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  • 1
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    The variability of the solar diameter (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: It is argued here that most of the variation in observations of the solar radius of over three centuries measure properties of the sun's limb darkening function and are affected by many sources of degradation of the solar image. They do not directly measure a true solar radius. From a long series of visual observations made by a single observer as well as recent photoelectric observations, evidence is found for periodicities in the apparent radius that occur in both modern and historical records. The magnitude of the observed variations is quite different in visual and photoelectric observations, suggesting that the process responsible for the periodicities is either one that modifies the solar limb darkening function or one that causes systematic variations in image blurring by the earth's atmosphere. A connection between solar magnetic activity an apparent radius seems likely, with evidence for such a relation dating back as fast as the Maunder minimum.
    Keywords: SOLAR PHYSICS
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    NASA TECHNICAL REPORTS
  • 2
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    Short-term changes in solar oscillation frequencies and solar activity (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown that the frequencies of solar rho-mode oscillations change significantly over periods as short as one month. These changes correlate significantly with variations in the strength of surface solar activity as measured by the average, over the sun's visible surface, of the magnitude of the line-of-sight magnetic field component from magnetograms. The frequency and mean magnetic variations are found to obey a linear relationship. It is seen that the mean frequency shift at any time depends on the history of solar activity over an interval of, at most, several months prior to the measurement and conclude that the dominant mechanism of the frequency shift is correlated with surface magnetic activity.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 373; L81-L84
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    NASA TECHNICAL REPORTS
  • 3
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    Spectral Information from Gapped Data. a Comparison of Technique (1984)
    In:  CASI
    Details
    Publication Date: 2014-08-21
    Description: The fast Fourier transformations (FFT) is used to estimate power spectra of continuous signals evenly sampled on discrete domains. The problem of finding power spectra on unevenly sampled domains, in particular a regularly spaced domain with gaps is discussed. The analysis of the ACRIM solar bolometric intensity data, obtained with a 3/5 on and 2/5 off duty cycle of approximately 100 minutes, would benefit from the techniques. The comparative effectiveness of three different analysis techniques applied to synthetic data generated on gapped domain is reported.
    Keywords: SOLAR PHYSICS
    Type: JPL Solar Seismology from Space.; p 293-303
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    NASA TECHNICAL REPORTS
  • 4
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    Inferring solar structure variations from photometric and helioseismic observations (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Present large scale photometric and helioseismic data may be related to spatial and temporal deviations from an otherwise static, spherical solar convection zone (SCZ). New space experiments combine precise photometric, helioseismic, and magnetic observational capabilities (like SOHO and MDI) and will provide data needed to understand the interaction of magnetic fields and global scale circulation in the SCZ. Even simple physical arguments make it clear that the anticipated accuracy of these new experiments virtually guarantees new constraints on models of the SCZ.
    Keywords: SOLAR PHYSICS
    Type: of the COSPAR 28th Plenary Meeting, The Hague, Netherlands, June 25-July 6, 1990. A91-34076 13-92) Advances in Space Research (ISSN 0273-1177); 171-184
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    NASA TECHNICAL REPORTS
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