Thermalization of O(D-1) atoms in the thermosphere

Measurements of the Doppler width of the 6300 Angstrom airglow emission lin e have been extensively used to determine the thermospheric temperature. Th is technique is based on the assumption that the bulk of the emitting O(D-1 ) atoms are thermalized in the region of the airglow source (200-300 km). A Monte Carlo stochastic model is used to calculate the energy distribution function of O(D-1) atoms in the daytime and nighttime thermosphere. Hot O(D -1) atoms are produced by exothermic processes and their thermalization is controlled by the competition between radiation, collisional quenching, and relaxation. It is found that the O(D-1) temperature departs from the backg round gas temperature not only in the upper thermosphere but also in the re gion of the bulk 6300 Angstrom emission. At 300 km for low solar activity c onditions, the model predicts an excess O(D-1) temperature of similar to 18 0 K during daytime and similar to 950 K at night. The temperature departure persists at lower altitudes as a result of the major contribution of the O -2(+) dissociative recombination source of hot D-1 atoms. Experimental evid ence based on the Fabry-Perot interferometer measurements on board the Dyna mics Explorer satellite confirms the existence of an O(D-1) temperature exc ess over the mass spectrometer/incoherent scatter (MSIS) value. It is concl uded that temperatures deduced from the 6300 Angstrom airglow line width ma y significantly exceed the ambient gas temperature in a way depending on so lar activity, local time, and observation geometry.