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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Io-phase motion and jovian decametre source locations

A second-order effect in the relationship between jovian decameter storms and the departure of Io from superior geocentric conjunction is explained on the basis of latitudinal variations in the earth-Jupiter viewing geometry. These variations are defined by the 12-year cycle in the jovicentric declination of the earth. In addition, it is found that the emission of the jovian decameter storm source Io-B (Io-C) is beamed from the northern (southern) magnetic latitudes. These conclusions are compatible with source positions derived from polarimetry and from considerations of planetary-limb shadowing.

Desch, M. D.↗
NASA NTRS1978

Modulation of the Jovian emission below 8 MHz

RAE-1 data on Jovian decametric emission between 1 and 8 MHz are analyzed to investigate modulation of the emission with respect to the rotation phase of the planet and Io phase as well as a possible variation with flux density of the rotation-phase and Io-phase control below 8 MHz. Attention is given to the observing interval, identification of Jovian emission, orbital-phase constraint, and calculated emission occurrence probabilities. Five frequencies are selected for the analysis (6550, 4700, 3930, 2200, and 1310 kHz), and System III coordinates are used to illustrate the rotation-phase behavior. The spectral distribution of peak flux density is examined along with the overall occurrence probability, the individual modulations, theoretical implications of invariance of active Io phases, and possible modulation by Europa. The results show that Io exerts a suprisingly high degree of control at the low frequencies, that rotation-phase control is only marginal, and that the manner in which Io control is found to vary with flux density is consistent with previous findings at higher frequencies.

Desch, M. D.↗
NASA NTRS1978

Frequency and time dependence of the Jovian decametric radio emissions - A nineteen-year high-resolution study

A nineteen-year catalog of observations has permitted detailed comparison of Jovian source characteristics at 10 frequencies from 5.6 to 30 MHz. The spectral morphology of Jupiter's decameter-wavelength radio sources was studied by means of high-resolution histograms of occurrence probability for intervals as small as 2 deg in Jovian system III longitude and the departure of Io from superior geocentric conjunction. Longitude histograms clearly exhibit a substantial shift in the source A and source B positions between 15 and 10 MHz. Similar diagrams isolate the dependence of each source on the position of Io, illustrating changes with frequency in the structures and sizes of the main probability maxima and in the positions of surrounding secondary peaks. Individual frequency probability histograms for both longitude and Io phase reveal new phenomena, such as a bridge of radiation through source B longitudes connecting sources A and C at 15 MHz and spectral modification of portions of the Io-related source B peak.

Thieman, J. R.↗
NASA NTRS1979

Significance of shock and body slip conditions on Jovian entry heating

The influence of the body and shock slip conditions on the heating of a Jovian entry body is investigated. The flow in the shock layer is considered to be axisymmetric, steady, laminar, viscous, and in chemical equilibrium. Realistic thermophysical and step-function spectral models are employed and results are obtained by implicit finite-difference and iteractive procedures. The freestream conditions correspond to a typical Jovian entry trajectory point. The results indicate that the effect of the slip conditions is significant when the altitudes are higher than 225 km and that the contribution of a radiative heat-flux term in the energy equation should not be neglected at any altitude.

Tiwari, S. N.↗
NASA NTRS1978

A time dependent model of the Jovian current sheet

Analysis of vector helium magnetometer measurements during the Pioneer 10 outbound pass through the Jovian magnetosphere reveals that the average location of the near-equatorial current sheet is a surface whose shape is determined by the velocity at which the magnetic perturbations produced by a rotating tilted dipole propagate to large radial distances. A model is presented which is a surface encircling the planet and rotating rigidly with it. Based on a linear fit to the times of the current sheet crossings, a formula is derived for the surface representing the average position of the near-equatorial current sheet in the Jovian magnetosphere.

Kivelson, M. G.↗
NASA NTRS1979

The Galilean satellites as a source of CO in the Jovian upper atmosphere

Material from the Galilean satellites of Jupiter ejected by energetic particles in the Jovian magnetosphere may provide large sources of oxygen to the parent planet. Formation of a CO molecule is the ultimate fate of an oxygen atom in the upper Jovian atmosphere. This high-altitude source of CO supports Beer and Taylor's (1978) observations and analysis, provided that the globally averaged O atom input flux is about 10 million per sq cm/sec and the eddy diffusion coefficient at the tropopause is around 1000 sq cm/sec. Implications for the possible presence of other atoms and molecules derived from the satellites are discussed.

Strobel, D. F.↗
NASA NTRS1979

The role of energetic particle precipitation in Jovian magnetospherics. I - Secondary electrons from the ionosphere of Jupiter

Escape of photoelectrons from the Jovian ionosphere produces only a meager source of thermal plasma for the inflated centrifugally unstable magnetosphere and is unable to account for the 100 eV thermal plasma temperatures of the magnetosphere. Since the Jovian magnetosphere is well populated with highly energetic electrons, the creation of secondaries and the energy degradation of the primaries precipitating into the lower ionosphere provide additional sources of magnetospheric thermal plasma as well as of the energy for further elevating the plasma temperatures in the top side ionosphere. The efficiencies with which escaping electrons are created by precipitating electrons with energies up to several MeV are computed using energetic electron transport and thermalization codes. The more energetic incident fluxes are far less efficient in creating escaping electrons than the lower energy fluxes with only 0.001% of the secondaries escaping for a 1 MeV source versus 3% for a 1 keV source. Incident fluxes of the order of 10 to 100 per sq cm per sec per eV between 100 eV and 100 keV are required to produce 50 eV escape fluxes comparable to those generated by solar EUV.

Swartz, W. E.↗
NASA NTRS1979

Plasma in the Jovian current sheet

A large body of spectral data for protons with energies greater than 200 keV has been analyzed. It is concluded that the main body of plasma in the Jovian current sheet observed by Pioneer 10 on its outbound pass probably has an energy well below the lowest threshold of the Pioneer 10 detectors. This premise is examined using a semiempirical model of the magnetic field in the magnetodisk and simple magnetohydrodynamic theory. Results indicate that the dominant contribution to the plasma pressure in the region from 25 to 65 Jovian radii is from as yet unobserved protons (ions) with energies of the order of 0.1 to 10 keV.

Goertz, C. K.↗
NASA NTRS1979

Simultaneous multifrequency observations of Jovian S bursts

The millisecond component of the Jovian decameter emission was studied at high resolution in order to examine the short-term behavior of the S-burst drift rates and to define the drift rate spectrum at high frequencies. By using dynamic spectra of 300 microsec and 3.3 kHz resolution and covering discrete frequency bands in the 26-33 MHz range, large systematic changes in the magnitude of the S-burst drift rates are observed on a time scale of seconds to minutes. The drift rate variability, its dependence on frequency, and absence of the predicted drift rate turnover in the spectrum are interpreted in terms of an ionospheric electron source. Low-resolution intensity-time tracings, abrupt changes in mean drift rates from group to group, and systematic variations in the group-to-group mean drift rates due to predictable temporal changes in the magnetic field gradient on the Io flux tube are discussed. These temporal changes are due to motion of the Io-associated magnetic flux tube in the Jovian magnetosphere.

Flagg, R. S.↗
NASA NTRS1979

First results on Jovian lightning

Longitudes and latitudes of 20 Jovian lightning flashes are plotted on the basis of observations of the dark side of Jupiter by an unidentified spacecraft. It is suggested that the mechanisms of lightning generation on Jupiter and earth may be similar, that convective electrification is the most plausible mechanism, and that observations of lightning may be used as a tracer of upwelling in the Jovian circulation. The observation of lightning flashes at high latitudes is shown to be consistent with the concept of convective cloud systems generated by internal heating.

Cook, A. F., II↗
NASA NTRS1979

Jovian electron propagation close to the sun /at about 0.5 AU/

On the basis of interplanetary electron flux measurements in the energy range 0.7-25 MeV made on the Mariner 10 spacecraft launched in 1973 for successive encounters with planet Mercury (R approximately equal 0.5 AU), it is shown that the dominant interplanetary flux of electrons close to the sun is Jovian in origin (except for times of solar flares) and that these observations are consistent with a three-dimensional diffusion-convection model which describes Jovian electron propagation in the outer solar system.

Eraker, J. H.↗
NASA NTRS1979

Cosmic ray ionization of the Jovian atmosphere

An approximate form of the Boltzmann equation has been used to obtain local ionization rates due to the absorption of galactic cosmic rays in the Jovian atmosphere. It is shown that the muon flux component of the cosmic-ray-induced cascade may be especially important in ionizing the atmosphere at levels where the total number density exceeds 10 to the 19th per cu cm (well below the ionospheric layers produced by solar EUV). A model containing both positive and negative ion reactions has been employed to compute electron and ion number densities. Peak electron number densities of the order of 1000 per cu cm may be expected even at relatively low magnetic latitudes. The dominant positive ions are NH4(+) and CnHm(+) cluster ions, with n at least 2; it is suggested that the absorption of galactic cosmic-ray energy at such relatively high pressures in the Jovian atmosphere (M about 10 to the 18th to 10 to the 20th per cu cm) and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.

Capone, L. A.↗
NASA NTRS1979

Discontinuities in Jovian sulphur plasma

The radial distribution of the Jovian sulfur plasma is discussed. Spectra of the ionized sulfur in the Jovian magnetosphere indicate a sharp discontinuity in visible sulfur emission at a radial distance of six Jupiter radii (Io orbit), outside of which emission is greatly reduced and the plasma is observed not to be in corotation with the planet. Possible explanations of this phenomenon include an effect of Io on the electron temperature outside its orbit, leading to the suppression of S II emission by second ionization, and a current system in Jupiter's ionosphere which prevents plasma from diffusing outward and decouples it from the corotation field. This discontinuity also requires reconciliation with Pioneer observations of the radial and pitch-angle diffusion of energetic charged particles.

Mekler, Y.↗
NASA NTRS1979

The mean Jovian temperature structure derived from spectral observations from 105 to 630 cm kaysers

Far infrared observations of the thermal emission of Jupiter are used to determine the temperature at 1 bar. High-altitude observations of the whole-disk brightness temperature of Jupiter in the range of 100 to 347 kaysers were inverted to obtain a P-T profile between 1.5 and 0.06 atm, assuming as opacity sources the H2 collisionally induced continuum and the rotation inversion bands of ammonia. The P-T profile derived from the spectrum reproduces the main features of the observed spectrum, with a slightly improved fit if the effects of ammonia haze opacity or NH3 supersaturation in the saturated region are taken into account. The Jovian temperature is found to be 160 + or - 7 K at 1 bar, and 105 + or - 3 K at the inversion level at 0.15 bar. The 1-bar temperature is shown to be consistent with Jovian interior models which match the observed gravitational moment.

Goorvitch, D.↗
NASA NTRS1980

Narrow-band Jovian Kilometric Radiation: a New Radio Component

A new component of Jupiter's radio spectrum is investigated. The component emits in a very narrow bandwidth (less than or equal to 40 kHz) near 100 kHz. Its waveform is a very smooth and gradual rise and subsequent fall in intensity, usually over two hours. The emission is polarized with left hand polarization associated with the Jovian northern magnetic hemisphere and right hand with the south. The emissions deviation from a strict system 3 rotation period repetition rate is examined. The emission source of the narrow band component which rotates 3 to 5 percent slower than all other forms of Jovian radio emission is determined from propagation considerations, coupled with the observed lack of corotation, to a source region near the equatorial plane at the outer edge of the Io plasma torus. The narrow band KOM (nKOM) form is examined using observations from the PRA instrument. The spectrum and occurrence statistics are described and contrasted with the tapered or broadband KOM (bKOM) characteristics.

Kaiser, M. L.↗
NASA NTRS1979

The phase of the ten-hour modulation in the Jovian magnetosphere /Pioneers 10 and 11/

The paper describes the study of the phase of the 10-hour modulation of energetic electrons seen by Pioneers 10 and 11 in the Jovian magnetosphere. Attention is given to the peaks rather than the valleys of each cycle because the peaks are where physically interesting features occur, such as particle acceleration, current sheets, etc. To identify the peaks, it is required that the instantaneous intensity be higher than the 5-hour running average and the 5-hour running average be greater than the 10-hour running average. These criteria select an interval rather than a point and it is determined that this interval is an appropriate estimate of the experimental uncertainty. When the phases of the peaks are plotted together, they create patterns which are discussed in terms of disk-like, clock-like, and rotating anomaly models of the magnetosphere. Each model fits some of the data, but no model explains all of the data convincingly. It is concluded that there is still no understanding of the configuration of the outer Jovian magnetosphere.

Fillius, W.↗
NASA NTRS1980

Energetic /approximately 100-keV/ tailward-directed ion beam outside the Jovian plasma boundary

The hot plasma instrument on the Voyager-2 spacecraft measured a nearly monoenergetic (100 keV) ion beam several hours after crossing the Jovian plasma boundary on the nightside of the planet. The beam, deduced to consist primarily of heavy ions, persisted for about four hours and originated from the general direction of Jupiter. The energy density of the beam was about several times the energy density of the magnetic field (beta greater than 1). This beam, a product of an as yet not understood Jovian plasma acceleration mechanism, provides a dramatic example of the energetic dynamics of Jupiter's magnetosphere.

Krimigis, S. M.↗
NASA NTRS1980

Periodicities in the Jovian magnetosphere - Magnetodisc models after Voyager

The Voyager 1 and 2 outbound observations of periodic double-peak flux maxima (which mark encounters with the magnetodisk) are separated into two distinct branches: a 'leading' branch (N to S disk crossings) and a 'trailing' branch (S to N disk crossings). On a plot of longitude versus radial distance, the leading branch has a positive slope and the trailing branch has a relatively flat slope. The two branches meet at 80 to 100 Jovian radii, beyond which periodic single peaks or closely spaced multiple peaks are generally observed. In the present paper, this structure is examined, using the three principal disk models which have been proposed to explain periodicities in the Jovian atmosphere.

Carbary, J. F.↗