Black swans or dragon kings? Fingerprints of solar storms help to explore solar physics scenarios and date historical sites
On 1-2 September 1859, telegraph systems across Europe and North America failed to function and started sparking, in some instances causing fires. Most of the northern and southern skies lit up in a brilliant light display, signalling a massive geomagnetic storm had hit the planet – now known as the “Carrington Event” – one of the strongest in documented history. Looking further into the past we see evidence for solar storms that are even more extreme.
New insights in the review help us better understand how extreme solar storms occur – helping society to better prepare – and how they can be used to better understand solar physics and how we can date the archaeological record with far greater accuracy than has been possible before.
These extreme solar storms take place against a background of longer-term fluctuations of solar activity. However, their exact cause and longer-term variations with the better-known sunspot cycles are still mysterious. Current models of physical processes in the Sun are still unable to reproduce the behaviour of our variable star. Understanding extreme solar storms and sunspot cycles may hold the key to better simulating and predicting the activity of the Sun and related space weather.
“We foresee that the annually-resolved radiocarbon measurements will lead to a breakthrough in understanding of the nature of extreme solar eruptive events, whether they belong to Dragon King or Black Swan families” says one of the new study’s authors Professor Ilya Usoskin from the University of Oulu.
Current comparisons between radiocarbon-identified extreme solar storms with historic observations are yet unable to distinguish between two competing solar physics scenarios. In the ‘Black Swan’ scenario, these events are simply larger-scale versions of regular solar storms. But in what’s known as the ‘Dragon King’ scenario, they are physical phenomena distinct from modern observations. As more extreme solar storms are identified from the radiocarbon record, they will help enhance our understanding of solar physics, and plan for future events.
Read also: Solar storms hit more locally than expected - current instrument network too sparse.
“Radiocarbon is a phenomenal tool to understand the past – not just to date archaeological objects but also to understand how the Earth actually works, from the critical processes within our Sun to those hidden deep in our oceans.” says Professor Timothy Heaton from the University of Leeds.
Detecting extreme solar storms is made possible by radiocarbon, a naturally occurring radioactive isotope that is produced in the atmosphere. When these solar storms take place, we see radiocarbon production levels spike far above natural levels. Over the past decade, efforts to measure yearly radiocarbon concentrations within the annual growth rings in ancient trees have confirmed four more extreme solar storms in our past, dating back to AD 993, AD 774, 660 BC, 5259 BC and even 7176 BC – while several other possible events are still being investigated.
Solar storms are not all bad, however. Peaks in radiocarbon levels seen during storms also allow key insights and unique benefits to scientists. The large spikes in radiocarbon are extremely helpful to archaeologists and environmental scientists when radiocarbon dating, allowing highly precise dates for sites that were built around the time of the extreme solar storms. Sometimes, we can even identify the unique storm fingerprints in the radiocarbon levels and date historical sites and events down to the exact year. Examples include dating the Latvian timber lake fortress at Lake Āraiši in Latvia. Read more: Tracing the largest solar storm in modern times from tree rings in Lapland.
Read more on the University of Leeds’ news: Massive solar storms provide new insights for archaeology and environmental science