Ionization rates due to the attenuation of 1‐100 Å nonflare solar X rays in the terrestrial atmosphere

Solar fluxes and absorption cross sections are reviewed for 1‐100 Å X rays. Review of the cross sections is extended to 300 Å to more completely validate the cross sections selected at shorter wavelengths. Convenient lists of the solar flux and appropriate cross sections are provided, and simple accurate formulas are given for them. Numerical rates for q, the total ion‐pair production rate, are tabulated for three nonflare solar conditions at various altitudes and solar zenith angles. Production rates due to other ionization sources important at these altitudes and angles are also tabulated. We show that q is distributed as 0.62∶0.17∶0.14∶0.07 for q(N2+)∶ q(O2+)∶ q(N+)∶q (O+) for 1‐100 Å X rays absorbed in normal composition air. The atomic ions result from dissociative ionization, mainly by photoelectrons. About half of these atomic ions are converted immediately into NO+ ions at the altitudes where 1‐100 Å X rays are absorbed, the E and D regions. Preliminary evidence, concerning excited ions directly formed during the atmospheric attenuation of 1‐100 Å X rays, suggests that the ions are ineffective as regards the ultimate ionic composition of the lower ionosphere as compared, for example, with NO+ + e → N + O. This major neutralization process allows atomic nitrogen to be formed in the ²D state. No survey of excited neutrals formed by the X‐ray photoelectrons was undertaken.