From Voyager-IRIS to Cassini-CIRS: Interannual variability in Saturn’s stratosphere?

J.A. Sinclair 1, * P.G.J. Irwin 1 L.N. Fletcher 1 T. Greathouse 2 S. Guerlet 3 J. Hurley 1 C. Merlet 1
* Corresponding author
1 AOPP - Department of Atmospheric, Oceanic and Planetary Physics [Oxford]
2 SwRI - Southwest Research Institute [San Antonio]
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
Abstract : We present an intercomparison of Saturn’s stratosphere between Voyager 1-IRIS observations in 1980 and Cassini-CIRS observations in 2009 and 2010. Over a saturnian year (∼29.5 years) has now passed since the Voyager flybys of Saturn in 1980/1981. Cassini observations in 2009/2010 capture Saturn in the same season as Voyager observations (just after the vernal equinox) but one year later. Any differences in Saturn’s atmospheric properties implied by a comparison of these two datasets could therefore reveal the extent of interannual variability. We retrieve temperature and stratospheric acetylene and ethane concentrations from Voyager 1-IRIS (View the MathML sourceΔν̃=4.3cm-1) observations in 1980 and Cassini-CIRS (View the MathML sourceΔν̃=15.5cm-1) ‘FIRMAP’ observations in 2009 and 2010. We observe a difference in temperature at the equator of 7.1 ± 1.2 K at the 2.1-mbar level that implies that the two datasets have captured Saturn’s semiannual oscillation (SSAO) in a slightly different phase suggesting that its period is more quasi-semiannual. Elevated concentrations of acetylene at 25°S in 1980 with respect to 2010 imply stronger downwelling at the former date which may also be explained by a difference in the phase of the SSAO and its dynamical forcing at low latitudes. At high-southern and high-northern latitudes, stratospheric temperatures and hydrocarbon concentrations appear elevated in 1980 with respect to 2009/2010. This could be an artefact of the low signal-to-noise ratio of the corresponding observations but might also be explained by increased auroral activity during solar maximum in 1980.
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Submitted on : Monday, November 17, 2014 - 5:32:10 PM
Last modification on : Wednesday, May 15, 2019 - 3:52:24 AM

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J.A. Sinclair, P.G.J. Irwin, L.N. Fletcher, T. Greathouse, S. Guerlet, et al.. From Voyager-IRIS to Cassini-CIRS: Interannual variability in Saturn’s stratosphere?. Icarus, Elsevier, 2014, 233, pp.281-292. ⟨10.1016/j.icarus.2014.02.009⟩. ⟨hal-01083712⟩

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