Ionization contribution by cosmic X-rays

Abstract

The contribution of cosmic X rays in the production of ionization in the nighttime D region is discussed in the light of observed X-ray flux emissions from the various celestial X-ray sources and from the galactic background. The cumulative effect of several sources when they are in transit at close time intervals can amount to a sizable fraction of all nighttime sources, which consist principally of scattered Ly α and Ly β. Above 95 km, the Ly β contribution is generally far in excess of the production due to cosmic X rays, but, at and around 90 km, the relative importances of cosmic X rays and scattered Ly α depend on the variation of the scattered Ly α flux, its variations with time, the nighttime concentrations of nitric oxide, and on the variations in the flux from the sources. Since some of these are uncertain, exact contributions are difficult to establish, but a marginal ionospheric effect around 90 km levels from cosmic X-ray sources seems possible at low latitudes.