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  • 1
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    Speed of sound in the solar interior (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The sound speed of the solar interior is directly determinable on the basis of the frequencies of solar 5-min oscillations, irrespective of solar model, and relying only on a simple asymptotic description of the oscillations in terms of trapped acoustic waves. It is plausible that, by using this asymptotic determination as an initial trial in a more accurate inversion, and imposing constraints of smoothness on the solution resulting from the iteration, a good model representing the large scale structure of the sun which satisfies the observed frequencies may be determined.
    Keywords: SOLAR PHYSICS
    Type: Nature (ISSN 0028-0836); 315; 378-382
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  • 2
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    Simulations of magnetic-flux transport in solar active regions (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The evolution of several observed solar active regions is simulated by solving a transport equation for magnetic flux at the photosphere. The rates of rotation, meridional flow, and diffusion of the flux are determined self-consistently in the calculations. The findings are in good quantitative agreement with previous measures of the rotation rate and diffusion constant associated with photospheric magnetic fields. Although the meridional velocities are consistent in direction and magnitude with recently reported poleward flows, relatively large uncertainties in the velocity determinations make this result inconclusive.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 102; 1-2
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  • 3
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    Soft X-ray images of the solar corona with a normal-incidence Cassegrain multilayer telescope (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: High-resolution images of the sun in the soft X-ray to EUV regime have been obtained with normal-incidence Cassegrain multilayer telescopes operated from a sounding rocket in space. The inherent energy-selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The Cassegrain telescopes provided images in bands centered at 173 and 256 A. The bandpass centered at 173 A is dominated by emission from the ions Fe IX and Fe X. This emission is from coronal plasma in the temperature range (8-14) x 10 to the 6th K. The images have angular resolution of about 1.0-1.5 arcsec and show no degradation because of X-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to everlying cool prominences are visible in the images. The density structure of polar plumes, which are thought to contribute to the solar wind, has been derived from the observations out to 1.7 solar radii.
    Keywords: SOLAR PHYSICS
    Type: Science (ISSN 0036-8075); 241; 1781-178
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  • 4
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    Simulations of the gross solar magnetic field during sunspot cycle 21 (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Regarding new bipolar magnetic regions as sources of flux, the evolution of the radial component of the solar photospheric magnetic field during 1976-1984 has been simulated with a spatial resolution of about 34,000 km, and the corresponding evolution of its absolute value averaged over the visible disk is derived. For nominal values of the transport parameters, this simulated gross field is in close, though imperfect, agreement with the observed gross field and its associated indices of solar activity. By analyzing the response of the simulated gross field to variations in the transport parameters and the source properties, it is found that the simulated field originates in newly erupted bipolar regions. The lifetimes of these regions are almost always less than three mo. Consequently, the strength of the simulated gross field is a measure of the current level of solar activity, and any recurrent patterns with lifetimes in excess of six mo must reflect the continuing eruption of new flux at 'active longitudes' rather than the persistence of old flux in long-lived magnetic structures.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 106; 251-268
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  • 5
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    Solar Doppler shifts - Sources of continuous spectra (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Oscillation observations can be used to study nonoscillatory solar phenomena that exhibit Doppler shifts. The paper discusses several effects of these phenomena and their associated temporal and spatial power spectra: (1) they limit the signal-to-noise ratio and sometimes detectability of oscillation modes; (2) there is the potential for better understanding and/or detection of solar phenomena; (3) large-scale convection may spatially modulate oscillation modes, leading to a continuous background spectrum; and (4) in regions of the spectrum where the resolution to separate modes is lacking one can determine upper limits for the integrated effects of modes.
    Keywords: SOLAR PHYSICS
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  • 6
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    High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It has been recognized that very long duration X-ray events (lasting several hours) are frequently associated with coronal mass ejection. Thus, Sheeley et al. (1983) found that the probability of the occurrence of a coronal mass ejection (CME) increases monotonically with the X-ray event duration time. It is pointed out that the association of long-duration, or long-decay, X-ray events (LDEs) with CMEs was first recognized from analysis of solar images obtained by the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL) slitless spectroheliograph. Recently high-resolution Bragg crystal X-ray spectrometers have been flown on three spacecraft, including the Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission (SMM), and the Japanese Hinotori spacecraft. In the present paper, P78-1 X-ray spectra of an LDE which had its origin behind the solar west limb on November 14, 1980 is presented. The obtained data make it possible to estimate temperatures of the hottest portion of the magnetic loops in which the emission arises.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 292; 309-318
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  • 7
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    Flare onset at sites of maximum magnetic shear (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Observations of the transverse component of the Sun's photospheric magnetic field obtained with the MSFC vector magnetograph show where the fields are nonpotential. The correlation was studied between locations of nonpotential fields and sites of flare onset for four different active regions. The details of the active region AR 4711 are outlined. Similar results are presented for three other regions: AR 2372 (April 1980), AR 2776 (November 1980), and AR 4474 (April 1984). For all four regions it is shown that flares initiate at sites on the magnetic neutral line where the local field deviates the most from the potential field. The results of this study suggest that flares are likely to erupt where the shear is equal to or greater than 85 degrees, the field is equal to or greater than 10000 G, and there is strong shear (equal to or greater then 80 degress) extending over a length equal to or greater than 8000 km.
    Keywords: SOLAR PHYSICS
    Type: NASA, Goddard Space Flight Center, Max 1991: Flare Research at the Next Solar Maximum. Workshop 1: Scientific Objectives; p 61-80
    Format: application/pdf
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  • 8
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    Acquisition and Reduction Procedures for MOF Doppler-Magnetograms (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Defects in the first magneto-optical filter (MOF) magnetograms, particularly the problem of the apparent contamination between velocity and magnetic fields, are discussed. It is found that a correct acquisition and reduction procedure gives cleaner results. A vector magnetograph is suggested. The vector field at coronal levels is calculated, using one MOF longitudinal magnetogram.
    Keywords: SOLAR PHYSICS
    Type: ESA, Seismology of the Sun and Sun-Like Stars; p 185-188
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  • 9
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    The Effects of Seeing on Noise (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-21
    Description: The effect of the supergranulation velocity field combined with seeing smearing of the solar image on the measurement of solar oscillations is discussed. Depending on the nature of the observational velocity determination scheme, the image motions can shift the background velocity pattern and produce a source of noise that reduces the quality of the observations. The magnitude of this effect is estimated and observational results which are consistent with this estimate are presented.
    Keywords: SOLAR PHYSICS
    Type: Solar Seismology from Space.; p 263-270
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  • 10
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    White-light and radio sounding observations of coronal transients (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A concerted search for coronal transients was conducted with the 'Solwind' coronagraph during the solar occultations of the two Helios spacecraft in October/November 1979. The polarization angle and bandwidth of the linearly polarized S-band downlink signal were monitored at the three 64-m tracking stations of the NASA Deep Space Network to determine coronal Faraday rotation and spectral broadening. A one-to-one correspondence could be established between abrupt disturbances in the two signal parameters and the passage of a white-light transient through the signal ray path from spacecraft to earth. The white-light morphology and the additional information provided by the radio sounding coverage are presented for each of the five distinct events recorded. Although no specific example could be observed in sufficient detail in both white light and Faraday rotation to derive the small-scale magnetic structure, some qualitative descriptions of the orientation and rough estimates of the magnitude of the transient magnetic field could be made.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 98; 341-368
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