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A thousand years of solar activity are recorded with pinpoint precision

An international team of researchers has reconstructed solar activity with unprecedented precision over the last 1,000 years, using radiocarbon measurements in tree rings.

These results, which revealed solar events unknown to scientists, help scientists better understand the dynamics of the Sun, as well as improve the accuracy of dating organic materials using radiocarbon. The results of the study were recently published in the scientific journal Nature Geoscience.

It is known that what is happening in the center of the sun can only be observed through what is happening on its surface, as sunspots, for example, reveal the degree of solar activity, so the more sunspots on the surface of the sun, this indicates an increase in its central activity.

Although sunspots have been known since ancient times, their detailed documentation was only possible with the invention of the telescope about 400 years ago. Thanks to this, we know today that the number of spots changes in regular cycles of 11 years, and that there are long-term cycles of solar activity that leave their mark on the Earth’s climate.

However, reconstructing how solar activity evolved before the start of the systemic records has remained difficult to this day, so scientists seek to develop innovative methods to study solar activity in the distant past through the effects it leaves on the surface of the Earth.

Solar activity and tree rings

For this purpose, an international research team led by the Swiss Federal Institute of Technology in Zurich (ETH Zurich) according to the institute’s press release, tracked the path of the sun over an 11-year cycle using measurements of the radiocarbon concentration in tree rings.

To reconstruct solar activity over a period of a thousand years with a high time resolution of which the margin of error does not exceed one year, the researchers used, according to a statement by the Swiss Institute, rings of ancient trees found in England and Switzerland whose ages could be determined precisely by calculating the rings. These organic materials contain an important amount of carbon, including a very small part of radiocarbon, one radioactive atom for every thousand billion carbon atoms.

By calculating the number of radiocarbon atoms considering that half of it decays within 5700 years, which is the period known as the half-life, scientists were able to deduce the concentration of radiocarbon present in the atmosphere when the growth ring was formed, as the radiocarbon is mainly produced by cosmic particles, which are The solar magnetic field moves it away from Earth to a greater or lesser extent depending on the strength of the solar activity.

Regular cycles in a thousand years

Using an advanced spectrometer, the researchers reconstructed the entire solar activity over the period between 969 and 1933 AD.

The results obtained allowed them to confirm the regularity of the solar activity cycle every 11 years, and revealed that the disparity in the intensity of activity between apogee and perihelion during one cycle increases with the increase in solar activity and contracts during periods of decline. This new observation will allow scientists to better understand the inner dynamics of the sun, according to the researchers.

Diagram of the changes in solar activity during the last thousand years (Swiss Federal Institute of Technology)

The results of the study also confirmed some exceptional solar events, such as the one that occurred in 993 and called the “Solar Particle event”, during which the sun threw high-energy particles such as protons into space. These particles, if they reach the ground, lead to a slight increase in radiocarbon production.

The authors of the study revealed two other previously unknown events of this type that occurred in 1052 and 1279, indicating that such events, which could interfere with and disrupt electronic circuits on Earth and satellites, occur more frequently than previously thought.

Given the existence of tree ring archives over the past 14,000 years, researchers want in the near future to use their method to determine annual radiocarbon concentrations from the end of the last ice age to today.

The researchers emphasized that the data contained in the new study can be used to more accurately date organic matter using radiocarbon. This data has already been included in the latest release of the internationally recognized radio carbon calibration (IntCal) curves.

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