Observation of Atomic Oxygen in the Mesosphere and Thermosphere of Earth with the THz Heterodyne Spectrometer GREAT

Atomic oxygen governs photochemistry and energy balance of the mesosphere and lower thermosphere of the Earth. Its concentration is extremely difficult to measure with remote sensing techniques since it has only few optically active transitions. Current indirect measurements involve photochemical models and the results are not always in agreement, particularly when obtained with different instruments. In addition, altitudes above 100 km are not covered by these methods. We report on direct measurements of the 4.7-THz fine-structure transition of atomic oxygen at 4.7448 THz using the German Receiver for Astronomy at Terahertz Frequencies on board the Stratospheric Observatory for Infrared Astronomy. Our measurements agree well with atmospheric models and satellite observations below 100 km.