Overview of the I0 flyby. The spectrograms show the perpendicular power density, polarization, ellipticity, and polar angle. The white lines show the cyclotron frequency of S⁺ (dotted), SO⁺ (dashed) ${\text{SO}}_2{}^{+}$ (solid), and ${\text{SO}}_3{}^{+}$ (dash-dotted) and the magenta line O⁺. The orange box shows an interval of ${\text{SO}}_2{}^{+}$ wave activity, the purple box mirror modes in Io’s wake region, and the red box a period of ${\text{SO}}_3{}^{+}$ wave activity. Details about the orange, red, and purple boxes are given in Fig. 3.