Variations of ¹⁴C around AD 775 and AD 1795 – due to solar activity

Abstract

The motivation for our study is the disputed cause for the strong variation of 14 C around AD 775. Our method is to compare the 14 C variation around AD 775 with other periods of strong variability. Our results are: (a) We see three periods, where 14 C varied over 200 yr in a special way showing a certain pattern of strong secular variation: after a Grand Minimum with strongly increasing 14 C, there is a series of strong short-term drop(s), rise(s), and again drop(s) within 60 yr, ending up to 200 yr after the start of the Grand Minimum. These three periods include the strong rises around BC 671, AD 775, and AD 1795. (b) We show with several solar activity proxies (radioisotopes, sunspots, and aurorae) for the AD 770s and 1790s that such intense rapid 14 C increases can be explained by strong rapid decreases in solar activity and, hence, wind, so that the decrease in solar modulation potential leads to an increase in radioisotope production. (c) The strong rises around AD 775 and 1795 are due to three effects, (i) very strong activity in the previous cycles (i.e. very low 14 C level), (ii) the declining phase of a very strong Schwabe cycle, and (iii) a phase of very weak activity after the strong 14 C rise -very short and/or weak cycle(s) like the suddenly starting Dalton minimum. (d) Furthermore, we can show that the strong change at AD 1795 happened after a pair of two packages of four Schwabe cycles with certain hemispheric leadership (each package consists of two Gnevyshev-Ohl pairs, respectively two Hale-Babcock pairs). We show with several additional arguments that the rise around AD 775 was not that special. We conclude that such large, short-term rises in 14 C (around BC 671, AD 775, and 1795) do not need to be explained by highly unlikely solar super-flares nor other rare events, but by extra-solar cosmic rays modulated due to solar activity variations.

School of Teacher, Nanjing Xiao Zhuang University, Nanjing, 210000, China

“…Therefore, the peaks of 14 C and 10 Be may have different origins, which challenges the SPE origin. Meanwhile, there are also several problems with the interpretation of these 14 C events as SPEs 13,17,18 , including no definite historic records of strong aurorae or sunspots around AD 775 and AD 994 19,20 , the inferred solar fluence (>30 MeV) value is inconsistent with the occurrence probability distribution for SPEs 21,22 , and whether the Sun can produce such large proton events is still debated 23 Meanwhile, gamma-ray photons produced by high-energy explosions can also generate 14 C events, such as supernovae 1, 3 , short gamma-ray bursts 24,25 , and pulsar outbursts 18 . A supernova remnant, named Vela Jr., has an age of t = 2, 000 − 13, 000 yr at a distance less than 400 parsecs 26 , which is a promising candidates to cause the BC 3371 event.…”

New sunspots and aurorae in the historical Chinese text corpus? Comments on uncritical digital search applications

“…Hayakawa et al () then speculated whether there was a series of several large coronal mass ejections within 1 month. There were in fact several likely true aurorae in AD 992 Apr, Oct, and Dec in northern and central Europe, indicating a solar activity level which is not exceptional (see also Neuhäuser & Neuhäuser , Stephenson ). Since it is dubious to interpret this Korean record as an aurora, it is not justified to deduce the Dst index or storm strength from this observation—it does not even indicate a storm.…”

“…… both East Asian and European records suggest that the answer seem to be in the negative … [T]here is little sign for unusual solar activity . The lack of strong aurorae (and sunspot sightings) between AD 774 and 786 led Chapman et al () and Neuhäuser & Neuhäuser () to cast doubt on the flare hypothesis, so that Neuhäuser & Neuhäuser () suggested instead that solar activity dropped markedly for a few years. This suggestion is consistent with weak solar wind and, hence, strong cosmic ray influx and radioisotope production on Earth.…”

Sun, Ocean, Nuclear Bombs, and Fossil Fuels: Radiocarbon Variations and Implications for High-Resolution Dating

“…Suggested mechanisms for the AD 774/775 event include a solar proton event (Melott & Thomas 2012, Usoskin et al 2013, Jull et al 2014, galactic short γ-ray bursts (Hambaryan & Neuhäuser 2013), and solar activity modulated by extrasolar cosmic rays (Neuhäuser & Neuhäuser 2015). The solar proton scenario is mostly accepted, because there is no known supernova remnant corresponding to this event, and historical evidence points to increased auroral activity during this period.…”