SME observations of O_2(^1Δ_g) nightglow: An assessment of the chemical production mechanisms

Abstract

Solar Mesosphere Explorer (SME) observations of the 3 a.m. 1.27 μm nightglow at 45°N latitude, averaged over the period 10–31 July 1984, are reported. From the deduced volume emission rates, we derive the O_2(a^1Δ_g) night-time production rates for the 80–100 km altitude range. Utilizing the mean SME-acquired 3 p.m. ozone profile for the same latitude and time period and an updated photochemical model, we determine night-time O, O_3, H, OH, HO_2, and H_2O_2 profiles. These are used in calculating the rates of reactions which are sufficiently exothermic to produce O_2(^1Δ) or excited states of OH or HO_2, which could transfer their energy to O_2 to form O_2(^1Δ). Of these reactions, most have rates that are quite small compared with the observed night-time O_2(^1Δ) production rate. For several others, laboratory experiments have found O_2(^1Δ) yields which are insufficient for simulating the observed O_2(^1Δ). Using yields of O_2(^1Δ) based on published laboratory and observational studies, we find that the sum of two reaction sequences can approximate the SME measurements: (1) O + O + M and (2) H + O_3 followed by OH^∗ + O_2.

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