Fig. 4: Illustration of the search for SEP events.
From: Tracing ancient solar cycles with tree rings and radiocarbon in the first millennium BCE
a Detrended Δ14C record (blue) with 2-σ uncertainties. b Changes between the 3-yr average before and after the event. The 3-σ range of about 4.5 ‰ is particularly emphasized for positive values, since this threshold value is exceeded only in 663 BCE during the first millennium BCE for two consecutive years.
