Response of nightside ionosphere and ionotail of Venus to variations in solar EUV and solar wind dynamic pressure

Journal Article · Sun Apr 01 04:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA095iA04p04075· OSTI ID:5223115

Brace, L H; Theis, R F ^[1]; Mihalov, J D ^[2]

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1. NASA Goddard Space Flight Center, Greenbelt, MD (United States)
2. NASA Ames Research Center, Moffett Field, CA (United States)

It is a widely held view that the Venusian nightside ionosphere, at least at solar maximum, is formed primarily by the nightward flow of ions which are created on the dayside by photoionization. Suprathermal electrons are believed to be a secondary source. This view is brought into question by in situ measurements made from the Pioneer Venus Orbiter (PVO). Measurements of the electron density, N{sub e}, the solar wind dynamic pressure, P{sub sw}, and the total solar EUV flux, V{sub EUV}, are employed to examine variations in the average N{sub e} of the nightside ionosphere in response to variations in the solar wind and the solar EUV flux. The authors examine both the main nightside ionosphere (142-600 km) and the nightside ionosphere at very high altitudes (1400-2500 km), a region known as the ionotail. They find that the orbit to orbit variations in the average N{sub e} are caused primarily by changes in P{sub sw} produce more or less proportional decreases in the density at all altitudes. This behavior is consistent with the view that nightward ion flow is controlled by the height of the dayside ionopause, which should be depressed at times of high P{sub sw}. The influence of the EUV flux on N{sub e} variations in the ionotail and in the main ionosphere is quite different at the two altitudes, however. The average ionotail density varies directly with the solar EUV flux, while the average density in the main ionosphere varies slightly inversely with the EUV flux. The absence of a strong positive correlation in the lower ionosphere is inconsistent with the nightward flow theory.

• OSTI ID: 5223115
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:A4; ISSN JGREA; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CORRELATIONS
DIMENSIONS
ELECTRON DENSITY
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
FUNCTIONS
HEIGHT
ION DRIFT
IONIZATION
LEPTONS
PHOTOIONIZATION
PLANETARY IONOSPHERES
PLANETS
PLASMA DENSITY
PLASMA PRESSURE
PRESSURE EFFECTS
RADIATIONS
RESPONSE FUNCTIONS
SOLAR ACTIVITY
SOLAR RADIATION
SOLAR WIND
STELLAR RADIATION
VARIATIONS
VENUS PLANET