An updated model of the hot nitrogen atom kinetics and thermospheric nitric oxide

New observations and reanalysis of previous measurements suggest an upward revision of the measured thermospheric nitric oxide density. Our previous model of NO production by fast N(S-4) atom collisions with O-2 has been updated. It includes the effect of soft solar X rays, Auger electrons, and a detailed treatment of N-2 dissociative ionization channels. In addition, new calculations indicate that the transfer of translational energy in N + N-2 collisions is less efficient than in the hard sphere approximation. This result leads to reevaluation of the energy dependent relaxation cross section and to an upward revision of the reacting efficiency of collisions of N with O-2 to form nitric oxide. The calculated peak NO density increases by a factor of similar to 2 when the effect of superthermal nitrogen atoms is included. The model response of the N(S-4) energy distribution function and NO density to solar cycle variations is presented. The NO density at 110 km changes from 5.4 x 10(7) to 1.3 x 10(8) cm(-3) when the solar F-10.7 index varies from 70 to 245, but its response depends on the magnitude of the soft X ray increase with solar activity.