Least-squares spectral analysis spectrograms of Saturn radio emissions from 2004 to 2018. The color-coded spectrograms show the modulation power as a function of universal time in the horizontal axis and the modulation rate in the vertical axis. Panels a–d respectively show the results for the northern hemisphere SKR, the southern hemisphere SKR, the 5 kHz NB emissions (in both hemispheres), and the 20 kHz NB emissions (in both hemispheres). Panel e shows the Cassini latitudes during its Saturn orbital journey. The green and orange lines are the northern and southern SKR periods as derived by Ye et al. (2018). The blue and pink lines are the northern and southern PPO periods as derived by Provan et al. (2013, 2016, 2019).