Lower-thermospheric infra-red emissions from minor species during high-latitude twilight—B. Analysis of 15 μm emission and comparison with non-LTE models

Abstract

During the DYANA campaign, a Skylark VI rocket, known as SISSI-1 and containing an infra-red grating spectrometer and other onboard instruments including an atomic-oxygen sensor, was launched at dawn twilight from Esrange, Kiruna, Sweden. Molecular vibrational emission features of carbon dioxide at 4.3 and 15.0 μm, nitric oxide at 5.3 μm, and ozone at 9.6 μm were measured in the lower thermosphere. The experimental results were discussed in part A ( Grossman et al, 1994, J. atmos. terr. Phys. 56, 1885–1897). In this paper (part B), we analyzed the CO 215μm data in terms of the radiative and collisional excitation and loss processes involved and compared the experimental results to non-LTE radiance models. Good agreement is obtained over a range of altitudes and wavelengths between the predictions of the ARC line-by-line non-LTE radiance code and the experimental data for SISSI-1, as well as between model simulations and data from a similar payload known as M-I1 launched under drastically different conditions as part of the MAP/WINE campaign. The data sets provide useful opportunities for more stringent tests of the important role of atomic oxygen in CO 2 15 μm non-LTE radiance models than available until now and for determining the region of applicability of the LTE assumption, as well as for investigating a lower-thermospheric energy balance.