Observation of anomalous temperatures in the daytime O(D-1) 6300 angstrom thermospheric emission: A possible signature of nonthermal atoms

A study of the effect of a thermospheric population of nonthermal O(D-1) at oms on the 6300 Angstrom emission is undertaken based on a comparison betwe en daytime observations from space and theoretical simulations. Vertical te mperature profiles deduced from 6300 Angstrom airglow emission measurements using the Fabry-Perot interferometer (FPI) instrument onboard the Dynamics Explorer 2 (DE 2) satellite are compared to the MSIS-90 model. Metastable O(D-1) temperatures about 150 K larger than the MSIS neutral kinetic temper ature are deduced from the 6300 Angstrom line profiles observed during dayt ime, when the satellite altitude is higher than 400 km. We propose a theore tical explanation for this difference, based on the presence of a nontherma l O(D-1) population in the line-of-sight of the instrument. Monte Carlo sim ulations of the nonthermal O(D-1) energy distribution function are used to calculate the red line emission and to simulate the FPI behavior, including the line-of-sight integration. The comparison between the simulated data a nd the FPI ones as well as sensitivity tests allow us to conclude that the presence of nonthermal atoms in the instrument field of view is the most li kely explanation of the observed discrepancy.