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“It poses significant challenges to prevalent dynamo theories of the solar cycle.” — Indeed, but such theories were always speculative anyway.
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Dec. 12, 2022: So you thought you knew the solar cycle? Think again. A new paper published in Frontiers in Astronomy and Space Sciences confirms that there is more to solar activity than the well-known 11-year sunspot cycle. Data from Stanford University’s Wilcox Solar Observatory (WSO) reveal two solar cycles happening at the same time, and neither is 11 years long.

“We call it ‘the Extended Solar Cycle,’” says lead author Scott McIntosh of NCAR. “There are two overlapping patterns of activity on the sun, each lasting about 17 years.”

Solar physicists have long suspected this might be true. References to “overlapping solar cycles” can be found in research literature as far back as 1903. A figure from the new Frontiers paper seems to clinch the case:

The top panel shows sunspot counts since 1976. The curve goes up and down every 11 years, which explains why everyone thinks the…