Long-Term Modulation of Solar Cycles

Solar activity has a cyclic nature with the ~11-year Schwabe cycle dominating its variability on interannual timescale. However, solar cycles are significantly modulated in length, shape and magnitude, from near-spotless grand minima to very active maxima. The ~400-year-long direct sunspot-number series is inhomogeneous quality too short study robust parameters of long-term variability. cosmogenic-isotope proxy extends timescale twelve millennia provides crucial observational constraints dynamo modulation. Here, we present brief up-to-date overview at centennial--millennial timescales. occurrence maxima discussed as well existing quasi-periodicities such centennial Gleissberg, 210-year Suess/de Vries 2400-year Hallstatt cycles. It shown that contain an important random component have no clock-like phase locking implying lack memory. A yet comprehensive review theoretical perspectives explain observed features framework models presented, including nonlinearity stochastic fluctuations dynamo. We keep gaining knowledge processes driving new data acquainted developed.