Observations of atomic deuterium in the mesosphere from ATLAS 1 with ALAE Instrument

During the first ATLAS mission, the ALAE Lyman α spectrophotometer collected various measurements of hydrogen and deuterium atoms, from the mesosphere, the thermosphere, the exosphere and the interplanetary medium. In this paper is presented a preliminary analysis of some observations of atomic deuterium, which Lyman α emission is excited by resonance scattering of solar photons. Nadir measurements along the sunlit Earth part of the orbit show that the emission changes as a function of solar zenith angle. Comparison with a simple model shows that, from the shuttle altitude of 300 km and at low solar zenith angles, the line‐of‐sight probes atomic deuterium down to 80 km of altitude (where O 2 absorption is complete), whereas at angles from 60° to 90°, the mesospheric part of the emission progressively vanishes. Then, the remaining emission mainly consist of the thermospheric part ( z ≥ 100 km). This type of observations provides a sounding of atomic deuterium at its peak production and concentration, and D atoms can be used as a proxy to H atoms (which cannot be observed from a satellite) in this particularly active region of the mesosphere.