共查询到20条相似文献，搜索用时 765 毫秒
1.
William D. Cochran 《Icarus》1977,31(3):325-347
An analysis of the structure of the Jovian atmosphere, primarily based on center-to-limb variations (CTLV) of the equivalent width of the hydrogen quadrupole 4-0 S(1) line, is presented. These data require that the atmosphere have regions of both long- and short- scattering mean free paths. Two alternative cloud structures which fit the data are developed. The first is a two-cloud model (TCM) consisting of a thin upper cloud and a lower semi-infinite cloud, with absorbing gas between the clouds and above the upper cloud. The second model is a reflecting-scattering model (RSM), in which a gas layer lies above a haze consisting of scattering particles and absorbing gas. The cloud-scattering phase function in both models must have a strong forward peak. The CTLV data require, however, the presence of a backscattering lobe on the phase function, with the backscattering intensity about 4% of the forward scattering. The decrease in reflectivity of all regions from the visible to the ultraviolet is explained by the presence of dust particles mixed with the gas. Most of the ultraviolet absorption in the atmosphere must occur above the upper cloud layer. Particles with a uniform distribution of radii from 0.0 to 0.1 μm with a complex index of refraction varying as λ?2.5 are used. The contrast in reflectivity between belts and zones may be explained by the larger concentration of dust in the belts than in the zones. Spatially resolved ultraviolet limb-darkening curves will help to determine the dust distribution of the Jovian atmosphere. The visible methane bands at λλ 6190, 5430, and 4860 Å are analyzed in terms of these models. We derive a methane-to-hydrogen mixing ratio of 2.8 × 10?3, which is about 4.5 times the value for solar composition. 相似文献
2.
Guido Visconti 《Icarus》1981,45(3):638-652
We present computations of the photodissociation coefficients for NH3, N2H4, PH3, and H2S in the Jupiter atmosphere. The calculations take into account multiple scattering and absorption using the radiative-transfer method known as δ-Eddington approximation. The atmospheric models include two cloud layers of variable thickness and haze layers above the upper cloud and between the clouds. One of the results of the radiative computations deal with the reflectivity of the Jovian atmosphere as a function of wavelength. A comparison with available data on the albedo of the planet gives some important indications about mixing ratios and distributions of gases and aerosols. The results for the photolysis rates are compared with similar rates obtained by considering either the direct flux or the flux determined by the molecular gas absorption alone. The latter is usually the approximation used in aeronomic models. The results of this comparison show that a considerable difference exists with direct flux photodissociation but significant differences with molecular absorption flux exist only in atmospheric regions where photodissociation is relatively small. 相似文献
3.
The theory of formation of pressure-broadened methane lines and collision-narrowed hydrogen quadrupole lines in a Jovian atmosphere is studied in detail for a physically realistic model of the planet's lower atmosphere. Only observations of the center-to-limb (CTL) variations of the equivalent width of absorption lines for both of these molecules can identify the structure of the visible cloud layers. Observations of the CTL variation of methane and hydrogen quadrupole lines are the most suitable for studying the Jovian atmosphere. The CTL variations for hydrogen are much greater and more sensitive to variations of the properties of the thin upper tropospheric cloud layer than the corresponding observations of methane lines. A detailed comparison of hydrogen quadrupole with methane lines is made for the same continuum conditions, enabling us to develop a detailed understanding of the formation of the collision-narrowed hydrogen quadrupole lines in a Jovian atmosphere. 相似文献
4.
High spatial resolution infrared and visible data obtained by the Voyager 1 spacecraft have been analyzed simultaneously to infer properties of the deep cloud structure of the Jovian troposphere in the 1- to 4-bar pressure range. Influence of the ammonia upper cloud layer, in the 5μm Jovian window, has been investigated through a cloud model derived from far ir Voyager IRIS measurements. The attenuation, computed with an anisotropic scattering formulation, is too weak to explain 5-μm measurements and provides evidence for existence of a cloud structure at deeper levels. The main conclusions derived from the present analysis are summarized below: (1) the deep cloud structure appears to be vertically associated with the NH3 upper layer; (2) the ammonia cloud is mainly responsible for the visible appearance of the Jovian equatorial region; (3) the deep cloud structure exhibits a grey opacity in the 5-μm window; (4) coldest 5-μm spectra can be interpreted by the existence of a thick cloud layer located at levels in the 180–195°K temperature range. Implications of these results are discussed in conjunction with predictions of dynamical and thermochemical models. NH4SH is shown to be a likely candidate for the main deep cloud constituent. An even deeper thick H2O cloud may be present too, but should not be responsible for the observed spread in 5-μm brightness temperatures. 相似文献
5.
V.G. Teifel 《Icarus》1977,30(1):138-154
Results of photoelectric measurements of the intensity in CH4 5430, 6190, and 7250 Å absorption bands, CH4 absorption lines in the 3ν3 band, and the NH3 6457.1 Å line are examined from the point of view of a model which takes into account the role of multiple scattering inside a homogeneous semi-infinite cloud layer in the formation of absorption components in the Jovian spectrum. Introduced are a number of simple ratios between depths of lines and bands and the parameters which characterize the properties of the cloud layer and the atmosphere above the clouds for occurrence of the Henyey-Greenstein scattering phase function at various degrees of asymmetry in g. The CH4 content inside the cloud layer is determined as an equivalent thickness on the mean free path between scattering events. The latter was found to be equal to AL ? 10 ± 2 m-amagat at g = 0.75 or AL ? 20 ± 3 m-amagat at g = 0.5 along all the above-mentioned CH4 absorption bands. For NH3 it is AL ? 31 ± 4 cm-amagat at g = 0.75 and AL ? 62 ± 8 cm-amagat at g = 0.5.The weakening of the CH4 absorption bands toward the edges of the Jovian disc requires a volume scattering coefficient in the cloud layer of σa ～ 10?6 cm?1. The mean specific abundance of NH3 obtained within the cloud layer does not contradict the calculated abundance of saturated gaseous ammonia. 相似文献
6.
Results are given for polarization measurements of both the entire Jupiter disk and its centre for seven wavelength regions in the 0.373–0.800 μm range. Interpretation of these observations is based on two model atmospheres: (A) The cloud layer particles and molecules are mixed with a constant ratio. (B) A gas layer with small optical thickness, τ0, is situated above the cloud layer which consists of aerosol particles. The aerosol particles are considered to be non-absorbing spheres, their size distribution being normal Gaussian. The index of refraction for the particles is considered to be independent of wavelength in the above spectral range. An approximate method is used for the determination of parameters of the Jovian atmosphere. This method was tested by evaluation of the parameters for the Venus cloud layer: The refractive index was found to be n = 1.435 ± 0.015, the square of the logarithmic dispersion of the radius of particles σ2 = 0.12 and the mean geometrical radius of particles r0 = 0.74 μm which agree well with exact values given by Hansen and Arking (1971). For the atmosphere of Jupiter it was found: n = 1.36 ± 0.01, σ2 ? 0.3, r0 ? 0.2 μm. This refractive index for the particles agrees well with the ammonia cloud layer hypothesis. 相似文献
7.
8.
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
9.
Spatially resolved reflectivities from 3000 to 6600 Å of three positions from the center to the limb of the Jovian Equator, North Equatorial Belt, and North Tropical Zone are analyzed to determine the vertical distribution and wavelength dependence of various sources of blue and uv absorption. Six different models of the distribution of absorbing dust particles are examined. In each model, the variation of dust optical depth and cloud single-scattering albedo are determined. Only those models having dust above the upper NH3 cloud layer will fit the data. The high altitude dust distribution is approximately uniform over the three regions examined. The contrast in reflectivity of the belts and zones may be modeled by a different cloud single-scattering albedo in the different regions. 相似文献
10.
We carried out a spectral observation of traces of the comet impacts within the wavelength region between 440 and 830 nm. Three dark spots of fragments K, E, and G impact sites were investigated. The spectrum of these dark spots shows no special emission or absorption lines in this observation. The global spectral feature resembles that of Jovian zone cloud rather than that of the belt. While the continuum reflectivity of the dark spots of K and E sites is less than 0.42 at 600 nm, that of the G site is 0.33. These values should be interpreted as an upper limits because of the influence of atmospheric seeing. The equivalent width of the absorption lines at the K sites is also derived. Both the continuum reflectivity and the equivalent width of the dark spots are smaller than those of any Jovian zonal cloud. This indicates that the dark spots are low-albedo cloud formed at the upper atmosphere. 相似文献
11.
It is suggested that in a reducing environment such as the Jovian atmosphere, GeH4 may be spectroscopically active. Absorption features might be detectable in the 4.7μ window in the Jovian upper atmosphere. 相似文献
12.
The Pioneer 10 ultraviolet photometer observations of the Jovian hydrogen torus are analyzed to obtain the angular distribution. The cloud is asymmetric about Io, where the atoms presumably originate, with the greater density occurring in the trailing portion. A simple model which assumes Jeans escape from the atmosphere of Io is developed and compared to the observations. The results suggest that the exospheric temperature is high (～3000 K) and that the ionization lifetime of the cloud atoms is ～1 × 105 sec. 相似文献
13.
A. P. Vidmachenko 《Kinematics and Physics of Celestial Bodies》2016,32(4):189-195
To identify temporal variations of the characteristics of Jupiter’s cloud layer, we take into account the geometric modulation caused by the rotation of the planet and planetary orbital motion. Inclination of the rotation axis to the orbital plane of Jupiter is 3.13°, and the angle between the magnetic axis and the rotation axis is β ≈ 10°. Therefore, over a Jovian year, the jovicentric magnetic declination of the Earth φ m varies from–13.13° to +13.13°, and the subsolar point on Jupiter’s magnetosphere is shifted by 26.26° per orbital period. In this connection, variations of the Earth’s jovimagnetic latitude on Jupiter will have a prevailing influence in the solar-driven changes of reflective properties of the cloud cover and overcloud haze on Jupiter. Because of the orbit eccentricity (e = 0.048450), the northern hemisphere receives 21% greater solar energy inflow to the atmosphere, because Jupiter is at perihelion near the time of the summer solstice. The results of our studies have shown that the brightness ratio A j of northern to southern tropical and temperate regions is an evident factor of photometric activity of Jupiter’s atmospheric processes. The analysis of observational data for the period from 1962 to 2015 reveals the existence of cyclic variations of the activity factor A j of the planetary hemispheres with a period of 11.86 years, which allows us to talk about the seasonal rearrangement of Jupiter’s atmosphere. 相似文献
14.
Martin S. Spergel 《Earth, Moon, and Planets》1977,17(2):123-131
Modeling of the Jovian atmosphere shows that cosmic ray induced albedo neutron decay is inadequate to account for Pioneer 10 and 11 projected electron levels on Jupiter. High energy solar protons must also be excluded as an important neutron decay source. Analysis of neutron flux data near the top of the Jovian atmosphere can lead to the determination of He/H2 and3He/4He ratios for the Jovian atmosphere. 相似文献
15.
A. P. Vidmachenko 《Kinematics and Physics of Celestial Bodies》2016,32(6):283-293
From our investigation of the behavior of changes in the visible brightness of Jupiter observed since 1850, it follows that the 22.3-year Hale magnetic cycle of solar activity produces the dominating influence on the processes taking place in the troposphere at a level of forming the upper boundary of clouds. The maximum values of the integral brightness of Jupiter fall on the solar cycle with the highest value of the Wolf number for the last 165 years (around 1957). The lowest estimates of brightness were obtained in 1855, when the Wolf number in the 12th solar-activity cycle was smallest. The analysis of the reflectance of Jupiter’s hemispheres in the visible spectral range for 1962–2015 revealed the alternating increase in the brightness of southern and northern tropical and middle regions for one rotation period of Jupiter about the Sun. Such a change in brightness and the increase in the activity of different hemispheres of the planet may indicate the periodic global alteration in the circulation system, the structure of cloud layers, and the overcloud haze. This suggests the interrelation between the observed variations in the reflectance of the considered latitudinal belts of Jupiter and the change in the axial tilts of the planet itself and its magnetic field to the orbital plane, i.e., the seasonal alteration in the atmosphere. The comparison of the temporal dependence of the activity factor A j of the Jovian hemispheres in the visible spectral range with the change in the solar-activity index R shows that, from 1962 to 1995, these parameters almost synchronously changed, though the response of the visible cloud layer somewhat lagged behind the regime of exposure of the atmosphere to the Sun. The analysis shows that, when the planet is moving along the orbit, the reflectance of Jupiter’s hemispheres varies in response to the 21-percent change in the exposure of different hemispheres with a lag of 6 years. Such a lag coincides with the radiation- relaxation time of the hydrogen–helium atmosphere under the Jovian conditions. Desynchronization in their behavior that occurred after 1997 may be explained by the unbalanced influence of the three mentioned causes on the atmosphere of the planet. 相似文献
16.
Observations of Io suggest that it may have an atmosphere in which sodium vapor, ammonia, and nitrogen are important constituents. Several atmospheric models consisting of these gases are treated here. These are tested as a function of total content against the Pioneer 10 observations and for stability against escape. The results suggest that the atmosphere is very tenuous and that the interpretation of the ionosphere detected by Pioneer 10 by a static model may be inconsistent with the sodium cloud observations. It is postulated that ionization may also be escaping and that sodium may be comparable in content in the atmosphere with some molecular constituent such as NH3 or N2. Sodium and this molecular component then dominate the atmosphere. It is also suggested that particle precipitation contributes to heating of the atmosphere and to the production of ionization; furthermore, the difference between day- and nighttime ionospheres and possible trailing and leading side effects may relate to the nature of the particle energy distributions. These distributions may be the result of the peculiar interaction of Io with the Jovian magnetosphere. 相似文献
17.
苏梅克-列维9号彗星(SL9)与木星相撞后，在木星上观测到的以常速度(～450m／s)向外扩展的圆环意味着这是碰撞在木星大气中引起的线性波动．我们选取：非旋转、无粘性、密度分层、不可压缩的木星大气模型，而且木星大气以水平速度U=b az运动；给出初始扰动压力P(r；0)作为碰撞的初始条件，用流体力学方程组求解了彗木相撞中的惯性引力波．结果表明：当木星大气以速度U=U0(～170m／s)运动时，彗星碎片的大部分能量都用来产生内波，同时还得到彗星碎片的撞击深度H与水平相速Vp的关系式．当木星大气以速度为U=b az运动时，木星大气的扰动能量不再是在动能和势能间均分。 相似文献
18.
An important feature observed in the wake of the Jupiter-comet clash was the appearance of the ring structure axisymmetrically positioned around the center of the impact. The persistent expansion of the dark rings and its speed indicated an outward propagating gravity wave (Benka, 1995). We employ an analytical model of constant density, uniform finite depth and inviscid fluid layer to investigate the wave motion produced by the impact of Comet Shoemaker-Levy 9 on the Jovian atmosphere. The relevant thermal effects are neglected and an explosion resulting from the collision is then described by an initial impulsive pressure at the surface of the Jovian atmosphere. Under the assumption that all the kinetic energy of a comet fragment is completely converted into the energy of wave motions in the Jovian atmosphere, an analytical formula describing the relationship between the resulting wave motion in the atmosphere and the parameters of a comet fragment (the radius, density and speed) is derived. Results from the present simple analytical model give a qualitative agreement with observations regarding the distance and speed of the waves. 相似文献
19.
《Chinese Astronomy and Astrophysics》2005,29(2):203-212
After the collision of Comet Shoemaker-Levy 9 (SL9) with Jupiter, some ring structures were observed propagating outwards at a constant speed (∼450 m/s) on the Jovian surface. These are thought to be linear waves caused by the collision. A linear model of the collision is presented, in which the Jovian atmosphere is considered as an irrotational, inviscid, stratified and incompressible fluid layer moving at a speed of U = b + az. We take an initial impulsive pressure p(r; 0) as the initial condition and solve the fluid dynamics equations for inertia-gravity waves. It is found that most part of the perturbation energy is used to produce internal waves when Jovian atmosphere moves at a constant speed (U = Uo (∼170 m/s)). A relation between the impact depth H and the horizontal phase speed vp is deduced. Finally, the inertia-gravity waves are discussed for the case U = b + az and it is found that the perturbation energy is then not divided equally between kinetic energy and potential energy because of the effect of a shear. 相似文献
20.
It is now recognized that a number of neutral-plasma interaction processes are of great importance in the formation of the Io torus. One effect not yet considered in detail is the charge exchange between fast torus ions and the atmospheric neutrals producing fast neutrals energetic enough to escape from Io. Since near Io the plasma flow is reduced, the neutrals of charge exchange origin are not energetic enough to leave the Jovian system; these neutrals are therefore distributed over an extensive region as indicated by the sodium cloud. It is estimated here that the total neutral injection rate can reach 1027 s?1 if not more. New ions subsequently created in the distributed neutral atomic cloud as a result of charge exchange or electron impact ionization are picked up by the corotating magnetic field. The pick-up ions are hot with initial gyration speed near the corotation speed. The radial current driven by the pickup process cannot close in the torus but must be connected to the planetary ionosphere by field-aligned currents. These field-aligned currents will flow away from the equator at the outer edge of the neutral cloud and towards it at the inner edge. We find that the Jovian ionospheric photoelectrons alone cannot supply the current flowing away from the equator, and torus ions accelerated by a parallel electric field could be involved. The parallel potential drop is estimated to be several kV which is large enough to push the torus ions into the Jovian atmosphere. This loss could explain the sharp discontinuous change of flux tube content and ion temperature at L = 5.6 as well as the generation of auroral type hiss there. Finally we show that the inner torus should be denser at system III longitudes near 240° as a result of the enhanced secondary electron flux in this region. This effect may be related to the longitudinal brightness variation observed in the SII optical emissions. 相似文献