Flux Tube Properties and Interchange Instabilities in Jupiter's Middle Magnetosphere

Wang, Jian‐Zhao and Bagenal, Fran and Wing, Simon and Delamere, Peter A. and Ma, Xuanye and Wilson, Robert J. and Ebert, Robert W. and Valek, Philip W. and Allegrini, Frederic and Dols, Vincent and Ray, Licia C. and Spitler, Chynna and Clark, George and Mauk, Barry H. (2025) Flux Tube Properties and Interchange Instabilities in Jupiter's Middle Magnetosphere. Geophysical Research Letters, 52 (21): e2025GL117. ISSN 0094-8276

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Abstract

Plain Language Summary: Jupiter's magnetosphere is filled with plasma primarily sourced from Io's escaping atmosphere. Due to the planet's rapid rotation and the high loading rate of plasma from Io, the structure and dynamics of the magnetosphere are strongly influenced by centrifugal forces. The plasma is confined within flux tubes, which are bundles of magnetic field lines that guide and contain plasma through space. Radial plasma transport is mainly facilitated by flux tube interchange, a process in which two neighboring flux tubes exchange positions. The stability of the magnetosphere against such interchange motion depends on the radial distributions of two competing properties: the total plasma content and the internal energy density (or entropy) of each flux tube. In Jupiter's middle magnetosphere, flux tube content decreases with increasing radial distance, driving outward plasma transport and destabilizing the system. In contrast, flux tube entropy increases with distance, exerting a net inward force on the plasma and promoting stability. When considered together, the entropy term typically dominates on average, resulting in a system that is generally stable against interchange motion.