Solar EUV measurements at Venus based on photoelectron emission from the Pioneer Venus Langmuir Probe

Journal Article · Fri Jul 01 04:00:00 EDT 1988 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA093iA07p07282· OSTI ID:5182655

Brace, L H; Hoegy, W R; Theis, R F ^[1]

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1. NASA Goddard Space Flight Center, Greenbelt, MD (USA)

The photoelectron current from the Pioneer Venus Langmuir probe has provided measurements of the solar extreme ultraviolet flux at Venus since 1979. This current is the product of the photoelectric yield of the collector and the solar spectrum at wavelengths short enough to cause emission. Calculations show that approximately 51% of the emission is due to Lyman {alpha} (1,216 {angstrom}), 46% is produced by wavelengths between 550 and 1,100 {angstrom}, and less than 3% is due to wavelengths longer than Lyman {alpha}. Thus, the Langmuir probe provides a direct measure of the total solar EUV flux, including most of the wavelengths that produce the Venus ionosphere and heat and excite neutrals in the thermosphere. The measurement technique is described, and the daily average measurements of photocurrent obtained between 1979 and 1987 are presented. The photocurrents exhibit variations related to the solar cycle and solar rotation, as well as a major 7.2-month periodicity. The authors present three indices of EUV based on the measurements: (1) the photoemission current itself, (2) the total EUV flux, and (3) an F{sub 10.7}-like solar index. These are compared with related measurements made simultaneously at Earth. These data may also help solar physicists track the intensity of EUV emission regions on the Sun while they are not visible from the Earth. The EUV flux profile of a solar flare event is also illustrated. In the future the method also could be applied on a comet mission to obtain the incident solar EUV flux, to measure the EUV extinction profiles of the cometary atmosphere, and to sample directly the dust and gas environment of the comet through the ionization the dust and gas produce when they impact the collector.

• OSTI ID: 5182655
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 93:A7; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COMETS
COMPARATIVE EVALUATIONS
ELECTRIC PROBES
ELECTROMAGNETIC RADIATION
EMISSION
EVALUATION
EXTREME ULTRAVIOLET RADIATION
HEATING
LANGMUIR PROBE
MEASURING METHODS
PLANETARY IONOSPHERES
PLANETS
PROBES
RADIATIONS
SOLAR ACTIVITY
SOLAR CYCLE
SOLAR FLARES
SOLAR FLUX
SOLAR RADIATION
STELLAR RADIATION
ULTRAVIOLET RADIATION
VARIATIONS
VENUS PLANET