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  • SOLAR PHYSICS  (4)
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  • 1
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    Effects of diffusion and mass flows on C IV and Si IV lines formed in the solar atmosphere (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A model for the transition region is derived from an initial interpretation of EUV observations, assuming ionization equilibrium and constant elemental abundance with height. The effects of diffusion and mass flows are then included in the initial model and the emergent profiles of several C IV and Si IV lines are computed. It is found that diffusion and mass flows have a strong effect on both the emergent intensity and spectral shape of these lines. Diffusion acts to deplete the transition region of heavy ions to an extent which depends on the detailed temperature and density structure. The net effect is a weighting of the coronal emission relative to that in the transition. On the basis of the results, it is suggested that the downflows observed in the network in lines of C IV and Si IV could be due to gravitational settling of the ions following their injection, via diffusion, into the corona from spicules. When flows are superposed on the basic diffusion model, the rapid change in elemental abundance characteristic of the model is virtually eliminated and the coronal contribution to the emission in C IV and Si IV lines becomes negligible relative to that in the transition region. Flows have a strong effect on the computed line intensities and introduce large asymmetries into the line shapes.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 250
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. I - Estimate of the electron velocity distribution functions. II - The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 68; Dec. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Nonequilibrium ionization due to thermal diffusion and mass flows (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Recent calculations of diffusion coefficients are used in the continuity equation to compute ion populations of carbon in the solar transition region. Thermal diffusion causes strong departures from ionization equilibrium in the region where the temperature gradient is steepest. Mass-conserving flows are also included in our calculations. These dominate over thermal diffusion depending on the magnitude of the flows and also lead to departures from ionization equilibrium. These results have important implications for the interpretation of EUV line emission.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 241
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    HRTS II EUV observations of a solar ephemeral region (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: HRTS II has been used to observe the EUV emission of a small bipolar magnetic feature or ephemeral region, where strong EUV line enhancement exhibits contrasts (measured relative to the quiet sun) which range from 10 to 70. The substantiality of the Lyman-alpha and C II-O V emission, and the absence of any measurable emission in coronal forbidden lines, sets a temperature range for the loop's active part of the order of 16,000-300,000 K. The use of the ratios of allowed lines as temperature diagnostics yields temperatures that are very near ionization equilibrium temperatures, and the use of chromospheric lines to form a wavelength standard yields absolute velocities ranging in magnitude from zero to 12 km/sec for C IV, N IV, and O V. This flow is interpreted as a siphon flow.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 278; 428-440
    Format: text
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    NASA TECHNICAL REPORTS
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