The Galileo Probe detected 20% ``solar'' water vapor to 10 bars or deeper, a puzzling result. We postulate that Jupiter's deep atmosphere contains at least solar water, and propose here a model of moist upwellings and dry downwellings which allows local dry regions to extend to 10 bars or deeper. We envision a deep adiabatic atmosphere extending in some regions to the 6-bar condensation level, producing explosive moist convection, cloudiness, and upwelling. Such upwellings (zones?) follow a moist adiabat above cloud base; most of the condensate rains out. The dry downwellings (belts?) cool by radiation,thereby becoming denser than upwelling air within the cloud region. We propose, however, that they cool insufficiently to become denser than the upwellings (and deep atmosphere) below the condensation level; the downwellings therefore remain dry far below cloud base. This curious situation requires the work generated above cloud base to be used primarily for maintaining subsidence below cloud base, rather than for increasing the total kinetic energy of the atmosphere or being lost to dissipation. We suggest that the net work performed by this heat engine cycle is near zero, which in steady state implies int (1/rho )updp=int (1/rho )downdp. We use the Voyager Equatorial Zone occultation data to specify the upwelling temperature at 1 bar, which we extend downward as a moist adiabat; we take Galileo Probe data for the downdraft. Assuming zero net work, we find that a deep water abundance of 1-3 times solar implies a dry downdraft extending to 10-30 bars, with a (virtual temperature) stability at the base of the downdraft of 5-15deg K. Our model also suggests partial cancellation of the thermal winds within the cloud and below cloud base, tentatively implying that a substantial fraction of the cloud top flow is deep barotropic, and possibly explaining the constancy of Jupiter's mean zonal winds despite changes in the weather layer over time.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996