Radiative-Convective Latitudinal Gradients for Jupiter and Saturn Models with a Radiative Zone

Abstract

Local radiative-convective thermal structure is calculated on Jupiter and Saturn under the assumption that a low opacity zone exists near the 2000-K depth, as suggested by T. Guillot et al. (1994a, Icarus112, 337-353). The opacity is uncertain, and a simple but qualitatively accurate model is used to explore a range of opacities. Under the assumption of local radiative-convective equilibrium, insolation gradients lead to latitudinal temperature gradients in the shell outside the stably stratified radiative zone near 2000 K, and to a latitudinal variation in the emission to space. Measurements of the net heat balance (solar and planetary radiation) do not yet extend to high enough latitudes to test these predictions. On Jupiter and especially Saturn, the preference for westerly surface motion may be due to equator-to-pole temperature gradients in this shell. It is speculated that the dynamical response to radiative forcing due to low opacity near the 2000-K level may limit latitudinal temperature gradients and may be an important drive for meteorology on the outer planets. © 1999 Academic Press.