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Keywords:

  • Highly vibrationally excited OH;
  • Airglow;
  • Mesopause chemistry

Abstract

[1] Absolute concentrations (cm–3) of highly vibrationally excited hydroxyl (OH) are derived from measurements of the volume emission rate of the υ = 9 + 8 states of the OH radical made by the SABER instrument on the TIMED satellite. SABER has exceptionally sensitive measurement precision that corresponds to an ability to detect changes in volume emission rate on the order of ~5 excited OH molecules per cm3. Peak zonal annual mean concentrations observed by SABER exceed 1000 cm–3 at night and 225 cm–3 during the day. Measurements since 2002 show an apparent altitude-dependent variation of the night OH(υ = 9 + 8) concentrations with the 11 year solar cycle, with concentrations decreasing below ~ 95 km from 2002 to 2008. These observations provide a global database for evaluating photochemical model computations of OH abundance, reaction kinetics, and rates and mechanisms responsible for maintaining vibrationally excited OH in the mesopause region.