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At least 1,459 records · Page 81
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NASA NTRS1990

Global four-band spectral classification of Jupiter's clouds - Color/albedo units and trends

Voyager 2 digital images of Jupiter have been used to construct a global data base of cloud reflectance in four spectral bands: three wideband 'colors' with effective wavelengths at 431 nm, 564 nm, and 599 nm, plus the narrowband CH4 filter centered at 621 nm. This data base has been spectrally classified at 0.5 deg resolution to separate the complex scene into cloud color/albedo units on a pixel-by-pixel basis, revealing 20 distinct and five tentative units. These include both large, globally distributed units and very small, localized units. Global color maps and unit membership maps are used to highlight associations and trends.

Thompson, W. Reid↗
NASA NTRS1990

Comparison of plasma wave measurements in the bow shocks at Earth, Jupiter, Saturn, Uranus and Neptune

Plasma wave measurements from the Voyager 2 crossing of Neptune's bow shock are presented and compared with measurements from the bow shocks of Earth, Jupiter, Saturn, and Uranus. The wave amplitudes above 0.01fp, when normalized to the solar wind ion thermal energy density at each planet, are significantly higher at the outer planets than at Earth. Despite the differences in amplitude, the shock spectra of all the planets can be fitted to curves of similar form in this frequency range. The total normalized electric field energy densities exhibit an exponential dependence on ion thermal Mach number, Magnetosheath wave energies are comparable at all of the planets when normalized to the downstream plasma pressure.

Moses, S. L.↗
NASA NTRS1990

Lick Jupiter-Voyager reference star catalogue (Klemola, Morabito, and Taraji 1978): Documentation for the machine-readable version

The machine-readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The catalog contains accurate equatorial coordinates for 4983 stars in a band of sky against which cameras of the Voyager spacecraft were pointed for observations in the region of Jupiter during the flyby. All of the reference stars are in the range 6 hr 00 min to 8 hr 04 min in right ascension (1950), declination zones +16 to +23 degrees, and 8 hr to 31 min to 8 hr 57 min, zones +08 to +14 degrees. Mean errors of the positions are about 0.4 sec.

Warren, Wayne H., Jr.↗
NASA NTRS1990

Zonal motion and structure in Jupiter's upper troposphere from Voyager infrared and imaging observations

Global digital maps of Jupiter's upper-tropospheric temperature have been generated at the 270- and 150-mb pressure levels, together with IR cloud optical depths at 5 and 45 microns and the ammonia abundance near the 680-mb pressure level, on the basis of Voyager IRIS north-south mapping sequences. Attention is given to the 270-mb and 45 micron data; global digital maps are presented for violet and orange reflectivities. The dominant upper tropospheric thermal structures move at a rate far different from that of the cloud indicators, and are noted to remain stationary relative to the planet's bulk rotation. Strong stationary features are found at a zonal wavenumber of 9 near 15 deg N latitude and of 11 near 20 deg latitude.

Magalhaes, Julio A.↗
NASA NTRS1990

Electrical conductivity of Jupiter's shallow interior and the formation of a resonant of a resonant planetary-ionospheric cavity

The present consideration of hydrogenic atmospheric reactions on Jupiter, to a depth of 4000 km, notes the primary ion constituents at these depths to be both positive and negative ions of molecular hydrogen contributing less than 20 percent to total electrical conductivity by free electrons. An electrical surface defined by the boundary beneath which the interior is electrically conducting exists at depths which vary according to EM wave frequency, from 1100 km for 1 mHz to 3000 for 1 MHz. The presence of a lower electrical boundary within the shallow interior suggests that a planetary-ionosphere resonant cavity analogous to the earth-ionosphere cavity may exist.

Sentman, D. D.↗
NASA NTRS1990

Jupiter's north and south polar aurorae with IUE data

Observations of Jupiter's auroral H2 emissions with the IUE spacecraft, from 1978 through 1990, show that aurorae at the two poles are similar in several respects: (1) emission intensity is modulated with magnetic longitude, north peak emission at lambda (III) (1965) 200 deg, south peak at (1965) about 20 deg; (2) emission intensity and degree of modulation are comparable for both poles; and (3) attenuation by hydrocarbons varies in phase with the intensity, peak attenuation coinciding approximately with peak emission. Increases in the hydrocarbon column are an indicator of either enhanced penetration depth and, thus, energy of the auroral primaries, or of increases in the high-altitude hydrocarbon content caused by modification of the local atmosphere.

Livengood, T. A.↗
NASA NTRS1991

Thermal maps of Jupiter - Spatial organization and time dependence of stratospheric temperatures, 1980 to 1990

The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH4 band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and midlatitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm midlatitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than about 30,000 kilometers. The amplitudes of the waves vary on a time scale of about 1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than + or - 30 meters/sec.

Orton, Glenn S.↗
NASA NTRS1991

Evidence for aggregate particles in the atmospheres of Titan and Jupiter

The present optical-property calculations for aggregate particles allow most of the photometric and polarimetric observations for the Titan atmosphere to be explainable in terms of aggregate particles, whose mean projected area equals that of an 0.14-micron radius sphere; these would contain monomers of near-0.06-micron radius. Such aggregate particles may further account for the observed optical properties of Jupiter's high-altitude haze, and could ultimately furnish an essential constraint on the Titan's coupled surface/atmosphere evolution.

West, Robert A.↗
NASA NTRS1991

The 2-micron polar haze of Jupiter

Model spectra have been constructed for the CH4 lines of the polar regions of Jupiter in such as way as to encompass the hydrogen pressure-induced opacity and haze layers revealed by high-resolution spectroscopy. Comparisons between observation and model spectra indicate that, for optically thin haze models, the polar haze is primarily located between the 70 and 5 mbar pressure levels; for opaque haze models, the top of the haze layers lies in the vicinity of the 15-mbar level. It is concluded that the polar haze is widely distributed over both polar regions and exhibits no strong correlation with auroral activities.

Kim, Sang J.↗
NASA NTRS1990

Monitoring Jupiter's hectometric emission

The feasibility of long-term monitoring of the Jovian hectometric radiation component (nominal range between 0.3 to 3 MHz) is considered. It is recommended that long-term monitoring of Jupiter at frequencies around 1 MHz should be conducted either from a high-orbit earth satellite or from the surface of the moon. Such a program would eventually provide a record of rotation period changes revealing secular variations in the Jovian magnetic field, with a sensitivity much higher than could be achieved from the earth.

Carr, Thomas D.↗
NASA NTRS1991

Studies of asteroids, comets, and Jupiter's outer satellites

Observational, theoretical, and computational research was performed, mainly on asteroids. Two principal areas of research, centering on astrometry and photometry, are interrelated in their aim to study the overall structure of the asteroid belt and the physical and orbital properties of individual asteroids. Two highlights are: detection of CN emission from Chiron; and realization that 1990 MB is the first known Trojan type asteroid of a planet other than Jupiter. A new method of asteroid orbital error analysis, based on Bayesian theory, was developed.

Bowell, Edward↗
NASA NTRS1991

Infrared variability of Jupiter and Saturn

Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn, and of the enigmatic satellite of Saturn, Titan. The 5 micron spectral region of these objects is transparent to deep levels, and is therefore particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. In Titan, 5 micron observations probe atmospheric layers at or near the surface. Ground-based spectroscopy complements Voyager, Galileo, and Cassini measurements. The spectroscopy is sensitive to lower mixing ratios for selected molecules, while the on-board mass and infrared spectrometers probe molecules and levels that are inaccessible form the ground. The observations also provide time-based data for preparation of the upcoming missions.

Knacke, Roger↗
NASA NTRS1991

Ground-based observations of comets, the Jupiter plasma Torus, and Io

Aspects of cometary and magnetospheric physics were investigated by means of ground-based astronomical spectroscopy. High-throughput, dual-etalon Fabry-Perot spectrometers were used to obtain very high resolution spectra of atomic, molecular, and ionic emission lines from the diffuse gases and plasmas associated with comets and the Jupiter plasma torus. The Fabry-Perot spectrometers were also used with a charge coupled device (CCD) camera to obtain images of these extended emission sources in individual spectral lines at high spectral resolution. A new program using the McMath solar-stellar spectrograph to observe emission lines from Io was recently initiated. The McMath spectrograph has a high resolution mode which allows the detection of narrow, relatively faint emission lines superimposed on Io's reflected solar spectrum.

Scherb, Frank↗
NASA NTRS1991

Global scale auroral emissions on Jupiter

Jupiter's aurora are normally confined to limited regions around the magnetic poles. Our collected spectra show that very unusual periods of global scale auroral activity occurred during September and November of 1988. During the global scale events, the H2 and H3(+) emissions remained confined to their unusual auroral zones, but strong, unidentified emissions appeared in the vicinity of the H2 quadrupole lines. This would suggest that unusual periods of widespread magnetospheric dumping occurred.

Trafton, L.↗
NASA NTRS1991

The upper ionospheres of Jupiter and Saturn

The electron-density profiles of Jupiter's and Saturn's ionospheres are modeled with a 1D chemical diffusive model incorporating measured parameters of the neutral atmospheric structure. The Voyager RSS ion-density data are modeled by accounting for ion chemistry, the H3(+) recombination-rate coefficient, and H2O chemistry. Electron-density peaks for both ionospheres are 900-1000 km lower in the model than the measured values, and the role of vibrational excitation of H2 is discussed in converting H(+) to H2(+) and H3(+). Vertical ion flow is also considered which can maintain the plasma peaks under the conditions of electrical fields or horizontal neutral winds. An assumed influx of H2O molecules of a specific quantity is theorized to reproduce the measured values on Saturn when combined with a vertical plasma drift.

Majeed, Tariq↗
NASA NTRS1992

The complete polarization state of a storm of millisecond bursts from Jupiter

Normal bursts with right-hand (RH) elliptical polarization, millisec S-bursts with RH elliptical polarization, and S-bursts with left-hand (LH) elliptical polarization, are presently observed in an extended storm of decametric radiation from Jupiter's Io-related source, 'Io-B'. This radiation was 100 percent elliptically polarized at all frequencies in the 14-31 MHz range measured. For an 80-min period, there was a mixture of RH and LH elliptically polarized S bursts in the 14-20 MHz range. An examination of the origin of a Faraday-rotation difference between RH and LH elliptical bursts suggests that some Faraday rotation occurs in the Io torus; this was traversed more centrally by the LH bursts from the southern auroral zone than the HH bursts from the northern auroral zone.

Dulk, G. A.↗
NASA NTRS1992

A model of convection and corotation in Jupiter's magnetosphere - Ulysses predictions

The Ulysses Jupiter encounter will include the first spacecraft pass through the dusk magnetosphere and will allow new tests of Jovian convection and corotation models. The Cheng and Krimigis (1989) model is extended to suggest that corotation lag occurs principally within the magnetodisk proper, which extends out to about 60-70 Rj. It is predicted that outside this radius, in the premidnight sector, spin-up to near corotation may occur owing to a local reduction in the outward mass transport rate. The mass loss may occur mainly in the dawn sector, to the magnetospheric wind and the dawn magnetosheath.

Cheng, A. F.↗