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Energy exchanges in Saturn’s polar regions from Cassini observations: Eddy-zonal flow interactions
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  • Peter L Read,
  • Arrate Antuñano,
  • Greg Colyer,
  • Simon Cabanes,
  • Teresa del Rio-Gaztelurrutia,
  • Agustín Sánchez-Lavega
Peter L Read
Oxford University, Oxford University

Corresponding Author:[email protected]

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Arrate Antuñano
University of Leicester, University of Leicester
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Greg Colyer
University of Oxford, University of Oxford
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Simon Cabanes
DICEA, Sapienza Università di Roma, Via Eudossiana 18, 00184 Rome, Italy., DICEA, Sapienza Università di Roma, Via Eudossiana 18, 00184 Rome, Italy.
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Teresa del Rio-Gaztelurrutia
Universidad País Vasco UPV/EHU, Universidad País Vasco UPV/EHU
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Agustín Sánchez-Lavega
Universidad del Pais Vasco UPV/EHU, Universidad del Pais Vasco UPV/EHU
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Saturn’s polar regions (polewards of ∼ 63◦ planetocentric latitude) are strongly dynamically active with zonal jets, polar cyclones and the intriguing north polar hexagon wave. Here we analyse measurements of horizontal winds, previously obtained from Cassini images by Antun ̵̃ano et al. (2015), to determine the spatial and spectral exchanges of kinetic energy (KE) between zonal mean zonal jets and nonaxisymmetric eddies in Saturn’s polar regions. Eddies of most resolved scales generally feed KE into the eastward and westward zonal mean jets at rates between 4.3 ×10−5 and 1.4 ×10−4 W kg−1. In particular, the north polar jet (at 76◦N) was being energised at a rate of ∼ 10−4 W kg−1, dominated by the contribution due to the zonal wavenumber m = 6 north polar hexagon wave itself. This implies that the hexagon was not being driven at this time through a barotropic instability of the north polar jet, but may suggest a significant role for baroclinic instabilities, convection or other internal energy sources for this feature. The south polar zonal mean jet KE was also being sustained by eddies in that latitude band across a wide range of m. In contrast, results indicate that the north polar vortex may have been weakly barotropically unstable at this time with eddies of low m gaining KE at the expense of the axisymmetric cyclone. However, the southern axisymmetric polar cyclone was gaining KE from non-axisymmetric components at this time, including m = 2 and its harmonics, as the elliptical distortion of the vortex may have been decaying.
May 2022Published in Journal of Geophysical Research: Planets volume 127 issue 5. 10.1029/2021JE006973