On the umbra-penumbra area ratio of sunspots

✍ Scribed by P. N. Brandt; W. Schmidt; M. Steinegger

• Publisher: Springer
• Year: 1990
• Tongue: English
• Weight: 232 KB
• Volume: 129
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00154373

✦ Synopsis

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.