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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Moist convection and the abundance of water in the troposphere of Jupiter

A semiquantitative model is proposed for the narrow, moist convective plumes of the Jupiter troposphere which appears capable of explaining the apparent H2O vapor depletion in the 5-micron window without requiring a global depletion of oxygen from solar abundance. Chemical dessication is held to be unlikely, in virtue of its requirement for the many-fold enhancement of ammonia. Arguments based on mixing length theory are presented to justify a small filling factor, or ratio of the area occupied by updrafts to the total area.

Lunine, Jonathan I.↗
NASA NTRS1987

HCN and chromophore formation on Jupiter

Reaction paths for the formation of HCN and chromophores on Jupiter are suggested. The reactions involve photolysis of ammonia/acetylene mixtures. Experimental data supporting these pathways are reported.

Ferris, James P.↗
NASA NTRS1987

Polarization of low-frequency electromagnetic radiation in the lobes of Jupiter's magnetotail

The plasma wave instruments on the Voyager spacecraft have detected intense electromagnetic radiation within the lobes of Jupiter's magnetic tail down to the lowest frequency of the detector (10 Hz). During a yaw maneuver performed by Voyager 1 in the lobe of the Jovian magnetotail, a modulation appeared in the amplitudes of waves detected in the 10-, 17.8- and 31.1-Hz channels of the plasma wave analyzer, well below the local electron cyclotron frequency of 260 Hz. The lowest amplitudes occurred when the antenna axis was most nearly parallel to the magnetic field. Wave amplitudes in the 56.2-Hz and higher frequency channels remained nearly constant during the maneuver. From the cold-plasma theory of electromagnetic waves, it is concluded that the plasma frequency was between the 56.2- and 31.1-Hz channels where the parallel-polarized component of the spectrum cuts off. This implies a tail-lobe density between 0.000032 and 0.000015/cu cm. The left-hand cutoff frequency would then be below 10 Hz, consistent with either the Z-mode (L, X) or whistlers (R-mode) in the modulated channels.

Moses, S. L.↗
NASA NTRS1987

The magnetospheres of Jupiter, Saturn, and Uranus

The results published by U.S. scientists during 1983-1986 from studies related to the magnetospheres of Jupiter, Saturn, and Uranus are discussed. Consideration is given to the magnetic fields of these planets, charged particle environments, the interactions between the planetary rings and planetary satellites, the solar wind interactions, radio emissions, and auroras. Special attention is given to observations of (1) a small flux of energetic electrons and protons in the otherwise radiation-free environment in the magnetosphere under the rings of Saturn (interpreted as interactions of Galactic cosmic rays with the rings), (2) spokes, and (3) Saturn ring erosion.

Connerney, J. E. P.↗
NASA NTRS1987

Ion distributions in the dayside magnetosheaths of Jupiter and Saturn

Data from the Voyager 1 and 2 Plasma Science experiment in the dayside magnetosheaths of Jupiter and Saturn are analyzed. The ion distributions throughout the dayside magnetosheaths of both planets are well modeled by a two-temperature proton distribution. The two proton populations have comparable densities, and temperatures of 100 and 1000 eV. Similar two-temperature proton distributions are occasionally observed in earth's magnetosheath. Ion temperatures, densities, and bulk velocities for the four magnetosheath crossings are presented, confirming that sunward flow of up to 100 km/s occurs when the magnetosphere is expanding.

Richardson, John D.↗
NASA NTRS1987

A Jupiter Data Analysis Program (JDAP) research grant on wave accessibility and attributes

For more than thirty years the intense decametric radio emissions from Jupiter (DAM) and the corresponding auroral kilometric radiation from the Earth (AKR) have remained major radio science mysteries. Part of the problem, aside from their inherent complexity, has been the difficulty of measuring their source location and emission properties from limited observations. Progress has been made on this problem by locating the source directly, i.e., by analysis of the faraday rotation observed with Voyager as the wave path crossed the Io plasma torus, and indirectly by comparing the peak frequencies of the decametric emission with that at the foot of the Io flux tube. Progress was also made on the general question of how the emissions originate by finding properties of both the AKR and DAM which would imply emission by natural radio lasing.

Calvert, Wynne↗
NASA NTRS1987

Vibrationally excited molecular hydrogen in the upper atmosphere of Jupiter

A comprehensive theoretical model for vibrationally excited H2 in the upper atmosphere of Jupiter is presented. Theoretical calculations demonstrate the probable existence of significantly enhanced populations of vibrationally excited H2 in the Jovian upper atmosphere, especially in the auroral regions. It is also shown that this H2 is an important chemical sink of H(+) ions in the Jovian ionosphere and thus has a significant effect on the calculated ionospheric electron densities.

Cravens, T. E.↗
NASA NTRS1987

Observations of large-amplitude MHD waves in Jupiter's foreshock in connection with a quasi-perpendicular shock structure

Plasma and magnetic field observations performed onboard the Voyager 2 spacecraft have been used to investigate Jupiter's foreshock. Large-amplitude waves have been detected in association with the quasi-perpendicular structure of the Jovian bow shock, thus proving that the upstream turbulence is not a characteristic signature of the quasi-parallel shock.

Bavassano-Cattaneo, M. B.↗
NASA NTRS1987

Variability of ethane on Jupiter

Varying stratospheric temperature profiles and C2H6 altitude distributions furnish contexts for the evaluation of ethane abundances and distributions in the Jupiter stratosphere. Substantial ethane line emission and retrieved mole fraction variability is noted near the footprint of Io's flux tube, as well as within the auroral regions. It is suggested that this and other observed phenomena are due to the modification of local stratospheric chemistry by higher-order effects, which are in turn speculated to be due to the precipitation of charged particles along magnetic field lines.

Kostiuk, Theodor↗
NASA NTRS1988

Chemical constraints on the water and total oxygen abundances in the deep atmosphere of Jupiter

The mechanisms responsible for the observed H2O/H2 mixing ratio (HMR) in the Jovian troposphere are analyzed, with a focus on the relationship between HMR and O2 abundance and the abundance of the nonequilibrium trace gases CO and SiH4. The results of computations using a Jupiter atmosphere model consistent with recent observations (Bjoraker et al., 1986) are presented graphically and discussed in detail. It is found that the observed mixing ratios of CO (about 10 to the -9th) and SiH4 (upper limit 2-4 x 10 to the -9th) preclude O2 depletion and the presence of significant global H2O. The low observed HMRs (0.00003 at 6 bar) are tentatively attributed to local condensation in cloud-forming regions.

Fegley, Bruce, Jr.↗
NASA NTRS1987

The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter

Data from Voyager 2 observations of FUV electroglow in the sunlit atmospheres of Jupiter, Saturn, and Uranus are compiled in tables and graphs and analyzed theoretically, and an excitation mechanism is proposed. This mechanism is based on local acceleration of photoelectrons and ions by the electric field (consisting of field-aligned potentials) due to an ionospheric dynamo. Anomalous resistivity and plasma instabilities induced by field-aligned currents in the ionosphere are invoked to explain the field-aligned potentials, and the processes which might give rise to such currents are further explored.

Clarke, John T.↗
NASA NTRS1988

The predicted abundances of deuterium-bearing gases in the atmospheres of Jupiter and Saturn

The first set of comprehensive thermochemical equilibrium and chemical kinetic calculations on the chemistry of deuterium-bearing gases in the deep atmospheres of Jupiter and Saturn is presented. The sensitivity of the results to variations in elemental and isotopic abundances is studied. Isotopic fractionation effects in the C-13/C12, N-15/N-14, and O-18/O-16 ratios in nonequilibrium species such as CO, CO2, HCN, and N2 are briefly considered.

Fegley, Bruce, Jr.↗
NASA NTRS1987

Galileo's new route to Jupiter

NASA's 22-month-long Galileo mission to Jupiter will be devoted to direct sampling of its atmosphere. Attention is presently given to a novel trajectory for the Galileo mission that uses gravity assist from one flyby of Venus and two of the earth. The mission involves an orbiter, carrying ten instruments, and an atmospheric probe, containing six instruments. The novel trajectory concept offers a range of launch and arrival dates. An account is given of the mission profile assuming a November 4, 1989 launch date.

Casani, John R.↗
NASA NTRS1988

Infrared polar brightenings on Jupiter. IV - Spatial properties of methane emission

Different polar 'hot spot' differences are revealed between the northern and southern hemispheres of Jupiter by 7.8-micron observations made with NASA's Mauna Kea IR Telescope Facility. While the northern hot spot is fixed, relative to system III coordinates, at 180 + or - 10 deg longitude and 60 + or - 10 deg latitude, the southern hot spot is fixed with respect to neither the system III longitude and latitude, nor the subpolar point, or even Io's position. Voyager I IRIS data show the north polar hot spot to be more extended in longitude than latitude.

Caldwell, John↗
NASA NTRS1988

Infrared polar brightenings on Jupiter. V - A thermal equilibrium model for the north polar hot spot

Voyager IRIS instrument records of the IR hydrocarbon emissions from Jupiter's north polar region are presently studied to determine the spatial and other characteristics of the north polar hot spot. Attention is given to a thermal equilibrium model that exploits the asymmetry found in 7.8-micron emission of stratospheric methane with respect to system III longitude in order to estimate stratospheric zonal wind velocity. This model accurately predicts the observed asymmetry in acetylene's 13.6-micron emission; this requires, however, enhanced acetylene abundance in the hot spot, as well as ethane depletion. Energetic charged particles are suggested to be the most probable cause of these effects.

Halthore, Rangasayi↗
NASA NTRS1988

A possible detection of Jupiter's northern auroral S1(1) H2 quadrupole line emission

An upper limit is presently determined for the mean intensity of the Jupiter northern Auroral UV/thermal hot spot's S1(1) H2 quadrupole emission, over an 8 sq arcsec illuminated beam; the value obtained is 4.2 X 10 to the -6th W/sq m per sr. It is suggested that the nonradiative deexitation of the H2 molecules via collisions with H may have been underestimated by Kim and Maguire (1986), due to uncertainties concerning auroral H density.

Trafton, L.↗
NASA NTRS1988

Potential vorticity and layer thickness variations in the flow around Jupiter's Great Red Spot and White Oval BC

Using Voyager images, layer thickness variations in the flow around Jupiter's Great Red Spot (GRS) and White Oval BC were investigated by treating potential vorticity as a conserved tracer. Fluid trajectories around the GRS and the White Oval BC were calculated assuming the flow to be frictionless, adiabatic, hydrostatic, and steady in the reference frame of the vortex. The data obtained constitute a useful diagnostic which will help to differentiate between models of Jovian vortices. Implications of the observations were studied in the context of a one-layer quasi-geostrophic model in which a thin upper weather layer, which contains the vortex, is supported hydrostatically by a much deeper lower layer.

Dowling, Timothy E.↗
NASA NTRS1988

H2 spectroscopy and a diurnally changing cloud on Jupiter

Spectroscopic observations of H2 in specific longitude regions of Jupiter as they rotate from limb to limb are reported. Data obtained in the 3-0 S(0) and S(1) lines using a CCD detector and a spectrograph with either echelle or plane gratings at the Cassegrain focus of the 24-inch telescope at Whipple Observatory during April-June 1983 are presented in extensive tables and graphs and analyzed in detail, modeling spatial and temporal variations at seven latitudes. An east-to-west increase in the equivalent line widths is attributed to the combined action of internal and solar heating of a convective layer, resulting in diurnal changes in the vertical cloud structure. It is inferred that the hydrogen observed is mainly in an equilibrium thermodynamic state, with small amounts of nonequilibrium hydrogen at high altitudes.

Cunningham, Cindy C.↗