A Note on Solar Cycle Length during the Medieval Climate Anomaly

TL;DR

This paper reconstructs the solar cycle length during the Medieval Climate Anomaly using historical observations, suggesting solar activity was not exceptionally intense and internal climate variability was likely the main driver.

Contribution

It introduces a novel reconstruction of solar cycle length during the MCA based on naked-eye sunspot and aurora sightings, addressing limitations of proxy data.

Findings

Solar cycle length during MCA was approximately 10.72 years.

Solar activity was likely not exceptionally intense during MCA.

Internal climate variability was probably the main driver of MCA.

Abstract

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. These proxies however 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 \pm 0.20 years) during the MCA using observations of naked-eye sunspot and aurora sightings. Thus, solar activity was most probably not exceptionally intense, supporting the view that internal variability of the coupled ocean-atmosphere system was the main driver of MCA.