共查询到20条相似文献，搜索用时 156 毫秒
1.
Sanjay S. Limaye 《Icarus》1984,57(3):362-385
Polarization observations obtained from the Orbiter Cloud Photopolarimeter (OCPP) show local, organized features whose morphology is similar to that of the ultraviolet clouds. No obvious correlation between the observed amount of polarization and relative brightness was found, suggesting that the polarization features are not due to variations in the unpolarized intensity alone, but rather to other causes such are the existence of a haze. Many of the features that can be seen even at 935 nm wavelength are believed to be signatures of local variations in the haze of submicron-size particles that have been detected from the OCCP data (K. Kawabata, D. L/ Cooffeen, J. E. Hansen, W. A. Lane, M. Sato, and L. D. Travis (1980). J. Geophys. Res.85, 8129–8140). Substantial variations in the structure and visibility of the polarization features that are observed suggest that the haze amount mixed with and above the main cloud layer may not be constant by varies with time. Some of these features last for least a few days thus allowing measurements of their apparent motions. The small number of measurements possible from the available data shows movements similar to those of the ultraviolet clouds in both direction and speed. According to Kawabata et al. the haze extends well above the main cloud layer to about 5 mb pressure level while the optical depth unity at 365 nm (corresponding to the level of the ultraviolet clouds tracked to infer the cloud-top level circulation) occurs at about 30 mb pressure level. Thus, the rapid retrograde circulation suggested by the movements of haze features in the polarimetry data would indicate that the layer in which such rapid circulation exists is fairly deep. 相似文献
2.
William I. Newman 《Icarus》1975,26(4):451-456
An analysis of the limb darkening component obtained by Ingersoll and Orton [Icarus21 (1974), 121–128] from the thermal infrared maps of Venus published by Murray, Wildey, and Westphal [J. Geophys. Res.68 (1963), 4813–4818] and Westphal, Wildey, and Murray [Astrophys. J.142 (1965), 799–802] shows that the Cytherean cloud tops were close to radiative equilibrium in 1962. A method for obtaining the optical depth, the extinction coefficient, and the extinction scale height from such data is derived and values are extracted from Marov's [Icarus16 (1972), 415–461] standard model of the Venus atmosphere. 相似文献
3.
The computed variation of the infrared flux and polarization of Venus as a function of phase angle, based upon multiple-scattering calculations for the cloud model of Kawabata et al. (1980) with an internal heat source, precludes the possibility of sulfuric acid as the composition of the haze particles located above the main cloud. Furthermore, our calculations reveal that the hazticle should have a large absorption coefficient at these wavelengths, i.e, . The optical thickness of the haze layer must be about 0.15 at λ = 3.4 μm. 相似文献
4.
L.A. SromovskyP.M. Fry 《Icarus》2002,157(2):373-400
The Galileo Probe sampled Jupiter's atmosphere at the edge of a 5-μm hot spot, where it found very little cloud opacity above the 700 mb level. Only τ=1-2 at λ=0.5 μm was inferred from Net Flux Radiometer observations (Sromovsky et al. 1998, J. Geophys. Res.103, 22,929-22,977), in seeming conflict with Chanover et al. (1997, Icarus128, 294-305) who inferred τ=6-8 above the 700 mb level (at λ∼0.9 μm) from 893-nm and 953-nm WFPC2 observations of a group of hot spots. Postulating a heterogeneous cloud structure is one way to resolve the conflict. We obtained a more satisfying resolution by reinterpretation of the HST observations with Probe-compatible assumptions about the vertical distribution of cloud particles. Assuming a physically thin upper (putative NH3) cloud with adjustable optical depth and effective pressure (peff<440 mb) and a physically thin midlevel (putative NH4SH) cloud with adjustable optical depth but a fixed pressure of 1.2 bars, we are able to fit WPFC2 observations with probe-consistent opacities in hot spot regions. With the same cloud pressures, but higher middle cloud opacities, we are even able to fit the visibly bright regions. Little variability is seen in the upper cloud. Best fits to October 1995 WFPC2 observations in dark regions (5-μm hot spots) yielded τupper=1.3-1.9 at 0.9 μm and peff=240 mb−270 mb, while in visibly bright regions between hot spots we obtained τupper=1.6-2.2 and peff=250 mb−290 mb. May 1996 observations yielded slightly higher values of τupper (1.8-2.3 and 2.0-2.8) and peff (250 mb−310 mb and 265 mb−320 mb). We found that the most important variable parameter is the opacity of the middle cloud, which ra nged from τ=1, 2 in dark regions, to τ=8-30 in bright regions. From limb darkening characteristics, we inferred a wavelength-dependent haze opacity ranging from 0.2±0.05 at 660 nm to 0.35±0.05 at 953 nm, and an effective haze pressure near 120 mb. We did not find it necessary to use low single scattering albedos that require effective imaginary indices, that are several orders of magnitude larger than the values of the main putative cloud components. 相似文献
5.
6.
The unexpectedly large scale height of Io's ionosphere (Kliore, A., et al., 1975, Icarus24, 407–410) together with the relatively large molecular weight of the likely principal constituent, SO2 (Pearl, J., et al., 1979, Nature280, 755–758), suggest a high ionospheric temperature. Electrical induction in Io's ionosphere due to the corotating plasma bound to the Jovian magnetosphere is one possible source for attainment of such high temperatures. Accordingly, unipolar induction models were constructed to calculate ionospheric joule heating numerically. Heating rates produced by highly simplified models lie in the range 10?9 to 10?8 W/m3. These heating rates are lower than those determined from uv photodissociative heating models (Kumar, S., 1980, Geophys. Res. Lett.7, 9–12) at low levels in the ionosphere but are comparable in the upper ionosphere. The low electrical heating rate throughout most of the ionosphere is due to the power limitation imposed by the Alfvén wings which complete the electrical circuit (Neubauer, F.M., 1980, J. Geophys. Res.85, 1171–1178). Contrary to the pre-Voyager calculations of Cloutier, P. A., et al. (1978, Astrophys. Space Sci.55, 93–112), our numerical results show that the J × B force density due to unipolar induction currents in the ionosphere is much less than the gravitational force density when the combined mass of the neutral species is included. The binding and coupling of the ionosphere is principally due to the relatively dense (possibly localized) neutral SO2 atmosphere. In regions where the ions and neutrals are collisionally coupled the ionosphere will not be stripped off by the J × B forces. However at a level above that (to which the ions move by diffusion only) the charged species would be removed. Thus there appears to be no need to postulate the existence of an intrinsic Ionian magnetic field as suggested by Kivelson, M. G., et al. (79, Science 205, 491–493) and Southwood, S. J., et al. (1980, J. Geophys. Res., in press) in order to retain the observed ionosphere. 相似文献
7.
In March 1979, the spectrum of Venus was recorded in the far infrared from the G.P. Kuiper Airborne Observatory when the planet subtended a phase angle of 62°. The brightness temperature was observed to be 275°K near 110 cm?1, dropping to 230°K near 270 cm?1. Radiance calculations, using temperature and cloud structure formation from the Pioneer Venus mission and including gaseous absorption by the collision-induced dipole of CO2, yield results consistently brighter than the observations. Supplementing the spectral data, Pioneer Venus OIR data at similar phase angles provide the constraint that any additional infrared opacity must be contained in the upper cloud, H2SO4 to the Pioneer-measured upper cloud structure serves to reconcile the model spectrum and the observations, but cloud microphysics strongly indicates that such a high particle density haze is implausible. The atmospheric environment is reviewed with regard to the far infrared opacity and possible particle distribution modifications are discussed. We conclude that the most likely possibility for supplementing the far-infrared opacity is a population of large particles in the upper cloud with number densities less than 1 particle cm?3 which has remained undetected by in situ measurements. 相似文献
8.
The infrared flux of Venus has been observed with a narrowband filter (λ = 3.6 μm, Δλ = 0.08 μm) from 1982 through 1984, covering a range of the phase angle α from 27 to 94°. Normalized values of flux at the Venus-Earth distance of 1 AU were (4.0–5.4) × 10?17W/cm2/cm?1 and the α dependence of the data is rather weak. Furthermore, when the evening terminator of Venus was seen, lower values of flux were obtained in contrast with higher values at the morning terminator. The α dependence is quite different from that of J.V. Martonchik and R. Beer (1975, J. Atmos. Sci.32, 1151–1156). Since we cannot find any significant problem in the two observational methods, the difference might suggest an intrinsic time variation of haze particles during these 10 years in the upper haze layer of the Venus cloud. 相似文献
9.
The interpretation of unexpected characteristics of Pioneer Venus temperature measurements, and of the large difference between these and the Venera results, is aided by new Venus temperature profiles derived from engineering measurements of the Pioneer Venus Small-Probe Net Flux Radiometer (SNFR) instruments. To facilitate correction of a temperature-dependent radiometric response, these instruments monitored the temperatures of their deployed radiation detectors. The accurate calibration of the temperature sensors, and their strong thermal coupling to the atmosphere, make it possible to deduce atmospheric temperatures within 2°K (at most altitudes) using a simple two-component thermal model to account for lag effects. These independent temperature profiles generally confirm to high accuracy, the small-probe results of A. Seiff, D. B. Kirk, R. E. Young, R. C. Blanchard, J. T. Findlay, G. M. Kelly, and S. C. Sommer (1980a, J. Geophys. Res.85, pp. 7903–7933) concerning vertical structure and horizontal contrast in the lower atmosphere, although the stable layer below 25 km is found to be slightly more stable (by about 0.4°K/km) and absolute temperatures are an average of 2°K higher. The measured Day-Night thermal contrast is compatible with predicted responses to the diurnal variation in solar heating, except near the cloud base, where 3–5°K differences may be due to thermal radiative heating differences associated with different cloud opacities. Temperature contrasts between latitudes 30 and 60° are roughly consistent with cyclostrophic balance. But pressure and temperature measurements by the Pioneer Venus Sounder probe at 4° latitude, when compared to Small-probe results, imply unreasonably large equatorward accelerations of 100 (m/sec)/day. Poleward accelerations compatible with cyclostrophic balance can be obtained if Sounder-probe temperatures are increased by a scale-factor correction reaching 6–7°K at 13 km. 相似文献
10.
Data on the thermal structure of the nightside middle atmosphere of Venus, from 84 to 137 km altitude, have been obtained from analysis of deceleration measurements from the third Pioneer Venus small probe, the night probe, which entered the atmosphere near the midnight meridian at 27°S latitude. Comparison of the midnight sounding with the morning sounding at 31°S latitude indicates that the temperature structure is essentially diurnally invariant up to 100 km, above which the nightside structure diverges sharply from the dayside toward lower temperatures. Very large diurnal pressure differences develop above 100 km with dayside pressure ten times that on the nightside at 126 km altitude. This has major implications for upper atmospheric dynamics. The data are compared with the measurements of G. M. Keating, J. Y. Nicholson, and L. R. Lake (1980, J. Geophys. Res., 85, 7941–7956) above 140 km with theoretical thermal structure models of Dickinson, and with data obtained by Russian Venera spacecraft below 100 km. Midnight temperatures are ～ 130°K, somewhat warmer than those reported by Keating et al. 相似文献
11.
Dmitrij V. Titov Wojciech J. Markiewicz Nikolay I. Ignatiev Li Song Sanjay S. Limaye Agustin Sanchez-Lavega Jonas Hesemann Miguel Almeida Thomas Roatsch Klaus-Dieter Matz Frank Scholten David Crisp Larry W. Esposito Stubbe F. Hviid Ralf Jaumann Horst U. Keller Richard Moissl 《Icarus》2012,217(2):682-701
Since the discovery of ultraviolet markings on Venus, their observations have been a powerful tool to study the morphology, motions and dynamical state at the cloud top level. Here we present the results of investigation of the cloud top morphology performed by the Venus Monitoring Camera (VMC) during more than 3 years of the Venus Express mission. The camera acquires images in four narrow-band filters centered at 365, 513, 965 and 1010 nm with spatial resolution from 50 km at apocentre to a few hundred of meters at pericentre. The VMC experiment provides a significant improvement in the Venus imaging as compared to the capabilities of the earlier missions. The camera discovered new cloud features like bright “lace clouds” and cloud columns at the low latitudes, dark polar oval and narrow circular and spiral “grooves” in the polar regions, different types of waves at the high latitudes. The VMC observations revealed detailed structure of the sub-solar region and the afternoon convective wake, the bow-shape features and convective cells, the mid-latitude transition region and the “polar cap”. The polar orbit of the satellite enables for the first time nadir viewing of the Southern polar regions and an opportunity to zoom in on the planet. The experiment returned numerous images of the Venus limb and documented global and local brightening events. VMC provided almost continuous monitoring of the planet with high temporal resolution that allowed one to follow changes in the cloud morphology at various scales.We present the in-flight performance of the instrument and focus in particular on the data from the ultraviolet channel, centered at the characteristic wavelength of the unknown UV absorber that yields the highest contrasts on the cloud top. Low latitudes are dominated by relatively dark clouds that have mottled and fragmented appearance clearly indicating convective activity in the sub-solar region. At ～50° latitude this pattern gives way to streaky clouds suggesting that horizontal, almost laminar, flow prevails here. Poleward from about 60°S the planet is covered by almost featureless bright polar hood sometimes crossed by dark narrow (～300 km) spiral or circular structures. This global cloud pattern can change on time scales of a few days resulting in global and local “brightening events” when the bright haze can extend far into low latitudes and/or increase its brightness by 30%. Close-up snapshots reveal plenty of morphological details like convective cells, cloud streaks, cumulus-like columns, wave trains. Different kinds of small scale waves are frequently observed at the cloud top. The wave activity is mainly observed in the 65–80° latitude band and is in particular concentrated in the region of Ishtar Terra that suggests their possible orographic origin. The VMC observations have important implications for the problems of the unknown UV absorber, microphysical processes, dynamics and radiative energy balance at the cloud tops. They are only briefly discussed in the paper, but each of them will be the subject of a dedicated study. 相似文献
12.
Tanja BosakAndrew P. Ingersoll 《Icarus》2002,158(2):401-409
Linear wave patterns in Jupiter's clouds with wavelengths strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere (F. M. Flasar and P. J. Gierasch, 1986, J. Atmos. Sci.43, 2683-2707). We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds (A. P. Ingersoll and D. W. Koerner 1989, Bull. Am. Astron. Soc.21, 943). We numerically analyze the linear stability of wavelike disturbances that have nonzero horizontal phase speeds in Jupiter's atmosphere and find that, if the static stability in the shear layer is very low (but still nonnegative), a deep vertical shear layer like the one measured by the Galileo probe (D. H. Atkinson et al. 1998, J. Geophys. Res.103, 22911-22928) can generate the instabilities. The fastest growing waves grow exponentially within an hour, and their wavelengths match the observations. Close to zero values of static stability that permit the growth of instabilities are within the range of values measured by the Galileo probe in a hot spot (A. Seiff et al. 1998, J. Geophys. Res.103, 22857-22889). Our model probes Jupiter's equatorial atmosphere below the cloud deck and suggests that thick regions of wind shear and low static stability exist outside hot spots. 相似文献
13.
G.S. Golitsyn 《Icarus》1984,60(2):289-306
A brief survey is given of the observational data on wind speeds in the atmosphere of Venus, as well as results of the theory of similitude and of a scale analysis for estimation of the wind speeds and temperature contrasts. It is shown that, in the lower portion of the atmosphere, containing roughly half of the mass, the first method produces results which are in somewhat better agreement with the measurements. Measurements of the wind distribution in the atmosphere are discussed. It is shown that, in the slowly rotating atmosphere of Venus, we should expect the Solberg mechanism of inertial instability of the circulation to be effective with respect to axisymmetrical perturbations. The numerical experiments of G.P. Williams (1968, J. Atmos. Sci., 25, 34–1045; 1970, Geophys. Fluid Dyn., 1, 357–369) indicate that in this case the circulation in the meridional plane can be broken down into a series of forward and reverse cells. The existence of such cells can serve to preserve the angular momentum of the planet with its atmosphere—the total momentum of the atmospheric frictional forces against the surface should on the average equal zero. This supports the hypothesis of G. Schubert et al. (1980, J. Geophys. Res., 85, 8007–8025) concerning the multicellular structure of the meridional circulation. Data are analyzed with regard to the time variability of the circulation. If the angular momentum of Venus′ atmosphere can change by 30% (which is not excluded by the presently available data; in Earth's atmosphere seasonal variations of the momentum reach 50%), then the relative variations in the length of a Venusian day will attain 10?3, i.e., several hours. The surface boundary layer is considered. It is shown that, due to the small transparency of the atmosphere to thermal radiation, heat transfer between the surface and the atmosphere should basically take place by turbulent heat exchange. The basic parameters of the dynamic and thermal regimes of this layer are estimated. Questions of light refraction in the boundary layer are discussed. A strict theory of refraction, developed for these conditions, confirms the preliminary rough estimates of V.I. Moroz (1976, Cosmic Res., 14, No. 5, 691–692; Space Sci. Rev., 25, 3–127), viz, that the horizon is visible on the panorama at a distance of order 100m, due to a relatively sharp negative gradient near the surface. 相似文献
14.
In this paper we evaluate the possibility of detecting, for the first time, the surface magnetic field of Jupiter (∼1 bar level) by observing the change of linear polarization induced by the Hanle effect on the H Lyman-alpha (Lyα) emission line of the planet. We find that, indeed, the Hanle effect, which results from the interaction between a local magnetic field and the atomic polarization induced by absorption of anisotropic radiation, is sensitive to relatively weak values of the strength of the magnetic fields expected on planets. First, we show that for the Lyα emission backscattered by atomic H in the presence of a magnetic field, the Hanle effect is polarizing. This new result is in total contrast to the depolarizing effect predicted and observed for emission lines scattered at right angles in solar prominences. Additionally, to estimate the polarization rate for the case of Jupiter, we have considered three magnetic field models: a dipole field for reference, an O4 based model [Connerney, J.E.P., 1981. The magnetic field of Jupiter—A generalized inverse approach. J. Geophys. Res. 86, 7679-7693], and finally, an O6 based model [Khurana, K.K., 1997. Euler potential models of Jupiter's magnetospheric field. J. Geophys. Res. 102, 11295-11306]. In all models, we show that for the jovian backscattered Lyα line, the Hanle effect does enhance the Lyα linear polarization; the polarization rate may exceed 2% at specific regions of the jovian disc, making detection possible either remotely or from an orbiter around Jupiter. In general, depending on the instrumental sensitivity and the observing strategy used, we show that accurate mapping of the linear polarization rate at the planetary surface (thermosphere) or off-disc (corona) may provide a rather accurate estimate of the jovian total magnetic field strength on large area scales. 相似文献
15.
We have computed line profiles and curves of growth for both reflected and transmitted radiation for typical lines in CO2 bands (in the photographic infrared) which occur in the spectrum of Venus. In our model the pressure variation with altitude was considered and the base of the cloud deck was set at the 2 bar level. The temperature was held constant at 250K and a Voigt profile was used for the lineshape. We also assumed that the scale height of the cloud particles was equal to the scale height of the gas. The calculations were made for four values of the scattering optical thickness (τc = 0.1, 1.0, 10, and 100) using a continuum single scattering albedo (which gives a Bond albedo of 0.896 for τc = 100, the value observed for Venus at these wavelengths). Curves of growth are also presented for reflected radiation which has been averaged over the visible disk for three values of the Venus phase angle (0, 86, and 166°). 相似文献
16.
The Galilean satellite eclipse technique for measuring the aerosol distribution in the upper Jovian atmosphere is described and applied using 30 color observations of the 13 May 1972 eclipse of Ganymede obtained with the 5-m Hale telescope. This event probes the South Temperate Zone. The observed aerosol lies above the visible cloud tops, is very tenuous and varies with altitude, increasing rapidly with downward passage through the tropopause. The aerosol extinction coefficient, κa (λ1.05 μm), is ～1.1 × 10?9 cm?1 in the lower stratosphere and ～1.1 × 10?8 cm?1 at the tropopause. The 1σ uncertainty in these values does not exceed 50% The observations require some aerosol above the tropopause but do not clearly determine its structure. The present analysis emphasizes an extended haze distribution, but the alternate possibility is not excluded that the stratospheric aerosol resides in a thin layer. The aerosol extinction increases with decreasing wavelength and indicates the particle radius to be ?0.2 μm. Larger radii are impossible. These overall results confirm Axel's (1972) suggestion of a small quantity of dust above the Jovian cloud tops and the optical depths are consistent with those required to explain the low uv albedo. 相似文献
17.
Four different data sets on Jupiter, one at 6, one at 11, and two at 21 cm, are compared to each other and with the synchrotron radiation model of the magnetosphere developed by I. de Pater (1981, J. Geophys. Res., 86, 3397–3422, 3423–3429). The model agrees with all these data sets, and hence was used to derive and interpret the characteristics of the thermal radiation component at all three wavelengths. The disk temperatures are 233 ± 17, 280 ±20, and 340 ± 26°K at 6, 11, and 21 cm, respectively. A comparison of the data with atmospheric model calculations strongly suggests that the disk is uniform at λ6 and λ11 cm near the center of the disk, where μ > 0.6?0.7. This may indicate a nonuniform distribution of ammonia at layers at and above the visible cloud layers. 相似文献
18.
We have analyzed the P6, P8, and P10 lines in the 0.7820 μm CO2 band of Venus using a scattering model. Our new results compare favorably with previous results from the 1.05 μm CO2 band. We considered nonabsorbing and absorbing clouds. We found that the anisotropic scattering mean free path for both models at the 0.2atm level is between 0.55 and 0.73km, a range close to the value of 1 km for terrestrial hazes. We used our scattering models to synthesize the 0.8226 μm H2O line, assuming that the clouds are composed of sulfuric acid drops, and found our nonabsorbing cloud required a sulfuric acid concentration of 82% by weight, while our thicker absorbing cloud required a concentration of 89%. A comparison of the variation of optical depth with height for our cloud models with the variation reported by Prinn (1973, Science182, 1132–1134) showed that, within a factor of 2, the variation for Prinn's thinnest cloud agreed with ours. Whitehill and Hansen (1973, Icarus20, 146–152) have recently confirmed the work of Regas et al. (1973a, J. Quant. Spectry. Radiative Transfer13, 461–463) which showed that two cloud layers are not required to explain the CO2 phase variation of Venus. Prinn's recent photochemical study of sulfuric acid clouds further supports a single, continuous cloud layer in the line formation region instead of two cloud layers with an extensive clear region between. The single layer model appears more likely because the maximum particle density in Prinn's cloud occurs in the clear region between the two layers in the models of Hunt (1972, J. Quant. Spectry. Radiative Transfer12, 405–419) and Carleton and Traub (1972, Bull. Amer. Astron. Soc.4, 362.). 相似文献
19.
The preliminary measurements by Pioneer 11 of the limb darkening and polarization of Titan at red and blue wavelenghts (M. G. Tomasko, 1980,J. Geophys. Res., 85, 5937–5942) are refined and the measurements of the brightness of the integrated disk at phase angles from 22 to 96° are reduced. At 28° phase, Titan's reflectivity in blue light at southern latitudes is as much as 25% greater than that at northern latitudes, comparable to the values observed by Voyager 1 (L. A. Sromovsky et al., 1981,Nature (London), 292, 698–702). In red light the reflectivity is constant to within a few percent for latitudes between 40°S and 60°N. Titan's phase coefficient between 22 and 96° phase angle averages about 0.014 magnitudes/degree in both colors—a value considerably greater than that observed at smaller phase from the Earth. Comparisons of the data with vertically homogeneous multiple-scattering models indicate that the single-scattering phase functions of the aerosols in both colors are rather flat at scattering angles between 80 and 150° with a small peak at larger scattering (i.e., small phase) angles. The models indicate that the phase integral, q, for Titan in both red and blue light is about 1.66 ± 0.1. Together with Younkin's value for the bolometric geometric albedo scaled to a radius of 2825 km, this implies an effective temperature in equilibrium with sunlight of 84 ± 2°K, in agreement with recent thermal measurements. The single-scattering polarizations produced by the particles at 90° scattering angle are quite large, >85% in blue light and >95% in red. A vertically homogeneous model in which the particles are assumed to scatter as spheres cannot simultaneously match the polarization observations in both colors for any refractive index. However, the observed polarizations are most sensitive to the particle properties near optical depth in each color, and so models based on single scattering by spheres can be successful over a range of refractive indices if the size of the particles increases with depth and if the cross section of the particles increases sufficiently rapidly with decreasing wavelenght. For example, with nr = 1.70, the polarization (and the photometry) are reproduced reasonably well in both colors when the area-weighted average radous of the particles, α, is given by α = (0.117 μm)(τred/0.5)0.217. While this model does not reproduce the large increase in brightness from 129 to 160° phase observed by Voyager 1, the observed increase is determined by the properties of the particles in the top few hundredths of an optical depth. Thus the addition of a very thin layer of forward-scattering aerosols on top of the above model offers one way of satisfying both the Pioneer 11 and Voyager 1 observations. Of course, other models, using bimodal size distributions or scattering by nonspherical particles, may also be capable of reproducing these data. 相似文献
20.
It is shown that Titan's surface and plausible atmospheric thermal opacity sources—gaseous N2, CH4, and H2, CH4 cloud, and organic haze—are sufficient to match available Earth-based and Voyager observations of Titan's thermal emission spectrum. Dominant sources of thermal emission are the surface for wavelenghts λ ? 1 cm, atmospheric N2 for 1 cm ? λ ? 200 μm,, condensed and gaseous CH4 for 200 μm ? λ ? 20 μm, and molecular bands and organic haze for λ ? 20 μm. Matching computed spectra to the observed Voyager IRIS spectra at 7.3 and 52.7° emission angles yields the following abundances and locations of opacity sources: CH4 clouds: 0.1 g cm? at a planetocentric radius of 2610–2625 km, 0.3 g cm?2 at 2590–2610 km, total 0.4 ± 0.1 g cm–2 above 2590 km; organic haze: above 2750 km; tropospheric H2: 0.3 ± 0.1 mol%. This is the first quantitative estimate of the column density of condensed methane (or CH4/C2H6) on Titan. Maximum transparency in the middle to far IR occurs at 19 μm where the atmospheric vertical absorption optical depth is A particle radius in the upper portion of the CH4 cloud is indicated by the apparent absence of scattering effects. 相似文献