Ionospheric Absorption byN2andO2of Certain Extreme Ultraviolet Solar Wavelengths

Abstract

Measurements are reported of the coefficients of absorption by the gases ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ of the emission from the H Lyman series 2-7, the resonance line 584A of He I, and twenty lines of ${\mathrm{H}}_2$ between 980A and 850A, the atomic lines likely being strong in solar radiation. For an atmosphere of constant relative composition the absorption coefficients are related to the atmospheric heights of maximum photoionization and maximum electron concentration by equations which allow for a constant temperature gradient, the inverse square decrease of gravity, and a recombination process which may vary with height. With these laboratory measurements for ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ and the known calculated absorption for O, ionosphere layer heights are computed for the simple case which assumes complete ${\mathrm{O}}_2$ dissociation above 100 km, no ${\mathrm{N}}_2$ dissociation, and two-body recombination. Although only the first assumption is probably secure, it appears that photoionization is capable of producing layers at heights which agree with observation.