A Note on Solar Cycle Length During the Medieval Climate Anomaly
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The growing interest in the Medieval Climate Anomaly (MCA) and its possible link to anomalous solar activity has prompted new reconstructions of solar activity based on cosmogenic radionuclides. However, these proxies do not sufficiently constrain the total solar irradiance (TSI) range and are often defined at low temporal resolution, inadequate to infer the solar-cycle length (SCL). We have reconstructed the SCL (average duration of 10.72±0.20 years) during the MCA using observations of naked-eye sunspot and aurora sightings. The solar activity was probably not exceptionally intense, supporting the view that internal variability of the coupled ocean–atmosphere system was the main driver of the MCA.
KeywordsSolar activity Medieval Climate Anomaly Solar cycle length Climatic system variability
The authors are grateful to I.G. Usoskin, L.E.A. Vieira, and H. Miyahara for their comments and data. Support from the Junta de Extremadura and Ministerio de Ciencia e Innovación of the Spanish Government (AYA2008-04864/AYA and AYA2011-25945) is gratefully acknowledged. We acknowledge the support from the Portuguese Science Foundation (FCT) through the project MEDIATIC (PTDC/AAC-CLI/103361/2008).
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