The role of spiral sunspots in the solar activity of October 1972

Abstract

From a collection of photographs of 192 knots relating to 68 flares of the activity region McMath 12094 of October 1972, and of spots and prominences, a correlation analysis was made which led to the following conclusions: 1. 1. Flare activity began in the region above the leader spot A(N) which had the highest twisted magnetic energy of all the spots in the group. It rapidly developed to the region above the follower S-spots, and then to regions outside the spot area. This evolutionary process was in step with the morphological changes and the rotational movement of the spots in the group. 2. 2. The flare activity around Spot A began in the interior of the twisted magnetic tube and was in step with the untwisting of magnetic features, and the flare knots spread from the vicinity of the umbra to the outside of the penumbra. When the knotted structure completely untwisted itself, the overall flare activity decreased in the region. 3. 3. A spiral spot was found to be a strong centre of attraction below a giant coronal prominence. This shows that coronal prominences are formed through the contraction of strong electrical currents in the corona. We also discussed the question whether the twisted magnetic structure of spot A could have provided most of the energy in the flare activity and lead to an instability.