Kinetic Simulations of Electron Acceleration by Dispersive Scale Alfven Waves in Jupiter's Magnetosphere

Electron acceleration by dispersive scale Alfven waves at Jupiter is investigated using a Gyrofluid-Kinetic-Electron model. Specifically, the simulations consider the propagation of an Alfven wave perturbation from the center of the Io plasma torus to high-latitude regions that are consistent with recent Juno satellite observations (e.g., Allegrini et al., 2017, https://doi.org/10.1002/2017GL073180; Mauk, et al., 2017a, https://doi.org/10.1038/nature23648; Mauk, et al., 2017b, https://doi.org/10.1002/2016GL072286; Szalay et al., 2018, https://doi.org/10.1029/2018JE005752). As in those observations, the energized electron spectra is broadband in nature and the majority of the energization is under the interaction of inertial Alfven waves at high latitudes. The extent of the energization associated with these waves is proportional to both the magnitude of the wave perturbation and the ratio of the torus to high-latitude density. Plain Language Summary Recent observations of the Juno satellite at Jupiter illustrate that the electron energy spectrum at high latitudes is observed to be broadband-that is, ranging in energies from tens of electron volts to tens and hundreds of kiloelectron volts. At Earth, such electron spectra are associated with electron energization by Alfven waves-which are transverse waves that travel along magnetic field lines in close analogy to waves on a string. In particular, at small scales (e.g., perpendicular scale lengths on the order of the ion orbit around the field line), kinetic effects allow for significant electric field generation that can efficiently accelerate electrons parallel to the field line. At these scales, the waves are known as dispersive Alfven waves. In this work, we, for the first time, present global-scale (entire dipolar field line) kinetic simulations of electron energization at Jupiter. We illustrate that these dispersive Alfven waves, sourced in the Io plasma torus, lead to broadband electron energization close to the Jupiter ionosphere that is qualitatively consistent with the Juno observations. We additionally illustrate how the presence of the Io plasma torus (which is a feature unique to the Jupiter ionosphere) affects the characteristics of this broadband energization.