Jupiter: An inhomogeneous atmospheric model analysis of spatial variations of the H2 4-0 S(1) line

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.     

Scattering in the atmosphere of Venus: III. Line profiles and phase curves for Rayleigh scattering

Spectral line profiles, curves of growth, and curves for the equivalent width of a line as a function of Venus phase angle have been computed for a Rayleigh scattering cloud and compared with those for a cloud of isotropic scatterers. The results are very similar for the two kinds of scattering, with the exception of the curves of equivalent width as a function of Venus phase angle. These latter curves exhibit the “inverse phase effect” and rule out the possibility that the scale height of the clouds can be much less than half the scale height of the gas. The optical depth of the clouds, τ_c, is approximately 100.     

Scattering in the atmosphere of Venus: II. Effect of varying the scale height of the scattering particles

We have made calculations for the variation of equivalent width with phase angle (for a Venus-like atmosphere except that the cloud particles scatter isotropically). The effect of temperature variations, within our model atmosphere, is shown to be small. The effect of changing the scale height of the cloud relative to the scale height of the gas is much larger.     

Formation of spectral lines in planetary atmosphere IV. Theoretical evidence for structure of the jovian clouds from spectroscopic observations of methane and hydrogen quadrupole lines

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.     

Voyager 1 imaging and IRIS observations of Jovian methane absorption and thermal emission: Implications for cloud structure

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.     

Photometry of Venus: II. Theoretical brightness distribution over the disk

Theoretical brightness distributions over the Venus disk have been computed for homogeneous and multilayered cloud models. With homogeneous models, the relative brightness does not depend very much on the optical properties of the cloud, except near the limb or for small phase angles. For multilayered cloud structures, the relative brightness is nearly fixed by the structures and the relative brightness is nearly fixed by the scattering function of the uppermost cloud; the vertical distribution of the absorption is unimportant if the spherical albedo of the planet is given. If the horizontal inhomogeneities currently seen on Venus are due to a layered structure, with an optical thickness of the upper cloud varying from point to point, large simplifications seem possible, and measured contrasts at various wavelengths should permit a test of such a model.     

Observations of the phase variation of Venus CO2 equivalent widths

We present equivalent widths of Venus CO₂ scans of the P branch (P8–P32) of the 5ν₃ band at 8689 Å, the P16 line of the 5ν₃ band, and the P14 line of the ν₁ + 5ν₃ band at 7820 Å covering phase angles between 5°.1 and 170°. The equivalent widths reach a minimum at 10°, in agreement with a phase function with a backward lobe at 160° which is caused by a single internal reflection within the cloud particles. This is evidence that Venus cloud particles are composed of liquid droplets. Maximum equivalent widths are observed at ～60°, a value which is closer to the maximum of single-layer Mie scattering models than to that of two-layer models. At high phase angles we observe equivalent widths greater than those computed from homogeneous scattering models, indicating that at high altitudes the mixing ratio of scattering particles to CO₂ increases with depth. At all phase angles, particularly at large phase angles, the temporal and spatial variations in the observed equivalent widths confuse the phase variation.     

On the interpretation of the “inverse phase effect” for CO2 equivalent widths on Venus

Computations of the equivalent widths of absorption lines as a function of planetary phase angle are made for a homogeneous cloud with particles having the properties (shape, refractive index, and size distribution) deduced from polarimetry of Venus. The computed equivalent widths show an “inverse phase effect” comparable to that which is observed for CO₂ lines on Venus. This result verifies a recent suggestion of Regas et al. that the existence of an inverse phase effect does not by itself imply the presence of multiple layers of scattering particles in the atmosphere of Venus.     

X-ray spectroscopy of the broad-line radio galaxy 3C 111

We present an ASCA observation of the broad-line radio galaxy 3C 111. The X-ray spectrum is well described by a model consisting of a photoelectrically absorbed power-law form. The inferred absorbing column density is significantly greater than expected on the basis of 21-cm measurements of Galactic H  I . Whilst this may be the result of intrinsic absorption from a circumnuclear torus or highly warped accretion disc, inhomogeneities and molecular gas within the foreground giant molecular cloud may also be responsible for some of this excess absorption. We also claim a marginal detection of a broad iron Kα line which is well explained as being a fluorescent line originating from the central regions of a radiatively efficient accretion disc. This line appears weak in comparison to those found in (radio-quiet) Seyfert nuclei. We briefly discuss the implications of this fact.     

Radiative transfer in spherical shell atmospheres. III. Application to Venus

We have introduced a method of partitioning the radiance emerging from a planetary atmosphere in proportion to the average number of scatterings in each atmospheric layer in order to gain a more fundamental understanding of the so-called level of line formation. A realistic model of the Venus atmosphere was used to compute the radiance for a range of phase angles and two planetary colatitudes, namely, 20 and 90°. We computed the core and continuum radiances for the P(16) line of 8689-Å CO₂ band and introduced two ways of computing an effective temperature. Both definitions yielded similar results. We found that these effective temperatures varied little with phase angles up to 120°, but fell rather rapidly beyond this point. Also colder effective temperatures were found as we went from equator to pole. The results obtained are all consistent with the spectroscopic temperature determination from CO₂ band studies. We have also defined an effective optical depth, τ_eff, which we feel gives a better understanding of the level of line formation than other definitions used to date.     

Five-minute oscillations of solar equivalent widths

Equivalent widths of weak and moderately strong Fraunhofer lines observed in an area roughly 3500 × 10000 km in extent are found to show small variations of the order of 1 mÅ, on a time scale of minutes. The dependence of amplitude on line strength and excitation closely fits that predicted for a compressional disturbance associated with temperature variations that manifest themselves in the equivalent widths. The rms amplitude is about 20K near τ₅₀₀₀ = 10^-2. These equivalent width variations frequently exhibit a 5-min periodicity and are accompanied by prominent oscillations of velocity. Power spectra of both quantities closely resemble each other and demonstrate that most of the equivalent width variations in the range 200 to 500 s are due to the thermal response of the atmosphere to 5-min oscillations. A systematic phase lag between velocity and equivalent width is observed, in the sense that temperature leads velocity by an average angle of 120°. This deviates significantly from 90° valid for standing adiabatic waves, showing that in the line-forming layers, τ₅₀₀₀ ≈ 10^-2, the 5-min oscillations are markedly affected by radiative exchange. The observed phase lag implies a radiative decay time of ≈40 s, a value which agrees with modelatmosphere predictions for the line-forming layers. Since the observed wave trains frequently show constant amplitude over a much longer time, a continuous feed-back of energy seems to occur.     

Secular and orbital variability of Cir X-1 observed in optical spectra

We have observed variations in the optical emission lines from the X-ray binary Circinus X-1. These variations may be attributed both to orbital variations and to long term secular changes in line strength. We have detected double-peaked H α emission lines on two occasions, providing the first direct evidence for an accretion disc in the system. The separation of the peaks was different on the two occasions, suggesting that the disc might have a different size. The equivalent width of the emission lines dropped by more than a factor of three between 1999 and 2000; this continues the trend seen in earlier data, so that the H α equivalent width has now declined by a factor of 20 since 1976. The emission lines do not appear to show signature of orbital motion, except for the data taken near phase 0, which show a significant velocity shift.
We have observed an absorption component to the He  i lines on one occasion. We suggest that, unlike the P Cygni profiles seen in X-ray spectra, this absorption does not arise in the accelerating zone of a radiatively driven wind. Instead, the absorption arises in material previously ejected from the system. It was only seen on this one occasion because the strength of the emission line had dropped dramatically.     

Monte Carlo Radiative Transfer Modeling of Lightning Observed in Galileo Images of Jupiter

We study lightning on Jupiter and the clouds illuminated by the lightning using images taken by the Galileo orbiter. The Galileo images have a resolution of ∼25 km/pixel and are able to resolve the shape of single lightning spots, which have half widths (radii) at half the maximum intensity in the range 45-80 km. We compare the shape and width of lightning flashes in the images with simulated flashes produced by our 3D Monte Carlo light-scattering model.The model calculates Monte Carlo scattering of photons in a 3D opacity distribution. During each scattering event, light is partially absorbed. The new direction of the photon after scattering is chosen according to a Henyey-Greenstein phase function. An image from each direction is produced by accumulating photons emerging from the cloud in a small range (bins) of emission angles. The light source is modeled either as a point or a vertical line.A plane-parallel cloud layer does not always fit the data. In some cases the cloud over the light source appears to resemble cumulus clouds on Earth. Lightning is estimated to occur at least as deep as the bottom of the expected water cloud. For the six flashes studied, we find that the clouds above the lightning are optically thick (τ>5). Jovian flashes are more regular and circular than the largest terrestrial flashes observed from space. On Jupiter there is nothing equivalent to the 30-40-km horizontal flashes that are seen on Earth.     

Spatio-temporal fluctuations in HeI 10830 Å line parameters: Evidence for spicule formation

The equivalent width, line depth, line width, and Doppler shift of the He i 10830 Å line were extracted from two time series of spectra. Scatter plots of time-averaged line depth, line width, and Doppler shifts, as well as the root mean square temporal fluctuation of these quantities against the time-averaged equivalent width at a few hundred spatial locations were obtained. The statistical behaviour of these line parameters and their fluctuations was used to infer plausible reasons for the fluctuations. Examination of these results showed that the line parameter fluctuations could be caused by fluctuations in the coronal UV radiation (which could drive the spicules) or by the appearance of density inhomogeneities such as spicules within the line forming domain. In either case, the data can be interpreted as representing the initial phases of spicules.     

Seasonal changes on Jupiter: 1. Factor of activity of the hemispheres

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.     

Temperature and pressure determinations in the Venus atmosphere by means of high-resolution spectra from 1 to 2.5 μm

Twenty-one bands of CO₂ and the 2-0 band of CO were analyzed for best temperature and pressure fits from Venus spectra obtained with the “Connes” interferometer at the Steward Observatory 2.25-m telescope during the spring of 1971. An average temperature of 241 ± 7°K, an effective pressure of 0.12 ± 0.06 atm, and an average two-way transmission abundance of 3 km-amagat were determined. No difference in temperature or pressure between hot bands, a double hot band, and regular bands was found. Our results were compared to model calculations for a reflecting layer and scattering atmosphere. The results indicate that, most likely, spectroscopic line formation occurs in a relatively clear space above a scattering cloud layer with a reasonably well-defined upper boundary.     

The physical conditions in the shells of type I supernovae

Two models of the origin of the spectrum of type I supernovae are analysed: (I) the photosphere of the ‘central remnant’ and the expanding shell are separated by a density cavity; (II) the ‘photosphere’ (the layer which produces the continuous spectrum) is the inner part of the expanding shell. The arguments are given in favour of model I. Opacity of the shell close to light maximum for λ>4000 Å is mostly due to Thomson scattering; soon after light maximum (and it may be already at light maximum) the shell becomes completely transparent in this region of the spectrum. The problem of the origin of the very large width and of the relatively high central residual intensities of the absorption lines in the spectra of type I supernovae are analysed. A very noticeable dispersion in the velocities of the radial gas motions in the shell is the principal cause of the large equivalent width of the absorption lines in the spectra of these supernovae. The role played by the inhomogeneities in the shell is also discussed. The depth of the strong absorption lines produced by a very inhomogeneous shell may be equal to the filling factor of the medium. From the analysis of the spectra of supernova 1972e a lower limit for the mass of the shell is obtained (M>10³¹ g). Then from the fact of absence of a detectable H-absorption line and a simultaneous presence of strong Siii absorption lines (6347, 6371 Å) in the spectrum of supernova 1972e it follows that the ratio Si/H is at least two or three orders greater than that for the ‘normal’ stars.     

The vibrational overtone spectrum of liquid methane in the visible and near infrared: Applications to planetary studies

The strengths of 10 bands in the absorption spectrum of liquid methane betwen 19 400 and 6190 Å have been measured. After a small correction for the polarizability of the liquid is applied, for the purpose of comparison with similar gas phase measurements, it is found that there is no temperature dependence of the band strengths between 95 and 295°K. Changes of band shape with temperature cause the 95°K laboratory spectra to resemble Saturn more than room temperature observations do. Gas phase absorption clearly dominates the liquid in planetary spectra, so liquid methane cannot be detected in the outer Solar System by Earth-based observations.     

Retrieval of ammonia abundances and cloud opacities on Jupiter from voyager IRIS spectra

A method is formulated to retrieve gaseous ammonia abundance and cloud opacities at 45 and 5 μm from Voyager IRIS data using a simplified atmospheric model and a two-stream radiative transfer approximation. Our goal is to obtain sufficient computational efficiency to permit global mapping of the relative horizontal variations of these parameters. A single cloud layer is invoked with a base pressure of 680 mbar and a scale height equal to 0.14 times the gas scale height. The NH₃ vertical distribution is modeled with a scale height equal to that of the cloud above 680 mbar and with a mole fraction independent of height at deeper levels. Measurements of brightness temperature as a function of emission angle from selected locations on the planet are used to verify the validity of the model and to constrain certain model parameters. It is found that the cloud particles can be treated as pure absorbers at 45 μm, but scattering must be included at 5 μm where a single scattering albedo of ∼0.75 is inferred. These results are used to develop a simple algorithm for the retrieval of ammonia abundance and cloud optical depths at 45 and 5 μm from measurements at 216, 225, and 2050 cm⁻¹.