Solar activity around AD 775 from aurorae and radiocarbon

Abstract

A large variation in 14 C around AD 775 has been considered to be caused by one or more solar super-flares within one year. We critically review all known aurora reports from Europe as well as the Near, Middle, and Far East from AD 731 to 825 and find 39 likely true aurorae plus four more potential aurorae and 24 other reports about halos, meteors, thunderstorms etc., which were previously misinterpreted as aurorae or misdated; we assign probabilities for all events according to five aurora criteria. We find very likely true aurorae in AD 743, 745, 762, 765, 772, 773, 793, 796, 807, and 817. There were two aurorae in the early 770s observed near Amida (now Diyarbakir in Turkey near the Turkish-Syrian border), which were not only red, but also green-yellow - being at a relatively low geo-magnetic latidude, they indicate a relatively strong solar storm. However, it cannot be argued that those aurorae (geo-magnetical latitude 43 to 50 deg, considering five different reconstructions of the geo-magnetic pole) could be connected to one or more solar super-flares causing the 14 C increase around AD 775: There are several reports about low- to mid-latitude aurorae at 32 to 44 deg geo-magnetical latitude in China and Iraq; some of them were likely observed (quasi-)simultaneously in two of three areas (Europe, Byzantium/Arabia, East Asia), one lasted several nights, and some indicate a particulary strong geo-magnetic storm (red colour and dynamics), namely in AD 745, 762, 793, 807, and 817 - always without 14 C peaks. We use 39 likely true aurorae as well as historic reports about sunspots together with the radiocarbon content from tree rings to reconstruct solar activity: From about AD 733 to 823, we see at least nine Schwabe cycles ...

24 pages with 1 table and 2 figures, paper to appear in Astronomical Notes 24 Apr 2015

References in corpus (7)

• Historical Sunspot Observations: A Review
• Causes of an AD 774-775 14C increase
• A solar cycle lost in 1793--1800: Early sunspot observations resolve the old mystery
• The butterfly diagram in the 18th century
• A solar super-flare as cause for the 14C variation in AD 774/5 ?
• The Chinese comet observation in AD 773 January
• A transient event in AD 775 reported by al-Tabari: A bolide - not a nova, supernova, or kilonova

Cited by in corpus (9)

• Risks for life on habitable planets from superflares of their host stars
• The earliest drawings of datable auroras and a two-tail comet from the Syriac Chronicle of Zūqnīn
• Historical Auroras in the 990s: Evidence for Great Magnetic Storms
• Do the Chinese Astronomical Records Dated AD 776 January 12/13 Describe an Auroral Display or a Lunar Halo? A Critical Re-examination
• Records of sunspot and aurora activity during 581-959 CE in Chinese official histories in the periods of Suí, Táng, and the Five Dynasties and Ten Kingdoms
• Unusual rainbows as auroral candidates: another point of view
• Orbit determination just from historical observations? Test case: The comet of AD 760 is identified as 1P/Halley
• The Celestial Sign in the Anglo-Saxon Chronicle in the 770s: Insights on Contemporary Solar Activity
• Portuguese eyewitness accounts of the great space weather event of 1582