2014
DOI: 10.1002/2013gl059078
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The long‐term steady motion of Saturn's hexagon and the stability of its enclosed jet stream under seasonal changes

Abstract: We investigate the long-term motion of Saturn's north pole hexagon and the structure of its associated eastward jet, using Cassini imaging science system and ground-based images from 2008 to 2014. We show that both are persistent features that have survived the long polar night, the jet profile remaining essentially unchanged. During those years, the hexagon vertices showed a steady rotation period of 10 h 39 min 23.01 ± 0.01 s. The analysis of Voyager 1 and 2 (1980)(1981) and Hubble Space Telescope and ground… Show more

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Cited by 47 publications
(79 citation statements)
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“…The most conspicuous difference between the two hemispheres is the presence of the hexagonal feature in the north. A seasonal effect for this major difference between the two polar regions can be ruled out since the hexagon has been observed in the north hemisphere every time high‐resolution observations have been available even during the long polar winter night [ Baines et al ., ; Sánchez‐Lavega et al ., ], while no hexagon has ever been observed in the south polar region, where only evanescent quasilinear features appear on some high‐resolution observations. An analysis of the two‐dimensional velocity field has allowed us to quantify the meandering of the jet associated to the hexagon, showing that it is fitted very well by a sinusoidal wave of wave number 6 and amplitude 0.5° (117 km).…”
Section: Discussionmentioning
confidence: 99%
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“…The most conspicuous difference between the two hemispheres is the presence of the hexagonal feature in the north. A seasonal effect for this major difference between the two polar regions can be ruled out since the hexagon has been observed in the north hemisphere every time high‐resolution observations have been available even during the long polar winter night [ Baines et al ., ; Sánchez‐Lavega et al ., ], while no hexagon has ever been observed in the south polar region, where only evanescent quasilinear features appear on some high‐resolution observations. An analysis of the two‐dimensional velocity field has allowed us to quantify the meandering of the jet associated to the hexagon, showing that it is fitted very well by a sinusoidal wave of wave number 6 and amplitude 0.5° (117 km).…”
Section: Discussionmentioning
confidence: 99%
“…It seems therefore that the eastward jet embedded in the hexagonal wave and its counterpart jet in the south are not being fed by eddy momentum injection. The absence of momentum injection by eddies might be caused by injection of energy at smaller scales not resolvable by the measurements or might reinforce the idea that the jets are, in fact, deeply rooted structures driven by the internal convection [ Aurnou and Olson , ; Kaspi et al ., ], making them insensitive at tropospheric level to the seasonal cycle [ Sánchez‐Lavega et al ., ].…”
Section: Turbulent Wind Componentsmentioning
confidence: 99%
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“…where A is the amplitude, is the frequency, and k is the zonal wavenumber, defined as k = 2 ∕L x , where L x is the zonal wavelength (k = n x ∕a). Models of Rossby wave stream functions typically include meridional and vertical wavenumbers, as well as a depth-dependent amplitude (e.g., Sánchez-Lavega et al, 2014). While it is clear from Figure 2 that the north ribbon propagated meridionally on the time scale of years, between 2006 and 2010 its poleward velocity was about 0.4 ∘ /year or 0.003 m/s.…”
Section: Wave Propagation and Dispersionmentioning
confidence: 99%
“…Within these polar regions, the dynamics at the upper cloud level is dominated by a permanent narrow eastward jet present in both hemispheres at 78°N and 73.9°S, and by an intense cyclonic circulation centered at each pole (Antuñano et al, 2015;Sayanagi et al, 2017). Furthermore, Saturn's polar regions present a large variety of cloud morphologies, including the hexagonal wave in the north polar region at 75.8°planetocentric latitude (Antuñano et al, 2015;Sánchez-Lavega et al, 2014;Sayanagi et al, 2016) and two stable polar cyclones, one at each pole (Antuñano et al, 2015;Baines et al, 2009;Dyudina et al, 2008;Fletcher et al, 2008;Sánchez-Lavega et al, 2006;Sayanagi et al, 2017).…”
Section: Introductionmentioning
confidence: 99%