Abstract
Two sunspot groups in symmetrical positions relative to the Sun's equator were flaring almost simultaneously. The larger northern group was highly irregular: the two main spots were surrounded by one and the same penumbra, the magnetic polarities were inverted and the inclination of the axis was exceptionally large and of the wrong direction. The larger southern flare consisted of two parallel ribbons that developed into a loop prominence. The two ribbons were moving sideways and upwards, forming a cone. The speed of this motion amounted to 10 km s−1 at the beginning and decreased to 2 km s−1 in the course of one hour. The streaming along the slopes of the cone indicates the direction of the magnetic fields.
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Waldmeier, M. A twin flare in symmetrical sunspot groups. Sol Phys 70, 93–96 (1981). https://doi.org/10.1007/BF00154393
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DOI: https://doi.org/10.1007/BF00154393