Fig 1 - uploaded by Maarten Roos-Serote
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The same area (longitude, latitude) on the night side of the planet, indicated by the rectangle, is observed at two different times not far apart. As the planet rotates, the area moves from A to B as seen by the observer. The observer's (spacecraft) position relative to the planet does not change noticeably. The emission angle of the observation changes.
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The upper jovian atmosphere is particularly transparent at wavelengths near 5μm. Levels well below the cloud layers, which are situated between 0.5 and 2bar, can be sounded. Large spatial variations of the brightness are observed, which are directly related to the opacity of the overlying cloud layer. Yet, the nature of the 5-μm absorber in the jov...
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... of the spacecraft, which is negligible in such a short time period. Fig. 1 illustrates the effect. All of these observations were recorded in the night side of the planet. Thus, we consider thermal radiation of Jupiter only and how this radiation is scattered by the clouds. In Fig. 2, the pair of radiance maps at 5 mm for the largest of these NIMS cubes, C9CYL03_04, are shown together with their respective ...
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... observed spectrum will have more in common with the hemispherically integrated spectrum than a direct line-of-sight spectrum. This has important consequences for the determinations of gas abundances since the contribution function for hemispherically integrated spectra peaks at lower pressures than for simple nadir sounding. This can be seen in Fig. 10 where the variation in the peak of the contribution function is plotted against wavelength for nadir-and hemispherically integrated observations. The difference in peak position is of the order of 1 bar. This will affect retrieved abundances, Table 3. The cloud again has a fractional scale height ¼ 0:5 and w 2 has been calculated for ...
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3) , A. di Sarra (4) , B. Clemesha (5) , and C. Zehner (2) (1) SERCO Italia, c/o ESA/ESRIN, via Galileo Galilei, Frascati (RM), Italy, Email: Stefano.Casadio@esa.int (2) ESA/ESRIN, via Galileo Galilei, Frascati (RM), Italy (3) Max-Planck Institute for Chemistry, Mainz, c/o EUMETSAT, Am Kavaleriesand 31, 64295 Darmstadt, Germany (4) ENEA, ACS-CLIM-O...
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... The observed effect is also unlikely to be due to limb darkening at high altitudes. Firstly, previous studies have shown that Jupiter's tropospheric clouds are highly scattering, which minimises the effect of limb darkening (Roos-Serote and Irwin, 2006;Giles et al., 2015). Figure 11: Identification of AsH 3 absorption features in the 5-μm window. ...
Jupiter's tropospheric composition is studied using high resolution spatially-resolved 5-micron observation from the CRIRES instrument at the Very Large Telescope. The high resolving power (R=96,000) allows us to spectrally resolve the line shapes of individual molecular species in Jupiter's troposphere and, by aligning the slit north-south along Jupiter's central meridian, we are able to search for any latitudinal variability. Despite the high spectral resolution, we find that there are significant degeneracies between the cloud structure and aerosol scattering properties that complicate the retrievals of tropospheric gaseous abundances and limit conclusions on any belt-zone variability. However, we do find evidence for variability between the equatorial regions of the planet and the polar regions. Arsine (AsH$_3$) and phosphine (PH$_3$) both show an enhancement at high latitudes, while the abundance of germane (GeH$_4$) remains approximately constant. These observations contrast with the theoretical predictions from Wang et al. (2016) and we discuss the possible explanations for this difference.
... This can be consistent with the previous imaging studies if the overlying opacity is dominant at visible wavelengths, obscuring the deeper cloud, but it may also suggest that the cloud tops may be deeper than the inferred and predicted height. A comparison between the visible and thermal data is particularly interesting given the previous apparent discrepancy in the Galileo studies of Jupiter, where the Near-Infrared Mapping Spectrometer (NIMS) and the Solid State Imager (SSI) provided different estimates of the contrasting cloud heights in the jovian atmosphere (Irwin et al., 2001; Banfield et al., 1998; Sromovsky and Fry, 2002; Roos-Serote and Irwin, 2006). The origin of the haze layers that define the upper troposphere and lower stratosphere remain mostly speculative. ...
... This can be consistent with the previous imaging studies if the overlying opacity is dominant at visible wavelengths, obscuring the deeper cloud, but it may also suggest that the cloud tops may be deeper than the inferred and predicted height. A comparison between the visible and thermal data is particularly interesting given the previous apparent discrepancy in the Galileo studies of Jupiter, where the Near-Infrared Mapping Spectrometer (NIMS) and the Solid State Imager (SSI) provided different estimates of the contrasting cloud heights in the jovian atmosphere ( Irwin et al., 2001;Banfield et al., 1998;Sromovsky and Fry, 2002;Roos-Serote and Irwin, 2006). ...
... The cloud parameters therefore cannot vary strongly with wavelength, as otherwise any spectral features would be more evident in the cool, optically thick spectra than in the warm cloud-free spectra. In this initial model, we therefore use a spectrally flat cloud, as has been previously suggested by both ground-based and space-based studies, including Drossart et al. (1982), Bézard et al. (1983), Bjoraker et al. (1986) and Roos-Serote and Irwin (2006). The scattering parameters for this cloud were fixed Figure 6: Fit obtained using nightside data from the equatorial zone. ...
... The conclusions drawn from Figure 12 are independent of the cloud location, provided that it is above the 1.2 bar level. This is in good agreement with the results from Roos-Serote and Irwin (2006), who performed a limb darkening analysis using pairs of 5 µm data cubes from Galileo NIMS. With g fixed at 0.8, they found that an optimum fit was obtained with ω = 0.9 ± 0.5. ...
Jupiter's tropospheric composition and cloud structure are studied using
Cassini VIMS 4.5-5.1 μm thermal emission spectra from the 2000-2001 flyby.
We make use of both nadir and limb darkening observations on the planet's
nightside, and compare these with dayside observations. Although there is
significant spatial variability in the 5-μm brightness temperatures, the
shape of the spectra remain very similar across the planet, suggesting the
presence of a spectrally-flat, spatially inhomogeneous cloud deck. We find that
a simple cloud model consisting of a single, compact cloud is able to reproduce
both nightside and dayside spectra, subject to the following constraints: (i)
the cloud base is located at pressures of 1.2 bar or lower; (ii) the cloud
particles are highly scattering; (iii) the cloud is sufficiently spectrally
flat. Using this cloud model, we search for global variability in the cloud
opacity and the phosphine deep volume mixing ratio. We find that the vast
majority of the 5-μm inhomogeneity can be accounted for by variations in
the thickness of the cloud decks, with huge differences between the cloudy
zones and the relatively cloud-free belts. The relatively low spectral
resolution of VIMS limits reliable retrievals of gaseous species, but some
evidence is found for an enhancement in the abundance of phosphine at high
latitudes.
... [21] Our examination (not shown) and the previous study [Roos-Serote and Irwin, 2006] both suggest that the magnitude of Jupiter's 5 mm spectra varies with time and space, but the shape of the spectra basically remains unchanged. Therefore, it is reasonable to assume that the ratio of wavelength-integrated radiance between the VIMS spectral range (i.e., 4.4-5.1 mm) and the complete spectral range (i.e., 4.4-5.6 mm) does not change significantly with time and space on Jupiter. ...
The emitted power of Jupiter and its meridional distribution are
determined from observations by the Composite Infrared Spectrometer and
Visual and Infrared Mapping Spectrometer onboard Cassini during its
flyby en route to Saturn in late 2000 and early 2001. Jupiter's
global-average emitted power and effective temperature are measured to
be 14.10 ± 0.03 Wm-2 and 125.57 ± 0.07 K,
respectively. Jupiter's 5 μm thermal emission contributes 0.7
± 0.1% to the total emitted power at the global scale, but it can
reach 1.9 ± 0.6% at 15°N. The meridional distribution of
emitted power shows a significant asymmetry between the two hemispheres
with the emitted power in the northern hemisphere 3.0 ± 0.3%
larger than that in the southern hemisphere. Such an asymmetry shown in
the Cassini epoch (2000-2001) is not present in the Voyager epoch
(1979). In addition, the global-average emitted power increased 3.8
± 1.0% between the two epochs. The temporal variation of
Jupiter's total emitted power is mainly due to the warming of
atmospheric layers around the pressure level of 200 mbar. The temporal
variation of emitted power was also discovered on Saturn. Therefore, we
suggest that the varying emitted power is a common phenomenon on the
giant planets.
Jupiter’s tropospheric composition is studied using high resolution spatially-resolved 5-µm observation from the CRIRES instrument at the Very Large Telescope. The high resolving power (R=96,000) allows us to spectrally resolve the line shapes of individual molecular species in Jupiter’s troposphere and, by aligning the slit north-south along Jupiter’s central meridian, we are able to search for any latitudinal variability. Despite the high spectral resolution, we find that there are significant degeneracies between the cloud structure and aerosol scattering properties that complicate the retrievals of tropospheric gaseous abundances and limit conclusions on any belt-zone variability. However, we do find evidence for variability between the equatorial regions of the planet and the polar regions. Arsine (AsH3) and phosphine (PH3) both show an enhancement at high latitudes, while the abundance of germane (GeH4) remains approximately constant. These observations contrast with the theoretical predictions from Wang et al. (2016) and we discuss the possible explanations for this difference.
In its decade of operation the Cassini mission has allowed us to look deep
into Saturn's atmosphere and investigate the processes occurring below its
enshrouding haze. We use Visual and Infrared Mapping Spectrometer (VIMS)
4.6-5.2 micron data from early in the mission to investigate the location and
properties of Saturn's cloud structure between 0.6 and 5 bars. We average
nightside spectra from 2006 over latitude circles and model the spectral limb
darkening using the NEMESIS radiative transfer and retrieval tool. We present
our best-fit deep cloud model for latitudes between -40 and 50 degrees, along
with retrieved abundances for NH3, PH3 and AsH3. We find an increase in NH3
abundance at the equator, a cloud base at ~2.3 bar and no evidence for cloud
particles with strong absorption features in the 4.6-5.2 micron wavelength
range, all of which are consistent with previous work. Non-scattering cloud
models assuming a composition of either NH3 or NH4SH, with a scattering haze
overlying, fit limb darkening curves and spectra at all latitudes well; the
retrieved optical depth for the tropospheric haze is decreased in the northern
(winter) hemisphere, implying that the haze has a photochemical origin. Our
ability to test this hypothesis by examining spectra at different seasons is
restricted by the varying geometry of VIMS observations over the life of the
mission, and the appearance of the Saturn storm towards the end of 2010.
Jupiter’s tropospheric composition and cloud structure are studied using Cassini VIMS 4.5–5.1 μm thermal emission spectra from the 2000–2001 flyby. We make use of both nadir and limb darkening observations on the planet’s nightside, and compare these with dayside observations. Although there is significant spatial variability in the 5-μm brightness temperatures, the shape of the spectra remain very similar across the planet, suggesting the presence of a spectrally-flat, spatially inhomogeneous cloud deck. We find that a simple cloud model consisting of a single, compact cloud is able to reproduce both nightside and dayside spectra, subject to the following constraints: (i) the cloud base is located at pressures of 1.2 bar or lower; (ii) the cloud particles are highly scattering; and (iii) the cloud is sufficiently spectrally flat. Using this cloud model, we search for global variability in the cloud opacity and the phosphine deep volume mixing ratio. We find that the vast majority of the 5-μm inhomogeneity can be accounted for by variations in the thickness of the cloud decks, with huge differences between the cloudy zones and the relatively cloud-free belts. The relatively low spectral resolution of VIMS limits reliable retrievals of gaseous species, but some evidence is found for an enhancement in the abundance of phosphine at high latitudes.
Using high-resolution Cassini ISS images with wavelengths ranging from the ultraviolet to the near infrared, we have retrieved Saturn’s atmospheric aerosol structure and properties for a broad range of latitudes in the southern hemisphere. The observations are consistent with two distinct layers of haze above a scattered cloud. Each layer is characterized by a vertical location, an optical thickness, and an effective mean particle size, all of which vary with latitude. The tropospheric haze is optically thickest and extends to the greatest heights (∼40 mbar) over the equator; its top surface is at significantly greater depths (∼150 mbar) at mid-latitudes. The height of the haze correlates well with position of the tropopause as indicated by the temperature field. Beneath this haze, we find a scattered denser cloud responsible for small-scale contrasts at an average depth of 1.75 ± 0.4 bar, with some features as deep as 2.5 bar or greater.
