Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsa21a..11s&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SA21A-11
Physics
3359 Radiative Processes, 3360 Remote Sensing, 0340 Middle Atmosphere: Composition And Chemistry
Scientific paper
Four vibrational states of ozone - O3(000), O3(100), O3(010), and O3(001) - were observed simultaneously in the lower mesosphere (50-75 km). LTE abundances of the vibrationally excited molecules were calculated from the measured ground state O3 values. Comparison of calculated and measured mixing ratios of O3(100), O3(010), and O3(001) showed each vibrationally excited state to be significantly underpopulated wrt LTE values. Non-LTE abundances of vibrationally excited ozone were calculated using a 1-D photochemical model. These non-LTE model values agree with the measurements. Both of these results hold for both daylight and night time conditions. The dominant non-LTE mechanism at 50-75 km is found to be spontaneous emission. The importance of our results is that they provide direct observational confirmation of non-LTE behavior that previously has been inferred from indirect measurements, or on the basis of purely modeling studies. Ground-based data we present were obtained using the 12-meter radio telescope and liquid He temperature receivers at Kitt Peak, AZ (32o N lat., 112o W long.). Emission line spectra correspond to rotational transitions from ozone near 240 GHz. Unlike the vibrational states, LTE conditions hold for rotational state populations well into the thermosphere. Species altitude profiles are derived based on sensitivity of the line shape to pressure. These mesospheric measurements have their lower altitude limit (50 km) set by stability of the spectral baseline and by the increase of pressure broadened line width with decrease in altitude. The 75 km upper altitude limit is determined by decreased ozone abundance and consequent diminished signal.
Clancy Todd R.
Sandor Brad J.
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