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On the umbra-penumbra area ratio of sunspots

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Abstract

The area ratio of umbra to penumbra (Au/Ap) was investigated for a series of 126 sunspots observed around the maximum of solar activity in 1980. Plotting log (Au) as function of log (Ap) a linear relation is obtained with a slope of 1.10, yielding an average ratio Au/Ap of 0.24 for small spots and of 0.32 for large spots. This deviates noticeably from the commonly adopted constant value of Au/Ap = 0.21 (Allen, 1973) used e.g. for modelling the sunspot irradiance deficit (cf. Willson et al., 1981) from the Solar Geophysical Data.

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Authors and Affiliations

  1. Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-7800, Freiburg, F.R.G.

    P. N. Brandt & W. Schmidt

  2. Institut für Astronomie, Universitätsplatz 5, A-8010, Graz, Austria

    M. Steinegger

Authors
  1. P. N. Brandt
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  2. W. Schmidt
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  3. M. Steinegger
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Mitteilungen aus dem Kiepenheuer-Institut Nr. 328

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Brandt, P.N., Schmidt, W. & Steinegger, M. On the umbra-penumbra area ratio of sunspots. Sol Phys 129, 191–194 (1990). https://doi.org/10.1007/BF00154373

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  • DOI: https://doi.org/10.1007/BF00154373

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