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Solar cycle study of interplanetary Lyman-alpha variations - Pioneer Venus Orbiter sky background results
Ajello, J. M.; Stewart, A. I.; Thomas, G. E.; Graps, A.
AA(California Institute of Technology, Jet Propulsion Laboratory, Pasadena), AB(Colorado, University, Boulder), AC(Colorado, University, Boulder), AD(Colorado, University, Boulder)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 317, June 15, 1987, p. 964-986. (ApJ Homepage)
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NASA/STI Keywords:
Interplanetary Medium, Lyman Alpha Radiation, Solar Cycles, Solar Wind, Ultraviolet Spectra, Hydrogen Atoms, Isophotes, Pioneer Venus 1 Spacecraft, Solar Activity, Solar Flux, Solar Wind Velocity, Twenty-Seven Day Variation
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The authors have completed an analysis of the Pioneer Venus (PV) interplanetary Lyalpha (IP Lyalpha) sky background observations obtained from 1979 to 1985. This data set completes the first solar cycle maximum to minimum study of IP Lyalpha. A reanalysis of earlier IP Lyalpha observations by OGO 5 and Mariner 10 is also presented. It is found that the 27 day disk-averaged variation of the integrated solar Lyalpha flux and the longitudinally averaged IP Lyalpha intensities from Pioneer Venus observations have the same solar cycle variation of 1.8 from 1979 to 1985. This variation leads to an estimate of the variation of the solar line center flux over the solar cycle. The analysis shows that the interplanetary H density is 0.07±0.01 cm-3. Thus the interplanetary H/He ratio far from the Sun inside the heliopause is 7±3. A general IP Lyalpha backscatter model is developed.

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