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Annual numbers of storms (storm days) of different Gosling et al. (1991) sizes from 1932, the beginning of the Kp index, to 2011 (top panel) and similarly for NOAA G storm sizes (third panel). The second panel shows the yearly sunspot number (vertical lines indicate years of sunspot maximum), while the bottom panel shows the number of G storms/solar cycle. Note that the persistent low levels of storm activity during the recent solar minimum are unprecedented during this 80-year period. In particular, 2008–2011 had the lowest number of small or G1 storms recorded in the Kp index based on this analysis.
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