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  • 1
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    Microflares in the solar magnetic network (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Localized brightenings are found throughout the magnetic network in quiet sun image sequences obtained in the C IV 1548 A line by the SMM satellite's UV spectrometer and polarimeter. Some bright sites are short-lived, while others persist. Plots of the intensity fluctuations show that the enhancements at both short- and long-lived sites are the result of localized impulsive heating events that occur intermittently at the short-lived sites and in more rapid succession at the long-lived ones. The number of these events and their visibility in the wings of the C IV line are consistent with their identification as the explosive events seen in UV spectra.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 323; 380-390
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Preflare magnetic and velocity fields (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares
    Keywords: SOLAR PHYSICS
    Type: Energetic Phenomena on the Sun: The Solar Maximum Mission Flare Workshop. Proceedings; 33 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Magnetic location of C IV events in the quiet network (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Ultraviolet Spectrograph and Polarimeter (UVSP) observations of C IV intensity in the quiet sun were examined and compared to magnetograms and He I 10830 A spectroheliograms from Kitt Peak National Laboratory. The observations were made between 3 and 9 April, 1985. Spatially rastered UVSP intensity measurements were obtained at 11 wavelength positions in the 1548 A line of C IV. It was concluded that the stochastic process whereby convective shuffling of loop footprints leads to many topically dissipative events in active regions and the larger bipoles treated here continues to operate in regions of fewer, weaker flux loops, but the resulting events above threshold are less frequent.
    Keywords: SOLAR PHYSICS
    Type: NASA. Goddard Space Flight Center Coronal and Prominence Plasmas; p 383-387
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    The excitation of helium resonance lines in solar flares (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Helium resonance line intensities are calculated for a set of six flare models corresponding to two rates of heating and three widely varying incident fluxes of soft X-rays. The differing ionization and excitation equilibria produced by these models, the processes which dominate the various cases, and the predicted helium line spectra are examined. The line intensities and their ratios are compared with values derived from Skylab NRL spectroheliograms for a class M flare, thus determining which of these models most nearly represents the density vs temperature structure and soft X-ray flux in the flaring solar transition region, and the temperature and dominant mechanaism of formation of the helium line spectrum during a flare.
    Keywords: SOLAR PHYSICS
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  • 5
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    Frequent ultraviolet brightenings observed in a solar active region with solar maximum mission (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations of the temporal behavior of ultraviolet emission from bright points within an active region of the sun are reported. Frequent and rapid brightenings in Si IV and O IV line emission are seen. The observations suggest that intermittent heating events of modest amplitude are occurring at many sites within an active region. By selecting the brightest site at any given time within an active region and then sampling its behavior in detail within a 120 s interval, it is found that about two-thirds of the samples show variations of the Si IV line intensity. The brightenings typically last about 40-60 s; intensity increases of about 20-100 percent are frequently observed. The results suggest that heating due to magnetic field reconnection within an active region is proceeding almost stochastically. Events involving only a modest release of energy occur the most frequently.
    Keywords: SOLAR PHYSICS
    Type: AD-A162870 , AFGL-TR-85-0329 , Astrophysical Journal, Part 1 (ISSN 0004-637X); 283; 879-886
    Format: text
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  • 6
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    Helium resonance lines in the flare of 15 June 1973 (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Time sequences of He I and He II resonance line intensities at several sites within the flare of June 15, 1973 are derived from observations obtained with Naval Research Laboratory's Slitless Spectroheliograph on Skylab. The data are compared with predictions in six model flare atmospheres based on two values for the heating rate and three for the flux of photoionizing coronal X-rays and EUV. A peak ionizing flux more than 1000 times that in the quiet sun is indicated. Implications for the common practice of deriving stellar coronal fluxes from He II 1640 A fluxes assuming dominance of the recombination mechanism, are discussed.
    Keywords: SOLAR PHYSICS
    Type: AD-A225185 , Solar Physics (ISSN 0038-0938); 120; 2 19
    Format: text
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