Behaviour of the O 2 infrared atmospheric (0-0) band in the middle atmosphere during evening twilight and at night

Measurements of the 0-0 band of the Infrared Atmospheric System of the molecular oxygen during early night-time show a non-negligible fraction of the emission which is a remnant of the very high concentration of atmospheric O ₂( a¹Δ_g) during the day. The importance of this contribution decreases progressively after sunset. The complexity of the photochemistry during twilight, involving fast variation in the concentration of the atmospheric compounds and in the solar fluxes, makes it difficult to study the decay of the daytime emission. We have developed a detailed treatment of the different processes governing the production and loss mechanisms of the O ₂( a¹Δ_g) at times near sunset and during the night. This model is capable of explaining the remnant observed in measurements carried out by rocket-borne instrumentation.