Solar data (upper panels) and STFT calculations (lower panels). Left: sunspot number data from 1818 to the present and STFT. The Gleissberg cycle is shown in the bottom of the figure; above this is the Schwabe (11 yr) cycle, and above this, its half and one-third harmonic cycles are also found. Additionally, and mixed with the one-third of the Schwabe cycle, another changing variation of 3–4 yr is continuously present in the data. Middle: STFT of a shorter record of sunspot number (1947 to present) and right: the same for the Ca ii K flux of the Sun between 1976–2015. The variability of 3−4 yr is also well detected in the two shorter datasets.
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