Whistler-Mode Waves and Associated Electron Distributions in Jupiter’s Middle and Outer Magnetosphere

Whistler-mode waves are a wave mode in plasma occurring near and below the electron cyclotron frequency. They are commonly observed in planetary magnetospheres and play a crucial role in accelerating and precipitating magnetospheric electrons. Using Juno’s observations, we investigate these waves in Jupiter’s magnetosphere, focusing on the region between 20 and 80 Jupiter radii on the post-midnight-to-dawn side. Observations from the Waves instrument show that these waves primarily occur in the lobes, where the magnetic field is strong and plasma density is low, rather than in the central magnetodisk, where the field is weaker and plasma is denser. Simultaneous electron measurements from JADE-E, combined with dispersion relation analysis, indicate that these waves are likely driven by a mono-directional electron population between ∼0.1 and 10 keV propagating anti-Jupiter-ward. Further controlled studies show that a local flux minimum at ∼0.3 keV in the electron energy spectrum, commonly observed during whistler-mode waves, is critical for wave growth. Based on their direction of motion, we suggest that these mono-directional electrons and the whistler-mode waves they generate are related to magnetosphere-ionosphere coupling. Our findings offer new insights into the interplay between whistler-mode waves and electrons in Jupiter’s magnetosphere.