Global changes in the 0-70 km thermal structure of the Mars atmosphere derived from 1975 to 1989 microwave CO spectra

J = 1 - 2 (C-12)O (230 GHz) and (C-13)O (220 GHz) spectra of Mars obtained during the particularly favorable opposition of Mars in 1988 are analyzed. A CO mixing ratio is derived for November 1988 which agrees with a determination from 1967 observations. It is demonstrated that if the mixing ratio of CO was not drastically different in early 1980 and early 1982, the low- to midlatitude average thermal structure of the Mars atmosphere at these times was consistent with clear-air radiative-convective equilibrium conditions. Mars atmospheric temperature profiles derived from (C-12)O spectra are also presented.