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Conference Papers Year : 2023

The first direct measurement of the saturnian stratospheric winds

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

Abstract

<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 and versions

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

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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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