Solar cyclic activity over the last millennium reconstructed from annual ¹⁴C data

作者：Ilya Usoskin, S. K. Solanki, N. A. Krivova, Bernhard Hofer, G. A. Kovaltsov, Lukas Wacker, Nicolás Brehm, Bernd Kromer · 发表于：University of Oulu Repository (University of Oulu) · 年份：2021 · 被引用次数：88 · 研究领域：Solar and Space Plasma Dynamics、Geomagnetism and Paleomagnetism Studies、Astro and Planetary Science

Aims: The 11-year solar cycle (Schwabe cycle) is the dominant pattern of solar magnetic activity reflecting the oscillatory dynamo mechanism in the Sun’s convection zone. Solar cycles have been directly observed since 1700, while indirect proxy data suggest their existence over a much longer period of time, but generally without resolving individual cycles and their continuity. Here we reconstruct individual solar cycles for the last millennium using recently obtained ¹⁴C data and state-of-the-art models. Methods: Starting with the ¹⁴C production rate determined from the so far most precise measurements of radiocarbon content in tree rings, solar activity was reconstructed in the following three physics-based steps: (1) correction of the ¹⁴C production rate for the changing geomagnetic field; (2) computation of the open solar magnetic flux; and (3) conversion into sunspot numbers outside of grand minima. All known uncertainties, including both measurement and model uncertainties, were straightforwardly accounted for by a Monte-Carlo method. Results: Cyclic solar activity is reconstructed for the period 971–1900 (85 individual cycles) along with its uncertainties. This more than doubles the number of solar cycles known from direct solar observations. We found that the lengths and strengths of well-defined cycles outside grand minima are consistent with those obtained from the direct sunspot observations after 1750. The validity of the Waldmeier rule (cycles with fast-rising ph...