Wave frequency as a function of average spectrogram power. (a) example 1 (category I), (b) example 2 (category II), and (c) example 3 (category III). The grey horizontal dashed lines indicate the lower and upper frequency limits for the observed wave. The magenta color dashed-dotted lines in each panel indicate the upper-hybrid (≈ electron plasma) frequency for each respective time of observation. For each wave mode, the frequency extent (or width), ∆f, is marked in each panel.