Deep Atmosphere Research Articles

A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90-120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft and ground-based observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission owing to a lack of data and of an adequate observing geometry. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 microm, extending from 90 to 120 km altitude, and of night-side O2 emission extending from 95 to 100 km. The CO2 emission peak occurs at approximately 115 km and varies with solar zenith angle over a range of approximately 10 km. This confirms previous modelling, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96 km +/- 1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted.

Planetary atmospheres with ALMA

Thanks to its sensitivity, spatial resolution and instantaneous uv-coverage, ALMA will permit many new studies related to the general topic of the couplings between chemistry and dynamics in planetary atmospheres. It will include: (1) three-dimensional mapping of composition, temperatures and winds in the atmospheres of Mars, Venus and Titan; (2) several aspects of Giant Planet composition and dynamics, such as the origin of oxygen, the evolution of Shoemaker–Levy 9 products in Jupiter’s atmosphere, and the deep atmosphere structure and meteorology; (3) the study of tenuous and distant atmospheres (Io, Enceladus, Pluto, Triton and other Kuiper Belt objects).

Numerical models of Saturn's long-lived anticyclones

New measurements of the dynamical properties of the long-lived Saturn's anticyclonic vortex known as “Brown Spot” (BS), discovered during the Voyager 1 and 2 flybys in 1980–1981 at latitude 43.1° N, and model simulations using the EPIC code, have allowed us to constrain the vertical wind shear and static stability in Saturn's atmosphere (vertically from pressure levels from 10 mbar to 10 bars) at this latitude. BS dynamical parameters from Voyager images include its size as derived from cloud albedo gradient (6100 km East–West times 4300 km North–South), mean tangential velocity ( 45 ± 11 m s −1 at 2400 km from center) and mean vorticity ( 4.0 ± 1.5 × 10 −5 s −1 ) , lifetime >1 year, drift velocity ( 5.3 ± 0.1 m s −1 ) relative to Voyager's System III rotation rate, mean meridional atmospheric wind profile at cloud level at its latitude and interactions with nearby vortices (pair orbiting and merging). An extensive set of numerical experiments have been performed to try to reproduce this single vortex properties and its observed mergers with smaller anticyclones by varying the vertical structure of the zonal wind and adjusting the static stability of the lower stratosphere and upper troposphere. Within the context of the EPIC model atmosphere, our simulations indicate that BS's drift velocity, longevity and merging behavior are very sensitive to these two atmospheric properties. The best results at the BS latitude occur for static stability conditions that use a Brunt–Väisäla frequency constant in the upper troposphere (from 0.5 to 10 bar) above 3.2 × 10 −3 s −1 and suggest that the wind speed slightly decays below the visible cloud deck from ∼0.5 to 10 bar at a rate ∂ u / ∂ z ∼ 2 – 6 m s −1 per scale height. Changing the vortex latitude within the band domain introduces latitude oscillations in the vortex but not a significant meridional migration. Simulated mergers always showed orbiting movements with a typical merging time of about three days, very close to the time-span observed in the interaction of real vortices. Although these results are not unique in view of the unknowns of Saturn's deep atmosphere, they serve to constrain realistically its structure for ongoing Cassini observations.

Geomagnetic field strength 3.2 billion years ago recorded by single silicate crystals

The strength of the Earth's early geomagnetic field is of importance for understanding the evolution of the Earth's deep interior, surface environment and atmosphere. Palaeomagnetic and palaeointensity data from rocks formed near the boundary of the Proterozoic and Archaean eons, some 2.5 Gyr ago, show many hallmarks of the more recent geomagnetic field. Reversals are recorded, palaeosecular variation data indicate a dipole-dominated morphology and available palaeointensity values are similar to those from younger rocks. The picture before 2.8 Gyr ago is much less clear. Rocks of the Archaean Kaapvaal craton (South Africa) are among the best-preserved, but even they have experienced low-grade metamorphism. The variable acquisition of later magnetizations by these rocks is therefore expected, precluding use of conventional palaeointensity methods. Silicate crystals from igneous rocks, however, can contain minute magnetic inclusions capable of preserving Archaean-age magnetizations. Here we use a CO2 laser heating approach and direct-current SQUID magnetometer measurements to obtain palaeodirections and intensities from single silicate crystals that host magnetite inclusions. We find 3.2-Gyr-old field strengths that are within 50 per cent of the present-day value, indicating that a viable magnetosphere sheltered the early Earth's atmosphere from solar wind erosion.

Isotopic Fractionation of Nitrogen in Ammonia in the Troposphere of Jupiter

Laboratory measurements of the photoabsorption cross section of ^(15)NH_3 at wavelengths between 140 and 220 nm are presented for the first time. Incorporating the measured photoabsorption cross sections of ^(15)NH_3 and ^(14)NH_3 into a one-dimensional photochemical diffusive model, we find that at 400 mbar, the photolytic efficiency of ^(15)NH_3 is about 38% greater than that of ^(14)NH_3. In addition, it is known that ammonia can condense in the region between 200 and 700 mbar, and the condensation tends to deplete the abundance ratio of ^(15)NH_3 and ^(14)NH_3. By matching the observed ratio of ^(15)NH_3 and ^(14)NH_3 at 400 mbar, the combined effect of photolysis and microphysics produces the ratio of (2.42 ± 0.34) × 10^(-3) in the deep atmosphere, in excellent agreement with the Galileo spacecraft measurements. The usefulness of the isotopic composition of ammonia as a tracer of chemical and dynamical processes in the troposphere of Jupiter is discussed.

A spectrum of an extrasolar planet

Of the over 200 known extrasolar planets, 14 exhibit transits in front of their parent stars as seen from Earth. Spectroscopic observations of the transiting planets can probe the physical conditions of their atmospheres. One such technique can be used to derive the planetary spectrum by subtracting the stellar spectrum measured during eclipse (planet hidden behind star) from the combined-light spectrum measured outside eclipse (star + planet). Although several attempts have been made from Earth-based observatories, no spectrum has yet been measured for any of the established extrasolar planets. Here we report a measurement of the infrared spectrum (7.5-13.2 microm) of the transiting extrasolar planet HD 209458b. Our observations reveal a hot thermal continuum for the planetary spectrum, with an approximately constant ratio to the stellar flux over this wavelength range. Superposed on this continuum is a broad emission peak centred near 9.65 microm that we attribute to emission by silicate clouds. We also find a narrow, unidentified emission feature at 7.78 microm. Models of these 'hot Jupiter' planets predict a flux peak near 10 microm, where thermal emission from the deep atmosphere emerges relatively unimpeded by water absorption, but models dominated by water fit the observed spectrum poorly.

To the depths of Venus: Exploring the deep atmosphere and surface of our sister world with Venus Express

With its comprehensive suite of near-infrared instruments, Venus Express will perform the first detailed global exploration of the depths of the thick Venusian atmosphere. Through the near-daily acquisition of Visible and Infrared maps and spectra, three infrared-sensing instruments—the Planetary Fourier Spectrometer (PFS), the Venus Monitoring Camera (VMC), and the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)—will comprehensively investigate the Thermal structure, meteorology, dynamics, chemistry, and stability of the deep Venus atmosphere. For the surface, these instruments will provide clues to the emissivity of surface materials and provide direct evidence of active volcanism. In so doing, ESA's Venus Express Mission directly addresses numerous high-priority Venus science objectives advanced by America's National Research Council (2003) decadal survey of planetary science.

Long-term variations in the microwave brightness temperature of the Uranus atmosphere

We present a self-consistent, 36-year record of the disk-averaged radio brightness of Uranus at wavelengths near 3.5 cm. It covers nearly half a uranian year, and includes both equatorial and polar viewing geometries (corresponding to equinox and solstice, respectively). We find large (greater than 30 K) changes over this time span. In agreement with analyses made of more limited microwave data sets, our observations suggest the changes are not caused by geometric effects alone, and that temporal variations may exist in the deep uranian troposphere down to pressures of tens of bars. Our data also support an earlier suggestion that a rapid, planetary-scale change may have occurred in late 1993 and early 1994. The seasonal record presented here will be useful for constraining dynamical models of the deep atmosphere, and for interpreting observations made during Uranus' 2007 equinox passage. As part of a multi-wavelength observing campaign for this event, the Goldstone-Apple Valley Radio Telescope (GAVRT) project will continue to make frequent, single-dish observations near 3.5 cm.

The EPIC atmospheric model with an isentropic/terrain-following hybrid vertical coordinate

The explicit planetary isentropic coordinate (EPIC) atmospheric model has been upgraded to use a hybrid vertical coordinate, ζ, that transitions continuously from potential temperature, θ, aloft to a function of a pressure coordinate, σ, that is terrain following near topography. The result is a model that simulates terrestrial and gas-giant atmospheres equally well. Considering that surface pressure varies by orders of magnitude from one planet to the next whereas topography has a roughly similar geometric scale everywhere, we define σ in terms of log p rather than the traditional p. We include a pure-sigma region at the bottom that allows for accurate modeling of the planetary boundary layer (PBL) for terrestrial applications and the deep atmosphere for gas-giant applications. We describe the functional form for ζ ( θ , σ ) , the method used to calculate θ, and the method used to calculate the hybrid vertical velocity, ζ ˙ , all of which are new. Potential temperature is only predicted in the pure-sigma region while in the hybrid region it is found diagnostically; in a complementary manner, pressure is predicted in the hybrid region and at the surface but found diagnostically in the pure-sigma region. The hybrid vertical velocity, ζ ˙ , is calculated directly near the beginning of each timestep rather than iteratively at the end. A brief description of the model's new turbulence scheme is included. To compare with previous models and to illustrate the flexibility of the hybrid coordinate, we run the Held–Suarez benchmark for Earth and a published Great Dark Spot simulation for Neptune.

Radiative shocks in stellar atmosphere: Structure and turbulence amplification

The structure of radiative shock waves propagating through partially ionized hydrogen gas in stellar atmospheres is discussed. Basic equations including the radiation transfer and the method of their self-consistent solution are described. The most striking result is that the ratio of the radiative flux to the total energy flux of the shock wave very rapidly enlarges with increasing upstream velocity, so that for Mach number larger than 7, the major part of the shock energy is irreversibly lost due to dissipation processes. The understanding of the “missing temperature”, called microturbulence by the astrophysicists, which appears when we want to modelling the width of stellar line profiles, is discussed. It is shown that the turbulence amplification in the atmosphere of a radially pulsating star is not only due to the global compression of the atmosphere during the pulsation. Strong shock waves propagating from the deep atmosphere to the very low density layers also play a role in the turbulence variation, especially when they become very strong i.e. , hypersonic. For shocks, the predicted turbulence amplification predicted by classical models is overestimated with respect to stellar observations when the compression rate becomes larger than 2 which corresponds to a limit Mach number near 2. Thus, when radiative effects take place, the present turbulence amplification theory breaks down. A new approach is required.

Initial results of the Netlander imaging ground‐penetrating radar operated on the Antarctic Ice Shelf

The objective of the Netlander mission was to land 4 small geophysical stations on the surface of Mars to study the deep interior, subsurface, surface and atmosphere of the planet. Included in the payload was a ground penetrating radar (GPR) designed to retrieve not only the distance but also the direction of the reflectors, thus providing a simplified 3D imaging of the subsurface. In this paper we report initial results obtained during the RANETA campaign on the Antarctic ice shelf. Data from two soundings of the ice‐bed rock interface are analyzed, demonstrating the capability of the radar to disentangle echoes from different reflecting facets of the bed rock.

Daytime Cycle of Low-Level Clouds and the Tropical Convective Boundary Layer in Southwestern Amazonia

Abstract During the wet season in the southwestern Amazon region, daytime water transport out of the atmospheric mixed layer into the deeper atmosphere is shown to depend upon cloud amounts and types and synoptic-scale velocity fields. Interactions among clouds, convective conditions, and subcloud-layer properties were estimated for two dominant flow regimes observed during the 1999 Tropical Rainfall Measuring Mission component of the Brazilian Large-Scale Biosphere–Atmosphere (TRMM-LBA) field campaign. During daytime the cloud and subcloud layers were coupled by radiative, convective, and precipitation processes. The properties of cloud and subcloud layers varied according to the different convective influences of easterly versus westerly lower-tropospheric flows. The most pronounced flow-regime effects on composite cloud cycles occurred under persistent lower-tropospheric flows, which produced strong convective cloud growth with a near absence of low-level stratiform clouds, minimal cumulative attenuation of incoming solar irradiance (∼25%), rapid daytime mixed-layer growth (>100 m h−1), and boundary layer drying (0.22 g kg−1 h−1), high convective velocities (>1.5 m s−1), high surface buoyancy flux (>200 W m−2), and high latent heat flux (600 W m−2) into cloud layer. In contrast, persistent westerly flows were less convective, showing a strong morning presence of low-level stratiform genera (>0.9 cloud amount), greater cumulative attenuation of incoming solar irradiance (∼47%), slower mixed-layer growth (<50 m h−1) with a slight tendency for mixed-layer moistening, and a delayed peak in the low-level cumuliform cloud cycle (2000 versus 1700 UTC). The results reported in this article indicate that numerical models need to account for cloud amounts and types when estimating water vapor transport to the cloud layer.

Settling barium fluxes in the Arabian Sea: Critical evaluation of relationship with export production

Abstract Time series measurement of biogenic and barium fluxes was made using nine sediment traps deployed in the western, central and eastern part of the Arabian Sea with the objective of evaluating barium as a proxy for surface ocean productivity. Our observations show a strong linear correlation between Baexcess fluxes and biogenic opal and organic carbon (Corg) fluxes, indicating a biogenic origin of particulate Ba. However, the correlation between biogenic and Baexcess fluxes is remarkably strong in areas of uniform productivity like the central Arabian Sea, when compared to regions of episodic productivity. The processes that precipitate particulate Ba appear to be less active during periods of high biogenic flux. A large discrepancy is documented between the export flux calculated from the barium-based algorithm [Francois, R., Honjo, S., Manganini, S.J., Ravizza, G.E., 1995. Biogenic barium fluxes to the deep sea: implications for paleoproductivity reconstruction. Global Biogeochemical Cycles 9, 289–303] and from Corg fluxes [Sarnthein, M., Winn, K., Duplessy, J.C., Fontugne, M.R., 1988. Global variations of surface ocean productivity in low and mid latitudes: influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years. Paleoceanography 3, 361–399] at different depths. However, ∼35% increase in Ba fluxes and a concomitant increase in Ba/Corg ratios are documented between 919 and 2002 m water depth in the western Arabian Sea. This increase may be due either to barite formation within the fecal pellets of mesozooplankton thriving at deeper levels or to scavenging of Ba by Mn oxyhydroxides. Manganese oxyhydroxides seem to act as a prominent scavenging phase for particulate Ba when the Mnexcess content in the settling particles exceeds ∼200 ppm, especially in the western and central Arabian Sea where in situ precipitation of Mn oxides is reported. The estimated preservation efficiency of Ba in the Arabian Sea sediments ranges between 50% and 61%. This is two-fold higher than the global average, suggesting that Ba may be a promising proxy for paleoproductivity estimation.

Chemical Constraints on the Water and Total Oxygen Abundances in the Deep Atmosphere of Saturn

The mechanisms responsible for the observed H2O/H2 mixing ratio (HMR) in the Jovian troposphere are analyzed, with a focus on the relationship between HMR and O2 abundance and the abundance of the nonequilibrium trace gases CO and SiH4. The results of computations using a Jupiter atmosphere model consistent with recent observations (Bjoraker et al., 1986) are presented graphically and discussed in detail. It is found that the observed mixing ratios of CO (about 10 to the -9th) and SiH4 (upper limit 2-4 x 10 to the -9th) preclude O2 depletion and the presence of significant global H2O. The low observed HMRs (0.00003 at 6 bar) are tentatively attributed to local condensation in cloud-forming regions.

Photochemistry in Outer Solar System Atmospheres

The photochemistries of the H2-He atmospheres of the gas giants Jupiter, Saturn and ice giants Uranus and Neptune and Titan’s mildly reducing N2 atmosphere are reviewed in terms of general chemical and physical principles. The thermochemical furnace regions in the deep atmospheres and the photochemical regions of the giant planets are coupled by vertical mixing to ensure efficient recyling of photochemical products. On Titan, mass loss of hydrogen ensures photochemical evolution of methane into less saturated hydrocarbons. A summary discussion of major dissociation paths and essential chemical reactions is given. The chapter ends with a overview of vertical transport processes in planetary atmospheres.

On the Relationship between the Continuum Enhancement and Hard X‐Ray Emission in a White‐Light Flare

We investigate the relationship between the continuum enhancement and the hard X-ray (HXR) emission of a white-light flare on 2002 September 29. By reconstructing the RHESSI HXR images in the impulsive phase, we find two bright conjugate footpoints (FPs) on the two sides of the magnetic neutral line. Using the thick-target model and assuming a low-energy cutoff of 20 keV, the energy fluxes of non-thermal electron beams bombarding FPs A and B are estimated to be 1.0 10^10 and 0.8 10^10 ergs/cm^2/s, respectively. However, the continuum enhancement at the two FPs is not simply proportional to the electron beam flux. The continuum emission at FP B is relatively strong with a maximum enhancement of about 8% and correlates temporally well with the HXR profile; however, that at FP A is less significant with an enhancement of only about 4-5%, regardless of the relatively strong beam flux. By carefully inspecting the Halpha line profiles, we ascribe such a contrast to different atmospheric conditions at the two FPs. The Halpha line profile at FP B exhibits a relatively weak amplitude with a pronounced central reversal, while the profile at FP A is fairly strong without a visible central reversal. This indicates that in the early impulsive phase of the flare, the local atmosphere at FP A has been appreciably heated and the coronal pressure is high enough to prevent most high-energy electrons from penetrating into the deeper atmosphere; while at FP B, the atmosphere has not been fully heated, the electron beam can effectively heat the chromosphere and produce the observed continuum enhancement via the radiative backwarming effect.

Solar system science with SKA

Radio wavelength observations of solar system bodies reveal unique information about them, as they probe to regions inaccessible by nearly all other remote sensing techniques and wavelengths. As such, the SKA will be an important telescope for planetary science studies. With its sensitivity, spatial resolution, and spectral flexibility and resolution, it will be used extensively in planetary studies. It will make significant advances possible in studies of the deep atmospheres, magnetospheres and rings of the giant planets, atmospheres, surfaces, and subsurfaces of the terrestrial planets, and properties of small bodies, including comets, asteroids, and KBOs. Further, it will allow unique studies of the Sun. Finally, it will allow for both indirect and direct observations of extrasolar giant planets.

Retrieval of water in Jupiter's deep atmosphere using microwave spectra of its brightness temperature

Despite several spacecraft encounters and numerous groundbased investigations, we still do not know much about Jupiter's deep atmosphere; in fact, the Galileo probe results were so different than anyone had anticipated, that we understand even less about this planet's atmosphere now than before the Galileo mission. We formulate four basic questions in Section 1.3, which, if solved, would help to better understand the chemistry and dynamics in Jupiter's atmosphere. We believe that three out of the four questions (explanation of NH 3 altitude profile, characterization of hot spots, altitude below which the atmosphere is uniformly mixed) may be solved from passive sounding of Jupiter's deep (∼ tens of bars) atmosphere via a radio telescope orbiting the planet. Question nr. 4 (the water abundance in Jupiter's deep atmosphere) has been singled out by the Solar System Exploration Decadal Survey as a key question, since the water abundance in Jupiter's deep atmosphere is tied in with planet formation models. In this paper we investigate the sensitivity of microwave retrievals to the composition of Jupiter's deep atmosphere, in particular the water abundance. Based upon present uncertainties in the ammonia abundance and other known and unknown absorbers, including uncertainties in clouds (density and index of refraction), and uncertainties in the thermal structure and lineshape profiles, we conclude that the retrieval of water at depth from microwave spectra (disk-averaged and locally) will be highly uncertain. We show that, if the H 2O lineshape profile would be accurately known (laboratory data are needed!), an atmosphere with a near-solar H 2O abundance can likely be distinguished from one with an abundance of 10–20×solar O based upon the difference in their microwave spectra at wavelengths ≳ 50 cm . This would be sufficient to distinguish between some proposed scenarios by which Jupiter acquired its inventory of volatile elements heavier than helium. If, in addition, limb-darkening measurements are obtained (again, the H 2O lineshape profile should be known), tighter constraints on the H 2O abundance can be obtained (see also Janssen et al., 2004, this issue).

Evidence for temporal change at Uranus' south pole

Analysis of Hubble Space Telescope images of Uranus taken between 1994 and 2002 shows evidence for temporal changes in zonal brightness patterns in the south polar region. Between 1994 and 2002, a relatively bright ring developed near 70° S. The pole itself, which was the brightest area of the southern hemisphere in 1994, has become relatively dark. The polar collar at 45° S has also become brighter relative to the rest of the southern polar region. Comparison of images through different filters suggests that the change is occurring at pressures of 2–4 bars in the atmosphere. A change at this depth is consistent with radio measurements which indicate seasonal variability in Uranus' deep atmosphere. Disk-integrated photometry at visible wavelengths also exhibits variability on seasonal (∼ decades) timescales. The observed changes are not predicted by existing dynamical models of Uranus' atmosphere.

Updated Galileo probe mass spectrometer measurements of carbon, oxygen, nitrogen, and sulfur on Jupiter

The in situ measurements of the Galileo Probe Mass Spectrometer (GPMS) were expected to constrain the abundances of the cloud-forming condensible volatile gases: H 2O, H 2S, and NH 3. However, since the probe entry site (PES) was an unusually dry meteorological system—a 5-μm hotspot—the measured condensible volatile abundances did not follow the canonical condensation-limited vertical profiles of equilibrium cloud condensation models (ECCMs) such as Weidenschilling and Lewis (1973, Icarus 20, 465–476). Instead, the mixing ratios of H 2S and NH 3 increased with depth, finally reaching well-mixed equilibration levels at pressures far greater than the lifting condensation levels, whereas the mixing ratio of H 2O in the deep well-mixed atmosphere could not be measured. The deep NH 3 mixing ratio (with respect to H 2) of (6.64±2.54)×10 −4 from 8.9–11.7 bar GPMS data is consistent with the NH 3 profile from probe-to-orbiter signal attenuation (Folkner et al., 1998, J. Geophys. Res. 103, 22847–22856), which had an equilibration level of about 8 bar. The GPMS deep atmosphere H 2S mixing ratio of (8.9±2.1)×10 −5 is the only measurement of Jupiter's sulfur abundance, with a PES equilibration level somewhere between 12 and 15.5 bar. The deepest water mixing ratio measurement is (4.9±1.6)×10 −4 (corresponding to only about 30% of the solar abundance) at 17.6–20.9 bar, a value that is probably much smaller than Jupiter's bulk water abundance. The 15N/ 14N ratio in jovian NH 3 was measured at (2.3±0.3)×10 −3 and may provide the best estimate of the protosolar nitrogen isotopic ratio. The GPMS methane mixing ratio is (2.37±0.57)×10 −3; although methane does not condense on Jupiter, we include its updated analysis in this report because like the condensible volatiles, it was presumably brought to Jupiter in icy planetesimals. Our detailed discussion of calibration and error analysis supplements previously reported GPMS measurements of condensible volatile mixing ratios (Niemann et al., 1998, J. Geophys. Res. 103, 22831–22846; Atreya et al., 1999, Planet. Space Sci. 47, 1243–1262; Atreya et al., 2003, Planet. Space Sci. 51, 105–112) and the nitrogen isotopic ratio (Owen et al., 2001b, Astrophys. J. Lett. 553, L77–L79). The approximately three times solar abundance of NH 3 (along with CH 4 and H 2S) is consistent with enrichment of Jupiter's atmosphere by icy planetesimals formed at temperatures <40 K (Owen et al., 1999, Nature 402 (6759), 269–270), but would imply that H 2O should be at least 3×solar as well. An alternate model, using clathrate hydrates to deliver the nitrogen component to Jupiter, predicts O/H⩾9×solar (Gautier et al., 2001, Astrophys. J. 550 (2), L227–L230). Finally we show that the measured condensible volatile vertical profiles in the PES are consistent with column-stretching or entraining downdraft scenarios only if the basic state (the pre-stretched column or the entrainment source region) is described by condensible volatile vertical profiles that are drier than those in the equilibrium cloud condensation models. This dryness is supported by numerous remote sensing results but seems to disagree with observations of widespread clouds on Jupiter at pressure levels predicted by equilibrium cloud condensation models for ammonia and H 2S.