Microwave spectra of terrestrial mesospheric CO

Mesospheric CO was observed in absorption against the moon in early December 1979 at a wavelength of 1.3 mm and in early December 1980 at 2.6 mm with the 10.4-m millimeter wavelength telescope at the Owens Valley Radio Observatory. No significant change in the column density of CO above about 65 km is found between the 1979 and 1980 observations. Comparison with other published spectra of mesospheric CO suggests a large seasonal variation (about a factor of 2-3) in the column density of CO above 65 km, with a maximum in winter and a minimum in summer. It is concluded that the understanding of CO in the mesosphere can be improved with earth-based microwave measurements, but data with high signal-to-noise ratios must be obtained.