electron Temperature Probe. The number of such events is insufficient to fully define their morphology but enough to provide an indication of the wave amplitudes, scale sizes, occurrence altitudes, and local time variation. The density variations were quasi-sinudoidal, with wavelengths of the order of 1 km along the nearly horizontal trajectory near periapsis. Nearly all of the wave events were encountered within an altitude band lying between 140 and 160 km, a region containing the steep negative N(sub e) gradient just above the ionospheric peak. The waves generally did not fill the occurrence band but were seen primarily as isolated events on curves taken intermittently as PVO crossed through the band. Peak-to-trough amplitudes (delta N/N) were in the range of 5% to 50%. The latitudinal extent of the waves could not be resolved because volt-ampere curves were obtained only intermittent, however, their occurrence on both inbound and outbound passages through the wave band suggests that the waves sometimes exist in layers that extend over at least 15 deg of latitude. The generation mechanism for these waves is unknown, but we suspect that it involves the steep density gradient that separates the main nightside ionosphere from the tenuous, and probably rapidly flowing plasma above.
Document ID
19950039566
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Brace, Larry H.
(Univ. of Michigan, Ann Arbor, MI United States)
Date Acquired
August 16, 2013
Publication Date
December 14, 1993
Publication Information
Publication: Geophysical Research Letters
Volume: 20
Issue: 23
ISSN: 0094-8276
Subject Category
Lunar And Planetary Exploration
Accession Number
95A71165
Funding Number(s)
CONTRACT_GRANT: NAG2-644
Distribution Limits
Public
Copyright
Other

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