On the relationship between the solar soft X ray flux and thermospheric nitric oxide: An update with an improved photoelectron model

An improved photoelectron model is used to reevaluate the effect of solar soft X rays on lower thermospheric nitric oxide. The improvements include an extension of the upper bound of the energy grid from 450 to 800 eV, extension of the solar spectrum from 19 Å down to 11 Å, the incorporation of Auger ionization for wavelengths shortward of the K shell edge, and the inclusion of a non zero yield of N(² D ) from dissociative ionization of N 2 by electron impact. The impact of each of these upgrades is studied with a one‐dimensional photochemical model and compared with previously published nitric oxide observations. It is shown that for conditions of high solar activity the photochemical model can now produce over twice as much nitric oxide for a given level of soft X ray input. The net effect of these changes is to reduce significantly the need for extremely large 18–50 Å solar flux values in the model in order to reproduce NO observations which have peak densities of the order of 2×10 8 cm −3 .