C03_08

Finding smaller solar particle events from tree-ring ¹⁴C time-series data

Uusitalo J^1,2,3, Hackman T^1,3, Oinonen M^1,2

¹University Of Helsinki, Helsinki, Finland, ²Finnish Museum of Natural History, Helsinki, Finland, ³Department of Physics, Helsinki, Finland

Tree-ring ¹⁴C measurements are an excellent way for studying past solar particle events (SPEs) and other anomalous astronomical phenomena. Following the discovery of the AD 774 solar storm by Miyake et al. in 2012, the number of annually resolved tree-ring ¹⁴C measurements have grown significantly. Since then, these annually resolved measurements have led to new discoveries that are similar in magnitude with the Miyake event. However, assuming a power-law distribution for SPEs, one would expect there to be many more less intense particle events causing smaller ¹⁴C spikes, yet only few such candidates have been found. One reason for this could be that it is hard to separate the signal from the statistical noise and short-term natural variability, caused mainly by the 11-year solar cycle, so many smaller events might end up being missed. However, it should be possible to spot new and so far unrecognized events using time-series methods specifically built for this purpose. In this work, we present one such new method that takes into account the respective ¹⁴C baseline, the sudden increase and the full shape of the event. Furthermore, we analyze and discuss how the longer-scale structures in ¹⁴C records, such as steep downslopes or uphill’s affect the general detectability of such small events.