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At least 217 records · Page 12

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NASA NTRS1983

Electric currents and voltage drops along auroral field lines

An assessment is presented of the current state of knowledge concerning Birkeland currents and the parallel electric field, with discussions focusing on the Birkeland primary region 1 sheets, the region 2 sheets which parallel them and appear to close in the partial ring current, the cusp currents (which may be correlated with the interplanetary B(y) component), and the Harang filament. The energy required by the parallel electric field and the associated particle acceleration processes appears to be derived from the Birkeland currents, for which evidence is adduced from particles, inverted V spectra, rising ion beams and expanded loss cones. Conics may on the other hand signify acceleration by electrostatic ion cyclotron waves associated with beams accelerated by the parallel electric field.

Stern, D. P.↗

NASA NTRS1984

Neutron and gamma-ray signatures for particle acceleration in solar flares

The production of neutrons, 4 to 7 MeW nuclear gamma rays, positrons and pions resulting from the interaction of flare accelerated particles with the solar atmosphere was calculated. For the energy spectra of these particles the Bessel function predicted by stochastic acceleration and power laws which could result from acceleration at large-scale planar shocks was used, with the thick-target model. It is assumed that in the interaction region the accelerated particles are isotropic. The neutron-to-2.223 MeV photon conversion factors for various flare locations on the Sun are derived by averaging conversion factors over these spectra. Comparing calculations with data confirms that for most gamma-ray flares the bulk of the accelerated particles remain trapped at the Sun and that these particles have spectra similar to the spectra of flare particles observed in interplanetary space.

Ramaty, R.↗

NASA NTRS2010

Shock-Driving CMEs Near the Sun, in the Interplanetary Medium, and Near Earth

The excellent correspondence between type II radio bursts and solar energetic particles (SEPs) made it clear that the same shock accelerates ions and electrons. A recent investigation involving a large number of I shocks revealed that about 35% of IP shocks do not produce type II bursts (radio quiet) or SEPs. Comparing the RQ shocks with the radio loud (RL) ones revealed some interesting results, which will be summarized in this poster. (1) There is no evidence for blast waves. (2) Even a small fraction (20%) of RQ shocks is associated with ion enhancements at the shock when the shock passes the spacecraft. (3) The primary difference between the RQ and RL shocks can be traced to the different kinematic properties of the associated CMEs, although the shock properties measured at 1 AU are not too different for the RQ and RL cases. This can be attributed to the interaction with the IP medium, which seems to erase the difference. More details can be found in Astrophysical Journal 710, 1111, 2010 (http://adsabs.harvard.edu/absZ2009arXivO9l2.4719G).

Gopalswamy, N.↗

NASA NTRS1976

Energetic particles of the outer regions of planetary magnetospheres

High energy particles, with energies above those attainable by adiabatic or steady-state electric field acceleration, have been observed in and around the outer regions of planetary magnetospheres. Acceleration by large amplitude sporadic cross-tail electric fields over an order of magnitude greater than steady-state convection fields is proposed as a source of these particles. It is suggested that such explosive electric fields will occur intermittently in the vicinity of the tail neutral line in the expansive phase of substorms. Laboratory and satellite evidence are used to estimate this electric potential for substorms at earth; values of 500 kilovolts to 2 megavolts are calculated, in agreement with particle observations. It is further suggested that these particles, which have been accelerated in the night side magnetosphere, drift to the dayside on closed field lines, and under certain interplanetary conditions can escape to regions upstream of the bow shock.

Tsurutani, B. T.↗

NASA NTRS1978

Energetic protons associated with interplanetary active regions 1-5 AU from the sun

Pioneer 11 has yielded data on approximately 100 energetic proton events at heliocentric distances between 1 and 2 AU. Measurements of absolute intensities, anisotropies, and crude energy spectra are studied in connection with interplanetary active regions (IAR's). It is found that in close vicinity to IAR's, the number of events observed per unit time interval is 10 times greater than in other areas of interplanetary space, and that the frequency of events has a maximum at plus or minus 5 hours of the time IAR edges are crossed. It is also noted that events in IAR vicinity have greater particle densities, softer energy spectra, and smaller time widths than other events. For many events associated with IAR's, particle anisotropies correspond to the net flow of particles along the interplanetary magnetic field toward the sun. This suggests that a mechanism in MHD shocks is responsible for local acceleration in the interplanetary medium.

Pesses, M. E.↗

NASA NTRS1978

Abundances of He and CNO ions in the ion pulses observed in the earth's magnetospheric environment

The abundance of He and CNO ions in the ion pulses which are frequently observed in the earth's magnetosheath, magnetotail, and near-by interplanetary space was analyzed and found to be highly variable. Based on the assumption that these ions are solar wind particles accelerated in the magnetospheric environment to the observed energies, it is suggested that this variability reflects the inhomogeneity of the solar atmosphere and/or the physical conditions under which the solar wind particles were energized.

Fan, C. Y.↗

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.↗

NASA NTRS1987

The interaction of quasiperpendicular shock waves in a collisionless plasma

The interaction between collisionless shocks is examined from a kinetic viewpoint using computer simulations of shock collisions spanning the range of ambient plasma and shock parameters typical of the interplanetary medium. It is found that the interaction between two subcritical, perpendicular shocks is largely fluidlike with no evidence for accelerated particles. The electromagnetic fields associated with each shock, but not the plasmas, pass through each other during the collision. This interaction is due to self-consistently generated electric fields which adjust to the value needed to bring to rest the two incoming streams. The interaction between two supercritical perpendicular collisionless shocks is similar to the subcritical case, in that the electromagnetic fields associated with each shock are transmitted whereas particles are not. However, the interaction is also highly dynamic with substantial acceleration of ions. Increasing the Mach number gives rise to an increasing number of energetic particles.

Cargill, P. J.↗

NASA NTRS1977

Solar energetic particles below 10 MeV

The information on solar acceleration and coronal propagation contained in low energy solar particle observations must be extracted from the effects of propagation in a dynamic interplanetary medium and the proximity of the earth's magnetosphere. The resulting separation reveals long-lived coronal injection and strong spatial ordering of coronal propagation.

Roelof, E. C.↗

NASA NTRS1981

Ionization states of heavy elements observed in the 1974 May 14-15 anomalous solar particle event

The charge states of heavy ions accelerated in the (3)He-Fe rich solar particle event of 1974 May 14-15 are determined using data from the Interplanetary Monitoring Platform-8. In addition to Fe(+11,12) both 0(+5) and Fe(+16,17,18) are also present suggesting variations in coronal temperatures over a range from approximately 400,000 to 5,000,000 K. The presence of 0(+5) and Fe(+16-18) may be explained by a resonant plasma heating mechanism proposed to account for the enhancements of (3)He and Fe.

Ma Sung, L. S.↗

NASA NTRS1975

Observations of Jovian accelerated particles both inside and outside the Jovian magnetosphere - Results from the Goddard-U. of New Hampshire experiment on Pioneer 10

This paper discusses measurements of the energetic-particle population inside Jupiter's magnetosphere as well as observations of energetic particles in interplanetary space that have escaped from that magnetosphere. The discussion is based on Pioneer 10 data obtained when the spacecraft was outside the bow shock but within about 1 AU of the planet and on electron data obtained near earth by various IMP spacecraft. Pioneer 10 particle measurements in the Jovian magnetosphere are reviewed, the differential proton and electron energy spectra are described, and it is suggested that very little particle acceleration occurs in the outer magnetosphere. Additional data are examined in regard to Jovian alpha particles, proton and electron angular distributions, protons in the inner magnetosphere, effects of Io on the proton flux, electron acceleration outside the bow shock, and observations of Jovian electrons near earth. All these data are shown to support the conclusion that most, if not all, quiet-time increases in low-energy electron fluxes near earth are of Jovian origin.

Trainor, J. H.↗

NASA NTRS1994

Statistical analysis of diffuse ion events upstream of the Earth's bow shock

A statistical study of diffuse energetic ion events and their related waves upstream of the Earth's bow shock was performed using data from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) satellite over two 5-month periods in 1984 and 1985. The data set was used to test the assumption in the self-consistent model of the upstream wave and particle populations by Lee (1982) that the particle acceleration through hydromagnetic waves and the wave generation are directly coupled. The comparison between the observed wave power and the wave power predicted on the observed energetic particle energy density and solar wind parameters results in a high correlation coefficient of about 0.89. The intensity of diffuse ions falls off approximately exponentially with the distance upstream from the bow shock parallel to the magnetic field with e-folding distances which vary from approximately 3.3 R(sub E) to approximately 11.7 R(sub E) over the energy range from 10 keV/e to 67.3 keV/e for both protons and alpha particles. After normalizing the upstream particle densities to zero bow shock distance by using these exponential variations, a good correlation (0.7) of the density of the diffuse ions with the solar wind density was found. This supports the suggestion that the solar wind is the source of the diffuse ions. Furthermore, the spectral slope of the diffuse ions correlates well with the solar wind velocity component in the direction of the interplanetary magnetic field (0.68 and 0.66 for protons and alpha particles) which concurs with the notion that the solar wind plays an important role in the acceleration of the upstream particles.

Trattner, K. J.↗

NASA NTRS1988

Observations related to the acceleration, injection, and interplanetary propagation of energetic protons during the solar cosmic ray event on February 16, 1984

This paper presents an analysis of data collected by the worldwide network of neutron monitors and from IMP-8 cosmic-ray telescopes, as well as by particle detectors on the GOES 5 and 6 and ICE satellites, on the solar cosmic ray event that took place on February 16, 1984. Using these data, the intensity-time (IT) profiles, the anisotropy-time profiles, the energy spectra, and the pitch angle distributions of the solar protons near earth were deduced. It was found that the solar protons propagated essentially scatter-free from the sun to the earth. The solar protons had easy access to the IMF lines to earth; the time from the onset to maximum intensity and the shape of the IT profiles at earth as a function of energy could be explained by the diffusion of the flare protons near the acceleration region. The energy spectrum of the solar flare protons injected into the undisturbed IMF at the sun was changing with time in both amplitude and shape. The observations suggest a shock acceleration process.

Debrunner, H.↗

NASA NTRS1986

Energetic ions upstream of planetary bow shocks: Fermi acceleration or leakage

Spacecraft observations of Jupiter, Saturn, and Earth planetary bow shocks are assessed. For Jupiter, the unique composition of magnetospheric plasma, where oxygen and sulfur ions are major components, and the simultaneous presence of MeV electrons enable identification of the upstream particles as originating from within the magnetosphere. The observations at Saturn are phenomonologically similar, but no unique tracer element exists which can identify the origin. Earth observations show that substantial energetic particle activity occurs within the Earth's plasma sheet when upstream ions and electrons are observed in the interplanetary medium. Observations of the three planets are discussed to compare in-situ acceleration in the foreshock region vs. leakage of already accelerated ions from the parent magnetosphere. It is concluded that the evidence favors magnetospheric leakage.

Krimigis, S. M.↗

DOE OSTI2026

The Effect of Large-scale Magnetic Fluctuations on Energetic Particle Profiles across Interplanetary Shocks

In situ observations of energetic particles associated with interplanetary (IP) shocks, known as energetic storm particle (ESP) events, often show time-intensity profiles quite different from predictions of classical diffusive shock acceleration theory. We use numerical simulations, including test-particle simulations and hybrid simulations (with fluid electrons and kinetic protons) for shocks propagating into a turbulent magnetic field to study the ESP intensity-time profiles across a strong IP shock. We find that several types of energetic particle intensity profiles similar to in situ observations can be produced in our simulations. The peak of energetic particle count is often near, but can be shifted from, the locations of the shock front, with the peak usually being observed downstream of the shock. These findings may help understand particle acceleration at both traveling IP shocks and shocks in other heliospheric and astrophysical environments.

Lo, Ming-Yuan [New Mexico Consortium (NMC), Los Al↗

NASA NTRS1974

Search by Mariner 10 for electrons and protons accelerated in association with Venus

Results of a search, with the aid of Mariner 10, for electrons and protons produced by acceleration occurring from the interaction of the solar wind and interplanetary field with the Venusian ionosphere. No evidence was found for Venus-associated particle fluxes with instrumentation capable of measuring flux variations approximately 1000 times smaller than those of the Mariner 5 detectors for charged particles, although the Mariner 10 measurements were made in the presence of an interplanetary particle flux that was extremely stable and characteristic of minimum solar activity. In addition, no evidence was obtained for electron or proton fluxes in the vicinity of the planet, nor any evidence for electron bursts in or near the observed bow shock, thus giving rise to the conclusion that Venus has no magnetosphere.-

Simpson, J. A.↗

NASA NTRS1988

Particle acceleration in impulsive solar flares

A model for second-step electron acceleration in impulsive solar flares is presented. The theory of stochastic particle acceleration is extended to include Coulomb energy losses which become important at low coronal heights. This inclusion successfully explains the observed steepening of interplanetary electron spectra below about 3 MeV following impulsive solar flares taking place at low coronal heights. It also explains the observed spectral differences of relativistic electrons in long-duration and impulsive flares.

Steinacker, J.↗

NASA NTRS1993

Magnetospheric models for electron acceleration and transport in the heliosphere

Electron transport and acceleration processes in the earth's magnetosphere have correspondences to analogous processes affecting electrons in the solar magnetosphere (i.e., heliosphere). Energetic electrons in planetary magnetospheres and the heliosphere are test particles probing transport and acceleration dynamics with minimal effects on dominant magnetic field configurations. Parallels are discussed relating to electron entry into the magnetospheres from interplanetary and interstellar space, circulatory transport processes, and acceleration by electric fields in boundary regions including shocks and magnetotails.

Cooper, J. F.↗