AN UPDATED MODEL OF THE HOT NITROGEN ATOM KINETICS AND THERMOSPHERIC NITRIC-OXIDE

New observations and reanalysis of previous measurements suggest an up ward 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 ch annels. In addition, new calculations indicate that the transfer of tr anslational energy in N + N-2 collisions is less efficient than in the hard sphere approximation. This result leads to reevaluation of the e nergy dependent relaxation cross section and to an upward revision of the reacting efficiency of collisions of N with O-2 to form nitric oxi de. The calculated peak NO density increases by a factor of similar to 2 when the effect of superthermal nitrogen atoms is included. The mod el response of the N(S-4) energy distribution function and NO density to solar cycle variations is presented. The NO density at 110 km chang es 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 th e soft X ray increase with solar activity.