The energy balance of planetary atmospheres‡

Abstract

We discuss the problem, of the energy balance of a planetary atmosphere: whether the atmospheric structure is under radiative control or whether it is significantly influenced by large scale fluid motions. The time constant for relaxation of the temperature by radiative transfer is shown to be largely independent of the atmospheric composition. The magnitude of the dynamical effects is obtained for a non‐rotating planet and it is shown that the lower atmosphere of Venus, where solar radiation is absorbed, is strongly dynamically controlled. It is probable, however, that a stratospheric region, under radiative control, exists above the visible cloud tops. The problem of rotating planets is more complex because free dynamical modes are known to be important. We conclude that Earth, Mars and Jupiter are all under dynamical control in their lower atmospheres: this conclusion is at least certain for Mars. Stratospheric radiative regimes may occur: close to the surface for Mars; two or three scale heights above the surface for Earth; and at pressures well below 1 mb on Jupiter.