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Communication Dans Un Congrès Année : 2023

The first direct measurement of the saturnian stratospheric winds

Bilal Benmahi
Thibault Cavalié
Thierry Fouchet
Emmanuel Lellouch
  • Fonction : Auteur
Raphael Moreno
Sandrine Guerlet
  • Fonction : Auteur
Aymeric Spiga
  • Fonction : Auteur
Deborah Bardet
  • Fonction : Auteur

Résumé

<p>Numerous past observations of Saturn&#160;by ground based and space telescopes have monitored&#160;the movements of clouds and derived direct measurements&#160; of tropospheric wind speeds, giving insights into the tropospheric circulation of the planet. The most remarkable feature is a broad and fast&#160; equatorial&#160;prograde jet, reaching 400-450 m/s. Saturn's stratospheric dynamics is less well known. At low latitudes, it is characterized by the thermal signature of an equatorial oscillation: the observed thermal structure implies that there is a strong oscillating vertical shear of the zonal winds throughout the stratosphere, however, wind speeds in this region cannot be measured by cloud-tracking techniques and remain unknown.</p><p>The objective of our study is to measure the stratospheric zonal winds&#160;of&#160;Saturn and&#160;unveil&#160;the circulation of this layer by observing it in the submillimeter range&#160;with&#160;the ALMA interferometer.&#160;For this, we observed the spectral&#160;lines&#160;of HCN at 354 GHz and CO at 345 GHz&#160;emitted&#160;from the limb of the planet. The pressure&#160;level&#160;at which we measure&#160;the winds is about 0.2&#160;mbar.&#160;Thanks&#160;to the high spatial and spectral resolution of ALMA observations at 345 GHz,&#160;we measured&#160;the central frequencies of the emission lines in the whole limb,&#160;subtracted&#160;the rigid rotation of the planet,&#160;and thus derived&#160;the Doppler shift due to the atmospheric motions of the probed layer,&#160;i.e.&#160;the stratospheric winds. The method we used in this study was first developed to observe the stratospheric winds in Jupiter (Cavali&#233; et al. 2021).&#160;</p><p>Saturn's rings have&#160;limited our wind observations to latitudes&#160;north of&#160;20&#176;S. The zonal winds obtained in the eastern and western&#160;limbs&#160;are&#160;consistent within error bars. We most&#160;noticeably&#160;detected&#160;a very&#160;broad&#160;eastward jet that spreads from 20&#176;S to 20&#176;N with an average speed of&#160;exceeding 250 m/s.</p>
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Dates et versions

obspm-03903693 , version 1 (16-12-2022)

Identifiants

Citer

Bilal Benmahi, Thibault Cavalié, Thierry Fouchet, Emmanuel Lellouch, Raphael Moreno, et al.. The first direct measurement of the saturnian stratospheric winds. 24th EGU General Assembly, May 2023, Vienne, Austria. ⟨10.5194/egusphere-egu22-11527⟩. ⟨obspm-03903693⟩
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