GRAY AND NONGRAY PLANETARY ATMOSPHERES STRUCTURE, CONVECTIVE INSTABILITY, AND GREENHOUSE EFFECT

Analytic expressions are derived for the atmospheric structure, greenhouse effect, and level of onset of convective instability in window gray and nongray planetary atmospheres. Where pressure-induced transitions or dust are principal sources of infrared opacity, gray approximations may have a strict relevance; but, even when permitted transitions are the opacity sources, the appropriate expressions for the nongray atmosphere are quite similar to those for the gray case. Constant lapse rates should occur in deep radiative equilibrium as well as deep convective equilibrium atmospheres. Atmospheres with polyatomic, condensable gases, pressure-sensitive opacities, and long-wavelength windows tend to have higher tropopauses and more extensive convective tropospheres than atmospheres with converse properties. The outer Jovian planets may have very extensive outer envelopes in radiative rather than convective equilibrium. The mean infrared optical depth, τ, for a nongray convective atmospheric greenhouse on the Earth is about 2; for Venus, several hundred. In the window gray case, T increases with τ about twice as fast for convective as for radiative atmospheres; in the nongray case, about four times as fast. © 1969.