Fig. 6

Output time series are displayed for SV Gauss coefficients of degrees and orders (2,0), (3,3) and (4,3). Top: Times series of the coefficients, spanning 2000 to 2019.75. The blue dotted line represents the Chaos-6-×9 model. The purple and cyan blue lines, respectively, represent the CE and HS model. Both CE and HS series are presented within a \(2\sigma\) interval. Bottom: time spectra of the corresponding SV Gauss coefficients with the same colour code. In green: the \(k^{-2}\) slope, where k is the frequency, i.e. one over the period