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Communication Dans Un Congrès Année : 2017

Saturn's stratospheric temperature and composition at the epoch of the 2017 summer solstice.

Résumé

Over the course of its 29.5-years orbit, Saturn undergoes significant seasonal changes, owing to its 26.7° axial tilt. 2017 marks the end of the 13-year exploration of the Saturnian system by the Cassini spacecraft and coincides with summer solstice in Saturn's northern hemisphere. Monitoring changes in temperature and composition in Saturn's stratosphere through seasons can teach us about dynamical, radiative and chemical processes governing its atmospheric structure and evolution. Here we report on thermal infrared spectroscopic observations of Saturn's stratosphere in March 2017 obtained with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted on the Gemini telescope. We retrieve vertical profiles of the temperature between latitudes 15°S and 87°N from the analysis of methane emission lines near 1245 cm<SUP>-</SUP><SUP>1</SUP>. The inferred zonally average thermal structure is validated against Cassini/CIRS measurements acquired in January and February 2017. These datasets (ground-based and space-based) are in excellent agreement. The 1-mbar temperature is found to increase moderately from 140K at 20°N to 145K at 60°N, then increases more sharply to reach 155K at 85°N. The overall meridional temperature gradient observed in 2017 resembles the one observed in 2004 in the southern summer hemisphere, where a warm ``polar hood'' was observed poleward of 70°S [Fletcher et al., 2008]. In contrast, a seasonal radiative-equilibrium model [Guerlet et al., 2014] predicts much smaller and smoother meridional temperature gradients with latitude. We further analysed Cassini/CIRS data acquired in 2014 over the northern hemisphere to study seasonal changes between 2014 and 2017. Surprisingly, the 1-mbar temperature has slightly cooled down in the region 25N-55N between these two dates, at odds with the moderate warming predicted by our radiative-equilibrium model. We will discuss several hypotheses to account for these model-observation mismatches. In addition, we also retrieve vertical profiles of ethane and acetylene volume mixing ratios from their emission lines recorded by TEXES near 822 and 728 cm-1 and will discuss their spatial distribution.
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Dates et versions

hal-03724476 , version 1 (15-07-2022)

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Sandrine Guerlet, Thomas K. Greathouse, Glenn S. Orton, Marine Martin-Lagarde, Leigh N. Fletcher, et al.. Saturn's stratospheric temperature and composition at the epoch of the 2017 summer solstice.. AAS/Division for Planetary Sciences Meeting #49, Oct 2017, Provo, UT, United States. ⟨hal-03724476⟩
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