Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........8h&link_type=abstract
Ph.D. Thesis California Inst. of Tech., Pasadena.
Astronomy and Astrophysics
Astronomy
Atmospheric Circulation, Microwave Frequencies, Radio Astronomy, Uranus Atmosphere, Atmospheric Composition, Atmospheric Temperature, Brightness, Polar Regions, Very Large Array (Vla)
Scientific paper
This thesis explores the atmosphere of Uranus using microwave observations at wavelengths from 1 to 20 cm, with primary emphasis on high resolution VLA data at wavelengths of 2 and 6 cm. While radio maps of Uranus have been published previously, this is the first detailed analysis and interpretation of such observations. Several features of the data are immediately clear. First, there are strong horizontal and vertical gradients in the atmospheric properties that control the radio brightness. Polar regions are much brighter than lower latitudes, and the deep troposphere appears much dimmer than would be expected based on the upper troposphere. Second, the intrinsic latitudinal brightness variations at 2 cm and 6 cm are highly correlated with each other and with Voyager infrared measurements, suggesting a common cause. Because these data sets probe different altitudes between 50 and 0.1 bar, the cause must be acting over this altitude range of about 250 km. Finally, the observed radio brightness features have not changed significantly in the 8 years between 1981 and 1989. Since radio brightness is a function of temperature and composition, the observations can be used to map these properties as a function of latitude and height. compositional changes are used as a tracer to infer the general circulation and some of the chemical processes of there atmosphere. The most likely interpretation of the data is that the Southern Hemisphere is dominated by a single meridional circulation cell, with an upwelling centered near -25 deg latitude that brings absorber rich air parcels from 50 bars up to the 0.1 bar region. As parcels rise, the absorber mixing ratio drops by a factor of about 100 between 25 and 10 bars, and then a further factor of 2 at higher altitudes. These depletions are probably due to condensation. The absorber depleted parcels then move poleward and descend, dominating the atmospheric composition over the pole down to 50 bars, but not deeper. This circulation is consistent with the zonal winds and upper atmospheric temperatures observed by Voyager in the context of a simple, linear, dynamical model.
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