Modelling of non-LTE limb spectra of i.r. ozone bands for the MIPAS space experiment

Abstract

A new model for calculating the populations of the ozone vibrational states under non-LTE (Local Thermodynamic Equilibrium) conditions is presented. In the model, 23 vibrational levels of the O 3 molecule, as well as three vibrational levels of the O 2 molecule and two vibrational levels of the N 2 molecule, are considered. The radiative transfer at the break-down of LTE was treated explicitly for 150 000 ro-vibrational transitions. The populations obtained were used to calculate limb radiances in various spectral regions of the 4.8 and 9.6 μm bands. Test retrievals of O 3 vertical volume mixing ratio (VMR) profiles with a radiance model disregarding non-LTE were performed in order to assess the potential impact of non-LTE effects on the retrieval of the O 3 abundances from MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) measurements.