A rocket measurement of thermospheric nitric oxide (NO) is used to evaluate the production of odd nitrogen by solar soft X rays (18–50 Å). The rocket observation was performed over White Sands Missile Range on November 9, 1981, at 1500 LT for solar maximum conditions ( F 10.7 = 233). The peak observed NO density was 6.3×10 7 cm −3 at 102 km. A photochemical model which included soft X rays was used for comparison with the data. The soft X rays create photoelectrons which lead to enhanced ionization of N 2 and thus increased odd nitrogen production. A good fit to the data was achieved using a soft X ray flux of 0.75 erg cm −2 s −1 .

Altitude profiles of the O + 834‐Å emission, obtained from rocket observations at moderate and high solar conditions, are compared with model calculations. The model showed that when viewing the atmosphere horizontally at altitudes below the F 2 layer, the 834‐Å intensity was virtually independent of the O + density. The 834‐Å intensity was found to be highly sensitive to the N 2 absorption cross section. Comparisons with model calculations suggest that absorption by N 2 is a factor of 10 lower than the currently accepted values. Agreement between calculated and observed intensities was obtained by adjusting the N 2 cross sections to 1×10 −19 , 4×10 −19 , and 1.2×10 −18 cm² at the O + triplet wavelengths of 832.75, 833.33, and 834.46 Å, respectively. This adjustment was required in order to simulate the overlap between rotational absorption lines of N 2 and the O + emission lines.

As measured by the Solar Mesosphere Explorer satellite, the density of nitric oxide at low latitudes (30°S to 30°N) and at 110 km (E‐region) decreased from a mean value of 3 × 107 molecules/cm³ in January 1982 to a mean value of 4 × 106 molecules/cm³ in April 1985. In addition, the nitric oxide density varied ±50% with a 27‐day period during times of high solar activity. The variation of nitric oxide correlates with variations in the solar Lyman‐alpha irradiance which is also measured by the Solar Mesosphere Explorer satellite. The Lyman alpha irradiance is interpreted as an index of the variations in the solar EUV and soft X‐ray flux. The hypothesis is proposed that the solar X‐ray flux between 20 and 100 Å has a larger variation than the solar EUV flux between 100 and 1050 Å and that the solar X‐rays produce photoelectrons which are the source of the nitric oxide.

Observations of the NII 2143 Å emission in the Earth's dayglow were obtained by a rocket‐borne spectrograph flown on November 9, 1981, and August 11, 1982. The ultraviolet spectra were analyzed using synthetic spectra to separate the contribution of the 2143 Å emission from the overlapping nitric oxide gamma band. The 2143 Å column emission rate profiles for both flights were quite similar with peak column emission intensities of approximately 500 Rayleighs at an altitude of 160 km. When the observed column emission rate profiles are compared with theoretical calculations, the production efficiency of this emission was found to be 0.10 ± 0.04. The 2143 Å emission varies by more than a factor of 3 over the solar cycle and therefore should be useful as an indicator of the solar EUV flux.