The Dark Spot in the atmosphere of Uranus in 2006: Discovery, description, and dynamical simulations

Hammel, Heidi B.; Sromovsky, L. A.; Fry, P. M.; Rages, K.; Showalter, M. R.; Pater, Imke de; Dam, Marcos A. van; LeBeau, Raymond P.; Deng, Xiaolong

doi:10.1016/j.icarus.2008.08.019

Cited by 42 publications

(40 citation statements)

References 22 publications

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“…The vortex motion is similar that in previous UDS work 6,15,16,19 , in that the vortex drifts gradually equatorward, a drift notably not observed at this magnitude with the actual UDS. The evolution of a cloud-free and a methane tracer simulation are shown in figure 14, reveal small changes in the drift rate and vortex side between the two cases.…”

Section: Current Resultssupporting

confidence: 86%

“…The dark, elliptical region was centered at 28 o N latitude and was roughly 1300 km (2 o ) in latitude and 2700 km (5 o ) in longitude. At the time of this discovery a bright companion was not simultaneously seen, but earlier observations show bright clouds at this latitude, which may have formed in an orographic manner about the vortex 6 .…”

Section: Critical Observationsmentioning

confidence: 85%

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Effects of Hemispheric Circulation on Uranian Atmospheric Dynamics and Methane Depletion

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LeBeau

Palotai

et al. 2012

4th AIAA Atmospheric and Space Environments Conference

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The solar system is filled with meteorological phenomena. For example, geophysical vortices range from hurricanes to the Great Red Spot on Jupiter to the Dark Spots of Uranus and Neptune. These Ice Giant vortices have exhibited unusual dynamical behaviors, such as the shape oscillations and meridional drift of the Great Dark Spot, discovered and observed in 1989 by Voyager II. On the other hand, the Uranian Dark Spot exhibited little to no drift over a similar stretch of observation when it appeared shortly before the spring equinox on Uranus in 2006. Another phenomenon is regions of persistent clouds, common in the banding patterns of the gas giants. The bright companion of the Great Dark Spot is a different type of persistent cloud, arising orographically as the vortex moved through the atmosphere. The Uranian Dark Spot may also have had a similar, although intermittent, cloud companion. Another notable long-lived cloud feature called S34 or the "Berg" in the southern hemisphere of Uranus, which drifted equatorward covering approximately 30 degrees in latitude over the course of a few years as equinox approached, having previously spent several years in the vicinity of 34 degrees south latitude. While this motion resembles in some ways that of the Great Dark Spot and its Bright Companion, there was no visible vortex associated with the Berg's cloud. A proposed cause of this unexpected drift is the development of a strong meridional, Hadley-cell circulation that caused the cloud (and a possible unseen companion vortex) to drift equatorward. This same circulation may account for observations that showed upper tropospheric methane gas (a primary cloud constituent on Uranus) in the southern hemisphere was preferentially accumulating near the equator while depleting near the south pole. This paper presents the first efforts to examine these phenomena by numerically modeling a full Uranian atmosphere. These simulations are designed to examine these changes in the Uranian atmosphere, probably related to the extreme seasonal change of this planet. While this research will improve our understanding of the Uranian atmosphere and the design of future missions to this system, it will also assist in understanding the similar dynamics on the other Ice Giant planet Neptune, and potentially with similar phenomena in Earth's atmosphere like hurricane drift. Nomenclaturec p = specific heat at constant pressure f = coriolis parameter g = gravitational acceleration h = hybrid layer thickness K = specific kinetic energy M = Montgomery potential 1 Graduate Student, p = pressure q = potential vorticty Q  = heat flux T = temperature u  = velocity z = altitude coordinate  = latitude  = Exner function  = pressure-based vertical coordinate  = potential temperature  = kinematic viscosity  = local vorticity  = planet rotation  = hybrid vertical coordinate

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Section: Current Resultssupporting

confidence: 86%

Section: Critical Observationsmentioning

confidence: 85%

Effects of Hemispheric Circulation on Uranian Atmospheric Dynamics and Methane Depletion

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LeBeau

Palotai

et al. 2012

4th AIAA Atmospheric and Space Environments Conference

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“…As shown in Fig. 11, the strongest indication of mid-latitude asymmetry comes from observations made between 1997 and 2005, which are based on HST imaging (Karkoschka 1998;Hammel et al 2001) and Keck imaging (Hammel et al 2001;Sromovsky and Fry 2005;Sromovsky et al 2007;Hammel et al 2009;Sromovsky et al 2009). The dotted curve in this figure is the sum of our symmetric fit and the all-data asymmetric fit to the differences from the symmetric fit, described later in the section and shown in the left panel of ) and 2009 HST imaging are in close agreement with 2012-2014 results.…”

Section: Evidence For Mid-latitude Asymmetrymentioning

confidence: 99%

“…Eleven years later, Hubble Space Telescope (HST) near-IR im-ages of Uranus revealed many more discrete cloud features, enabling the extension of wind measurements into the northern hemisphere (Karkoschka 1998), confirming an approximate N-S symmetry in the wind profile. Groundbased observations from the Keck II telescope, which combined a large aperture, near-IR wavelengths, and adaptive optics, produced a bounty of cloud features far beyond the Hubble results (Hammel et al 2001(Hammel et al , 2005Sromovsky and Fry 2005;Sromovsky et al 2007;Hammel et al 2009;Sromovsky et al 2009).…”

Section: Introductionmentioning

confidence: 99%

High S/N Keck and Gemini AO imaging of Uranus during 2012–2014: New cloud patterns, increasing activity, and improved wind measurements

Sromovsky

Pater

Fry

et al. 2015

Icarus

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Journal reference: Icarus (2015), http://dx.doi.org/10.1016/j.icarus.2015.05.029. ABSTRACTWe imaged Uranus in the near infrared from 2012 into 2014, using the Keck/NIRC2 camera and Gemini/NIRI camera, both with adaptive optics. We obtained exceptional signal to noise ratios by averaging 8-16 individual exposures in a planet-fixed coordinate system. These noise-reduced images revealed many low-contrast discrete features and large scale cloud patterns not seen before, including scalloped waveforms just south of the equator, and an associated transverse ribbon wave near 6• S. In all three years numerous small (600-700 km wide) and mainly bright discrete features were seen within the north polar region (north of about 55• N). Two small dark spots with bright companions were seen at middle latitudes. Over 850 wind measurements were made, the vast majority of which were in the northern hemisphere. Winds at high latitudes were measured with great precision, revealing an extended region of solid body rotation between 62• N and at least 83• N, at a rate of 4.08±0.015• /h westward relative to the planet's interior (radio) rotation of 20.88• /h westward. Near-equatorial speeds measured with high accuracy give different results for waves and small discrete features, with eastward drift rates of 0.4• /h and 0.1 • /h respectively. The region of polar solid body rotation is a close match to the region of small-scale polar cloud features, suggesting a dynamical relationship. The winds from prior years and those from 2012-2014 are consistent with a mainly symmetric wind profile up to middle latitudes, with a small asymmetric component of ∼0.09• /h peaking near ±30• , and about 60% greater amplitude if only prior years are included, suggesting a declining mid-latitude asymmetry. While winds at high southern latitudes (50• S -90• S) are unconstrained by groundbased observations, a recent reanalysis of 1986 Voyager 2 observations by Karkoschka (2015, Icarus 250, 294-307) has revealed an extremely large north-south asymmetry in this region, which might be seasonal. Greatly increased activity was seen in 2014, including the brightest ever feature seen in K images (de Pater et al. 2015, Icarus 252, 121-128), as well as other significant features, some of which had long lives. Over the 2012-2014 period we identified six persistent discrete features. Three were tracked for more than two years, two more for more than one year, and one for at least 5 months and continuing. Several drifted in latitude towards the equator, and others appeared to exhibit latitudinal oscillations with long periods. We found two pairs of long-lived features that survived multiple passages within their own diameters of each other. Zonally averaged cloud patterns were found to persist over 2012-2014. When averaged over longitude, there is a brightness variation with latitude from 55• N to the pole that is similar to effective methane mixing ratio variations with latitude derived from 2012 STIS observations (Sromovsky et al. 2014, Icarus 238, 137-155).

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“…Uranus Pathfinder's high-resolution atmospheric imaging campaign will seek the turbulent processes that force the wind system. Great dark spots have recently been observed on Uranus [28] and turbulence in the form of small-scale eddies may also be involved in their formation, however, a complete theory is not yet available. Observations of Uranus' atmosphere is crucial for understanding the energy and momentum cycle that powers jetstreams and large vortices in Ice Giant atmospheres.…”

Section: Uranus As An Ice Giantmentioning

confidence: 99%

Uranus Pathfinder: exploring the origins and evolution of Ice Giant planets

et al. 2011

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The "Ice Giants" Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA's Cosmic Vision 2015-2025. UP was proposed to the European Space Agency's M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines

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The Dark Spot in the atmosphere of Uranus in 2006: Discovery, description, and dynamical simulations

Cited by 42 publications

References 22 publications

Effects of Hemispheric Circulation on Uranian Atmospheric Dynamics and Methane Depletion

Effects of Hemispheric Circulation on Uranian Atmospheric Dynamics and Methane Depletion

High S/N Keck and Gemini AO imaging of Uranus during 2012–2014: New cloud patterns, increasing activity, and improved wind measurements

Uranus Pathfinder: exploring the origins and evolution of Ice Giant planets

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