Kinetic and spectroscopic requirements for the measurement of mesospheric ozone at 9.6 µm under non‐LTE conditions

Abstract

Radiative emission from transitions involving the vibration‐rotation bands of ozone in the 9.6 µm spectral region is readily detected by limb‐scanning instruments on orbiting satellites and such measurements are used to infer the ozone profile in the middle atmosphere. In the terrestrial mesosphere and lower thermosphere these transitions are predicted to depart from local thermodynamic equilibrium (LTE). The occurrence of non‐LTE complicates the interpretation of emission measurements in terms of the ozone abundance as the vibrational temperatures must be known a priori or calculated directly as part of the retrieval process. This in turn requires accurate knowledge of various kinetic and spectroscopic parameters used in a statistical equilibrium model to calculate the vibrational temperatures. Through detailed simulations of the forward and inverse retrieval problem we find that in order to achieve retrieved ozone concentrations accurate to 15% the collisional quenching rates must be known to better than 25% accuracy and that the distribution of energy within ozone upon recombination of O and O2 must be significantly improved. Collisional quenching rates are currently uncertain by more than a factor of 2.