HR: 0800h
AN: SA31B-08    [Abstracts]
TI: Low Altitude Characteristics of Ion-Neutral Coupling in the Venus Nightside Ionosphere; an Examination Using Pioneer Venus Orbiter Data
AU: * Grebowsky, J M
EM: joseph.m.grebowsky@nasa.gov
AF: NASA Goddard Space Flight Center, Code 695, Greenbelt, MD 20771, United States
AU: Hoegy, W R
EM: wrhoegy@gmail.com
AF: Leelanau Research, 13601 S. Beaver Pond Road, Empire, MI 49630, United States
AU: Hartle, R E
EM: richard.e.hartle@nasa.gov
AF: NASA Goddard Space Flight Center, CODE 613.0, Greenbelt, MD 20771, United States
AU: Kasprzak, W T
EM: wayne.t.kasprzak@nasa.gov
AF: NASA Goddard Space Flight Center, Code 699.0, Greenbelt, MD 20771, United States
AB: Archived data, available from Pioneer Venus Orbiter (PVO) covering over a full solar cycle from before the peak of cycle 21 (December 1978) past the peak of cycle 22 (October 1992), are used to study the uncoupling of the ionosphere from the neutral atmosphere. The early measurements provide solar maximum observations when there was characteristically a substantial nightside ionosphere. The late mission measurements were made under quiet solar conditions, more comparable to the state of the ionosphere that Venus Express has encountered. Evidence of ionospheric flow is sought by a comparison of the deduced ion densities from the Orbital Ion Mass Spectrometer (which assumed collection at the spacecraft velocity) with the measured electron density from the Orbital Electron Density Probe (which was independent of the ion velocity) and by the limited availability of Orbital Retarding Potential Analyzer Ion Drift Measurements. The evidence for flow at high altitudes is very evident during solar maximum in the comparison of the ion-electron measurements and perhaps at lower altitudes during solar minimum. The influence on the measurements of superthermal ions and impact ionization at low altitudes is discussed. A search was made for the presence of ion flows at low altitudes to determine where the ion dynamics uncoupled from the neutral atmosphere. In the region of strong-ion neutral coupling the neutral composition measurements (from the Orbital Neutral Mass Spectrometer) can show departures from nominal ambient conditions when the ion velocities and densities are sufficient to drag the neutrals. Analysis of the datasets of neutral, ion, and electron densities along with the magnetic field exhibits the correlation between the ions and neutrals on a variety of scales from large-scale behavior to small-scale fluctuations.
DE: 2423 Ionization processes (7823)
DE: 2437 Ionospheric dynamics
DE: 2459 Planetary ionospheres (5435, 5729, 6026)
DE: 5405 Atmospheres (0343, 1060)
DE: 5435 Ionospheres (2459)
SC: SPA-Aeronomy [SA]
MN: 2007 Joint Assembly