•We improve the chemical constraints on Jupiter’s deep water abundance.•A new formulation of eddy diffusion coefficient is proposed.•We estimate an uncertainty of the newly derived coefficient of ...less than 25%.•We reevaluate the water constraint provided by CO.
The bulk water abundance on Jupiter potentially constrains the planet’s formation conditions. We improve the chemical constraints on Jupiter’s deep water abundance in this paper. The eddy diffusion coefficient is used to model vertical mixing in planetary atmosphere, and based on laboratory studies dedicated to turbulent rotating convection, we propose a new formulation of the eddy diffusion coefficient for the troposphere of giant planets. The new formulation predicts a smooth transition from the slow rotation regime (near the equator) to the rapid rotation regime (near the pole). We estimate an uncertainty for the newly derived coefficient of less than 25%, which is much better than the one order of magnitude uncertainty used in the literature. We then reevaluate the water constraint provided by CO, using the newer eddy diffusion coefficient. We considered two updated CO kinetic models, one model constrains the water enrichment (relative to solar) between 0.1 and 0.75, while the other constrains the water enrichment between 3 and 11.
The Composite Infrared Radiometer–Spectrometer (CIRS) instrument, on the NASA Cassini Saturn orbiter, has been acquiring thermal emission spectra from the atmosphere of Titan since orbit insertion in ...2004. Observation sequences for measuring stratospheric temperatures have been obtained using both a nadir mapping mode and a limb viewing mode. The limb observations give better vertical resolution, and give information from higher altitudes, while the nadir observations provide more complete longitude coverage. Because the scale height of Titan's atmosphere is large enough so that emission from a grazing ray is influenced by horizontal temperature variations in the atmosphere, we have developed a two-dimensional temperature retrieval algorithm for reducing the limb spectra, which solves simultaneously for meridional and vertical temperature variations. The analyzed nadir mapping data have sampled nearly all longitudes at latitudes from about 90° S to 60° N, providing temperatures between pressure levels of about 5 to 0.2 mbar. The limb data covers latitudes between about 75° S and 85° N, and yields temperatures between about 1 and 0.005 mbar, at a small number of longitudes. The retrieved temperatures are consistent with early results from nadir observations Flasar, F.M., and 44 colleagues, 2005. Science 308, 975–978 between 0.5 and 5 mbar where both results are valid, with the warmest temperatures at the equator, and much stronger meridional temperature gradients in the northern (winter) hemisphere than in the southern. At higher altitudes not probed by nadir viewing, the limb data reveal that the stratopause is nearly 20 K warmer in the northern polar regions than at the equator and southern hemisphere, and that the altitude of the stratopause shifts from ≈0.1 mbar (300 km) near the equator to 0.01 mbar (400 km) poleward of about 40° N. When the gradient wind equation is used to construct a zonal mean wind, the reversal in sign of the temperature leads to capping of the winter westerly flow. The core of the resulting jet is about 190 m s
−1 in magnitude, spans between 30° N and 60° N, and peaks near 0.1 mbar. Estimates of the radiative heating associated with the radiative disequilibrium lead to a meridional overturning timescale of about three Earth years.
We use five and one-half years of limb- and nadir-viewing temperature mapping observations by the Composite Infrared Radiometer-Spectrometer (CIRS) on the Cassini Saturn orbiter, taken between July ...2004 and December 2009 (
L
S
from 293° to 4°; northern mid-winter to just after northern spring equinox), to monitor temperature changes in the upper stratosphere and lower mesosphere of Titan. The largest changes are in the northern (winter) polar stratopause, which has declined in temperature by over 20
K between 2005 and 2009. Throughout the rest of the mid to upper stratosphere and lower mesosphere, temperature changes are less than 5
K. In the southern hemisphere, temperatures in the middle stratosphere near 1
mbar increased by 1–2
K from 2004 through early 2007, then declined by 2–4
K throughout 2008 and 2009, with the changes being larger at more polar latitudes. Middle stratospheric temperatures at mid-northern latitudes show a small 1–2
K increase from 2005 through 2009. At north polar latitudes within the polar vortex, temperatures in the middle stratosphere show a ∼4
K increase during 2007, followed by a comparable decrease in temperatures in 2008 and into early 2009. The observed temperature changes in the north polar region are consistent with a weakening of the subsidence within the descending branch of the middle atmosphere meridional circulation.
•We develop a model for seasonal variations of atmospheric tides on Pluto.•We use HST observations and volatile transport models for tide predictions.•The tidal model matches observed wave activity ...from occultations.•We present scaling laws to predict variations in tides.
Pluto’s tenuous atmosphere exhibits remarkable seasonal change as a result of the planet’s substantial obliquity and highly eccentric orbit. Over the past two decades, occultations have revealed that the atmospheric pressure on Pluto has increased substantially, perhaps by a factor as large as 2 to 4, as the planet has moved from equinox towards solstice conditions. These data have also shown variations in the strength of the dynamical activity in the atmosphere, as revealed by the varying abundance and amplitude of spikes in the occultation light curves resulting from refractive focussing by atmospheric waves. Toigo et al. (Toigo et al. 2010. Icarus, 208, 402–411) explored the possibility that these waves are caused by solar-induced sublimation and diurnal deposition from N2 frost patches, driven by weak vertical winds resulting from the rising and sinking gas as it is released from or deposited onto the surface. Here, we extend this model to account explicitly for seasonal variations in average insolation and for the significant damping of vertical wave propagation by kinematic viscosity and thermal diffusivity (Hubbard et al. 2009. Icarus, 204, 284–289). Damping is extremely effective in suppressing vertical propagation of waves with vertical wavelengths of a few kilometers or less, and the dominant surviving tidal modes have characteristic vertical wavelengths λ∼10–13km. We estimate the expected strength and regional characteristics of atmospheric tides over the course of Pluto’s orbit for a variety of assumed spatial distributions of surface frost and atmospheric surface pressure. We compute the predicted strength of tide-induced wave activity based on the actual frost distribution observed on Pluto from Hubble Space Telescope (HST) observations (Stern et al. 1997. Astron. J., 113, 827; Buie et al. 2010. Astron. J., 139, 1128–1143), and compare the results to calculations for volatile transport models of Young (Young 2013. Astrophys. J., 766, L22) and Hansen et al. (Hansen et al. 2015. Icarus, 246, 183–191). We develop simple scaling rules to estimate the variation of the strength of tidal activity with surface pressure PS and solar declination δ⊙, and show that the maximum expected temperature perturbation at an atmospheric pressure of P=0.1Pa scales as dTmax∝cosδ⊙/PS. Wave activity is strongest in the near-equatorial region (latitude|ϕ|≲30°), being only weakly dependent on the detailed frost distribution. Using a 3-D time-dependent geometric optics ray-tracing code, we compute model light curves for the geometric circumstances of three high-SNR occultations (2002 August 21, 2006 June 12, and 2012 July 18), taking into account the detailed three-dimensional characteristics of the tides as different regions of the atmosphere are probed over the course of each occultation chord. We compare the strength and abundance of the scintillations in the models with those seen in the data, using both the HST frost maps and the volatile transport model predictions. The striking asymmetries in the strengths of spikes between ingress and egress seen in some events are reproduced in the tidal model simulations, due primarily to the latitudes probed during the occultation: occultations at high northern or southern latitudes uniformly have much weaker wave activity than more equatorial events. A surface pressure range of PS=1–2Pa provides the best match between models and observations. With the impending arrival of the New Horizons spacecraft at Pluto in 2015, we predict that wave activity in the upper atmosphere will be strongest at equatorial regions, and controlled in amplitude primarily by the surface pressure and damping effects, rather than by the detailed frost distribution. If Pluto’s atmosphere begins to collapse in the coming decades, we expect that future stellar occultations will provide evidence for greatly enhanced atmospheric wave activity.
► Jupiter’s south equatorial wind jet shows longitudinal velocity variation. ► Dark chevrons indicate a gravity-inertia wave with ∼25m/s relative phase speed. ► A second Rossby-like wave is also ...present with 40–60m/s relative phase speed. ► Asymmetry across the equatorial region is likely caused by the Great Red Spot.
A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5°S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and increasing with distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of ∼140m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7°N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n=75–100) with phase speed up to 25m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7±0.7-day period. This oscillating motion has a wavelength of ∼20° and a speed of 101±3m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of multiple wave modes, the difference in dominant cloud appearance between 7°N and 7.5°S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.
We analyze the relationship between Saturn's radiant energies and the 2010 giant storm with the Cassini observations. The storm increased the emitted power in a wide latitudinal band (20–55°N) with a ...maximum change of 9.2 ± 0.1% around 45°N from 2010 to 2011. Such a regional change caused the global‐average emitted power to increase by ~2.0 ± 0.2%. Saturn's giant storm occurs quasiperiodically (i.e., period approximately one Saturnian year), so it is possible that giant storms continuously modify the emitted power if the storm modification has a lifetime close to one Saturnian year. The hemispheric‐average emitted power in the southern hemisphere, which was mainly affected by the seasonal change, decreased by 8.5 ± 0.3% from 2004 to 2013. Our estimates also imply that the 2010 giant storm significantly modified the absorbed solar power of Saturn. The significant temporal variations of radiant powers should be considered in reexamining the value of Saturn's internal heat flux.
Key Points
The giant storm significantly modified Saturn's global radiant energies
Our results suggest that Saturn's internal heat should be reexamined
We also suggest a mechanism to trigger giant storms on Saturn
•Developed a Pluto GCM using 1D and 2D models for initial and boundary conditions.•Applied the GCM to previously published volatile transport models.•Thermal profiles are mostly isothermal with a ...strong inversion at the surface.•Sublimation winds are important in seasons with an appreciable atmosphere.•Predicted zonal winds mostly in gradient wind or angular momentum conservation balance.
Pluto’s atmospheric dynamics occupy an interesting regime in which the radiative time constant is quite long, the combined effects of high obliquity and a highly eccentric orbit can produce strong seasonal variations in atmospheric pressure, and the strong coupling between the atmosphere and volatile transport on the surface results in atmospheric flows that are quite sensitive to surface and subsurface properties that at present are poorly constrained by direct observations. In anticipation of the New Horizons encounter with the Pluto system in July 2015, we present a Pluto-specific three-dimensional general circulation model (GCM), PlutoWRF, incorporating the most accurate current radiative transfer models of Pluto’s atmosphere, a physically robust treatment of nitrogen volatile transport, and the flexibility to accommodate richly detailed information about the surface and subsurface conditions as new data become available. We solve for a physically self-consistent, equilibrated combination of surface, subsurface, and atmospheric conditions to specify the boundary conditions and initial state values for each GCM run. This is accomplished using two reduced versions of PlutoWRF: a two-dimensional surface volatile exchange model to specify the properties of surface nitrogen ice and the initial atmospheric surface pressure, and a one-dimensional radiative–conductive–convective model that uses the two-dimensional model predictions to determine the corresponding global-mean atmospheric thermal profile. We illustrate the capabilities of PlutoWRF in predicting Pluto’s general circulation, thermal state, and volatile transport of nitrogen by calculating the dynamical response of Pluto’s atmosphere, based on four different idealized models of Pluto’s surface ice distribution from Young (Young, L.A. 2013. Astrophys. J. 766, L22) and Hansen et al. (Hansen, C.J., Paige, D.A., Young, L.A. 2015. Icarus 246, 183). Our GCM runs typically span 30years, from 1985 to 2015, covering the period from the discovery of Pluto’s atmosphere to present. For most periods simulated, zonal winds are strongly forced by a gradient wind balance, relaxing in later (recent) years to an angular momentum conservation balance of the seasonal polar cap sublimation flow. Near-surface winds generally follow a sublimation flow from the sunlit polar cap to the polar night cap, with a Coriolis turning of the wind as the air travels from pole to pole. We demonstrate the strong contribution of nitrogen sublimation and deposition to Pluto’s atmospheric circulation. As New Horizons data become available, PlutoWRF can be used to construct models of Pluto’s atmospheric dynamics and surface wind regimes more constrained by physical observations.
Hubble Space Telescope Wide Field Planetary Camera 2 imaging data of Jupiter were combined with wind profiles from Voyager and Cassini data to study long-term variability in Jupiter’s winds and cloud ...brightness. Searches for evidence of wind velocity periodicity yielded a few latitudes with potential variability; the most significant periods were found nearly symmetrically about the equator at 0°, 10–12°N, and 14–18°S planetographic latitude. The low to mid-latitude signals have components consistent with the measured stratospheric temperature Quasi-Quadrennial Oscillation (QQO) period of 4–5
years, while the equatorial signal is approximately seasonal and could be tied to mesoscale wave formation. Robustness tests indicate that a constant or continuously varying periodic signal near 4.5
years would appear with high significance in the data periodograms as long as uncertainties or noise in the data are not of greater magnitude. However, the lack of a consistent signal over many latitudes makes it difficult to interpret as a QQO-related change. In addition, further analyses of calibrated 410-nm and 953-nm brightness scans found few corresponding changes in troposphere haze and cloud structure on QQO timescales. However, stratospheric haze reflectance at 255-nm did appear to vary on seasonal timescales, though the data do not have enough temporal coverage or photometric accuracy to be conclusive. Sufficient temporal coverage and spacing, as well as data quality, are critical to this type of search.
Retrievals performed on Cassini Composite Infrared Spectrometer data obtained during the distant Jupiter flyby in 2000/2001 have been used to generate global temperature maps of the planet in the ...troposphere and stratosphere, but to higher latitudes than were shown previously by Flasar et al. Flasar, F.M., 39 colleagues, 2004a. Nature 427, 132–135; Flasar, F.M., 44 colleagues, 2004b. Space Sci. Rev. 115, 169–297. Similar retrievals were performed on Voyager 1 IRIS data to provide the first detailed IRIS map of the stratosphere, and high latitudes in the troposphere. Thermal winds were calculated for each data set and show strong vertical shears in the zonal winds at low latitudes, and meridional temperature gradients indicate the presence of circumpolar jets, as well. The temperatures retrieved from the two spacecraft were also compared with yearly ground-based data obtained over the intervening two decades. Tropospheric temperatures reveal gradual changes at low latitudes, with little obvious seasonal or short-term variation Orton et al., 1994. Science 265, 625–631. Stratospheric temperatures show much more complicated behavior over short timescales, consistent with quasi-quadrennial oscillations at low latitudes, as suggested in prior analyses of shorter intervals of ground-based data Orton et al., 1991. Science 252, 537–542; Friedson, A.J., 1999. Icarus 137, 34–55. A scaling analysis indicates that meridional motions, mechanically forced by wave or eddy convergence, play an important role in modulating the temperatures and winds in the upper troposphere and stratosphere on seasonal and shorter timescales. At latitudes away from the equator, the mechanical forcing can be derived simply from a temporal record of temperature and its vertical derivative. Ground-based observations with improved vertical resolution and/or long-term monitoring from spacecraft are required for this purpose, though the Voyager and Cassini data given indications that the magnitude of the forcing is very small.
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