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| Titel |
The role of H2O in the Saturn ionosphere |
| VerfasserIn |
Donald Shemansky, Xianming Liu |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042120
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| Zusammenfassung |
| Stellar occultations in the Cassini Ultraviolet Imaging Spectrograph Experiment
observation program have provided measurements of the vertical profiles of H2
and and minor components of the atmosphere. The minor species identified and
measured in the extinction spectra to date are CH4, C2H2, and C2H4. Measurements of
abundance profiles are reported here, with limits on H2O content. The focus of this
paper is on H2O because of the importance of this species to the understanding of
upper atmospheric physical chemistry with significant consequences for ionospheric
properties and energy budget. Ionospheric theory published in several papers beginning
as early as 1984 have a common critical dependence on a sufficiently large H2O
mixing ratio to control the lifetime of the assumed dominant ion, H+. The vertical
extinction profiles, which extend down to an impact parameter of 300 km above the
1 bar pressure level, show no evidence of H2O in the spectrum at mid and low
latitudes, establishing a mixing ratio [H2O]/[H2] -¤ 4 Ã 10-8, compatible with
earlier global average measurements. The upper limit on H2O abundance at mid
latitude establishes a mixing ratio more an order of magnitude too low to influence
the ionosphere population in competition with calculated H+ + H2 X(v:J) charge
capture reaction rates. The analysis of the extinction spectra produces densities and
mixing ratios of the observed species and these results are reported and discussed. |
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