37th DPS Meeting, 4-9 September 2005
Session 22 Outer Planets II
Oral, Tuesday, September 6, 2005, 11:00am-12:30pm, Law LG19

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[22.04] Evolution of Water and Ammonia Clouds in the EPIC Jupiter Model

Cs. Palotai, T. Dowling (CPL/U. Louisville)

We present results for water and ammonia cloud structure in our fully dynamic, three-dimensional model of Jupiter's atmosphere, the EPIC model. Our current approach is to specify a realistic initial zonal-wind and temperature profile as a function of latitude and pressure, and then let the model produce a self-consistent, interactive cloud structure, including latent heating and precipitation. We consider this to be a necessary and illuminating first step before embarking on spin-up experiments, because it allows us to learn how the model parameters affect observable quantities. The typical model configuration uses 40--45 vertical layers ranging from 10 mb down to 8000 mb, with extra resolution placed in the cloud-forming regions. We find that cloud-base position and cloud thickness both vary strongly with latitude. Starting with a fully developed zonal-wind profile, the model's ammonia clouds form thin and thick regions that correspond to the positions of Jupiter's belts and zones, respectively. These belt-and-zone variations form in place quickly, rather than being slowly pushed into position vertically by a secondary circulation (which is almost negligible in these simulations because there is no imposed Rayleigh drag). The water-cloud structure versus latitude generally mirrors the ammonia clouds above, with the water-cloud base ranging from about 5 bars to about 3.5 bars, and the cloud-top level moving up in altitude when the cloud base moves down, and vice versa. Initializing water with a deep molar mixing ratio that is solar produces mostly ice-phase clouds, but some liquid-phase clouds do form at around 5 bars. Water-cloud precipitation generally starts as snow, which falls, turns into rain, falls further, and then evaporates. We will present animations of simultaneous ammonia and water-cloud evolution in the meridional plane. The model is available as open source from NASA's PDS Atmospheres Node.

This research is funded by NASA's Planetary Atmospheres and Outer Planet Research Programs.

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Bulletin of the American Astronomical Society, 37 #3
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