Theoretical analysis of interchange instability in Jupiter's inner magnetosphere
Wang Tingyue
Zhang Huasen
Yao Zhonghua
Zhang Binzheng
Feng Enhao
Fu Jingyuan
Abstract：Interchange instability is widespread in both engineering applications and natural environments and is recognized as one of the primary mechanisms for radial mass transport within Jupiter's magnetodisk.In this study,the dispersion relation and the instability criteria of the interchange instability in Jupiter's inner magneto-sphere are derived by considering the parameters of Jupiter's inner magnetosphere(Feng et al.,2025)and applying the ideal magnetohydrodynamic(MHD)theory without assuming the local approximation(i.e.,the perturbation wavelength is much smaller than the characteristic scale length).The mode number and growth rate of the domin-ant mode are obtained through theoretical analysis.Under the current parameters of Jupiter's inner magnetosphere,the interchange mode is found to be stable within the Io plasma torus,whereas unstable regions exist outside the torus.The unstable occurrence regions are given by the theoretical model.It is also found that the centrifugal force and density gradient outside the Io plasma torus jointly drive the interchange instability,while the curvature of the dipole magnetic field and entropy gradient exhibit stabilizing effects on the interchange mode.The growth rate of instability increases with the azimuthal mode number for values below 10,beyond which it saturates.Additionally,the growth rate decreases with increasing radial mode number.Compared to theoretical results from Newcomb(1961)and Ferrière et al.(1999),our theoretical model predicts instability regions almost identical to those of Ferrière's theoretical model,but differs from Newcomb's theoretical model,which suggests that the entire region outside the Io torus is unstable.This difference mainly arises because Newcomb's theoretical model adopts a slab geometry,which neglects the stabilizing effect of the curved magnetic field.It also shows that the growth rate of the dominant interchange mode in our theoretical model is close to that of Ferrière's theoretical model,indicating that the local approximation is suitable for describing the interchange instability of Jupiter's inner magnetosphere.However,the growth rate of the dominant mode in our theoretical model is approximately one order of magnitude higher than that of the numerical result.
Keywords：Jupitermagnetohydrodynamicsinterchange instability
Publication Date：2026-01-31
Online Publishing Date：2025-10-09(First online date of this platform, not the publication date of the document)
Pages：13( 95-107 )