Simultaneous Retrievals Of Nighttime O(P-3) And Total Oh Densities From Satellite Observations Of Meinel Band Emissions

Retrieving the total number density [OH], which is used in the chemical balance equations and is the sum of both ground and excited vibrational state populations, is a challenging problem to such a degree there exist no such estimates from recent space observations. We present a novel retrieval approach to simultaneously and self-consistently derive both [O(P-3)] and total [OH] in the nighttime mesosphere and lower thermosphere which operates with the Meinel band volume emission rates and their ratios. Its application to the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) observations shows a good agreement of the retrieved [O(P-3)] taking into account the measurement uncertainties and variation of model inputs used. However, retrieved [OH] show a large discrepancy, mainly above 90 km. SCIAMACHY [OH] is generally in good agreement with WACCM [OH] after accounting for uncertainties, while SABER OH is larger than WACCM [OH] by up to a factor of 2.Plain Language Summary The hydroxyl molecule plays an important role in the physics, chemistry, and dynamics of the middle and upper atmosphere region (60-120 km). Obtaining total hydroxyl density from its molecular emissions is a challenging problem to such a degree there exist no such estimates from the recent space observations. We present a novel approach to obtain both atomic oxygen and total hydroxyl densities in the middle and upper atmosphere from nighttime observations of the hydroxyl molecular emissions. We apply the new approach to two different space-based instrument observations of hydroxyl emissions at multiple infrared wavelengths. The atomic oxygen densities obtained from the two instruments using our new approach are in good agreement after taking into account uncertainties, while the hydroxyl densities show a large discrepancy.