Electron Energization by Inertial Alfvén Waves in Density Depleted Flux Tubes at Jupiter. Issue 5 (24th February 2023)

• Record Type: Journal Article
• Authors: Damiano, P. A.; Delamere, P. A.; Kim, E.‐H.; Johnson, J. R.; Ng, C. S.
• Is Part Of: Geophysical research letters. Volume 50:Issue 5(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-24
• Subjects: inertial Alfvén waves -- broadband electron energization -- kinetic simulations -- Jupiter -- magnetosphere; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL102467
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Juno satellite observations have illustrated substantial examples of broadband electron energization up to 10 5 –10 6 eV levels. In order to explain these observations, we use a hybrid gyrofluid kinetic‐electron model in an untilted dipolar topology to illustrate energization to high levels in weak current conditions by inertial Alfvén waves close to the Jupiter ionosphere for ambient plasma densities and magnetic field perturbations inferred from Juno satellite observations. The key to the high energization is the extremely low densities evident in the observations which necessitates the acceleration of electrons to very high velocities in order to carry the field‐aligned current. Plain Language Summary: Juno satellite observations have illustrated broadband energization that is associated with Alfvén waves which are electromagnetic waves with field vectors perpendicular to the background magnetic field that have common analogy to waves on a string. Specifically, the energization is associated with inertial Alfvén waves (IAWs) which are the limit of Alfvén waves when the perpendicular scale length of the wave is on the order of the electron skin depth whereby the waves can support significant parallel electric fields to accelerate electrons that lead to aurora. This energization is described as broadband since the range of energies extends from tens of eV to MeV levels. At Earth, IAWs are associated with electron energization to keV levels and so it has been a puzzle to explain the very high electron energies evident at Jupiter. In this work, we illustrate that for observed parameters, IAWs can energize electrons to much higher energies at Jupiter than in the terrestrial analogue. This is because the very low plasma densities evident in the high latitude Jupiter magnetosphere necessitates the IAW to generate a sufficiently large parallel electric field to accelerate a limited supply of electrons to correspondingly higher energies in order to carry the parallel current. Key Points: In Jupiter's density depleted flux tubes, inertial Alfvén waves can accelerate electrons to very high energies for modest parallel currents Due to the high energies, this energization can be manifest in primarily unidirectional electron beams It is expected that inertial Alfvén waves can explain observed electron energizations to 10 5 −10 6 eV levels