Seasonal and solar cycle variation of E-region nitric oxide

Measured electron density and NO(+) to O2(+) concentration ratio 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 concentration 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 concentration in summer in agreement with the summer enhancement of experimental NO(+) to O2(+) concentration ratio