Overview
- OIST researchers published their study Friday and dated a solar proton event to winter 1200 through spring 1201 using targeted tree‑ring carbon‑14 tests.
- Scientists used Fujiwara no Teika’s diary and other East Asian reports of red auroras and sunspots to focus the search before running ultra‑precise measurements on buried asunaro trees from northern Japan.
- The high‑precision data revealed shorter medieval solar cycles lasting seven to eight years, unlike the roughly 11‑year cycle seen today.
- The team classed the event as a sub‑extreme solar proton burst that can raise radiation levels enough to disrupt satellites, communications, and power systems and to endanger astronauts on deep‑space missions.
- Historical notes and tree‑ring signals did not always match, as with prolonged auroras recorded in 1204 and reports near a cycle minimum, so the team plans more cross‑checks to explain these gaps.