Sources of noise in solar limb definitions

  • S. L. Keil
  • S. P. Worden
3. Solar Oscillations Observational Evidence
Part of the Lecture Notes in Physics book series (LNP, volume 125)


We postulate that the rotation and evolution of solar surface structure can function as a source of noise in solar limb definition measurements. To test this hypothesis, we have produced a time series of 216 spectroheliograms taken at two minute spacings. These spectroheliograms were obtained in an Fe I line, formed at a depth similar to optical depth unity at the limb. We foreshortened this data in order to simulate the solar limb brightness profile and passed it through the finite Fourier transform definition (FFTD) algorithm used by Hill and his collaborators at SCLERA. In this work we were able to determine the amount of variation in solar limb position which is attributable to evolutionary changes in solar surface structure. We also artificially rotated one of these surface structure functions in order to determine the effects which surface structure rotation might have on limb position. In this paper, we conclude that rotation alone can produce power only at low frequencies (w ≲ 1 mHz). However, the evolution of solar surface structure exhibits a power spectrum which is similar to that observed with the SCLERA instrument at all of the frequencies. We also show that standing surface structure patterns can produce phase for a period of seven days such as the phase coherence found in the observations at SCLERA, although in the case of the latter, the periods are significantly longer.


Horizontal Transfer Random Data Intensity Fluctuation Intensity Pattern Phase Coherence 
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Copyright information

© Springer-Verlag 1980

Authors and Affiliations

  • S. L. Keil
    • 1
  • S. P. Worden
    • 1
  1. 1.Air Force Geophysics LaboratorySacramento Peak ObservatorySunspotNew Mexico

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