Analysis of Pioneer Venus Orbiter ultraviolet spectrometer Lyman α data from near the subsolar region

Pioneer Venus Orbiter ultraviolet spectrometer data from 20 orbits which span 3 years have been analyzed to determine the atomic hydrogen number density and vertical flux at the exobase as a function of solar zenith angle, F10.7 index, and spacecraft latitude. From 1979 through 1981 the exobase number density nc and flux ϕc are remarkably constant at nc = 6.0 ± 1.5 × 104 cm−3 and ϕc = 7.5 ± 1.5 × 107 cm−2 s−1 in the subsolar region. The integrated vertical column density above 110 km is 3.6 ± 1 × 1013 cm−2. An empirical relationship is determined between the line center solar flux at H Lyman α, πF0, and the F10.7 index. At 1 AU, πF0 = (2.0 + 1.1 × 10−2F10.7) × 1011 photons cm−2 s−1 Å−1.