This dissertation describes one of the first major studies of the Uranian atmosphere to be performed since the flyby of Voyager 2 in 1986. Observations of the planet were taken from three observatories in the summers of 1995 and 1996, and the disk-averaged and latitudinal reflectivities were modeled to derive the properties of scatterers in the visible atmosphere and their changes in the intervening decade. In addition the likely changes in the temperature profile are examined and methods for detecting them described. Narrowband images of Uranus in the near-infrared from Apache Point Observatory were acquired on three dates in 1995 and 1996. In order to best probe different levels of the stratosphere and upper troposphere the planetary geometric albedo was measured and modeled using 7 filters ranging from 1.28-2.36μm. At the time of the 1996 observations there had been an 20 ± 5 times increase in the stratospheric haze column density since Voyager. The results suggest an upper limit on the optical thickness, τ <= 15 of the lower H2S cloud at 1.58 μm. In addition the drastic increase in the haze column density masked the visual asymmetry of the CH4 cloud deck seen by Voyager (Rages et al. 1991). High-resolution images spanning 0.4-2.4 μm were made in the summer of 1995 with the Hubble Space Telescope and the Infrared Telescope Facility. In 1995 the haze column density above the CH4 cloud was a factor of 6 larger than during the 1986 Voyager flyby. In addition the CH4 cloud retained the asymmetry seen by Voyager, however the total cloud optical depth at visible wavelengths had decreased, to 0.2 ± 0.1 at -22.5o and 1.2 ± 0.4 at -65o latitude, possibly due to continuous heating of the southern hemisphere in that time. As a result of the decrease in CH4 cloud thickness and increase in haze particles the troposphere (and likely the effective temperature of the planet) is expected to have increased by 1-2 K, while the upper stratospheric temperature has increased by several degrees, depending upon the amount of haze at the time of observation.
- Pub Date:
- Physics: Astronomy and Astrophysics, Physics: Atmospheric Science