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  • 1
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    The magnetic network location of explosive events observed in the solar transition region (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Compact short-lived explosive events have been observed in solar transition region lines with the High-Resolution Telescope and Spectrograph (HRTS) flown by the Naval Research Laboratory on a series of rockets and on Spacelab 2. Data from Spacelab 2 are coaligned with a simultaneous magnetogram and near-simultaneous He I 10,380 -A spectroheliogram obtained at the National Solar Observatory at Kitt Peak. The comparison shows that the explosive events occur in the solar magnetic network lanes at the boundaries of supergranular convective cells. However, the events occur away from the larger concentrations of magnetic flux in the network, in contradiction to the observed tendency of the more energetic solar phenomena to be associated with the stronger magnetic fields.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 370; 775-778
    Format: text
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  • 2
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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
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  • 3
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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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  • 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
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  • 6
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    Simultaneous ultraviolet and X-ray observations of solar microflares (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We present a comparison of observations of a solar active region obtained with the Ultraviolet Spectrometer and Polarimeter (UVSP) and the Hard X-ray Imaging Spectrometer (HXIS) on board the Solar Maximum Mission (SMM). The data show many subflares and smaller events during a 9 hr period in which there were no major flares. This activity is associated with areas of complex, evolving magnetic fields. Events substantially smaller than subflares, identified in C IV 1548 A emission (T = 10(exp 5) K), are found to have impulsive counterparts in 3.5-5.5 keV X-ray emission characteristic of T approximately 10(exp 7) K. These 'microflares' are therefore true members of the flare family, reaching temperatures greater than that of the ambient solar corona. Plots of X-ray versus UV emission show that the emission from the smaller microflares is softer than that from the larger microflares and subflares. Distributions of solar flares with energy that are based on hard X-ray fluxes can be corrected using this X-ray/UV relationship. The corrected distributions suggest that microflares play a larger role in coronal heating than was indicated by analysis of the original distributions.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 472-479
    Format: text
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