Cloud features and zonal wind measurements of saturn's atmosphere as observed by Cassini/VIMS

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Abstract

We present an analysis of data about Saturn's atmosphere from Cassini's Visual and Infrared Mapping Spectrometer (VIMS), focusing on the meteorology of the features seen in the 5 μm spectral window. We present VIMS mosaics and discuss the morphology and general characteristics of the features backlit by Saturn's thermal emission. We have also constructed a zonal wind profile from VIMS feature tracking observation sequences using an automated cloud feature tracker. Comparison with previously constructed profiles from Voyager and Cassini imaging data reveals broad similarities, suggesting minimal vertical shear of the zonal wind. However, areas of apparent wind shear are present in the VIMS zonal wind profile at jet stream cores. In particular, our analysis shows that the equatorial jet reaches speeds exceeding 450 m s-1, similar to speeds obtained during the Voyager era. This suggests that recent inferences of relatively slower jet speeds of ∼275-375 m s-1 are confined to the upper troposphere and that the deep (>1 bar) jet has not experienced a significant slowdown. Our measurements of the numerous dark, spotted features seen in the VIMS mosaics reveals that most of these features have diameters less than 1000 km and reside in confined zonal bands between jet stream cores. We propose that these spot features are vortices and that VIMS and Imaging Science Subsystem are sensing the same vortices at two different pressure levels. The local structure at the zonal jet streams remains complex, as VIMS may be sensing cloud features that are deeper than the NH3 cloud deck.

Original languageEnglish (US)
Article numberE04007
JournalJournal of Geophysical Research: Space Physics
Volume114
Issue number4
DOIs
StatePublished - Apr 20 2009

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Saturn atmosphere
wind measurement
Earth atmosphere
zonal wind
Saturn
Spectrometers
spectrometer
spectrometers
Infrared radiation
atmosphere
jet stream
wind profiles
wind profile
vortex
Vortex flow
vortices
wind shear
Imaging techniques
Meteorology
Troposphere

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

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title = "Cloud features and zonal wind measurements of saturn's atmosphere as observed by Cassini/VIMS",
abstract = "We present an analysis of data about Saturn's atmosphere from Cassini's Visual and Infrared Mapping Spectrometer (VIMS), focusing on the meteorology of the features seen in the 5 μm spectral window. We present VIMS mosaics and discuss the morphology and general characteristics of the features backlit by Saturn's thermal emission. We have also constructed a zonal wind profile from VIMS feature tracking observation sequences using an automated cloud feature tracker. Comparison with previously constructed profiles from Voyager and Cassini imaging data reveals broad similarities, suggesting minimal vertical shear of the zonal wind. However, areas of apparent wind shear are present in the VIMS zonal wind profile at jet stream cores. In particular, our analysis shows that the equatorial jet reaches speeds exceeding 450 m s-1, similar to speeds obtained during the Voyager era. This suggests that recent inferences of relatively slower jet speeds of ∼275-375 m s-1 are confined to the upper troposphere and that the deep (>1 bar) jet has not experienced a significant slowdown. Our measurements of the numerous dark, spotted features seen in the VIMS mosaics reveals that most of these features have diameters less than 1000 km and reside in confined zonal bands between jet stream cores. We propose that these spot features are vortices and that VIMS and Imaging Science Subsystem are sensing the same vortices at two different pressure levels. The local structure at the zonal jet streams remains complex, as VIMS may be sensing cloud features that are deeper than the NH3 cloud deck.",
author = "Choi, {D. S.} and Adam Showman and Brown, {Robert H.}",
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N2 - We present an analysis of data about Saturn's atmosphere from Cassini's Visual and Infrared Mapping Spectrometer (VIMS), focusing on the meteorology of the features seen in the 5 μm spectral window. We present VIMS mosaics and discuss the morphology and general characteristics of the features backlit by Saturn's thermal emission. We have also constructed a zonal wind profile from VIMS feature tracking observation sequences using an automated cloud feature tracker. Comparison with previously constructed profiles from Voyager and Cassini imaging data reveals broad similarities, suggesting minimal vertical shear of the zonal wind. However, areas of apparent wind shear are present in the VIMS zonal wind profile at jet stream cores. In particular, our analysis shows that the equatorial jet reaches speeds exceeding 450 m s-1, similar to speeds obtained during the Voyager era. This suggests that recent inferences of relatively slower jet speeds of ∼275-375 m s-1 are confined to the upper troposphere and that the deep (>1 bar) jet has not experienced a significant slowdown. Our measurements of the numerous dark, spotted features seen in the VIMS mosaics reveals that most of these features have diameters less than 1000 km and reside in confined zonal bands between jet stream cores. We propose that these spot features are vortices and that VIMS and Imaging Science Subsystem are sensing the same vortices at two different pressure levels. The local structure at the zonal jet streams remains complex, as VIMS may be sensing cloud features that are deeper than the NH3 cloud deck.

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