Time series of solar activity (Φ) based on ¹⁰Be measured in polar ice cores for the past 9300 years. On the upper plot are the original data, while on the lower plot, the Fourier-filtered data are shown. Fluctuations at periods for t ≤ 380   yr (full line) were suppressed by a Fourier filter. To simulate geomagnetic field-strength variation, a random signal of similar amplitude to the original signal and a period of about 760 years were added (same approach as in Paper I) (dotted line).