Atomic oxygen emission at 63 µm as a cooling mechanism in the thermosphere and ionosphere

Abstract

FAR IR emission by atomic oxygen fine structure transitions is considered an important cooling mechanism in the Earth's upper atmosphere and ionosphere as well as in several astronomical objects. The cooling rates so far have only been calculated theoretically on the basis of local thermodynamic equilibrium. No experimental or theoretical determination of the fine structure excitation or quenching cross sections for mutual neutral atomic oxygen collisions has been reported. We report here the first spectrometrically measured atomic oxygen 63-µm emission profile at thermospheric altitudes (90–180 km). An energy-averaged quenching cross section for the O(³P₁) level was deduced. The importance of the 63-µm emission as a cooling process for both the neutral thermosphere and the ionosphere is much less than predicted.