ProQuest
Abstract/Details

## Saturn's atmosphere: structure and composition from cassini/cirs

Fletcher, Leigh Nicholas.   University of Oxford (United Kingdom) ProQuest Dissertations Publishing,  2007. U233573.

### Abstract (summary)

This thesis describes the analysis of thermal infrared spectra from Saturn measured by the Composite Infrared Spectrometer (CIRS) onboard the orbiting Cassini spacecraft (Flasar et al., 2004).  Many thousands of spectra in both the far (10 - 600 cm-1) and mid (600 - 1400 cm-1) infrared, acquired over the first three years of operations (2004-2007), have been analysed using a radiative transfer and optimal estimation retrieval algorithm (Irwin et al., 2004).  CIRS-spectra were used to deduce the vertical temperature structure and distribution of gaseous species with latitude throughout Saturn's upper troposphere and stratosphere and to infer the bulk composition of the gas giant. The temperature structure and para-hydrogen distribution over Saturn's northern (winter) and southern (summer) hemisphere were presented in Fletcher et al., (2007a). Hemispherically-symmetric small-scale temperature structures associated with zonal winds (Vasavada et al., 2006) are superimposed onto the seasonal temperature asymmetry for pressures greater than 100 mbar.  Seasonal asymmetries of stratospheric temperatures, tropopause height, radiative-convective boundary, para-H2 distribution and the inferred aerosol properties are discussed.  The existence of Saturn's hot south polar vortex was confirmed and a similar north polar hotspot was observed for the first time.  Infrared images were also used to study the temperatures associated with the north polar hexagon for the first time.  The temperature field was used to study Saturn's zonal, meridional and vertical wind velocities in the upper troposphere. Absorption and emission features in high spectral resolution (0.5 cm-1) data were used to derive vertical distributions of PH3, NH3, CH4, HD, 13CH4 and CH3D.  Saturn's carbon and phosphorus were found to be equally enhanced over solar abundances; the degree of ammonia saturation was found to be uniform with latitude, and HD is apparently depleted in the upper troposphere.  This work significantly improves the accuracy of elemental abundances and key isotopic ratios over previous studies and investigates the sensitivity of results to the poorly constrained vertical structure and optical properties of Saturn's tropospheric haze.

### Indexing (details)

Subject
Astronomy
Classification
0606: Astronomy
Identifier / keyword
DN118261; Pure sciences
Title
Saturn's atmosphere: structure and composition from cassini/cirs
Author
Fletcher, Leigh Nicholas
Number of pages
1
Degree date
2007
School code
0405
Source
DAI-C 70/47, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
University/institution
University of Oxford (United Kingdom)
University location
England
Degree
Ph.D.
Source type
Dissertation or Thesis
Language
English
Document type
Dissertation/Thesis
Note
Bibliographic data provided by EThOS, the British Library’s UK thesis service: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445756
Dissertation/thesis number
U233573
ProQuest document ID
301650692