Seasonal and solar cycle variation of E-region nitric oxide

Measured electron density and [NO⁺]/[O2⁺] data are used to deduce the seasonal and solar activity variation of E-region nitric oxide concentration. The results imply a strong dependence of [NO] on soft X rays leading to the possibility that dissociation of N2 by energetic photoelectrons is a major source of N(²D). Seasonal variations of the thermosphere apparently cause enhanced [NO] in summer in agreement with the summer enhancement of experimental [NO⁺]/[O2⁺].