Observations of the First Harmonic of Saturn Kilometric Radiation During Cassini's Grand Finale

Clear first harmonic emissions of Saturn Kilometric Radiation are discovered during the Cassini Grand Finale orbits. Both ordinary (O) and extraordinary (X) mode fundamental emissions accompanied by X mode harmonics are observed. Analysis shows that the frequency ratio between the fundamental and harmonic emissions is 2.01 +/- 0.08, and the harmonic emissions display weaker intensities than the fundamental, by 30-40 dB for the X-X (fundamental-harmonic) type harmonic and 10-30 dB for the O-X type harmonic. The intensity relations between the two types of harmonics, that is, O-X and X-X show different patterns that we attribute to different conditions of emission at the source. Direction-finding results shows that the fundamental and harmonic emissions are plausibly generated in the same source region. In agreement with previous studies at Earth, the generation of the two types of harmonics can be attributed to the cyclotron maser instability operating with different plasma density and electron energy distributions in the source region.

Automated summary

During the Cassini Grand Finale orbits, first harmonic emissions of Saturn Kilometric Radiation are discovered. Both ordinary and extraordinary mode fundamental emissions accompanied by X mode harmonics are observed. The frequency ratio between the fundamental and harmonic emissions is 2.01 +/- 0.08, and the harmonic emissions have weaker intensities than the fundamental emissions.