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1.
We present cloud structure models for Jupiter's Great Red Spot, Equatorial Zone, North Tropical Zone, North and South Temperate Zones, North and South Polar Regions, and North and South Polar Hoods. The models are based on images of Jupiter in three methane bands (between 6190 and 8900 Å) and nearby continuum. Radiative transfer calculations include multiple scattering and absorption from three aerosol layers, the topmost of which is a high thin haze and the lower two are called clouds. All models are computed relative to a similar model for the South Tropical Zone which fits methane absorption data and Pioneer photometry data well. Outstanding features suggested by the model results are the transition in the upper-cloud altitude to about 3 km lower altitude from the tropical zones to temperate zones and polar regions, a N/S asymmetry in cloud thickness in the tropical and temperate zones, the presence of aerosols up to about 0.3 bar in the Great Red Spot and Equatorial Zone, the need for a significant (τ ～ 0.75 to 1.0) aerosol content in this region in the Equatorial Zone, and perhaps an even higher and thicker cloud in the South Polar Hood. The haze layer above both polar hoods may exhibit different scattering properties than the haze which covers lower latitudes. In comparing the present results with models derived from polarization and infrared observations we conclude that polarization data are sensitive to aerosols in and above the upper cloud layer but insensitive to deeper cloud structure, and the converse is true for infrared data. 相似文献
2.
Images from three filters of the Voyager 1 wide-angle camera were used to measure the continuum reflectivity and spectral gradient near 6000 Å and the 6190-Å band methane/continuum ratio for a variety of cloud features in Jupiter's atmosphere. The dark “barge” features in the North Equatorial Belt have anomalously strong positive continuum spectral gradients suggesting unique composition, probably not elemental sulfur. Methane absorption was shown at unprecedented spatial scales for the Great Red Spot and its immediate environment, for a dark barge feature in the North Equatorial Belt, and for two hot spot and plume regions in the North Equatorial Belt. Some small-scale features, unresolvable at ground-based resolution, show significant enhancement in methane absorption. Any enhancement in methane absorption is conspicuously absent in both hot spot regions with 5-μm brightness temperature 255°K. Methane absorption and 5-μm emission are correlated in the vicinity of the Great Red Spot but are anticorrelated in one of the plume hot spot regions. Methane absorption and simultaneously maps of 5-μm brightness temperature were quantitatively compared to realistic cloud structure models which include multiple scattering at 5 μm as well as in the visible. A curve in parameter space defines the solution to any observed quantity, ranging from a shallow atmosphere and thin NH3 cloud to a deep atmosphere with a thick ammonia cloud. Without additional constraints, such as center-to-limb information, it is impossible to specify the NH3 cloud optical depth and pressure of a deeper cloud top independently. Variability in H2 quadrupole lines was also investigated and it was found that the constancy of the 4-0 S(1)-line equivalent width is consistent with the constancy of the methane 6190-Å band equivalent width at ground-based resolution, but the much greater variability of the 3-0 S(1) line is inconsistent with either the methane band or 4-0 S(1) line. In hot spot regions the 255°K brightness temperature requires a cloud optical depth of about 2 or less at 5 μm in the NH3 cloud layer. To be consistent with the observed 6190-Å methane absorption in hot spot regions, the NH3 cloud optical depth in the visible is about 7.5, implying that aerosols in hot spot regions have effective radii near 1 μm or less. 相似文献
3.
Application of a radiative-convective equilibrium model to the thermal structure of Uranus' atmosphere evaluates the role of hazes in the planet's stratospheric energy budget and places a lower limit on the internal energy flux. The model is constrained by Voyager and post-Voyager observations of the vertical aerosol and radiative active gas profiles. Our baseline model generally reproduces the observed tropospheric and stratospheric temperature profile. However, as in past studies, the model stratosphere from about 10(-3) to 10(-1) bar is too cold. We find that the observed stratospheric hazes do not warm this region appreciably and that any postulated hazes capable of warming the stratosphere sufficiently are inconsistent with Voyager and ground-based constraints. We explore the roles played by the stratospheric methane abundance, the H2 pressure-induced opacity, photochemical hazes, and C2H2, and C2H6 in controlling the temperature structure in this region. Assuming a vertical methane abundance profile consistent with that found by the Voyager UVS occultation observations, the model upper stratosphere, from 10 to 100 microbar, is also too cold. Radiation in the 7.8-micrometers band from a small abundance of hot methane in the lower thermosphere absorbed in this region can warm the atmosphere and bring models into closer agreement with observations. Finally, we find that internal heat fluxes < or approximately 60 erg cm-2 sec-1 are inconsistent with the observed tropospheric temperature profile. 相似文献
4.
Robert A. West 《Icarus》1979,38(1):34-53
This work presents results and analysis of center-to-limb variations and absolute reflectivity measurements of Jupiter's South Equatorial Belt (SEBs) and South Tropical Zone (STrZ) in three narrowband methane filters and three nearby continuum filters. The observations and data reduction are reported in Paper I. The data were analyzed in terms of plane-parallel but vertically inhomogeneous atmospheric models. Diffuse reflecting-scattering models (RSM) and two-cloud models (TCM) with and without an additional high, thin haze layer (required from Pioneer observations) were computed. Computations of multiple scattering were performed with a doubling technique. Anisotropic phase functions derived from Pioneer 10 photometry were used. Observations in the strong 8900-Å band severely constrain the position of the upper cloud top. To fit both the center-to-limb variations and absolute reflectivity, the STrZ cloud top must lie between 0.55 bar total pressure, if the aerosols are concentrated (small scattering mean free path), and 0.43 bar for the RSM model with 8 to 10 m-am CH4 per unit cloud optical depth. The 8900-Å data also constrain the cloud optical depth. If the cloud particles are concentrated, the top cloud must have optical depths between 1.5 and 2.5. The data at 7250 and 6190 Å are well suited to specify the level of the lower cloud. TCM models with concentrated aerosols have lower cloud-top pressure between 2.4 and 2.7 bars in the STrZ. To account for the small but significant differences between observations of the STrZ and SEBs, several configurations are allowed. An RSM model for the STrZ and a TCM model for the SEBs would constitute the greatest possible structural differences. RSM models were not satisfactory for the SEBs. If both the STrZ and SEBs are regions where the aerosols are concentrated, the upper cloud is slightly deeper (by 0.03 to 0.08 bar) in the SEBs; the cloud thickness is less (0 to 15%); and the lower cloud is deeper (by 0.4 to 0.8 bar). A forward scattering haze layer of the type derived from analysis of Pioneer 10 photometry is needed in the present STrZ and SEBs models at the 0.1-bar level to account for the limb darkening in the continuum. The haze could be concentrated in a thin layer or spread diffusely above the cloud top with little effect on the pressure level of the top cloud. A CH4/H2 mixing ratio of 1.2 to 1.5 × 10?3 is estimated from computations by W. D. Cochran of the hydrogen quadrupole absorption strength for present models. The smaller value was used to assign pressure levels stated above. 相似文献
5.
《Planetary and Space Science》1999,47(8-9):1077-1100
The geometric albedos of Uranus and Neptune, inferred from archived Hubble Space Telescope observations and from the ground-based measurements of Karkoschka, 1994, are modeled in the wavelength range 2200–4200 Å. The radiative transfer model, which includes Rayleigh–Raman scattering and Mie scattering by haze particles, aims at reproducing the fine structure of the geometric albedos at a resolution of 2–10 Å. The steep variation of the total optical depth allows to investigate the influences of both the stratospheric and tropospheric haze layers and that of the deep tropospheric cloud, although their relative importance is difficult to estimate accurately. Using the haze models of Baines et al., 1995, the optical properties of the Mie scatterers are inferred. The haze material on Uranus is characterized by a slowly decreasing imaginary index of refraction: ni varies from about 0.10 to 0.01–0.02 between 2200 and 4200 Å. Below 3000 Å, the absorptivity of Neptuness haze material is comparable to that on Uranus or slightly lower (ni ∼ 0.03–0.10). Above 3000 Å, it exhibits a steeper decrease (from 0.30 to 0.003). The main source of uncertainty at longer wavelengths is the reflectivity of the underlying (H2S ?) cloud. At shorter wavelengths, molecular scattering strongly dominates Mie scattering and the determination of the absorptivities is estimated to be accurate within a factor of 2. For Neptune, there is an additional uncertainty due to the inability of the initial haze model to provide a fit to the observed albedo. The Baines et al. model was modified by multiplying the number-densities of the hydrocarbons haze layers by a factor of 2.5–4.8, making it more consistent with the results of Pryor et al., 1992. For Uranus, these results suggest a darkening of the southern hemisphere since the Voyager epoch, in agreement with recent HST imaging. As a whole, the Neptunian haze seems to be more transparent than that of Uranus, possibly owing to the more turbulent dynamical state of the troposphere. Longwards of 3000 Å, the inferred absorptivities are consistent with laboratory measurements on tholins produced from CH4–H2 gas mixtures (Khare et al., 1987). The para-H2 mole fraction on both planets is constrained from the strength of a prominent H2 Raman feature at 2853 Å. On Uranus, at latitudes between 45 and 75°S and in the 50–500 mbar pressure range, the best agreement is obtained with an equilibrium para-H2 distribution. On Neptune, there is an indication of a slight departure from equilibrium in the same pressure range at mid-southern latitudes. Although this new method is significantly less accurate, its results are consistent with those of previous investigations based on the analysis of H2 quadrupole lines (Baines et al., 1995) and of the Voyager IRIS spectra (Conrath et al., 1998). 相似文献
6.
A model for the vertical cloud structure of Jupiter's Equitorial Plumes is deduced based on an analysis of Voyager images of the equitorial region in the 6190Å methane band and the 6000-Å continuum, and ground-based 8900-Å methane band images of Jupiter. A computer code that represents scattering and absorption from aerosol and gas layers was applied to a heirarchy of increasingly complex model aerosol structures to match the observations in the three wavelengths. The observations are consistent with a model for the vertical cloud structure of the equitorial region that consists of four aerosol layers. A high-altitude haze layer (HAL) with optical depth τ = 1 uniformly blankets the equitorial region at an altitude between 100 and 250 mbar. Below that, a middle-level cloud layer between 400 and 800 mbar contains the well-known Equatorial Plumes. The Plume clouds are optically thick (τ ≥ 12), bright clouds with single scattering albedo . They are probably composed of ammonia ice. The darker () interplume regions contain optically thinner clouds (2 ≤ τ ≤ 5) at the same altitude as the Plumes. An opaque cloud deck between 4000 and 6000 mbar, which is probably composed of water, forms the lowest model layer. In addition to these three layers, a thin forward scattering haze layer above 100 mbar was included in the models for consistency with previous work (Tomasko et al., 1978). We conclude that the vertical structure of the Equatorial Plume clouds is consistent with the hypothesis (Hunt et al., 1981) that the Plumes are caused by upwelling at the ammonia condensation level produced by bouyancy due to latent heat release from the condensation of water clouds nearly three scale heights below the Plumes. 相似文献
7.
A series of narrow-band images of Saturn was acquired on 7-11 February 2002 with an acousto-optic imaging spectrometer (AImS) at about 160 wavelengths between 500 and 950 nm. Our unique data set with high spectral agility and wide spectral coverage enabled us to extensively study the cloud structure and aerosol properties of Saturn's equatorial region at −10° latitude. Theoretical center-limb profiles based on twelve cloud models were fit to the observations at 23 wavelengths across the 619-, 727-, and 890-nm methane bands. A simultaneous multiwavelength multivariable fitting algorithm was adopted in varying up to 9 free parameters to efficiently explore the vast multidimensional parameter space, and a total of ∼12,000 initial conditions were tested. From the acceptable ranges of the model parameters, we obtained the following major conclusions: (1) the brightening of Saturn's equatorial region observed near 890 nm in February 2002 (I/F∼0.25 at the central meridian) results from high altitudes of a stratospheric haze layer (τ?∼0.05 above ∼0.04-bar level) and an upper tropospheric cloud (τ∼6 above ∼0.25-bar level), (2) if the upper tropospheric cloud is composed of ammonia ice particles and the Mie theory is applied, the mean particle size is larger than about 0.5 μm, (3) an optically thick cloud layer exists at a level of 0.5-2.2 bar below the upper cloud deck in Saturn's equatorial region. The ongoing observations by the Cassini spacecraft over wider spectral range and from various phase angles will further constrain Saturn's cloud structure and aerosol properties. 相似文献
8.
The three-dimensional structure of Saturn's intense equatorial jet from latitudes 8° N to 20° S is revealed from detailed measurements of the motions and spectral reflectivity of clouds at visible wavelengths on high resolution images obtained by the Cassini Imaging Science Subsystem (ISS) in 2004 and early 2005. Cloud speeds at two altitude levels are measured in the near infrared filters CB2 and CB3 matching the continuum (effective wavelengths 750 and 939 nm) and in the MT2 and MT3 filters matching two methane absorption bands (effective wavelengths 727 and 889 nm). Radiative transfer models in selective filters covering an ample spectral range (250-950 nm) require the existence of two detached aerosol layers in the equator: an uppermost thin stratospheric haze extending between the pressure levels ∼20 and 40 mbar (tropopause level) and below it, a dense tropospheric haze-cloud layer extending between 50 mbar and the base of the ammonia cloud (between ∼1 and 1.4 bar). Individual cloud elements are detected and tracked in the tropospheric dense haze at 50 and 700 mbar (altitude levels separated by 142 km). Between latitudes 5° N and 12° S the winds increase their velocity with depth from 265 m s−1 at the 50 mbar pressure level to 365 m s−1 at 700 mbar. These values are below the high wind speeds of 475 m s−1 measured at these latitudes during the Voyager era in 1980-1981, indicating that the equatorial jet has suffered a significant intensity change between that period and 1996-2005 or that the tracers of the flow used in the Voyager images were rooted at deeper levels than those in Cassini images. 相似文献
9.
We present a study of the vertical structure of clouds and hazes in the upper atmosphere of Saturn's Southern Hemisphere during 1994-2003, about one third of a Saturn year, based on Hubble Space Telescope images. The photometrically calibrated WFPC2 images cover the spectral region between the near-UV (218-255 nm) and the near-IR (953-1042 nm), including the 890 nm methane band. Using a radiative transfer code, we have reproduced the observed center-to-limb variations in absolute reflectivity at selected latitudes which allowed us to characterize the vertical structure of the entire hemisphere during this period. A model atmosphere with two haze layers has been used to study the variation of hazes with latitude and to characterize their temporal changes. Both hazes are located above a thick cloud, putatively composed of ammonia ice. An upper thin haze in the stratosphere (between 1 and 10 mbar) is found to be persistent and formed by small particles (radii ∼0.2 μm). The lower thicker haze close to the tropopause level shows a strong latitudinal dependence in its optical thickness (typically τ∼20-40 at the equator but τ∼5 at the pole, at 814 nm). This tropospheric haze is blue-absorbent and extends from 50 to 100 mbar to about ∼400 mbar. Both hazes show temporal variability, but at different time-scales. First, there is a tendency for the optical thickness of the stratospheric haze to increase at all latitudes as insolation increases. Second, the tropospheric haze shows mid-term changes (over time scales from months to 1-2 years) in its optical thickness (typically by a factor of 2). Such changes always occur within a rather narrow latitude band (width ∼5-10°), affecting almost all latitudes but at different times. Third, we detected a long-term (∼10 year) decrease in the blue single-scattering albedo of the tropospheric haze particles, most intense in the equatorial and polar areas. Long-term changes follow seasonal insolation variations smoothly without any apparent delay, suggesting photochemical processes that affect the particles optical properties as well as their size. In contrast, mid-term changes are sudden and show various time-scales, pointing to a dynamical origin. 相似文献
10.
An area scanning photometer has been used to obtain photometrically calibrated limb-darkening scans of Jupiter at four wavelengths: 6190, 6300, 7250, and 8200 Å. The first and third of these correspond to methane absorptions and the second and fourth to continuum regions near the 4-0 and 3-0 H2 quadrupole bands, respectively. Single-scattering albedos have been calculated for several areas on the planet at all four wavelengths assuming a semi-infinite, homogeneous, isotropically scattering atmosphere. The values obtained at the wavelengths of the quadrupole bands range from 0.98 over the NEB to ? 0.99 over the NTrZ and the bright band in the southern hemisphere. The single-scattering albedo values are used to show that the 5μm-emitting equatorial regions of the planet may be relatively clear and the tropical regions relatively cloudy. 相似文献
11.
Robert A. West Martin G. Tomasko Bradford A. Smith Mahendra P. Wijesinghe Lyn R. Doose Harold J. Reitsema Stephen M. Larson 《Icarus》1982,51(1):51-64
We present spatially resolved measurements of Saturn's absolute reflectivity in methane bands at 6190, 7250, and 8900 Å and in nearby continuum regions. Images were obtained through narrow-band interference filters with a 500 × 500-pixel charge-coupled device. Band/continuum ratios were measured to high accuracy by referencing to the ring brightness in each image. Several data processing techniques enhanced the quality of the observations. These are the use of the ring symmetry to find center position and orientation, accurate subtraction of ring light, and constrained image deconvolution. Uncertainty in the continuum absolute reflectivity is ±10%. Uncertainties in band/continuum ratios are from one to several percent. The Equatorial Zone was much brighter than any other latitude in the strong 8900 band image. Northern mid-latitudes were brighter than southern mid-latitudes. The latter observation indicates fewer high-altitude aerosols in the south, a possible result of atmospheric dynamics or seasonal sublimation of NH3 crystals. The data are tabulated and presented in a form suitable for quantitative scattering model analyses. 相似文献
12.
We analyze the temporal variation of the tropospheric cloud and haze in the jovian equatorial zone. In order to investigate the time evolution of the haze, we utilize a comprehensive set of archival WFPC2 images in the 953 and 893-nm wavelengths spanning over a decade of HST observations of Jupiter. We find that the latitude of the peak haze reflectivity experienced a southerly shift in between late-1998 and early-2001 (not to be confused with southerly bulk transport of haze particles themselves); before this shift, the latitude of peak reflectivity had remained relatively stable at +7° (planetographic latitude). We examine the average haze reflectivity at three equatorial latitudes (−5°, 0°, +5°) and find variability of amplitude ±20%. Equatorial clouds, which lie deeper than the haze, showed zonal mean variability with an amplitude of about 5% except during the global upheaval of 2006-2007 in which cloud reflectivity dropped up to 16% depending on latitude. An analysis of temporal correlation between zonally averaged cloud reflectivity and zonally averaged haze reflectivity indicates a time-lag of about 1200 days (with a lower limit of 800 days) between changes in cloud reflectivity and later changes in haze reflectivity, but limitations in the temporal coverage of even this extensive dataset make it impossible to rule out even longer time-lags. 相似文献
13.
R.D. Cess Barbara E. Carlson John Caldwell I.G. Nolt F.C. Gillett A.T. Tokunaga 《Icarus》1981,46(2):249-255
Ground-based observations of Jupiter show that the planet's stratospheric and tropospheric thermal emission are anticorrelated. The observations can possibly be explained by latitudinal variations in cloud altitude. These variations cause differential stratospheric heating by sunlight which is reflected off the clouds and then absorbed within the stratosphere by visible and near-infrared bands of methane. 相似文献
14.
Jupiter was observed in six continuum wavelength channels in the region 4100–8300 Å, using a silicon vidicon imaging photometer. Spectral reflectivities and high spatial resolution limb-darkening curves for several belts and zones have been extracted from the data. Simple model fits to the data yield information regarding spectral and spatial variations in single-scattering albedos and shape of particle single-scattering phase functions. Belts appear to be more backscattering than zones, particularly in the blue. The data are in moderate agreement with limb-darkening predicted by models derived from the center-to-limb variation in equivalent width of the H2 4-0 S(1) quadrupole line (Cochran, 1976) in the South Tropical Zone, but strongly disagree with the results of such models for the North Equatorial Belt. 相似文献
15.
Robert A. West 《Icarus》1983,53(2):301-309
Spatially resolved measurements of Saturn's reflectivity in the 6190-, 7250-, and 8996-Å methane bands are analyzed to determine cloud vertical structures in the Equatorial Zone, South Equatorial Belt, and North and South Temperate Regions near latitudes ±30°. Radiative transfer models are computed for a simple two-parameter structure. The parameters are A0, the methane column abundance in an aerosol-free layer at the top of the atmosphere, and A1, the specific abundance of methane in a semi-infinite homogeneous gas and cloud mixture deep in the atmosphere. For the Equatorial Zone, a model with A0 = 37 ± 3 m-am and A1 = 26 ± 2 m-am fits all three bands. For the North Temperate Region, a model with A0 = 39 m-am and A1 = 47 m-am comes close to fitting all three bands. For the South Equatorial Belt and South Temperate Region, a single A0 and A1 do not fit all three bands. The structure for the South Equatorial Belt resembles that for the North Temperate Region. The level where unit cloud optical depth occurs in the South Temperate Region is deeper than the corresponding level at other latitudes. Some suggestions are proposed to explain differences between model parameters derived using different absorption bands. 相似文献
16.
Brightness and linear polarization measurements at 678.5 nm for four south-north strips of Jupiter are studied. These measurements were obtained in 1997 by the Galileo photopolarimeter/radiometer. The observed brightness exhibits latitudinal variations consistent with the belt/zone structure of Jupiter. The observed degree of linear polarization is small at low latitudes and increases steeply toward higher latitudes. No clear correlations were observed between the degree of linear polarization and the brightness. The observed direction of polarization changes from approximately parallel to the local scattering plane at low latitudes to perpendicular at higher latitudes. For our studies, we used atmospheric models that include a haze layer above a cloud layer. Parameterized scattering matrices were employed for the haze and cloud particles. On a pixel-wise basis, the haze optical thickness and the single-scattering albedo of the cloud particles were derived from the observed brightness and degree of linear polarization; results were accepted only if they were compatible with the observed direction of polarization. Using atmospheric parameter values obtained from Pioneer 10 and 11 photopolarimetry for the South Tropical Zone and the north component of the South Equatorial Belt, this analysis yielded acceptable results for very few pixels, particularly at small phase angles. However, for almost all pixels, acceptable results were found when the parameterized scattering matrix of the cloud particles was adjusted to produce more negative polarization for single scattering of unpolarized light, especially at large scattering angles, similar to some laboratory measurements of ammonia ice crystals. Using this adjusted model, it was found that the derived latitudinal variation of the single-scattering albedo of the cloud particles is consistent with the belt/zone structure, and that the haze optical thickness steeply increases toward higher latitudes. 相似文献
17.
We analyzed a data cube of Neptune acquired with the Hubble STIS spectrograph on August 3, 2003. The data covered the full afternoon hemisphere at 0.1 arcsec spatial resolution between 300 and 1000 nm wavelength at 1 nm resolution. Navigation was accurate to 0.004 arcsec and 0.05 nm. We constrained the vertical aerosol structure with radiative transfer calculations. Ultraviolet data confirmed the presence of a stratospheric haze of optical depth 0.04 at 370 nm wavelength. Bright, discrete clouds, most abundant near latitudes −40° and 30°, had their top near the tropopause. They covered 1.7% of the observed disk if they were optically thick. The methane abundance above the cloud tops was 0.0026 and 0.0017 km-am for southern and northern clouds, respectively, identical to earlier observations by Sromovsky et al. (Sromovsky, L.A., Fry, P.M., Dowling, T.E., Baines, K.H., Limaye, S.S., [2001b]. Icarus 149, 459-488). Aside from these clouds, the upper troposphere was essentially clear. Below the 1.4-bar layer, a vertically uniform haze extended at least down to 10 bars with optical depth of 0.10-0.16/bar, depending on the latitude. Haze particles were bright at wavelengths above 600 nm, but darkened toward the ultraviolet, at the equator more so than at mid and high latitudes. A dark band near −60° latitude was caused by a 0.01 decrease of the single scattering albedo in the visible, which was close to unity. A comparison of methane and hydrogen absorptions contradicted the current view that methane is uniformly mixed in latitude and altitude below the ∼1.5-bar layer. The 0.04 ± 0.01 methane mixing ratio is only uniform at low latitudes. At high southern latitudes, it is depressed roughly between the 1.2 and 3.3-bar layers compared to low-latitude values. The maximum depression factor is ∼2.7 at 1.8 bars. We present models with 2° latitude sampling across the full sunlit globe that fit the observed reflectivities to 2.8% rms. 相似文献
18.
Low-pressure continuous-flow laboratory simulations of plasma induced chemistry in H2/He/CH4/NH3 atmospheres show radiation yields of hydrocarbons and nitrogen-containing organic compounds that increase with decreasing pressure in the range 2-200 mbar. Major products of these experiments that have been observed in the Jovian atmosphere are acetylene (C2H2), ethylene (C2H4), ethane (C2H6), hydrogen cyanide (HCN), propane (C3H8), and propyne (C3H4). Major products that have not yet been observed on Jupiter include acetonitrile (CH3CN), methylamine (CH3NH2), propene (C3H6), butane (C4H10), and butene (C4H8). Various other saturated and unsaturated hydrocarbons, as well as other amines and nitriles, are present in these experiments as minor products. We place upper limits of 10(6)-10(9) molecules cm-2 sec-1 on production rates of the major species from auroral chemistry in the Jovian stratosphere, and calculate stratospheric mole fraction contributions. This work shows that auroral processes may account for 10-100% of the total abundances of most observed organic species in the polar regions. Our experiments are consistent with models of Jovian polar stratospheric aerosol haze formation from polymerization of acetylene by secondary ultraviolet processing. 相似文献
19.
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. 相似文献
20.
Long-slit spectroscopy observations of Uranus by the United Kingdom InfraRed Telescope UIST instrument in 2006, 2007 and 2008 have been used to monitor the change in Uranus’ vertical and latitudinal cloud structure through the planet’s Northern Spring Equinox in December 2007.These spectra were analysed and presented by Irwin et al. (Irwin, P.G.J., Teanby, N.A., Davis, G.R. [2009]. Icarus 203, 287-302), but since publication, a new set of methane absorption data has become available (Karkoschka, E., Tomasko, M. [2010]. Methane absorption coefficients for the jovian planets from laboratory, Huygens, and HST data. Icarus 205, 674-694.), which appears to be more reliable at the cold temperatures and high pressures of Uranus’ deep atmosphere. We have fitted k-coefficients to these new methane absorption data and we find that although the latitudinal variation and inter-annual changes reported by Irwin et al. (2009) stand, the new k-data place the main cloud deck at lower pressures (2-3 bars) than derived previously in the H-band of ∼3-4 bars and ∼3 bars compared with ∼6 bars in the J-band. Indeed, we find that using the new k-data it is possible to reproduce satisfactorily the entire observed centre-of-disc Uranus spectrum from 1 to 1.75 μm with a single cloud at 2-3 bars provided that we make the particles more back-scattering at wavelengths less than 1.2 μm by, for example, increasing the assumed single-scattering albedo from 0.75 (assumed in the J and H-bands) to near 1.0. In addition, we find that using a deep methane mole fraction of 4% in combination with the associated warm ‘F’ temperature profile of Lindal et al. (Lindal, G.F., Lyons, J.R., Sweetnam, D.N., Eshleman, V.R., Hinson, D.P. [1987]. J. Geophys. Res. 92, 14987-15001), the retrieved cloud deck using the new (Karkoschka and Tomasko, 2010) methane absorption data moves to between 1 and 2 bars.The same methane absorption data and retrieval algorithm were applied to observations of Neptune made during the same programme and we find that we can again fit the entire 1-1.75 μm centre-of-disc spectrum with a single cloud model, providing that we make the stratospheric haze particles (of much greater opacity than for Uranus) conservatively scattering (i.e. ω = 1) and we also make the deeper cloud particles, again at around the 2 bar level more reflective for wavelengths less than 1.2 μm. Hence, apart from the increased opacity of stratospheric hazes in Neptune’s atmosphere, the deeper cloud structure and cloud composition of Uranus and Neptune would appear to be very similar. 相似文献