Potential Vorticity of Saturn's Polar Regions: Seasonality and Instabilities

Antuñano, Arrate; Río‐Gaztelurrutia, T. del; Sánchez‐Lavega, A.; Read, P. L.; Fletcher, Leigh N.

doi:10.1029/2018je005764

Cited by 8 publications

(13 citation statements)

References 43 publications

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“…A distinctive feature in the northern hemisphere is that the vortex is surrounded by a zonal wavenumber-6 "hexagonal" westerly jet which peaks at around 100 ms −1 . This jet was observed by Voyager in 1980 (Godfrey, 1988), and has persisted ever since, most likely resulting in two strong PV gradients within the polar region that constitute the strong cyclone vortex, and a nearby jet (Figure 3; Antuñano et al, 2019;Fletcher et al, 2018;Scott & Polvani, 2006). While there exists a jet at a similar latitude in the southern hemisphere, it is weaker (Sayanagi et al, 2018), and does not have the same wavenumber-6 pattern, despite having similar PV gradients (and as such potential for instabilities; Antuñano et al, 2019).…”

Section: Saturnmentioning

confidence: 94%

Polar Vortices in Planetary Atmospheres

Mitchell

Scott

Seviour

et al. 2021

Reviews of Geophysics

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A nearly ubiquitous feature of planetary atmospheres in the solar system are rapidly rotating flows in polar regions, that are generally referred to as polar vortices. These features may be explained by consideration of basic physical constraints. At the most fundamental level, rapidly rotating planets have a minimum of angular momentum on the axis of rotation, and a maximum at the equator. Due to their rotation, planetary bodies may be expected to develop polar cyclonic flow as a result of transport of air between different latitudes, which will tend to increase the angular momentum at high latitudes, and decrease it at low latitudes. Such transport may arise through a variety of forms, including turbulence and wave stresses or the induced circulation arising from local heating or cooling anomalies (Andrews et al., 1987).Transport of angular momentum alone, however, cannot be used directly to determine the development of cyclonic polar motions because background rotation and density stratification combine to place further dynamical constraints on the nature of the transport. An elegant way to view these constraints is through another dynamical quantity, the potential vorticity (PV), closely related to angular momentum and its conservation. PV, q, may be defined as,

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Section: Saturnmentioning

confidence: 94%

Polar Vortices in Planetary Atmospheres

Mitchell

Scott

Seviour

et al. 2021

Reviews of Geophysics

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“…The CSP condition, however, is only a necessary condition for instability, not a sufficient one. An alternative condition for instability was considered by Arnol'd (1966) and is often referenced as "Arnol'd's second stability theorem" (e.g. Dowling, 1995).…”

Section: Barotropically Unstable Flows In the Laboratorymentioning

confidence: 99%

“…Observational studies that have combined wind measurements from cloud motions with remotely sensed temperature retrievals (Read et al, 2006(Read et al, , 2009aAntuñano et al, 2019) and a geostrophic balance assumption for both Jupiter and Saturn, however, also indicate significant reversals of ∂Q/∂y. Figure 15a shows an example of a section of ∂Q/∂y in latitude and height in the southern hemisphere of Jupiter, based on data from the Cassini spacecraft (Read et al, 2006).…”

Section: Pv Structures: Observationsmentioning

confidence: 99%

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Baroclinic and barotropic instabilities in planetary atmospheres: energetics, equilibration and adjustment

Read

Kennedy

Lewis

et al. 2020

Nonlin. Processes Geophys.

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Abstract. Baroclinic and barotropic instabilities are well known as the mechanisms responsible for the production of the dominant energy-containing eddies in the atmospheres of Earth and several other planets, as well as Earth's oceans. Here we consider insights provided by both linear and nonlinear instability theories into the conditions under which such instabilities may occur, with reference to forced and dissipative flows obtainable in the laboratory, in simplified numerical atmospheric circulation models and in the planets of our solar system. The equilibration of such instabilities is also of great importance in understanding the structure and energetics of the observable circulation of atmospheres and oceans. Various ideas have been proposed concerning the ways in which baroclinic and barotropic instabilities grow to a large amplitude and saturate whilst also modifying their background flow and environment. This remains an area that continues to challenge theoreticians and observers, though some progress has been made. The notion that such instabilities may act under some conditions to adjust the background flow towards a critical state is explored here in the context of both laboratory systems and planetary atmospheres. Evidence for such adjustment processes is found relating to baroclinic instabilities under a range of conditions where the efficiency of eddy and zonal-mean heat transport may mutually compensate in maintaining a nearly invariant thermal structure in the zonal mean. In other systems, barotropic instabilities may efficiently mix potential vorticity to result in a flow configuration that is found to approach a marginally unstable state with respect to Arnol'd's second stability theorem. We discuss the implications of these findings and identify some outstanding open questions.

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“…Observational studies that have combined wind measurements from cloud motions with remotely sensed temperature retrievals (Read et al, 2006(Read et al, , 2009aAntuñano et al, 2019) and a geostrophic balance assumption for both Jupiter and Saturn, 620 however, also indicate significant reversals of ∂Q/∂y. Figure 15(a) shows an example of a section of ∂Q/∂y in latitude and height in the southern hemisphere of Jupiter, based on data from the Cassini spacecraft (Read et al, 2006).…”

Section: Jupitermentioning

confidence: 99%

Baroclinic and barotropic instabilities in planetary atmospheres - energetics, equilibration and adjustment

Read¹,

Lewis²,

Kennedy³

et al. 2019

Preprint

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Abstract. Baroclinic and barotropic instabilities, are well known as the mechanisms responsible for the production of the dominant energy-containing eddies in the atmospheres of the Earth and several other planets, as well as the Earth's oceans. Here we consider insights provided by both linear and nonlinear instability theories into the conditions under which such instabilities may occur, with reference to forced and dissipative flows obtainable in the laboratory, in simplified numerical atmospheric circulation models and in the planets of our Solar System. The equilibration of such instabilities is also of great importance in understanding the structure and energetics of the observable circulation of atmospheres and oceans. Various ideas have been proposed concerning the ways in which baroclinic and barotropic instabilities grow to large amplitude and saturate, whilst also modifying their background flow and environment. This remains an area that continues to challenge theoreticians and observers, though some progress has been made. The notion that such instabilities may act under some conditions to adjust the background flow towards a critical state is explored here in the context of both laboratory systems and planetary atmospheres. Evidence for such adjustment processes is found relating to baroclinic instabilities under a range of conditions where the efficiency of eddy and zonal mean heat transport may mutually compensate to maintain a nearly invariant thermal structure in the zonal mean. In other systems, barotropic instabilities may efficiently mix potential vorticity to result in a flow configuration that is found to approach a marginally unstable state with respect to Arnol'd's second stability theorem. We discuss the implications of these findings and identify some outstanding open questions.

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Potential Vorticity of Saturn's Polar Regions: Seasonality and Instabilities

Cited by 8 publications

References 43 publications

Polar Vortices in Planetary Atmospheres

Polar Vortices in Planetary Atmospheres

Baroclinic and barotropic instabilities in planetary atmospheres: energetics, equilibration and adjustment

Baroclinic and barotropic instabilities in planetary atmospheres - energetics, equilibration and adjustment

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