Showing papers by "Andrew P. Ingersoll published in 1984"

Structure and dynamics of Saturn's atmosphere

Abstract: The atmosphere of Saturn exhibits dynamical structures (jets, bands, spots, eddies) with horizontal scales ranging from one scale height (60 km) up to the planetary radius (60,000 km). Although the kinds of structures are the same as those on Jupiter, there are quantitative differences. First, Saturn's equatorial jet speed is four times greater and the jet width is two times wider than on Jupiter. Eastward jets at higher latitudes are also speedier and wider, but westward jets are slower compared with Jupiter. There are fewer spots in all size ranges, and no spot comparable in size to Jupiter's Great Red Spot. The rms eddy wind speed is lower, as is the conversion of eddy kinetic energy to zonal mean kinetic energy (the measured rate of conversion is positive but not significantly so). Saturn's convective regions, where eddy lifetimes are a few days or less, are more isolated and cover less area than on Jupiter. The basic causes of these differences have not been quantitatively identified. Basic differences between the two planets include Saturn's lower heat source, lower gravity, and consequently greater depth of atmosphere and deeper nonconducting fluid layers. Observed temperatures imply that the zonal winds decrease from cloud top upwards, but change more gradually below the cloud tops. One possibility is that zonal winds are constant on concentric cylinders that extend throughout the planet. However the observations, which are limited to cloud-top altitudes and above, do not preclude other configurations. It is remotely possible that Saturn's internal rate of rotation is different from that of its radio emissions. Dynamical models differ in their assumption about the interior and its dynamical interaction with the atmosphere. The time-dependent behavior of the large-scale structures offers a promising way of testing the models and choosing among the various assumptions.

Thermal tides in the atmosphere of Venus - Comparison of model results with observations

Abstract: A linearized primitive equation (LPE) model is developed to study thermal tides in the atmosphere of Venus. The LPE model describes diurnal and semidiurnal oscillations of a cyclostrophically balanced atmosphere in which zonal velocity varies with altitude and latitude. The numerical algorithm follows Staniforth and Daley. The solar thermal forcing is increased algebraically in time to separate the forced tidal response from free atmospheric oscillations. Parameters of the basic state and forcing agree with Pioneer Venus observations. Results of the model are compared with the solar-fixed component of brightness temperature variations measured by Taylor et al. and Elson using data from the Pioneer Venus orbiter infrared radiometer (OIR). The comparison is made by convolving the computed model radiances with the weighting functions of the OIR channels. Agreement between LPE model results and OIR observations is excellent. Two interesting features of the OIR data are accounted for, namely, the slow variation of phase with altitude and the dominance of the semidiurnal oscillation over the diurnal oscillation. Success of the LPE model opens the way for calculating tidal transports of heat and momentum and assessing the role of tides in maintaining the Venus super-rotation.

Atmospheric Dynamics of Uranus and Neptune: Theoretical Considerations

Abstract: Uranus, because of its pole-on orientation and low internal heat source, is in a dynamically different atmospheric regime from Jupiter and Saturn. Neptune resembles Jupiter and Saturn in orientation and internal heating, but its extremely long radiative time constant puts Neptune in a different class. Voyager observations of seasonal temperature gradients, equator-to-pole temperature gradients, infrared emission, Bond albedo, possible cloud structures (bands, spots, eddies), and cloud motions should greatly improve our ability to classify planetary atmospheres according to their dynamical regimes.