Approved for public release; distribution is unlimited / The production of nitric oxide by soft solar X-rays in the E-region of the ionosphere is investigated. An empirical expression for the variation in X-ray flux as a function of F10.7 is determined. This expression is incorporated into a one-dimensional diffusive photochemical model to compute nitric oxide densities. No results of these calculation are compared with NO observation from the Solar Mesosphere Explorer satellite. Variations of X-ray flux by a factor of 30 over the solar cycle can explain the observed variation in nitric oxide densities. / http://archive.org/details/investigationofp00duma / Lieutenant, United States Navy