Abstract
Mount Wilson sunspot drawings from 1966 through 1980 were used in conjunction with Hα filtergrams from Big Bear Solar Observatory to examine the origin of δ spots, spots with bipolar umbrae within one penumbra. Of the six cases we studied, five were formed by the union of non-paired spots. They are either shoved into one another by two neighboring growing bipoles or by a new spot born piggy-back style on an existing spot of opposite polarity. Proper motions of the growing spots take on curvilinear paths around one another to avoid a collision. This is the shear motion observed in δ spots (Tanaka, 1979). In the remaining case, the δ spot was formed by spots that emerged as a pair. Our findings indicate no intrinsic differences in the formation or the behavior between δ spots and spots of normal magnetic configuration.
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Tang, F. On the origin of δ spots. Sol Phys 89, 43–50 (1983). https://doi.org/10.1007/BF00211951
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DOI: https://doi.org/10.1007/BF00211951