Spectral window of the observations. The bottom panel shows the overall structure of the window with daily aliases indicated by the red marker where the ± 1d^-1 peaks reach about 80% of the strongest signal. The top panel displays a closer view revealing the monthly aliases (blue arrows) with a maximum signal at about 93% (dashed horizontal line). The region marked in blue denotes the size of the envelope of the monthly aliases which represents the length of a run in one month (which is about 5 days).