Physics
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993georl..20.2727h&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 20, no. 23, p. 2727-2730
Physics
4
Electron Energy, Extreme Ultraviolet Radiation, Ions, Night, Planetary Ionospheres, Solar Activity Effects, Solar Planetary Interactions, Venus (Planet), Electron Density Profiles, Pioneer Venus 1 Spacecraft, Planetary Magnetic Fields, Spatial Distribution, Temporal Distribution, Transport Properties
Scientific paper
Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter (PVO), and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV flux effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.
Brace Larry H.
Ho Chang-Ming
Luhmann Janet G.
Russell Christopher T.
Strangeway Robert J.
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