Secular variation of Δ14C during the medieval solar maximum: A progress report

Abstract

The Earth is within the Contemporaneous Solar Maximum (CSM), analogous to the Medieval Solar Maximum (MSM). If this analogy is valid, solar activity will continue to increase well into the 21st century. We have completed 75 single-ring and 10 double-ring measurements from AD 1065 to AD 1150 to obtain information about solar activity during this postulated analog to solar activity during the MSM. Δ14C decreases steadily during the period AD 1065 to AD 1150 but with cyclical oscillations around the decreasing trend. These oscillations can be successfully modeled by four cycles. These four frequencies are 1/52 yr-1, 1/22 yr-1, 1/11 yr-1, and 1/5.5 yr, i.e., the 4th harmonic of the Suess cycle, the Hale and Schwabe cycles and the 2nd harmonic of the Schwabe cycle.