Fig. 1.
Sunspot numbers taken from SILSO World Data Center (2007–2017) and averaged over the four months of each season are shown for a ten-year time period. The seasons 2007-08 and 2008-09 report a low sunspot number, while in seasons 2011-12, 2012-13, 2013-14, and 2014-15 a higher number is detected, before decreasing again afterwards. This approximately describes the solar activity cycle of 11 years (see, e.g., Solanki et al. 2006).
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