Relative energy of each intrinsic mode function as a function of the period (in days) calculated for (a) S ₄, (b) Equatorial Electrojet, (c) AL index, (d) AE index, (e) IMF-Bz, (f) IEF-Ex and (g) ε parameter. Red curves are for 1–15 March 2011, while green curves for the period 16–31 March 2011. Similarly to Figure 3, shaded colors (yellow, red, green) indicate three different intervals of periods: low periods (yellow), middle periods (red) and high periods (green). Black dashed lines indicate 12 h, 1 day and 2 days, respectively, while the red-dashed line is in correspondence with 18 h.