Large Sunspot Groups and Great Magnetic Storms: Magnetic Suppression of CMEs
E. W. Cliver, W. Pötzi, Astrid Veronig
Abstract
Abstract A solar spot group with a large area is not a requirement for a great magnetic storm. Nearly half (14/30) of all storms with a minimum Dst value ≤−300 nT from 1932–2014 originated in spot groups with corrected areas ≤1000 millionths of a solar hemisphere ( μ sh) on the day of the associated eruption. Over the same interval, spot groups with area 3000–4000 μ sh were ∼250 times more likely to give rise to a great storm than those with areas from 100–1000 μ sh, with the high percentage of great storms originating in small spot groups attributed primarily to the much higher occurrence frequency of such groups. Above ∼3500 μ sh, the ability of a spot group to produce a great storm appears to drop abruptly. For the 1932–2014 interval, we find that for the 71 days when a spot group had a measured daily area of 3000–3500 μ sh, five great storms were observed versus none for the 67 times when a group spot with an area from 3500 to ∼6000 μ sh was observed on the Sun. This is consistent with recent studies indicating that large spot groups on the Sun and stars can suppress coronal mass ejections.