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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Magnetopause characteristics inferred from three-dimensional energetic particle distributions

Three-dimensional distributions for 24- to 44.5 KeV protons (ions) are presented from the ISEE 1 medium-energy particles instrument during a magnetopause traversal at about 0145:00 hours UT on November 20, 1977. The use of these data and simple particle orbit geometry makes it possible to infer magnetopause boundary location, orientation, and velocity. The results are consistent with both overall boundary motions toward and away from the earth at velocities of 10-20 km/s and the presence of a surface wave on the boundary. For the case analyzed, the boundary appears stable and well defined, being capable of supporting trapped type distributions (conservation of the first and second adiabatic invariants) within a fraction of a gyroradius from the magnetosheath field where no trapping is observed.

Williams, D. J.↗
NASA NTRS1978

Dual spacecraft observations of energetic particles in the vicinity of the magnetopause, bow shock, and the interplanetary medium

Particle data obtained during a few orbits when the ISEE 1 and 2 spacecraft were on the front side of the magnetosphere are presented. Observations near the magnetopause and the bow-shock regions based on 32-sec averaged particle data are summarized. A more detailed picture of the particle features near these boundaries is given on the basis of 0.25-sec averages. Observations of low-energy particles in the upstream interplanetary medium are also examined.

Parks, G. K.↗
NASA NTRS1979

Coronal magnetic structure and the latitude and longitude distribution of energetic particles, 1-5 AU

The relation of the coronal magnetic field structure to the distribution of approximately 1 MeV protons in interplanetary space between 1 and 5 AU is discussed. After ordering the interplanetary data by its estimated coronal emission source location in heliographic coordinates, the multispacecraft measured proton fluxes are compared with coronal magnetic field structure infrared as observed in soft X-ray photographs and potential field calculations. Evidence for the propagation and possible acceleration of solar flare protons on high magnetic loop structure in the corona is presented. Further, it is shown that corotating proton flux enhancements are associated with regions of low coronal X-ray emission (including coronal holes), usually in association with solar wind stream structure.

Roelof, E. C.↗
NASA NTRS1980

Results of an ISEE-1 experiment to study the interactions between energetic particles and discrete VLF waves in the magnetosphere

Despite the malfunctioning of the digital portion of the experiment which is encoding the absolute amplitude of the wave spectrum with a fixed bias of approximately 20 dB, the analog portion of the instrument is acquiring excellent data concerning the wave function and relative amplitude. Results obtained over a 2-year period which have important implications for magnetospheric wave-particle interactions are examined in the areas of emission generation by nonconducted coherent waves, and cold plasma distribution in the inner magnetosphere.

Source record↗
NASA NTRS1980

The relationships between high latitude convection reversals and the energetic particle morphology observed by the Atmosphere Explorer

Simultaneous measurements of the auroral zone particle precipitation and the ion convection velocity by Atmosphere Explorer show a consistent difference between the location of the poleward boundary of the auroral particle precipitation and the ion convection reversal. The difference of about 1.5 degrees of invariant latitude is such that some part of the antisunward convection lies wholly within the auroral particle precipitation region. The nature of the convection reversals within the precipitation region suggests that in this region the convection electric field is generated on closed field lines that connect in the magnetosphere to the low latitude boundary layer.

Heelis, R. A.↗
NASA NTRS1980

Energy dependence and temporal evolution of the He-3/He-4 ratios in heavy-ion-rich energetic particle events

A study is presented of the energy dependence of the He-3/He-4 between 0.44 and 4.1 MeV per nucleon for six heavy-ion-rich events observed in 1974 and 1976. The observations were made using the low-energy dE/dx vs E Ultralow-Energy Particle telescope on IMP 8. It was found that all selected heavy-ion-rich events are also enriched in He-3: that the He-3/He-4 ratio decreases with decreasing energies; and that a rapid temporal evolution of the He-3/He-4 and the Fe/(H + He) ratios is strongly correlated during one event with the maximum value at the onset. These results are analyzed in terms of a model based on the preferential injection of He-3 and Fe resulting from turbulent ion heating and subsequent Fermi acceleration.

Moebius, E.↗
NASA NTRS1980

The relationships between high-latitude convection reversals and the energetic particle morphology observed by Atmosphere Explorer

A statistical investigation and a case study of simultaneous particle and ion convection velocity measurements from Atmosphere Explorer are presented. They show that at all local times between 1800 and 0600 hours the gross convection reversal boundary lies equatorward of the boundary between the discrete, highly structured boundary plasma sheet precipitation and the polar rain. This study indicates the existence of shear and rotational convection reversals on closed field lines; the observed morphology is consistent with a partially closed magnetosphere in which some portion of convection electric field is generated in the low-latitude boundary layer.

Heelis, R. A.↗
NASA NTRS1979

Observations of energetic particles in the near and far interplanetary medium

Recent experimental results suggest that acceleration of particles to energies as high as 30 MeV/nucleon is commonplace in the interplanetary medium beyond several AU, and that most of the less than approximately 10 MeV/nucleon particles observed near earth, especially at solar minimum, are predominantly interplanetary in origin. Experimental observations of the anomalous 'cosmic-ray' component and of corotating particle streams are reviewed, with emphasis on the composition of these interplanetary particles. These direct observations, although still rudimentary, are already providing constraints necessary for developing realistic theoretical descriptions of interplanetary acceleration mechanisms and should thus help in understanding similar processes in other astrophysical objects.

Gloeckler, G.↗
NASA NTRS1981

Time and energy dependence of heavy ion abundances in solar flare energetic particle events

Examples are presented of the time and energy dependence of the abundances and spectra of the major heavy ions He, C, O and Fe during solar flare events, taken from a survey using the UMD/MPI ULET telescope on IMP-8 during 1973-1977. In some cases, time variations were found in the O/He, O/C and Fe/O ratios which appear to be inconsistent with models based solely on rigidity dependent propagation in the interplanetary medium.

Mason, G. M.↗
NASA NTRS1981

Observations of the ionization states of energetic particles accelerated in solar flares

Results of a survey of ten solar flare particle events, in which the ionization states and spectra of 0.3 to 2.4 MeV/nuc He, C, O and Fe were measured, are reported. He+ was present in all events (He+/He++ approximately 0.1 to 0.25), and the mean ionization states of C, O and Fe are high. The distribution functions of He+, He++ and heavier elements are well represented by simple exponentials of the particle speed times its rigidity to a power n, where n is between O and 1, and equal e-folding values. Results are consistent with a model whereby ions are accelerated in the corona by multi-dimensional shocks out of a population taken from both hot and cold coronal regions.

Gloeckler, G.↗
NASA NTRS1981

A Supra-Thermal Energetic Particle detector (STEP) for composition measurements in the range approximately 20 keV/nucleon to 1 MeV/nucleon

A detector system is described, employing a time-of-flight versus residual energy technique which allows measurement of particle composition (H-Fe), energy spectral and anisotropies in an energy range unaccessible with previously flown sensors. Applications of this method to measurements of the solar wind ion composition are discussed.

Mason, G. M.↗
NASA NTRS1980

Energetic particle recurrence and escape during solar cycle 20

Low-energy solar particle data have been combined from a multi-spacecraft near-earth data set covering most of solar cycle 20 (1966-1976). Particle intensity profiles have been ordered in the natural heliographic coordinate system of the estimated high coronal connection longitude of the foot point of the interplanetary field line. The recurrence trends of approximately 1-MeV solar particles become more apparent in this coordinate system than when plotted versus time, and thereby extend the evidence for regions of continual injection and escape from the corona. Intercomparison of solar particles and solar wind streams in heliographic longitude suggests that the origin of stream-associated spatial particle events seen at 1 AU is solar rather than interplanetary.

Gold, R. E.↗
NASA NTRS1980

Observations of the mean ionization states of energetic particles in the vicinity of the earth's magnetosphere

The mean ionization states of 44-260 keV per charge ions observed as bursts in and near the earth's magnetosphere have been determined by using the particle data collected by the University of Maryland experiment on Imp 8. We find that during the period from October 1973 to December 1976 (1) the abundance ratio of heavy ions (Z greater than 2) to alphas ranges from 0.04 to 0.10, with a mean value of 0.08 plus or minus 0.02; (2) the energy spectra of alphas and Z greater than 2 ions in these bursts are adequately represented as exponentials in energy per charge with e-folding energies of 30-50 keV/Q; (3) the e-folding energies of both alpha particles and heavier ions are generally harder upstream from the bow shock than in the magnetotail and magnetosheath; and (4) the elemental abundances and ionization state distribution of the heavy ions are consistent with those of the corona at an equilibrium coronal temperature of 1-2 x 10 to the 6th K, which tends to support a solar wind origin for these particles.

Ma Sung, L. S.↗
NASA NTRS1981

Energetic particle spectra in finite shocks - The earth's bow shock

Particle acceleration and escape at the earth's bow shock wave are discussed in order to account for reported exponential fast particle spectra. A model is presented of particle acceleration in a finite two-dimensional shock perpendicular to the magnetic field, with particle parallel and perpendicular diffusion coefficients inversely proportional to each other. It is shown that the exponential particle energy per unit charge spectra observed by Ipavich et al. (1979) for the case of a radial solar wind magnetic field may be obtained if the fast particles escape the shock by means of resonant diffusion to unconnected field lines. The calculated e-folding value of the energy/charge ratio is found to be independent of the level of turbulence near the shock and in good agreement with observations. For the case of a nonradial solar wind magnetic field, the model is noted to predict that convection may be the dominant means of escape. It is also pointed out that the parallel and perpendicular diffusion coefficients may be measured indirectly at the bow shock.

Eichler, D.↗
NASA NTRS1981

Prediction of energetic particle behavior at high solar latitudes

Emphasis is placed on predictions of the galactic cosmic-ray flux at high heliographic latitudes. Recent work on gradient and curvature drifts in the large-scale heliospheric magnetic field wave modified the traditional argument that the cosmic rays should be essentially unmodulated over the solar poles. In fact, drift effects during the next solar cycle, when the International Solar Polar Mission is to fly, are predicted to cause considerable modulation in the polar regions. However, it is pointed out that the use of conventional drift formulae in the solar wind, which contains magnetic-field fluctuations with large amplitudes and perhaps systematic properties, is highly suspect. Prediction of cosmic-ray behavior over the solar poles is thus currently uncertain. Also considered is the behavior of the anomalous cosmic-ray component at high heliographic latitudes.

Fisk, L. A.↗
NASA NTRS1981

Radially propagating shock waves in the outer heliosphere - The evidence from Pioneer 10 energetic particle and plasma observations

At heliocentric distances between 14 and 22 AU, some 14 increases in the flux of 1 MeV protons have been identified over a 3 yr period by the NASA Goddard/University of New Hampshire cosmic-ray experiment on Pioneer 10. These increases appear to be associated with large solar flares. Combining the particle data with the Pioneer 10 plasma observations from the NASA/Ames plasma analyzer reveals that the particle increases are produced by radially propagating shock waves generated by the solar events. While the characteristics of these particle events in the distant heliosphere appear to differ greatly from those observed at 1 AU, they represent the evolution expected as the interplanetary magnetic field becomes almost azimuthal. These long-lived shocks provide a valuable in situ laboratory for directly studying particle acceleration under a variety of conditions. They may also represent a significant factor in producing the long-term modulation of galactic cosmic rays.

Mcdonald, F. B.↗