North Equatorial Belt Research Articles

The abundance and distribution of water vapor in the Jovian troposphere as inferred from Voyager IRIS observations

The Voyager IRIS spectra of the Jovian North Equatorial Belt (NEB) hot spots are reanalyzed using a radiative transfer model which includes the full effects of anisotropic multiple scattering by clouds. The atmospheric model includes the three thermochemically predicted cloud layers, NH3, NH4SH, and H2O. Spectrally dependent cloud extinction is modeled using Mie theory and the refractive indices of NH3 ice, NH4SH ice, water, and H2O ice. The upper tropospheric temperature profile, gas abundances, height-dependent parahydrogen profile, and vertical distribution of NH3 cloud opacity are retrieved from an analysis of the far-infrared (180-1200/cm) IRIS observations. With these properties constrained, the 5-micron (1800-2300/cm) observations are analyzed to determine the atmospheric and cloud structure of the deeper atmosphere (P of greater than 1.5 bars). The results show that the abundance of water is at least 1.5 times solar with 2 times solar (0.00276 mixing ratio relative to H2) providing the best-fit to the Voyager IRIS hot spot observations.

Charge‐coupled device spectral images of spatially resolved regions of Jupiter in the 6190‐ and 8900‐Å methane and 6450‐Å ammonia bands during the 1989 Opposition

High‐quality charge‐coupled device spectroscopic observations at different regions of Jupiter in the spectral regions λλ 6000–6600 and 8700–9200 Å at a resolution of 1.2 Å have been obtained. These spectra allowed us to obtain the center‐to‐limb curves of the equivalent widths of the CH4 6190‐Å band, the NH3 6450‐Å band, and the band depth of the 8900‐Å band, as well as their latitudinal distribution. Some asymmetries in the center‐to‐limb distribution of the equivalent widths of the CH4 6190‐Å and NH3 6450‐Å bands were detected, as well as a very prominent decrease toward the planetary limbs for the ammonia band. The latitudinal variations of the CH4 6190‐Å and NH3 6450‐Å equivalent widths were strongly correlated for fractional radii less than 0.4, with a maximum of absorption at the North Equatorial Belt. The South Equatorial Belt, undetectable at visible and near‐infrared continuum wavelengths, was discernable at λ = 8900 Å. Model computations for the Equatorial Region assuming three aerosol layer models gave some constraints on tropospheric atmospheric parameters during the 1989 Jupiter opposition date.

Midscale dynamical features observed during 1987 in the North Equatorial Belt of Jupiter

During the second half of 1987, we studied the motions and morphologic changes of features moving relative to a prominent dark oval and its associated “hollow” in Jupiter's North Equatorial Belt (NEB). Approximately 200 photographs and CCD images were analyzed and revealed numerous active, transient, and irregular bright albedo clouds which developed over the NEB between 7° and 11° north planetographic latitudes. These clouds, embedded in a high meridional shear region, had divergent motion fields with north-south intrinsic outflow motions. Moving at higher velocities than the oval, which was located at 16.4°N, they overtook and passed it, flowing around its southern boundary into the region of the hollow. No interaction, collision, or merging was observed. It is conjectured that the dark oval was a cyclonic vortex (“barge”) and that the bright spots were the result of localized convective activity. Using two “plumes” and one bright spot as tracers, we found evidence of abnormal high zonal velocities at 7°N in September 1987, with u ≈ 109 and 117 m sec −1. This could be related to the local activity of the features or to a transient increase in the magnitude of the equatorial jet at this latitude by ≈10 m sec −1.

Jupiter: Evidence for a Phosphine Enhancement at high Northern latitudes

Abstract High-resolution observations of the Q branch of the 2 ν 2 band of phosphine at 1972 cm −1 on Jupiter show an enhancement of the PH 3 concentration in the deep troposphere ( p ⩾1 bar) by about 60% at high Northern (∼50°N) latitudes compared to both the North Equatorial Belt and the Great Red Spot. Difference in photochemistry or in deep vertical diffusion of PH 3 could be involved to interpret such variations.

Tectonic evolution of the Sergipano Fold Belt, NE Brazil, during the Brasiliano orogeny

The Sergipano Fold Belt (SFB) represents the southern segment of a Brasiliano-age (∼600 Ma) continental collision zone which extends over NE Brazil and continues into Central Africa as the North Equatorial Fold Belt. Major sinistral transcurrent fault/shear zones and thrusts separate domains with individual lithological, tectonometamorphic and magmatic characteristics. The principal steeply-dipping strike slip zones trend east-west to WNW-ESE. Lithological correlations across the shears have not proved possible, which suggests that displacements were probably large, but as yet, are unquantified. Major folding and thrusting affected all the domains. Folds have a southerly vergence with NW-SE to WNW-ESE, trends, consistent with a NE-SW to NNE-SSW shortening direction; although small differences in shortening trends exist between individual domains. The southernmost allochthonous domain of carbonate to clastic shelf-slope sediments was subject to a single phase of folding and thrusting onto the São Francisco Craton, accompanied by greenschist-facies metamorphism. North of this domain lies the Macururé Domain, which is separated from the southernmost allochthonous domain by the major Sao Miguel do Aleixo transpressive shear zone. Polyphase deformation, amphibolite facies metamorphism and massive granitic intrusion characterize this domain. North of the Macururé Domain lie the migmatites and granites of the Poço Redondo Domain, which represent a deeper crustal level. They are separated from the Macururé Domain by the Belo Monte Shear. A late tectonic leucogranite in the Poço Redondo Domain yields a 600 Ma Rb/Sr isochron. Finally, the Poço Redondo Domain was overthrust from the north by the Canindé Gabbroic Complex, associated with carbonates, pelites and amphibolites metamorphosed to greenschist and upper amphibolite facies; this has previously been interpreted as an ophiolite sequence. Although the relative movements or absolute ages of the domains are unknown, their distinct geological differences suggest that they are separate crustal blocks which underwent large lateral movement during the Brasiliano collision.

CARBON MONOXIDE AND DISEQUILIBRIUM DYNAMICS IN SATURN AND JUPITER

High-resolution (v/Av ~ 30,000) spectra of Jupiter and Saturn were obtained in order to study the composition and dynamics of Jupiter and Saturn. The shapes of CO absorption lines in Jupiter are broad, consistent with line formation at F ~ 2-9 bars. This is strong evidence in favor of internal mixing as the source of CO in Jupiter. Further, we find that the O abundance at 1100 K must be nearly solar. No variations in CO abundance were found between the North Equatorial Belt, the North Tropical Zone, and the Great Red Spot. Because CO is very sensitive to variations in the rate of mixing, we conclude that there are no gross variations in mixing with location on Jupiter. We observed CO in Saturn for the first time. The source of CO in Saturn is uncertain, although theoretical arguments favor an external source to an internal one. If the rings of Saturn are the source of the oxygen that eventually leads to CO in Saturn, the rate of influx required imposes an upper limit to the lifetime of the rings off < 100 million years. We have also found the first evidence for GeH4 in the atmosphere of Saturn. Absorption lines in the P and R branch of GeH4 are observed although no evidence of the stronger Q branch is found. We postulate that scattered solar radiation may be responsible for altering the thermal spectrum in regions of very low flux such as the Q -branch region. The abundance of GeH4 is consistent with the expected disequilibration from internal mixing in Saturn. Finally, we found more acetylene in the stratosphere of Saturn as compared to Jupiter, indicating possibly faster mixing in the upper atmosphere ofthat planet.

Ground-based imaging of Jovian cloud morphologies and motions: II. The northern hemisphere from 1975 to 1985

Telescopic photographs of Jupiter obtained during one Jovian year (1975–1985) have been analyzed in order to study the morphology and motions of the great-scale cloud systems present in the northern hemisphere during the epoch pre- and post-Voyager flyby spacecraft mission (see Sanchez-Lavega and Rodrigo 1985, Astron. Astrophys. 148, 67–78, for a similar work in the southern hemisphere). The texture of the north equatorial belt (NEB) was characterized by a variable number of plumes, between 11 and 15 (a mean of 25% have high-albedo heads), rifts (tilted high-albedo clouds crossing the belt in the shear flow sense), and turbulent wavy patterns in the northern edge. We present interactions between these features as observed in 1985. Elongated dark “barges” and rows of small dark spots were observed near the northern edge of the NEB during specific epochs. The high-albedo north tropical zone (NTrZ) was generally homogeneous from 1977 to 1984, but in 1976 little red spots were observed in its interior, and a contrasting (visible and red wavelengths) narrow belt located in its center was present in 1985. However, the most interesting feature in this region was the development of a prominent double disturbance (NTrZD) during 1975 in the high-speed eastward jet at 24°N, of which we present a study of its morphology and kinematics. Pronounced albedo changes were observed in the NTB during the whole period analyzed. Color contrasts in the NTrZ-NTB-NTZ regions were measured in 1985 from broadband relative photometry. North of 34°N there were alternating albedo bands characterized by their longitudinal variability, by the presence of small light spots in the equatorial side of the eastward jets, and by elongated dark sections of the belts on the polar side. The zonal wind profile u( ϕ) measured during this Jovian year is in good agreement with that obtained from Voyager's images and from previous ground-based analysis.

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 NH 3 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 NH 3 cloud optical depth and pressure of a deeper cloud top independently. Variability in H 2 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 NH 3 cloud layer. To be consistent with the observed 6190-Å methane absorption in hot spot regions, the NH 3 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 and polarimetry of Saturn at 2640 and 7500 Å

We have reduced and tabulated photometry and polarimetry data at 2640 and 7500 Å observed by the Voyager 2 photopolarimeter experiment. Spatially resolved limb‐to‐terminator scans across Saturn's Equatorial Zone from 12° to 68° phase angle provide information on the altitude distribution of UV absorbing hazes and the phase function and polarizing properties of stratospheric and tropospheric aerosols. Limb‐to‐terminator scans across the northern hemisphere at 10° phase angle are used to study altitude variations of the tropospheric cloud at several latitudes. For the Equatorial Zone we find (1) the UV photometry and polarimetry are best fit by Rayleigh's phase matrix. (2) A stratospheric haze of small particles is allowed as long as the optical depth is near unity or less and the center of the haze layer is in the 30‐ to 70‐mbar region. A diffuse haze fits better than a thin layer, and the aerosol/gas mixing ratio diminishes above 10 mbar. The vertical distribution and optical depth of the haze differ significantly from models proposed by others. To be in agreement with ground based and other spacecraft data, the haze optical depth is about 0.4 at 2640 Å and decreases by a factor of 10 or more at 6400 Å. If the haze aerosol scattering properties are similar to those for spheres with mean radius 0.1 μm, their imaginary refractive index is 0.4 or larger at 2640 Å and the total column density above the tropopause is 109 cm−2. (3) UV contrasts between belts and zones are interpreted as altitude variations in the top of the tropospheric cloud. The altitudes derived here for three latitudes agree with altitudes derived from ground‐based methane band studies and analyses of polarization from Pioneer 11. A high altitude absorber is abundant in the polar regions. (4) At 7500 Å, the phase function of tropospheric aerosols in the Equatorial Zone is described by a synthetic two‐term Henyey‐Greenstein function with g1 = 0.54 ± 0.11, g2 = −0.47 ± 0.08, ƒ = 0.87 ± 0.03, and ω = 0.986. The single scattering albedo in the North Equatorial Belt is ω = 0.967. The Equatorial Zone tropospheric aerosols are positively polarizing at all the phase angles of our observations.

The tropospheric gas composition of Jupiter's north equatorial belt /NH3, PH3, CH3D, GeH4, H2O/ and the Jovian D/H isotopic ratio

The gas composition of the troposphere of Jupiter in the clearest regions of the North Equatorial Belt (NEB) was derived from the Voyager 1 IRIS data. The infrared spectrum for this homogeneous cloud free region was modeled to infer altitude profiles for NH3, PH3, GeH4 and H2O. The Profiles for NH3 and PH3 were found to be depleted in the upper troposphere but otherwise in agreement with their solar values at the 1 bar level. The mole fraction for CH3D was determined to be 3.5(+1.0 or -1.3) x 10 to the minus 7th power. The GeH4 mole fraction of 7+ or -2 x 10 to the minus 10th power at the 2 to 3 bar level is a factor of 10 lower than the solar value. The H2O mole fraction is approximately 1 x 0.00001 at the 2.5 bar level and is increasing to approximately 3 x 0.00001 at 4 bars where it is a factor of 30 lower than solar. Using IRIS infrared values for the mole fractions of CH3D and CH4 a value of D/H = 3.6(+1.0 or -1.4)x 0.00001 is derived. Assuming this Jovian D/H ratio is representative of the protosolar nebula, and correcting for chemical galactic evolution, yields a value of 5.5 - 9.0 x 0.00001 for the primordial D/H ratio and an upper limit of 1.8 to 2.4 x 10 to the minus 31st power cu cm for the present day baryon density.

Near‐ultraviolet scattering properties of Jupiter

The Voyager 2 photopolarimeter experiment obtained photometric observations of Jupiter at four phase angles between 20° and 80° and at various illumination angles from limb to terminator. These data were analyzed to determine the altitude distribution and scattering properties of the material responsible for Jupiter's low geometric albedo at 2400 Å. In polar regions the absorber must be higher than 40 mbar. In mid‐latitudes, center‐to‐limb measurements indicate that most of the absorbing material lies deeper than 100 mbar. Absolute reflectivity requires a considerable amount above 400 mbar. The maximum amount of solar UV flux below 2550 Å available for heating the stratosphere at 20° latitude is only 10−4 of the solar constant at Jupiter. The latitudinal distribution of stratospheric absorbers suggests that energy deposition from the magnetosphere is important in their formation. We examine the scattering properties of model atmospheres containing three distinct aerosol size distributions. Rayleigh's phase function fits our data at several phase angles better than any particle phase function. We derive an upper limit to the column abundance of particles larger than 0.05‐µm radius in the north tropical zone and north equatorial belt. These regions contain less than one extinction optical depth at 2400 Å of such particles above the 100‐mbar altitude. Rayleigh scattering from the top 100 mbar obscures effects due to scattering from the deeper absorbing particles over our range of phase angles. We are unable to determine whether the absorbers are particulate or molecular.

Cloud forms on Saturn

The imaging photopolarimeter (IPP) on Pioneer Saturn provided spin‐scan images of Saturn's cloudtops. Only subtle departures from a uniform brightness distribution were apparent, except in the polar regions. At other latitudes the images show only a few features; they primarily support the conclusion that the visible atmosphere is a deep haze. Belts and zones are seen, and some detail in a zone near ±60° latitude. The North Equatorial Belt consists of two dark belts separated by a brighter zone exhibiting longitudinal structure.

High spatial and spectral resolution 10-μm observations of jupiter

Ten-micrometer spectra of the North Tropical Zone, North Equatorial Belt, and Great Red Spot at a spectral resolution of 1.1 cm −1 are compared to synthetic spectra. These ground-based spectra were obtained simultaneously with the Voyager 1 encounter with Jupiter in March, 1979. The NH 3 vertical distribution is found to decrease with altitude significantly faster than the saturated vapor pressure curve and is different for the three observed regions. Spatial variability in the NH 3 mixing ratio could be caused by changes in the amount of NH 3 condensation or in the degree of the NH 3 photolysis. The C 2H 6 emission at 12 μm has approximately the same strength at the North Tropical Zone and North Equatorial Belt, but it is 30% weaker at the Great Red Spot. A cooler temperature inversion or a smaller abundance of C 2H 6 could explain the lower C 2H 6 emission over the Great Red Spot.

Infrared scans of Jupiter

We present spatial scans at eight wavelengths between 7.8 and 24 μm along Jupiter's meridian and along the Equatorial Zone, the North Equatorial Belt, and the South Tropical Zone. Some features of these scans are differences in brightness temperatures between the Great Red Spot and the surrounding South Tropical Zone, a higher temperature at high northern latitudes than high southern latitudes, equal or possibly higher temperatures of zones than belts at 7.8 μm in contrast to higher temperatures of belts at other observed wavelengths, very strong limb darkening at 8.9 μm possibly due to a large scale height or a nonuniform distribution of solid NH 3 particles, and inhomogenities within belts and zones.

Spatially resolved reflectivities of Jupiter during the 1976 opposition

Spatially resolved absolute reflectivities of several regions of the Jovian disk in the wavelength region 3000 to 10760 Å are presented. Spectra were obtained of the central meridian and limbs of the Equatorial Region, North Equatorial Belt, and North Tropical Zone. Equivalent widths of several CH 4 and NH 3 bands are measured. The spatial variations of continuum reflectivity and absorption band profiles are shown in various ratio spectra.

On the nature of the blue and ultraviolet absorption in the Jovian atmosphere

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 NH 3 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.

Five micron limb-darkening and the structure of the Jovian atmosphere

By observing the transit of various cloud features across the Jovian disk, Terrile and Westphal (1977) have constructed limb-darkening curves for three regions in the 4.6 to 5.1 μm band. Several models currently employed in describing the radiative or dynamical properties of planetary atmospheres are here examined to understand their implications for limb-darkening. The statistical problem of fitting these models to the observed data is reviewed and methods for applying multiple regression analysis are discussed. Analysis of variance techniques are introduced to test the viability of a given physical process as a cause of the observed limb-darkening. The intermediate flux region of the North Equatorial Belt appears to be in only modest departure from radiative equilibrium. The limb-darkening curve for the South Temperate Belt is rich in structure and cannot be satisfactorily ascribed to any single physical mechanism; a combination of several, as yet unidentified, processes is likely involved. The hottest areas of the North and South Equatorial Belts exhibit limb-darkening curves that are typical of atmospheres in convective equilibrium. In this case, we derive a measure of the departure of the lapse rate from the dry adiabatic value ( η≅1.68), which furnishes strong evidence for a phase transition at unit optical depth in the NEB and SEB. Although the system NH 3H 2S cannot be entirely ruled out, the freezing of an aqueous ammonia solution is shown to be consistent with the parameter fit and solar abundance data, while being in close agreement with Lewis' (1969a) cloud models.

Silicon vidicon imaging of jupiter: 4100- to 8300-Å absolute reflectivities and limb darkening of spatially resolved regions

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 H 2 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.

Spectrophotometry of Jupiter

Spectrophotometric maps of Jupiter were made between 24 and 27(UT) November 1974 on the McMath Solar Telescope at Kitt Peak National Observatory. We report a comparison between observed scaled reflectivities of the Jovian North Tropical Zone and the North Equatorial Belt at System II longitudes between 195 and 205 degrees. The belt/zone reflectivity ratios between 430 and 740nm are related to the optical transmission curves of the organic and/or sulfur polymers synthesized by Khare and Sagan in a simulated Jovian atmosphere.

Spatially resolved absolute spectral reflectivity of Jupiter: 3390–8400 Å

Observational determinations of the absolute spectral reflectivities of visually distinct regions of Jupiter are presented. The observations cover the 3390–8400 Å region at 10 Å resolution, and they are compared with observations using 150–200 Å filters in the 3400–6400 Å range. The effective reflectivities for several regions (on the meridian) in the 3400–8400 Å range are: South Tropical Zone, 0.76±0.05; North Tropical Zone, 0.68±0.08; South Equatorial Belt, 0.63±0.08; North Equatorial Belt, 0.62±0.04; and the Great Red Spot, 0.64±0.09. Reflectivities near the limb are also observed. The appropriate blue and red reflectivities are tabulated in support of the Pioneer 10 and 11 imaging photopolarimeter experiments. For the regions listed above, equivalent widths of molecular bands vary as: CH 4 (6190 Å), 14–16 Å; CH 4 (7250 Å), 77–86 Å; and NH 3 (7900 Å), 87–95 Å. Significant differences from the results of C. B. Pilcher, R. G. Prinn, and T. B. McCord (“Spectroscopy of Jupiter: 3200 to 11200 Å,” J. Atmos. Sci. 30, 302–307.)