next up previous
Next: Schedule Up: No Title Previous: Observations and Instrumentation

Modeling

The 17-24 band is a region of interest because it forms in the 50 to 500 mbar pressure regions. This is particularly useful because it allows us to ``sound'' the conditions at many different levels of the stratosphere and upper troposphere. The spatial resolution acquired by our observations will allow effective analysis of temperature in two dimensions, depth and latitude. The spacing of the pixels will allow the three key regions of the planet to be examined, the equator, mid-latitudes, and the poles. The IRIS dataset only obtained data up to 400 . The goal is to expand this dataset to 570 , testing to see if the results match those of Voyager, and to constrain the atmospheric energy transport in a different season.

Analysis will begin using a radiative-convective model for Uranus constructed by the author's faculty advisor Mark Marley (1995). It is based upon a model constructed to examine the structure of Titan's atmosphere (McKay 1989). The model consists of 42 plane-parallel layers spaced equally in log P from 2.5 bars to 20 bars. A second dimension will be added by the PI to allow for the study of latitudinal variations. Calculations take place in the thermal infrared over 56 spectral intervals between 5.7 and 0.33 cm, which will be modified to fit the MIRAC bandpasses. The technique begins with an atmospheric model, which is allowed to relax to radiative equilibrium by continual iterations until the net flux across each layer is zero. Layers that exceed the adiabatic lapse rate are deemed to be convective. Three radiative and two convective zones are allowed for. The equation of radiative transfer is then solved for in each band until radiative equilibrium is reached. This is run until the final converged model is convectively stable in all the radiative layers. From the final model will come energy transport as a function of latitude, and the new observations will allow a seasonal comparison.

The model is particularly useful for solving the thermal evolution problem since it has the capabilities to compute temperature changes over time. For half of the 84 year orbital period each pole receives no insolation. Yet at summer solstice for the southern hemisphere, Voyager discovered the polar regions to be similar in temperature, attributable to the time lag. It is well established for Jupiter and Saturn that the heat flow is similar at all latitudes, and since Wallace's models show that latitudinal temperature variations are virtually independent of the magnitude of internal heat flow, the heat flow problem need only be treated in one dimension.



next up previous
Next: Schedule Up: No Title Previous: Observations and Instrumentation



Charles Walter
Wed May 31 11:43:13 MDT 1995