The effects of plasma beta and anisotropy on compressional poloidal modes in the magnetosphere

Abstract:

We simulate a self-consistent magnetic field that satisfies force balance with a radially localized, axis symmetric and anisotropic plasma pressure. We find that the magnetic field strength decreases near the high plasma pressure region and a magnetic field dip form favorably for larger plasma beta>0.5 for lower anisotropy. Then we perform linear analysis on obtained self-consistent equilibria for eigenmode of second harmonic compressional poloidal modes of sufficiently high azimuthal number. We investigate the effect of anisotropic thermal pressure of ring current on the eigenfrequency of poloidal modes and the characteristics of compressional magnetic field component. We find that the eigenfrequency is reduced at the outer edge of the thermal pressure peak while increases at the inner edge. Compressional magnetic field component can be found primarily within 10 degrees of the equator on both inner and outer edge, with stronger compressional magnetic field component on the outer edge. Larger plasma beta and smaller anisotropy can increase the change of eigenfrequency and the strength of the compressional magnetic field component. The critical condition on plasma beta and pressure anisotropy of Alfvenic ballooning instability due to pressure gradient is also identified.