Polar Vortices in Planetary Atmospheres

Mitchell, Dann; Scott, R. K.; Seviour, William J. M.; Thomson, Stephen I.; Waugh, Darryn W.; Teanby, N. A.; Ball, Emily

doi:10.1029/2020rg000723

Cited by 14 publications

(14 citation statements)

References 182 publications

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“…A polar vortex was also observed on Neptune's south pole in the near‐ and mid‐IR as well as at radio wavelengths (de Pater et al., 2014; Fletcher et al., 2014; Luszcz‐Cook et al., 2010; Tollefson et al., 2021). Since polar vortices appear to be common features on planets (Mitchell et al., 2021) and the formation of central polar cyclones on ice giant planets have been predicted from modeling studies (Brueshaber et al., 2019), it seems likely that this feature on Uranus also indicates the presence of a compact polar vortex.…”

Section: Introductionmentioning

confidence: 95%

Evidence of a Polar Cyclone on Uranus From VLA Observations

Akins

Hofstadter

Butler

et al. 2023

Geophysical Research Letters

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Uranus' obliquity affords unique opportunities for polar observing, which can contribute to our general understanding of polar circulation processes on giant planets. Our current understanding of Uranus' polar circulation (we define the pole as >60° latitude) suggests net subsidence as the characteristic feature of vertical motion. This pattern is inferred from emission and reflection contrasts in multi-wavelength observations (de Pater et al., 1989(de Pater et al., , 1991Hofstadter & Butler, 2003;Roman et al., 2020;Sromovsky et al., 2019), which suggest depletion of absorbing gases at the poles down to 10s of bars. Zonal wind profiles of polar latitudes, estimated nominally at 1.5 bar, have been most recently updated by Karkoschka (2015) at southern latitudes based on Voyager 2 images and Sromovsky et al. ( 2015) at northern latitudes based on Keck observations. Mean zonal wind speeds decay monotonically from a maximum of 250 m/s near 60° to near-zero at 90°, and there appears to be significant asymmetry between the northern and southern pole zonal wind profiles (Karkoschka, 1998;Sromovsky & Fry, 2005;. This asymmetry, as well as analyses of Voyager gravity measurements, suggests that zonal wind speeds are vertically confined globally and should decay with altitude in the upper troposphere (e.g., see Fletcher et al. ( 2020) for a recent review). As new observations and analysis techniques push limitations of spatial resolution and sensitivity, new features have emerged in images of Uranus that complicate this broader picture. For example, complex polar features have been observed at the CH 4 weather level, including a multitude of compact bright features in the northern hemisphere suggestive of small-scale vertical convection acting against net subsidence (Sromovsky et al., 2012. At many wavelengths, this is the first solstice for which ground-based and near-Earth observatories are sufficiently sensitive to resolve fine details in polar thermal emission. This is certainly true for microwave observations with the VLA, which underwent an order of magnitude bandwidth upgrade in 2012 that significantly improved the achievable sensitivity. Unlike mid-infrared, near-infrared, and visible observations, which have informed our understanding of Uranus' circulation at and above the H 2 S and CH 4 cloud levels, microwave observations are sensitive to thermal emission from deeper in the troposphere (primarily 10-50 bar at the poles). Post-upgrade VLA observations of Uranus are now sufficiently sensitive to resolve faint zonal banding patterns at lower latitudes at the 10 bar level. Observations of Uranus in 2015 described by Molter et al. (2021), specifically the Ku band (2 cm) image, provided evidence of latitudinal structure in tropospheric thermal emission at Uranus'

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Section: Introductionmentioning

confidence: 95%

Evidence of a Polar Cyclone on Uranus From VLA Observations

Akins

Hofstadter

Butler

et al. 2023

Geophysical Research Letters

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“…We vary obliquity, eccentricity, and dust scaling and use a diagnostic called "effective diffusivity" to understand horizontal mixing in the polar regions in an idealized MGCM. Effective diffusivity is a geometric description of the stirring in a flow and has been well used to study mixing in Earth's stratospheric polar vortices (e.g., Haynes & Shuckburgh 2000a, 2000bAbalos et al 2016), as well as across hurricane eyewalls, which have an annular vorticity structure similar to Mars's current polar vortices (Hendricks & Schubert 2009;Mitchell et al 2021). Hendricks & Schubert (2009) find two regions of high effective diffusivity (indicating strong mixing) in simulations of unstable rings of vorticity-an inner mixing region within the annulus, and an outer mixing region outside of the annulus.…”

Section: Atmospheric Circulationmentioning

confidence: 99%

The Importance of Isentropic Mixing in the Formation of the Martian Polar Layered Deposits

Ball,

Seviour,

Mitchell

2023

Planet. Sci. J.

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Layers of ice and dust at the poles of Mars reflect variations in orbital parameters and atmospheric processes throughout the planet's history and may provide a key to understanding Mars's climate record. Previous research has investigated transport changes into the polar regions and found a nonlinear response to obliquity that suggests that Mars may currently be experiencing a maximum in transport across the winter poles. The thickness and composition of layers within the polar layered deposits (PLDs) are likely influenced by changes in horizontal atmospheric mixing at the poles, which is an important component of the transport of aerosols and chemical tracers. No study has yet investigated horizontal mixing alone, which may be influenced by polar vortex morphology. We show that mixing in an idealized Martian global climate model varies significantly with obliquity and dust abundance by using a diagnostic called effective diffusivity, which has been used to study the stratospheric polar vortices on Earth and to understand their role as a mixing barrier but has not been applied to Mars's polar vortices. We find that mixing in the winter southern hemisphere doubles with either an octupling of dust loading or an increase in obliquity from 10° to 50°. We find a weaker response to changing dust loading or obliquity in the northern hemisphere. We demonstrate that horizontal mixing is an important component of transport into Mars’s polar regions, may contribute to the formation of the PLDs, and presents effective diffusivity as a useful method to understand mixing in the Martian atmosphere.

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“…The stratospheric polar vortex plays a pivotal role in stratosphere-troposphere interactions. In the Northern Hemisphere, the Arctic stratospheric polar vortex (APV) (Waugh et al 2017, Mitchell et al 2021 forms in autumn, peaks in winter, and decays by early spring, with the strongest variability from January to March (supplementary figure S1). APV alterations, such as strengthening due to ozone depletion or weakening from stratospheric sudden warming, deeply impact Northern Hemisphere's surface climate (Haynes et al 1991, Baldwin and Dunkerton 2001, Ambaum and Hoskins 2002, Thompson et al 2006, Domeisen and Butler 2020, Baldwin et al 2021, Scaife et al 2022, Tian et al 2023.…”

Section: Introductionmentioning

confidence: 99%

Southern Hemispheric jet swing linked to Arctic stratospheric polar vortex

Xie,

Ma,

et al. 2024

Environ. Res. Lett.

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Our study reframes our understanding of stratosphere-troposphere interactions, traditionally thought to be confined within individual hemispheres, by introducing a novel cross-hemispheric link. We demonstrate that strong boreal winter Arctic stratospheric polar vortex (APV) boosts the transmission of upper tropospheric waves from Northern Hemisphere’s mid-high latitudes to the equator. Facilitated by the tropical central and eastern Pacific’s “westerly bridge”, these waves reach Southern Hemisphere’s mid-high latitudes. The entire process shows a “semicircular road”. Waves reaching the Southern Hemisphere affect the circulation through wave-flow interaction, causing a southward swing of the Southern Hemispheric westerly jet center. This displacement weakens the subtropical jet and strengthens the polar jet, resulting in increased subtropical precipitation and decreased mid-latitude precipitation in the Southern Hemisphere during austral summer. Correspondingly, a weak APV may lead to the opposite result. Our findings underscore APV’s broader impact on the tropospheric atmosphere, extending beyond prior knowledge.

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Polar Vortices in Planetary Atmospheres

Cited by 14 publications

References 182 publications

Evidence of a Polar Cyclone on Uranus From VLA Observations

Evidence of a Polar Cyclone on Uranus From VLA Observations

The Importance of Isentropic Mixing in the Formation of the Martian Polar Layered Deposits

Southern Hemispheric jet swing linked to Arctic stratospheric polar vortex

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