5 Long-Term Variability

Systematic variations from cycle-to-cycle and over many cycles could be significant discriminators in models of the solar cycle and might aid in predicting future cycles. Several key aspects of long-term variability have been noted: a 70-year period of extremely low activity from 1645 to 1715 (the Maunder Minimum); a gradual increase in cycle amplitudes since the Maunder Minimum (a Secular Trend); an 80 – 90 year variation in cycle amplitudes (the Gleissberg Cycle); a two-cycle variation with odd numbered cycles higher than the preceding even numbered cycles (the Gnevyshev–Ohl Effect); a 205-year cycle in radio isotope proxies (the Suess Cycle); and other long term variations seen in radio isotopes. These aspects of long-term variability are examined in this section.

 5.1 The Maunder Minimum
 5.2 The secular trend
 5.3 The Gleissberg Cycle
 5.4 Gnevyshev–Ohl Rule (Even–Odd Effect)
 5.5 Long-term variations from radioisotope studies
 5.6 The Suess cycle

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