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| Titel |
Spatial Variability in the Stratosphere of Uranus |
| VerfasserIn |
Glenn Orton, Lawrence Trafton, Thérèse Encrenaz, John Lacy, Leigh Fletcher, James Sinclair, Julianne Moses, Cedric Leyrat, Eric Pantin |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102767
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| Publikation (Nr.) |
 EGU/EGU2015-2166.pdf |
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| Zusammenfassung |
| Observations of spatial variability in the atmosphere of Uranus have been limited to cloud
properties and temperatures in the troposphere from a combination of spacecraft and
ground-based observations. We report observations of the spatial distribution of (1) the
stratospheric temperature field and (2) the distribution of stratospheric acetylene from
ground-based mid-infrared observations using giant telescopes that resolve the planet
spatially. (1) Temperatures in the stratosphere were derived from spectral scanning of the H2
rotational S(1) quadrupole using the TEXES spectrometer at the Gemini North observatory in
2007, near Uranus’ equinox at high resolution (R=55,000). The H2 S(1) line was mapped by
scanning the slit longitudinally across the entire disk of the planet. The observed
radiances from the line center emerge primarily from the 0.1-0.3mbar pressure level. As
expected for the “thermally inverted” stratosphere, the planet is limb brightened at all
latitudes, generally consistent with the predictions for the temperature structure
derived from Spitzer IRS disk-averaged spectra (Orton et al. 2014 Icarus 243, 494). A
cut through the central meridian shows a generally smooth variability, with the
(IAU-defined) northern hemisphere emerging from winter darkness marginally brighter
than the southern hemisphere, consistent with a smooth meridional gradient of
temperatures. A cut across the equator reveals an ostensible central brightening, as
well as equal brightening toward the limbs. (2) The distribution of C2H2 in the
stratosphere was derived from images of thermal emission made in 2009 using the
mid-infrared imager/spectrometers VISIR at the Very Large Telescope and T-ReCS at
the Gemini South Observatory using a 13.04-μm moderate-band (NeII_2) filter.
Because the continuum in this spectral region is so faint, the upwelling radiation
is dominated by acetylene emission from roughly the same pressure level at the
radiation from the H2 S(2) quadrupole line. Although the general center-to-limb
structure is consistent with predictions from the C2H2 distribution derived from the
low-eddy-diffusion rate models fitting the Spitzer IRS data (Orton et al. 2014 Icarus 243,
471), there is a strong bifurcation between a lower-latitude, low-radiance region and
higher-latitude high-radiance region with a distinct boundary near ~25°latitude from the
equator in both northern and southern hemispheres. Given the apparent smooth
meridional variability of temperature, this implies a distinct boundary of higher vs.
lower C2H2 abundance regions that is most likely to be maintained dynamically. |
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