Is the Suess cycle present in historical naked-eye observations of sunspots? |
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| Authors: | LH Ma JM Vaquero |
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| Institution: | 1. National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China;2. Departamento de Física Aplicada, Universidad de Extremadura, Avda. de la Universidad s/n, 10071 Cáceres, Spain |
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| Abstract: | Sunspot numbers are available for the past four centuries. However, solar activity indices with a longer time span are required by geophysicists and solar physicists. The yearly naked-eye sunspot number in the past is reconstructed using observations recorded in historical documents. Some studies from different solar proxies (including radiocarbon and aurora records) show the presence of the so-called Suess cycle (around 200 years) in solar variability. In this work, a modified Lomb–Scargle periodogram analysis is used to investigate the Suess cycle in naked-eye observations of sunspots during 200 BC–1918 AD. The most relevant characteristic of the periodogram is a cycle with a frequency very close to the Suess cycle, though this cycle is not significant statistically. |
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