Detection of Jovian kilometric and hectometric auroral radio harmonics with Juno/Waves in situ measurements

Auroral radio emissions from Earth, Saturn, and Jupiter are now known to all be generated by the cyclotron maser instability near the electron cyclotron fundamental frequency fce. This common generation mechanism results in similar wave properties in terms of beaming and polarization. However, while harmonics at 2 × fce and 3 × fce have been identified in the terrestrial and kronian cases, none of the components of Jupiter's auroral radio spectrum had been associated with harmonics. In this study, we confirm the existence of first harmonic emissions for the Jovian broadband-kilometric (bKOM) and hectometric (HOM) components (200-700 kHz) in 6 cases using in situ data from Juno/Waves observations close to the source. Among these cases, 2 second harmonics were also identified. These harmonics are three orders of magnitude weaker than the associated fundamental and were identified in regions where the fₚe/fce (fₚe the electron plasma frequency) ratio is of the order of 10^-2. This discovery confirms the universality of the CMI and suggests that harmonics in the decametric range could exist.