A new study of ice core samples has found the link between sunspot activity and the Sun's solar cycle isn't as strong as previously thought.
Researchers have found the Sun's eleven-year solar cycle continued normally during the Maunder Minimum between 1645 and 1715, when sunspot activity was unusually low.
This was also a time when northern Europe experienced unusually cold conditions.
The discovery, reported in Geophysical Research Letters, comes as the Sun approaches solarmax, the climax of its cycle, when its north and south magnetic poles flip.
The researchers were looking for solar cycle variations by studying beryllium-10 isotope concentrations in ice core samples.
Showers of heavy isotopes including beryllium-10, are produced when cosmic rays, a high-energy mix of protons, electrons, and atomic nuclei from outside the solar system, collide with molecules in the Earth's atmosphere.
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Increased solar wind activity as the Sun moves towards solar max, reduces the amount of cosmic rays reaching Earth.
Time scales
By studying beryllium-10 levels in ice cores, scientists can determine the level of solar activity at a given time.
Drawing on two independent ice core records, Owens and colleagues modelled solar activity back to 1610, before the Maunder Minimum.
"Between 1650 to 1710 there were no sunspots recorded, even though there were lots of professional astronomers around at the time," says study lead author Dr Mathew Owens of the University of Reading in the United Kingdom.
"Yet despite the lack of sunspots, the Sun's magnetic field was still churning over its natural eleven-year solar cycle."
"It shows sunspots are a symptom not a cause for the solar cycle."
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