* Astronomy

Members Login
Post Info TOPIC: Uranus atmosphere


L

Posts: 130163
Date:
RE: Uranus atmosphere
Permalink  
 


Title: Dynamics of cloud features on Uranus
Author: Lawrence Sromovsky, Patrick Fry

Near-infrared adaptive optics imaging of Uranus by the Keck 2 telescope during 2003 and 2004 has revealed numerous discrete cloud features, 70 of which were used to extend the zonal wind profile of Uranus up to 60° N. We confirmed the presence of a north-south asymmetry in the circulation (Karkoschka, Science 111, 570-572, 1998), and improved its characterisation. We found no clear indication of long term change in wind speed between 1986 and 2004, although results of Hammel et al. (2001, Icarus 153, 229-235) based on 2001 HST and Keck observations average ~10 m/s less westward than earlier and later results, and 2003 observations by Hammel et al. (2005, Icarus 175, 534-545) show increased wind speeds near 45° N, which we don't see in our 2003-2004 observations. We observed a wide range of lifetimes for discrete cloud features: some features evolve within ~1 hour, many have persisted at least one month, and one feature near 34° S (termed S34) seems to have persisted for nearly two decades, a conclusion derived with the help of Voyager 2 and HST observations. S34 oscillates in latitude between 32° S and 36.5° S, with a period of ~1000 days, which may be a result of a non-barotropic Rossby wave. It also varied its longitudinal drift rate between -20° /day and -31° /day in approximate accord with the latitudinal gradient in the zonal wind profile, exhibiting behaviour similar to that of the DS2 feature observed on Neptune (Sromovsky et al., Icarus 105, 110-141, 1993). S34 also exhibits a superimposed rapid oscillation with an amplitude of 0.57° in latitude and period of 0.7 days, which is approximately consistent with an inertial oscillation.

Read more (2336kb, PDF)



__________________


L

Posts: 130163
Date:
Permalink  
 

Title: Methane on Uranus: The case for a compact CH4 cloud layer at low latitudes and a severe CH4 depletion at high-latitudes based on re-analysis of Voyager occultation measurements and STIS spectroscopy
Author: Lawrence Sromovsky, Patrick Fry, Joo Hyeon Kim

Lindal et al. (1987, J. Geophys. Res. 92, 14987-15001) presented a range of temperature and CH4 profiles for Uranus that were consistent with 1986 Voyager radio occultation measurements. A localized refractivity slope variation near 1.2 bars was interpreted to be the result of a condensed CH4 cloud layer. However, models fit to near-IR spectra found particle concentrations in the 1.5-3 bar range (Sromovsky et al. 2006, Icarus 182, 577-593, Sromovsky and Fry 2008, Icarus 193, 211-229, Irwin et al. 2010, Icarus 208, 913-926), and a recent analysis of STIS spectra argued that aerosol particles formed diffusely distributed hazes, with no compact condensation layer (Karkoschka and Tomasko 2009, Icarus 202, 287-309). Trying to reconcile these results, we reanalysed the occultation observations with a He volume mixing ratio reduced from 0.15 to 0.116, which is near the edge of the 0.033 range given by Conrath et al. (1987, J. Geophys. Res., 15003-10). This allowed us to obtain saturated CH4 mixing ratios within the putative cloud layer and to reach above-cloud and deep CH4 mixing ratios compatible with STIS spectral constraints. Using a 5-layer vertical aerosol model with two compact cloud layers in the 1-3 bar region, we find that the best fit pressure for the upper layer is virtually identical to the pressure range inferred from the occultation analysis for a methane mixing ratio near 4% at 5 deg S, arguing that Uranus does indeed have a compact methane cloud layer. While our cloud model can fit the latitudinal variations in spectra between 30 deg S and 20 deg N using the same temperature and CH4 profiles, closer to the pole, the model requires the introduction of an increasingly strong upper tropospheric depletion of CH4 at increased latitudes, in rough agreement with the trend identified by Karkoschka and Tomasko (2009, Icarus 202, 287-309).

Read more (694kb, PDF)



__________________


L

Posts: 130163
Date:
Permalink  
 

Title: Uranus at equinox: Cloud morphology and dynamics 
Author: Lawrence Sromovsky, Patrick Fry, Heidi Hammel, William Ahue, Imke de Pater, Kathy Rages, Mark Showalter, Marcos van Dam 

As the 7 December 2007 equinox of Uranus approached, ring and atmosphere observers produced a substantial collection of observations using the 10-m Keck telescope and the Hubble Space Telescope. Those spanning the period from 7 June 2007 through 9 September 2007 we used to identify and track cloud features, determine atmospheric motions, characterize cloud morphology and dynamics, and define changes in atmospheric band structure. We confirmed the existence of the suspected northern hemisphere prograde jet, locating its peak near 58 N, and extended wind speed measurements to 73 N. For 28 cloud features we obtained extremely high wind-speed accuracy through extended tracking times. The new results confirm a small N-S asymmetry in the zonal wind profile, and the lack of any change in the southern hemisphere between 1986 (near solstice) and 2007 (near equinox) suggests that the asymmetry may be permanent rather than seasonally reversing. In the 2007 images we found two prominent groups of discrete cloud features with very long lifetimes. The one near 30 S has departed from its previous oscillatory motion and started a significant northward drift, accompanied by substantial morphological changes. The complex of features near 30 N remained at a nearly fixed latitude, while exhibiting some characteristics of a dark spot accompanied by bright companion features. Smaller and less stable features were used to track cloud motions at other latitudes, some of which lasted over many planet rotations, though many could not be tracked beyond a single transit. A bright band has developed near 45 N, while the bright band near 45 S has begun to decline, both events in agreement with the idea that the asymmetric band structure of Uranus is a delayed response to solar forcing, but with a surprisingly short delay of only a few years. 

Read more (4231kb, PDF)



__________________


L

Posts: 130163
Date:
Permalink  
 

Mystery storms rage across face of Uranus

Read more



__________________


L

Posts: 130163
Date:
Permalink  
 

Weather on the Outer Planets Only Goes So Deep

What is the long-range weather forecast for the giant planets Uranus and Neptune? These planets are home to extreme winds blowing at speeds of over 1000 km/hour, hurricane-like storms as large around as Earth, immense weather systems that last for years and fast-flowing jet streams. Both planets feature similar climates, despite the fact that Uranus is tipped on its side with the pole facing the sun during winter. The winds on these planets have been observed on their outer surfaces; but to get a grasp of their weather systems, we need to have an idea of what is going on underneath. For instance, do the atmospheric patterns arise from deep down in the planet, or are they confined to shallower processes nearer the surface? New research at the Weizmann Institute of Science, the University of Arizona and Tel Aviv University, which was published online today in Nature, shows that the wind patterns seen on the surface can extend only so far down on these two worlds.
Read more



__________________


L

Posts: 130163
Date:
Permalink  
 

Keck observations bring weather of Uranus into sharp focus

uracolor12A_SM9_RR-7_15_BGR-12_24.jpg

Thanks to a new technique applied at the Keck Observatory, Uranus is coming into sharp focus through high-resolution infrared images, revealing in incredible detail the bizarre weather of the seventh planet from the sun.
The images were released in Reno, Nev. today (Oct. 17, 2012) at a meeting of the American Astronomical Society's Division of Planetary Sciences and provide the best look to date of Uranus's complex and enigmatic weather.

Read more



__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard