Joule heating and nitric oxide in the thermosphere

The effect of Joule heating on the density of nitric oxide in the thermosphere was studied using observations from the Student Nitric Oxide Explorer (SNOE) satellite and model calculations from the Thermospheric Ionosphere Electrodynamics General Circulation Model for a Joule heating event that occurred on 25 September 1998. Model results and SNOE observations from fifteen orbits were compared in the latitude range 82°S to 82°N over the altitude range 100-150 km. Joule heating which occurred in the 55°- to 60°-latitude region produced a meridional wind blowing equatorward and a gravity wave propagating equatorward, which caused an increase in the temperature of the thermosphere in the 20°- to 75°-latitude region. When the heated thermosphere was illuminated by solar radiation, the density of nitric oxide increased over this entire latitude region because of a temperature-sensitive reaction between ground state nitrogen atoms and molecular oxygen. In the 24 hours following the Joule heating event, the increased nitric oxide diffused downward from the 150-km region to the 110-km level of the thermosphere.