Abstract
A study of ephemeral active regions (ER) identified on good quality full-disk magnetograms reveals:
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(1)
On the average 373 and 179 ER were present on the Sun in 1970 and 1973 respectively. The number varies with the solar cycle.
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(2)
The median lifetime of ER depends on observation quality and selection rules but is estimated as about 12 hr for our data.
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(3)
The latitude distribution is very broad but not uniform. The distribution peaks near the equator and shows variations similar to distributions of large active regions.
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(4)
The longitude distribution is essentially homogeneous.
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(5)
The spatial orientation of ER is almost random. In 1973 there is a hint of an excess of new cycle orientations at high latitudes.
A comparison of parameters of ER and regular active regions suggests that ER are the small-scale end of a broad spectrum of active regions. The role of ER in the light of present theories of solar activity is investigated but is not yet clear. Heating of the chromosphere and corona may be significantly affected by ER.
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Harvey, K.L., Harvey, J.W. & Martin, S.F. Ephemeral active regions in 1970 and 1973. Sol Phys 40, 87–102 (1975). https://doi.org/10.1007/BF00183154
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DOI: https://doi.org/10.1007/BF00183154