Solar activity reconstructed over a millennium

This quote from the report stood out: ‘there are long-lasting periods of strong and weak solar activity, which is also reflected in the climate on Earth.’ Worth noting as we proceed through a period of weak activity right now.
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An international team of researchers led by ETH Zurich has reconstructed solar activity back to the year 969 using measurements of radioactive carbon in tree rings, reports Phys.org.

Those results help scientists to better understand the dynamics of the sun and allow more precise dating of organic materials using the C14 method.

What goes on in the sun can only be observed indirectly. Sunspots, for instance, reveal the degree of solar activity—the more sunspots are visible on the surface of the sun, the more active is our central star deep inside.

Even though sunspots have been known since antiquity, they have only been documented in detail since the invention of the telescope around 400 years ago. Thanks to that, we now know that the number of spots varies in regular eleven-year cycles and that, moreover, there are long-lasting periods of strong and weak solar activity, which is also reflected in the climate on Earth.

However, how solar activity developed before the start of systematic records has so far been difficult to reconstruct.

An international research team led by Hans-Arno Synal and Lukas Wacker of the Laboratory of Ion Beam Physics at ETH, which included the Max Planck Institute for Solar System Research in Göttingen and Lund University in Sweden, has now traced back the sun’s eleven-year cycle all the way to the year 969 using measurements of the concentration of radioactive carbon in tree rings.

At the same time, the researchers have thus created an important database for more precise age determination using the C14 method. Their results were recently published in the scientific journal Nature Geoscience.

Solar activity from tree rings

To reconstruct solar activity over a millennium with an extremely good time resolution of just one year, the researchers used tree-ring archives from England and Switzerland.

In those tree rings, whose ages can be precisely determined by counting the rings, there is a tiny fraction of radioactive carbon C14, with only one out of every 1000 billion atoms being radioactive. From the known half-life of the C14 isotope—around 5700 years—one can then deduce the concentration of radioactive carbon present in the atmosphere when the growth ring was formed.

As radioactive carbon is mainly produced by cosmic particles, which in turn are kept away from the Earth to a greater or lesser extent by the magnetic field of the sun—the more active the sun, the better it shields the Earth—it is possible to deduce solar activity from a change in the concentration of C14 in the atmosphere.

Continued here.