MOIST CONVECTION AND THE VERTICAL STRUCTURE AND WATER ABUNDANCE OF JUPITERS ATMOSPHERE

We explore the consequences of moist convection on Jupiter with a one-dimensional version of the cumulus parameterization used in the GISS general circulation model. The model predicts the collective effects of an ensemble of moist convective plumes on a conditionally unstable atmosphere. Heating/cooling and drying/moistening of the large-scale environment occur through compensating subsidence, detrainment of updraft air at cloud top, and evaporation and melting of falling condensate. Dry convective adjustment and stratiform cloud formation are included to remove superadiabatic lapse rates and supersaturated humidities, respectively. The model also transports parahydrogen fraction as a passive tracer. We make two different assumptions about how convection operates on Jupiter. In the first scenario we assume that convection dominates all other processes, modifying an initial temperature and moisture profile until it reaches neutral stability. Three regimes are possible: Pure moist convective, mixed moist-dry convective, and primarily dry convective. The outcome depends on the assumed deep water abundance, efficiency of condensate evaporation, and initial temperature profile. Relative humidity just below cloud top is low in the moist convective regime but increases steadily with depth. Isolated dry convection layers in the mixed regime produce sharp vertical variations of relative humidity and multiple water cloud layers. In all cases, severe water depletion is possible only over a narrow range of altitudes. In particular, the water vapor profile inferred by Bjoraker et al. (1986, Astrophys. J. 311, 1058-1072) cannot be reconciled with the effects of moist convection, regardless of whether the deep abundance is subsolar, solar, or supersolar. Significant cloud-base stable layers a scale height or less in depth form when condesate evaporation and dry convection are important, but the degree of stabilization is always considerably less than the theoretical limit. Convective transports produce subequilibrium parahydrogen fractions and small or negative gradients near the visible cloud level. We also examine the alternative assumption that a quasiequilibrium prevails between moist convection and other processon Jupiter. In this scenario we calculate the cumulus mass flux consistent with the Jovian internal heat flux and diagnose the large-scale vertical advection required to balance the convective heating. The equilibrium configuration for near-neutral static stability is a series of thin convection layers capped by thin cloud layers and a "staircase" vertical profile of temperature, humidity, and parahydrogen fraction. © 1990.