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  • SOLAR PHYSICS  (4)
  • Geophysics  (1)
  • 1
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    The kinetic effects of Alfven wave pressure in the solar wind (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The results of a kinetic model for the radial evolution of the proton component of the solar wind in the presence of Alfven waves are presented. The calculation is based on general quasi-linear equations developed to describe the temporal and spatial evolution of the ion distribution functions of a multispecies plasma in presence of waves, using a short wavelength expansion. These equations include new wave-particle interaction terms arising from temporal and spatial inhomogeneities in the plasma. Numerical solutions are obtained of these equations specialized to the case of Alfven waves in a spherically symmetric solar wind. The Alfven wave effects on the proton distribution function vary strongly in velocity space. Protons with small transverse velocities are primarily decelerated with respect to the wave rest frame. This deceleration becomes less important with increasing transverse velocity, as wave induced diffusion to larger transverse velocity becomes the dominant effect. The competition of these effects results in interesting distortions of evolving proton distribution functions which give rise the wave acceleration well known from fluid theory.
    Keywords: SOLAR PHYSICS
    Type: Contrib. to the Fourth Solar Wind Conf.; p 19-25
    Format: text
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  • 2
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    Suprathermal protons in the interplanetary solar wind (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Using the Mariner 5 solar wind plasma and magnetic field data, we present observations of field-aligned suprathermal proton velocity distributions having pronounced high-energy shoulders. These observations, similar to the interpenetrating stream observations of Feldman et al. (1974), are clear evidence that such proton distributions are interplanetary rather than bow shock associated phenomena. Large Alfven speed is found to be a requirement for the occurrence of suprathermal proton distribution; further, we find the proportion of particles in the shoulder to be limited by the magnitude of the Alfven speed. It is suggested that this last result could indicate that the proton thermal anisotropy is limited at times by wave-particle interactions
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 81; June 1
    Format: text
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  • 3
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    The distance to the heliospheric VLF emission region (1995)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Two major episodes of heliospheric VLF emissions near 3 kHz have been observed by the Voyager spacecraft in 1983/84 and 1992/3. This higher-frequency component is apparently triggered by solar wind transients with sufficiently large spatial extents and energies to continue to propagate as shocks in the heliosheath. Entrainment of previously unshocked material and changed flow conditions in the heliosheath both tend to slow the shock propagation. The shock evolution is not self-similar. Rather, it is intermediate to two blast-wave similarity solutions in the moving solar wind frame. In one solution the shock moves as time to the 2/3 power and in the other as time to the 4/5 power. Using these models, the shock/Forbush decrease observed at Voyager 2 in September, 1991 and the turn-on of the 1992 emission is consistent with an emission region distance of approximately 130 AU (assuming no additional slowing of the shock in the heliosheath). If the termination shock was at approximately 70 AU when the transient shock collided with it, the true distance to the source region was probably closer to approximately 115 AU.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)303-(9)306
    Format: text
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  • 4
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    Collisionless shock formation and the prompt acceleration of solar flare ions (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The formation mechanisms of collisionless shocks in solar flare plasmas are investigated. The priamry flare energy release is assumed to arise in the coronal portion of a flare loop as many small regions or 'hot spots' where the plasma beta locally exceeds unity. One dimensional hybrid numerical simulations show that the expansion of these 'hot spots' in a direction either perpendicular or oblique to the ambient magnetic field gives rise to collisionless shocks in a few Omega(i), where Omega(i) is the local ion cyclotron frequency. For solar parameters, this is less than 1 second. The local shocks are then subsequently able to accelerate particles to 10 MeV in less than 1 second by a combined drift-diffusive process. The formation mechanism may also give rise to energetic ions of 100 keV in the shock vicinity. The presence of these energetic ions is due either to ion heating or ion beam instabilities and they may act as a seed population for further acceleration. The prompt acceleration of ions inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission can thus be explained by this mechanism.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 189; 1-2
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  • 5
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    Energization of Ions in near-Earth current sheet disruptions (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-16
    Description: In this study we examine observations made by AMPTE/CCE of energetic ion bursts during seven substorm periods when the satellite was located near the neutral sheet, and CCE observed the disruption cross-tail current in situ. We compare ion observations to analytic calculations of particle acceleration. We find that the acceleration region size, which we assume to be essentially the current disruption region, to be on the order of 1 R(sub E). Events exhibiting weak acceleration had either relatively small acceleration regions (apparently associated with pseudobreakup activity on the ground) or relatively small changes in the local magnetic field (suggesting that the magnitude of the local current disruption region was limited). These results add additional support for the view that the particle bursts observed during turbulent current sheet disruptions are due to inductive acceleration of ions.
    Keywords: Geophysics
    Type: NASA/CR-95-207163 , NAS 1.26:207163 , Paper-94GL03384 , Geophysical Research Letters (ISSN 0094-8534); 22; 5; 627-630
    Format: application/pdf
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