Calculation of infrared limb emission by ozone in the terrestrial middle atmosphere: 2. Emission calculations

Abstract

The spectrally integrated limb radiance is calculated for ozone and for carbon dioxide in the 9–11 μm spectral interval for tangent heights between 30 and 100 km for noon and midnight conditions using a high‐resolution, line‐by‐line radiative transfer model that incorporates nonlocal thermodynamic equilibrium (NLTE) energy level populations in the transmittance calculations and NLTE source functions. The radiances assuming local thermodynamic equilibrium (LTE) are compared to the NLTE radiances. The NLTE ozone limb radiance is equal to the LTE radiance below 55 km at noon and below 70 km at midnight. The largest difference between the LTE and NLTE spectrally integrated ozone radiances occurs near 96 km in tangent height at noon and near 93 km at midnight. The difference between radiances decreases significantly from noon to midnight and is dependent on the portion of the spectral interval that is observed. Because of the uncertainty in the chemical pumping process, limb radiances utilizing two statistical equilibrium models of ozone are compared, yielding a maximum 32% difference in the spectrally integrated radiance at a tangent height of 84 km. Overlap of ozone spectral lines from bands possessing different source functions is not significant in calculating the infrared limb emission from the mesosphere and lower thermosphere. Finally, carbon dioxide is predicted to be responsible for a significant fraction of the total limb radiance in the 9–11 μm spectral interval in the daytime upper mesosphere and lower thermosphere. The implications of NLTE radiative transfer on the remote sensing of ozone are discussed.