Confidence limits for the (a) IMF c₄, (b) instantaneous amplitude, and (c) instantaneous frequency. The blue and the black lines are the means and their 3σ confidence limits, respectively. The red line is the average of the 3σ lower limit of the instantaneous amplitude. This red line is the threshold for distinguishing between the high- and low-amplitude durations of the intermittent oscillations. In (a) and (b), the units on the y axis are 10³ counts s⁻¹.