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  • SOLAR PHYSICS  (290)
  • 2005-2009
  • 1975-1979  (290)
  • 1950-1954
  • 1
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    Coronal changes associated with a disappearing filament (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Skylab/ATM observations of a disappearing filament near the center of the solar disk are described using XUV and H-alpha spectroheliograms, X-ray filterheliograms, and photospheric magnetograms. The temperature of the coronal plasma as the filament disappeared is estimated to have been in excess of 6 million K, and it is noted that the time history of the soft X-ray and microwave fluxes displayed the gradual-rise-and-fall (GRF) signature, suggesting that the present event may have properties that are characteristic of a wide class of long-duration X-ray and radio events. A comparison with other spatially resolved long-duration X-ray events indicates that all such long-lived bursts involve transients in the outer corona and that some two-thirds of them involve either the eruption or the major activation of a prominence. It is also found that long-lived events are characterized by the appearance of new emission loops in the lower corona during the declining phase of the X-ray emission and that these loops sometimes disappear after the X-ray events and sometimes remain indefinitely.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 45; Dec. 197
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  • 2
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    Enhancement of solar heavy nuclei at high energies in the 4 July 1974 event (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Relative abundances of energetic nuclei in the July 4, 1974, solar event are presented. The results show a marked enhancement of abundances that systematically increase with nuclear charge numbers in the range of the observation (Z between 6 and 26) for energies above 15 MeV/nucl. While such enhancements are commonly seen below 10 MeV/nucl, most observations at higher energies are found to be consistent with solar-system abundances. The energy spectrum of oxygen is observed to be significantly steeper than most other solar events studied in this energy region. It is proposed that these observations are characteristic of particle populations at energies of the order of 1 MeV/nucl and that the anomalous features observed may be the result of the high-energy extension of such a population that is commonly masked by other processes or populations that might occur in larger solar events.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 55; Dec. 197
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  • 3
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    The reconnection of magnetic field lines in the solar corona (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Skylab XUV coronal spectroheliograms and photospheric magnetograms are compared. This comparison shows that, as new bipolar magnetic fields emerge through the solar surface into the corona, the new coronal fields interact with the old ones in a manner that suggests the reconnection of the field lines.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 196; Mar. 15
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  • 4
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    Forbidden lines of highly ionized iron in solar flare spectra (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 196; Mar. 1
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  • 5
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    XUV observations of coronal magnetic fields (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Spectroheliograms obtained with the Naval Research Laboratory's Extreme Ultraviolet Spectrograph (S082A) on Skylab are compared with Kitt Peak National Observatory magnetograms. A principal result is the characteristic reconnection of flux from an emerging bipolar magnetic region to previously existing flux in its vicinity. Examples of the disappearance of magnetic flux from the solar atmosphere are also shown. The results of a particularly simple, potential field calculation are shown for comparison with the Skylab observations.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 40; Jan. 197
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  • 6
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    Atmospheric turbulence and the apparent instantaneous diameter of the sun (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Astrometric data are perturbed by turbulent density fluctuations in the atmosphere over the frequency range from 0.0001 to 10 Hz by amounts that would limit the accuracy of solar-diameter measures significantly. Power spectra of the perturbations are compared with meteorological data to argue that thermal turbulence is dominant above 0.001 Hz and that mechanical turbulence (weather) is important below that frequency. Noise power in astrometry should be comparable under night or day conditions, but site location may be important for the strength of slowly passing waves.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics; 59; 2, Ju; July 197
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  • 7
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    A newly observed solar feature - Macrospicules in He II 304 A (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: He II 304 A spectroheliograms, obtained with the NRL extreme-ultraviolet slitless spectrograph during the Skylab mission, show spikelike structures at the sun's polar limb which resemble the familiar H-alpha spicules. However, the relatively large size and long life of these He II features has led to distinguishing them by the name 'macrospicules'. The macrospicules appear as protuberances or jets, ranging from 5 to over 60 sec in length, from 5 to 30 sec in width, and from 5 to over 40 minutes in lifetime. Perhaps the most radical departure from H-alpha spicules is that macrospicules occur only within the chromospheric boundaries of coronal holes. Thus macrospicules are most easily visible over the solar poles due to the coronal holes normally present there, and much less frequently at lower latitudes during limb passage of relatively rare, low-latitude coronal holes.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 197; May 1
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  • 8
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    Electromagnetic instabilities driven by unequal proton beams in the solar wind (1976)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The paper sets forth a numerical investigation of the linear dispersion relation for typical solar wind conditions at 1 AU during those times (high-speed streams) when a secondary beam of protons drifting relative to the main proton component is present. Three beam-driven instabilities were found to occur as the beam drift velocity approaches the Alfven speed: (1) a pure, field-aligned magnetosonic wave that is most important at relatively high beta and/or high beam drift speeds; (2) an oblique magnetosonic wave having highest growth rates 15-30 deg from the magnetic field; and (3) an oblique Alfven wave having maximum growth rates at increasing angle to the magnetic field. The linear growth rates for the field-aligned magnetosonic and the Alfven oblique modes are investigated as a function of relative beam density, varying anisotropic pitch angle distributions for the various components, electron temperature, and electron heat flux.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 81; June 1
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  • 9
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    Spectrum of mean free paths near earth in the solar cosmic ray event of April 29, 1973 (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 83; June 1
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  • 10
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    Radiation transfer through a model sunspot (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A cylindrically symmetric model for a sunspot atmosphere using the similarity principle of Schlueter and Temesvary for the magnetic field configuration is presented. The equations of magnetostatic equilibrium are used, augmented by a radial Evershed flow. The LTE radiative transfer equations for the Stokes vector were solved under a variety of conditions for a ray emerging from a typical penumbral point. The contribution from isolated lines to the broadband circular polarization in sunspot penumbrae is evaluated using a more realistic model sunspot atmosphere than has hitherto been considered. Results indicate that the inclusion of a velocity field along the magnetic field vector is unable to give a net circular polarization of sufficient magnitude, although the variation with the angle between the line-of-sight and the magnetic field vector is in qualitative agreement with observations. The corresponding results for the net linear polarization are satisfactory.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 63; Sept
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