Power spectrum as a function of frequency for 29 years (black line); ratio of the power spectrum to that of the fitted mode as a function of frequency (orange line) showing the remaining modes not included in the model. The remaining l = 4 modes are located on the left side of the l = 0 − 2 pair, while the remaining l = 5 modes with a lower amplitude are located on the right side of the l = 0 − 2 pair. (see also Fig. 17).