Evolution with solar activity of the atomic hydrogen density at 100 kilometers of altitude

Abstract

This note clarifies an important point of the Vidal-Madjar et al. (1973) paper. In fact, some of the results presented in that paper are sensitive to the choice of the exospheric temperature. Because Vidal-Madjar et al. used a rough estimation of that parameter, neglecting the geomagnetic heating, systematic differences appeared in their results. The use of a more precise representation of the exospheric temperature here allows us to present in particular a better evaluation of the atomic hydrogen density evolution at 100-km altitude. This density variation seems to be rather large and at least a factor of 3 between 2 × 107 and 6 × 107 atoms cm−3. Furthermore, all the densities of atomic hydrogen at 500-km altitude, recalculated with the use of a better representation of the exospheric temperature parameter, are listed here for 3 consecutive years (1969, 1970, and 1971).