1,652 research outputs found
A dispersive wave pattern on Jupiter's fastest retrograde jet at S
A compact wave pattern has been identified on Jupiter's fastest retrograding
jet at 20S (the SEBs) on the southern edge of the South Equatorial Belt. The
wave has been identified in both reflected sunlight from amateur observations
between 2010 and 2015, thermal infrared imaging from the Very Large Telescope
and near infrared imaging from the Infrared Telescope Facility. The wave
pattern is present when the SEB is relatively quiescent and lacking large-scale
disturbances, and is particularly notable when the belt has undergone a fade
(whitening). It is generally not present when the SEB exhibits its usual
large-scale convective activity ('rifts'). Tracking of the wave pattern and
associated white ovals on its southern edge over several epochs have permitted
a measure of the dispersion relationship, showing a strong correlation between
the phase speed (-43.2 to -21.2 m/s) and the longitudinal wavelength, which
varied from 4.4-10.0 deg. longitude over the course of the observations.
Infrared imaging sensing low pressures in the upper troposphere suggest that
the wave is confined to near the cloud tops. The wave is moving westward at a
phase speed slower (i.e., less negative) than the peak retrograde wind speed
(-62 m/s), and is therefore moving east with respect to the SEBs jet peak.
Unlike the retrograde NEBn jet near 17N, which is a location of strong vertical
wind shear that sometimes hosts Rossby wave activity, the SEBs jet remains
retrograde throughout the upper troposphere, suggesting the SEBs pattern cannot
be interpreted as a classical Rossby wave. Cassini-derived windspeeds and
temperatures reveal that the vorticity gradient is dominated by the baroclinic
term and becomes negative (changes sign) in a region near the cloud-top level
(400-700 mbar) associated with the SEBs, suggesting a baroclinic origin for
this meandering wave pattern. [Abr]Comment: 19 pages, 11 figures, article accepted for publication in Icaru
Seasonal Variability of Saturn's Tropospheric Temperatures, Winds and Para-H from Cassini Far-IR Spectroscopy
Far-IR 16-1000 m spectra of Saturn's hydrogen-helium continuum measured
by Cassini's Composite Infrared Spectrometer (CIRS) are inverted to construct a
near-continuous record of upper tropospheric (70-700 mbar) temperatures and
para-H fraction as a function of latitude, pressure and time for a third of
a Saturnian year (2004-2014, from northern winter to northern spring). The
thermal field reveals evidence of reversing summertime asymmetries superimposed
onto the belt/zone structure. The temperature structure that is almost
symmetric about the equator by 2014, with seasonal lag times that increase with
depth and are qualitatively consistent with radiative climate models. Localised
heating of the tropospheric hazes (100-250 mbar) create a distinct perturbation
to the temperature profile that shifts in magnitude and location, declining in
the autumn hemisphere and growing in the spring. Changes in the para-H
() distribution are subtle, with a 0.02-0.03 rise over the spring
hemisphere (200-500 mbar) perturbed by (i) low- air advected by both the
springtime storm of 2010 and equatorial upwelling; and (ii) subsidence of
high- air at northern high latitudes, responsible for a developing
north-south asymmetry in . Conversely, the shifting asymmetry in the
para-H disequilibrium primarily reflects the changing temperature structure
(and the equilibrium distribution of ), rather than actual changes in
induced by chemical conversion or transport. CIRS results interpolated to
the same point in the seasonal cycle as re-analysed Voyager-1 observations show
qualitative consistency, with the exception of the tropical tropopause near the
equatorial zones and belts, where downward propagation of a cool temperature
anomaly associated with Saturn's stratospheric oscillation could potentially
perturb tropopause temperatures, para-H and winds. [ABRIDGED]Comment: Preprint accepted for publication in Icarus, 29 pages, 18 figure
Far infrared and submillimeter brightness temperatures of the giant planets
The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely
Vesivirus 2117 capsids more closely resemble sapovirus and lagovirus particles than other known vesivirus structures
Vesivirus 2117 is an adventitious agent that in 2009, was identified as a contaminant of CHO cells propagated in bioreactors at a pharmaceutical manufacturing plant belonging to Genzyme. The consequent interruption in supply of Fabrazyme and Cerezyme (drugs used to treat Fabry and Gaucher disease respectively), caused significant economic losses. Vesivirus 2117 is a member of the Caliciviridae; a family of small icosahedral viruses encoding a positive sense RNA genome. We have used cryo-electron microscopy and three dimensional image reconstruction to calculate a structure of vesivirus 2117 virus like particles as well as feline calicivirus and a chimeric sapovirus. We present a structural comparison of several members of the Caliciviridae, showing that the distal P domain of vesivirus 2117 is morphologically distinct from that seen in other known vesivirus structures. Furthermore, at intermediate resolutions we found a high level of structural similarity between vesivirus 2117 and Caliciviridae from other genera, such as sapovirus and rabbit haemorrhagic disease virus. Phylogenetic analysis confirms vesivirus 2117 as a vesivirus closely related to canine vesiviruses. We postulate that morphological differences in virion structure seen between vesivirus clades may reflect differences in receptor usage
The Origin of Nitrogen on Jupiter and Saturn from the N/N Ratio
The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA's
Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia
absorption features on both Jupiter and Saturn in February 2013. Ammonia is the
principle reservoir of nitrogen on the giant planets, and the ratio of
isotopologues (N/N) can reveal insights into the molecular
carrier (e.g., as N or NH) of nitrogen to the forming protoplanets, and
hence the source reservoirs from which these worlds accreted. We targeted two
spectral intervals (900 and 960 cm) that were relatively clear of
terrestrial atmospheric contamination and contained close features of
NH and NH, allowing us to derive the ratio from a single
spectrum without ambiguity due to radiometric calibration (the primary source
of uncertainty in this study). We present the first ground-based determination
of Jupiter's N/N ratio (in the range from to
), which is consistent with both previous space-based studies
and with the primordial value of the protosolar nebula. On Saturn, we present
the first upper limit on the N/N ratio of no larger than
for the 900-cm channel and a less stringent
requirement that the ratio be no larger than for the
960-cm channel ( confidence). Specifically, the data rule out
strong N-enrichments such as those observed in Titan's atmosphere and in
cometary nitrogen compounds. To the extent possible with ground-based
radiometric uncertainties, the saturnian and jovian N/N ratios
appear indistinguishable, implying that N-enriched ammonia ices could
not have been a substantial contributor to the bulk nitrogen inventory of
either planet, favouring the accretion of primordial N from the gas phase
or as low-temperature ices.Comment: 33 pages, 19 figures, manuscript accepted for publication in Icaru
Neptune at Summer Solstice: Zonal Mean Temperatures from Ground-Based Observations 2003-2007
Imaging and spectroscopy of Neptune's thermal infrared emission is used to
assess seasonal changes in Neptune's zonal mean temperatures between Voyager-2
observations (1989, heliocentric longitude Ls=236) and southern summer solstice
(2005, Ls=270). Our aim was to analyse imaging and spectroscopy from multiple
different sources using a single self-consistent radiative-transfer model to
assess the magnitude of seasonal variability. Globally-averaged stratospheric
temperatures measured from methane emission tend towards a quasi-isothermal
structure (158-164 K) above the 0.1-mbar level, and are found to be consistent
with spacecraft observations of AKARI. This remarkable consistency, despite
very different observing conditions, suggests that stratospheric temporal
variability, if present, is 5 K at 1 mbar and 3 K at 0.1 mbar during
this solstice period. Conversely, ethane emission is highly variable, with
abundance determinations varying by more than a factor of two. The retrieved
C2H6 abundances are extremely sensitive to the details of the T(p) derivation.
Stratospheric temperatures and ethane are found to be latitudinally uniform
away from the south pole (assuming a latitudinally-uniform distribution of
stratospheric methane). At low and midlatitudes, comparisons of synthetic
Voyager-era images with solstice-era observations suggest that tropospheric
zonal temperatures are unchanged since the Voyager 2 encounter, with cool
mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25-50
{\mu}m mapping of tropospheric temperatures and para-hydrogen disequilibrium
suggests a symmetric meridional circulation with cold air rising at
mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the
equator and poles (super-equilibrium para-H2 conditions). The most significant
atmospheric changes are associated with the polar vortex (absent in 1989).Comment: 35 pages, 19 figures. Accepted for publication in Icaru
Observational constraints on the atmospheres of Uranus and Neptune from new measurements near 10 micron
Uranus was detected at 10.3, 11.6 and 12.5 micrometers approximately 1 micrometer spectral bandpasses, with respective brightness temperatures of 74.0 + 0.9 or -1.1, 67.6 + 0.5 or -0.7, and 65.5 + 0.6 or -0.7 K and the first detection of Neptune at 10.3 micrometers with a brightness temperature of 77.5 + 0.7 or -0.9 K. We also detected Neptune at 11.36 micrometers with 2% spectral resolution at 81.0 + 0.8 or -0.9 K. The 10 micrometers continuous of both Uranus and Neptune may in part be due to reflected solar radiation as well as thermal emission. If all of the observed flux is reflected light, then the maximum geometric albedo of Uranus is 0.115 + or - 0.020, and that of Neptune is 0.229 + or - 0.043. In the context of previous observations in this region, the maximum stratospheric C2H6 mixing ratio is found to be 3 x 10 to the -8 power for Uranus and 3 x 10 to the -6 power for Neptune. A value for the maximum mixing ratio in the stratosphere of Neptune on the order of 1 - 0.004 appears to be consistent with the available data
EVOLUTION OF THE STRATOSPHERIC TEMPERATURE AND CHEMICAL COMPOSITION OVER ONE TITANIAN YEAR
Since the Voyager 1 (V1) flyby in 1980, Titans exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titan year or 29.5 Earth years was completed in May 2010). In this study we search for temporal variations affecting Titans atmospheric thermal and chemical structure within that year. We process Cassini CIRS data taken during the Titan flybys from 2006-2013 and compare them to the 1980 V1IRIS spectra (re-analyzed here). We also consider data from Earth-based and -orbiting observatories (such as from the ISO, re-visited). When we compare the CIRS 2010 and the IRIS data we find limited inter-annual variations, below the 25 or35 levels for the lower and middle, or the high latitudes, respectively. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50degN to 50degS, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by GCM and photochemical models. However, some exceptions exist among the most complex hydrocarbons (C4H2 and C3H4), especially in the North. In the Southern latitudes, since 2012, we see a trend for an increase of several trace gases, possibly indicative of a seasonal atmospheric reversal. At the Northern latitudes we found enhanced abundances around the period of the northern spring equinox in mid-2009 (as in Bampasidis et al. 2012), which subsequently decreased (from 2010-2012) returning to values similar to those found in the V1 epoch a Titanian year before
Space shuttle low pressure auxiliary propulsion subsystem design definition Subtask A report
Space shuttle low pressure, hydrogen oxygen auxiliary propulsion subsystem requirements, tradeoffs, and concept selectio
Time variability of Neptune's horizontal and vertical cloud structure revealed by VLT/SINFONI and Gemini/NIFS from 2009 to 2013
New observations of Neptune's clouds in the near infrared were acquired in October 2013 with SINFONI on ESO's Very Large Telescope (VLT) in Chile. SINFONI is an Integral Field Unit spectrometer returning a 64 × 64 pixel image with 2048 wavelengths. Image cubes in the J-band (1.09-1.41 μm) and H-band (1.43-1.87 μm) were obtained at spatial resolutions of 0.1″and 0.025″per pixel, while SINFONI's adaptive optics provided an effective resolution of approximately 0.1″. Image cubes were obtained at the start and end of three successive nights to monitor the temporal development of discrete clouds both at short timescales (i.e. during a single night) as well as over the longer period of the three-day observing run. These observations were compared with similar H-band observations obtained in September 2009 with the NIFS Integral Field Unit spectrometer on the Gemini-North telescope in Hawaii, previously reported by Irwin et al. (2011) [Icarus, 216, 141-158], and previously unreported Gemini/NIFS observations at lower spatial resolution made in 2011.We find both similarities and differences between these observations, spaced over four years. The same overall cloud structure is seen with high, bright clouds visible at mid-latitudes (30-40°N,S), with slightly lower clouds observed at lower latitudes, together with small discrete clouds seen circling the pole at a latitude of approximately 60°S. However, while discrete clouds were visible at this latitude at both the main cloud deck level (at 2-3 bar) and in the upper troposphere (100-500 mb) in 2009, no distinct deep (2-3 bar), discrete circumpolar clouds were visible in 2013, although some deep clouds were seen at the southern edge of the main cloud belt at 30-40°S, which have not been observed before. The nature of the deep sub-polar discrete clouds observed in 2009 is intriguing. While it is possible that in 2013 these deeper clouds were masked by faster moving, overlying features, we consider that it is unlikely that this should have happened in 2013, but not in 2009 when the upper-cloud activity was generally similar. Meanwhile, the deep clouds seen at the southern edge of the main cloud belt at 30-40°S in 2013, should also have been detectable in 2009, but were not seen. Hence, these observations may have detected a real temporal variation in the occurrence of Neptune's deep clouds, pointing to underlying variability in the convective activity at the pressure of the main cloud deck at 2-3 bar near Neptune's south pole and also in the main observable cloud belt at 30-40°S.</p
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