The role of nonflare X radiation in the<i>D</i>region

Abstract

A compilation of short wavelength nonflare solar X-ray spectrums is used to evaluate the role of X radiation in the formation of the unperturbed D region. lonization contributions by solar hydrogen Lyman α and galactic cosmic radiation are compared with the contribution by X radiation. It is concluded that the pronounced dependence of X-ray flux on solar activity results in a model in which the D region is controlled by X radiation. At solar maximum the D region is found to be produced by X radiation and cosmic radiation. Lyman α becomes important at middle D-region altitudes about halfway between solar maximum and solar minimum. At solar minimum the D region is produced by cosmic, Lyman α, and X radiation in the lower, middle, and upper altitudes, respectively.