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  • 1
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    A sunspot periodicity and the solar rotation (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A least squares power spectrum analysis of daily sunspot numbers for the last 122 years yielded a statistically significant peak at 12.0715 plus or minus .002 days period. This feature at 11.685 days (sidereal) of the sunspot spectrum is discussed in relation to the peak at 12.22 days (sidereal) which Dicke found in his oblateness data. The data is attributed to the Sun's core if the core rotates at either 12.0715 days or 24.1430 days period (synodic). It is suggested that spacecraft observations combined with correlative analysis of solar surface features between eastern and western hemispheres could further reveal a basic core periodicity. A Dicke type space oblateness experiment is discussed for providing better photospheric observations than a ground instrument to determine the core periodicity.
    Keywords: SOLAR PHYSICS
    Type: NASA. Goddard Space Flight Center Study of the Solar Cycle from Space; p 175-194
    Format: text
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  • 2
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    Reverse Current in Solar Flares (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An idealized steady state model of a stream of energetic electrons neutralized by a reverse current in the pre-flare solar plasma was developed. These calculations indicate that, in some cases, a significant fraction of the beam energy may be dissipated by the reverse current. Joule heating by the reverse current is a more effective mechanism for heating the plasma than collisional losses from the energetic electrons because the Ohmic losses are caused by thermal electrons in the reverse current which have much shorter mean free paths than the energetic electrons. The heating due to reverse currents is calculated for two injected energetic electron fluxes. For the smaller injected flux, the temperature of the coronal plasma is raised by about a factor of two. The larger flux causes the reverse current drift velocity to exceed the critical velocity for the onset of ion cyclotron turbulence, producing anomalous resistivity and an order of magnitude increase in the temperature. The heating is so rapid that the lack of ionization equilibrium may produce a soft X-ray and EUV pulse from the corona.
    Keywords: SOLAR PHYSICS
    Type: NASA-TM-79749 , SU-IPR-752
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Energetic particles in solar flares (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The various manifestations of energetic particles in solar flares are examined, and possible mechanisms for the acceleration of these particles are considered. Hard X-ray observations and possible mechanisms for the production of the dominant form of solar energetic particles, electrons with energies between 10 and 100 keV, are discussed, with consideration of thin-target models, thick-target models and thick-target models with reverse currents, and first-phase acceleration mechanisms for energetic electrons emitting impulsive microwave and fast-drift Type III radio bursts as well as impulsive hard X rays, which are detected themselves 20 min after the flare at 1 AU are considered. Radio evidence on the number, energy and pitch-angle distributions of energetic particles produced during solar flares is summarized, and observations at 1 AU of proton and electron energy spectra, the proton/electron ratio and energetic particle events rich in He-3 from solar flares are discussed. Finally, consideration is given to gamma-ray evidence of nuclear reactions in flares and white-light flares
    Keywords: SOLAR PHYSICS
    Format: text
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  • 4
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    Reverse Current in Solar Flares (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The theory that impulsive X ray bursts are produced by high energy electrons streaming from the corona to the chromosphere is investigated. Currents associated with these streams are so high that either the streams do not exist or their current is neutralized by a reverse current. Analysis of a simple model indicates that the primary electron stream leads to the development of an electric field in the ambient corona which decelerates the primary beam and produces a neutralizing reverse current. It appears that, in some circumstances, this electric field could prevent the primary beam from reaching the chromosphere. In any case, the electric field acts as an energy exchange mechanism, extracting kinetic energy from the primary beam and using it to heat the ambient plasma. This heating is typically so rapid that it must be expected to have important dynamical consequences.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-149464 , SU-IPR-678 , AD-A035617
    Format: application/pdf
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  • 5
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    A sunspot periodicity and its possible relation to solar rotation (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A least-squares power-spectrum analysis of 122 years of Zurich daily sunspot numbers yields a statistically significant peak at a 12.0715 + or - 0.002 day period. This feature of the sunspot spectrum may be associated with the peak at 12.22 days (sidereal) which Dicke (1976) found in his oblateness data, and may be attributable to the sun's core if it rotates at either a 12.0715-day or a 24.1430-day period (synodic).
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 227
    Format: text
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  • 6
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    Reverse current in solar flares (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: We examine the proposal that impulsive X-ray bursts are produced by high-energy electrons streaming from the corona to the chromosphere. It is known that the currents associated with these streams are so high that either the streams do not exist or their current is neutralized by a reverse current. Analysis of a simple model in which the reverse current is stable indicates that the primary electron stream leads to the development of an electric field in the ambient corona which (a) decelerates the primary beam and (b) produces a neutralizing reverse current. It appears that, in some circumstances, this electric field could prevent the primary beam from reaching the chromosphere. In any case, the electric field acts as an energy exchange mechanism, extracting kinetic energy from the primary beam and using it to heat the ambient plasma. This heating is typically so rapid that it must be expected to have important dynamical consequences.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 218
    Format: text
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  • 7
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    The rapid heating of coronal plasma during solar flares - Nonequilibrium ionization diagnostics and reverse currents (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Keywords: SOLAR PHYSICS
    Type: AD-A079047 , Astrophysical Journal; vol. 224
    Format: text
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  • 8
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    Energetic particles in solar flares. Chapter 4 in the proceedings of the 2nd Skylab Workshop on Solar Flares (1978)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The recent direct observational evidence for the acceleration of particles in solar flares, i.e. radio emission, bremsstrahlung X-ray emission, gamma-ray line and continuum emission, as well as direct observations of energetic electrons and ions, are discussed and intercorrelated. At least two distinct phases of acceleration of solar particles exist that can be distinguished in terms of temporal behavior, type and energy of particles accelerated and the acceleration mechanism. Bulk energization seems the likely acceleration mechanism for the first phase while Fermi mechanism is a viable candidate for the second one.
    Keywords: SOLAR PHYSICS
    Type: NASA-TM-79660 , Jan 01, 1976 - Dec 31, 1977; Boulder, CO; United States
    Format: application/pdf
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