A Curious History of Sunspot Penumbrae
Daily records of sunspot group areas compiled by the Royal Observatory, Greenwich, from May of 1874 through 1976 indicate a curious history for the penumbral areas of the smaller sunspot groups. On average, the ratio of penumbral area to umbral area in a sunspot group increases from 5 to 6 as the to...
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Veröffentlicht in: | Solar physics 2013-09, Vol.286 (2), p.347-356 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | Daily records of sunspot group areas compiled by the Royal Observatory, Greenwich, from May of 1874 through 1976 indicate a curious history for the penumbral areas of the smaller sunspot groups. On average, the ratio of penumbral area to umbral area in a sunspot group increases from 5 to 6 as the total sunspot group area increases from 100 to 2000 μHem (a μHem is 10
−6
the area of a solar hemisphere). This relationship does not vary substantially with sunspot group latitude or with the phase of the sunspot cycle. However, for the sunspot groups with total areas |
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ISSN: | 0038-0938 1573-093X |
DOI: | 10.1007/s11207-013-0291-y |