Understanding the Cloud Structure on the Giant Planets.

The Equilibrium Cloud Condensation Model, or ECCM, is a thermochemical equilibrium model used to predict a multi-layer cloud structure on the giant planets. The model calculates upper limits for the cloud concentrations. In this dissertation, the effect of precipitation on the concentration of Jupiter’s water clouds is explored following the preliminary formulations of cloud microphysics. Precipitation time scales and maximum precipitation rate are calculated to estimate the water cloud concentration more realistically. In another part of the dissertation, the ECCM is combined with microwave radiometry data to assess the composition and structure of clouds in the troposphere of Uranus. In particular, constraints on phosphine are obtained. Phosphine is expected to be in thermochemical equilibrium in the deep troposphere of Uranus. Its presence in the upper troposphere is indicative of deep atmospheric convection. However, no measurements have yet revealed phosphine in the troposphere of the ice giant planets, Uranus and Neptune. Radiative transfer analysis of microwave observations with the Very Large Array radio telescope and the Sub-Millimeter Array were carried out using new phosphine vapor absorption coefficients to determine if phosphine or another species can explain the microwave opacity in the 2 to 6 bar region. Phosphine is found to play a significant role. In the region of the clouds, elemental abundances of phosphorus, nitrogen, oxygen, and sulfur were found to range from 4-10, 0.008-0.6, 0-10, and 0.5-4 times their solar elemental abundances, respectively. It is important to point out that these are only cloud region values, and do not necessarily represent the elemental abundances in the interior of the planet. Nevertheless, the relatively low elemental abundances of nitrogen and oxygen in the upper troposphere of Uranus indicate possible removal of ammonia and water in the interior, perhaps through the formation of an ionic ocean.PHDAtmospheric and Space ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/96156/1/mihalka_1.pd

Fresh clouds: A parameterized updraft method for calculating cloud densities in one-dimensional models

a b s t r a c t Models of cloud condensation under thermodynamic equilibrium in planetary atmospheres are useful for several reasons. These equilibrium cloud condensation models (ECCMs) calculate the wet adiabatic lapse rate, determine saturation-limited mixing ratios of condensing species, calculate the stabilizing effect of latent heat release and molecular weight stratification, and locate cloud base levels. Many ECCMs trace their heritage to Lewis (Lewis, J.S. [1969]. Icarus 10, 365-378) and Weidenschilling and Lewis (Weidenschilling, S.J., Lewis, J.S. [1973]. Icarus 20, 465-476). Calculation of atmospheric structure and gas mixing ratios are correct in these models. We resolve errors affecting the cloud density calculation in these models by first calculating a cloud density rate: the change in cloud density with updraft length scale. The updraft length scale parameterizes the strength of the cloud-forming updraft, and converts the cloud density rate from the ECCM into cloud density. The method is validated by comparison with terrestrial cloud data. Our parameterized updraft method gives a first-order prediction of cloud densities in a ''fresh'' cloud, where condensation is the dominant microphysical process. Older evolved clouds may be better approximated by another 1-D method, the diffusive-precipitative Ackerman and Marley (Ackerman, A.S., Marley, M.S. [2001]. Astrophys. J. 556, 872-884) model, which represents a steady-state equilibrium between precipitation and condensation of vapor delivered by turbulent diffusion. We re-evaluate observed cloud densities in the Galileo Probe entry sit