Characteristics of compressional eigenmodes in the inner-magnetosphere

Abstract:

We study the transport characteristics of MHD compressional waves incident on the plasmasphere from the outer magnetopshere with accompanying resonant absorption into transverse mode via mode conversion and the excitation behavior of the eigenmodes where the Alfven speed has a typical nonmonotonic profile in radial direction. By using invariant imbedding method (IIM) that allows numerically exact calculations, we present numerically the exact eigenmode structures excited in the magnetosphere and show that the virtual resonant modes are mainly excited ones whose eigenfrequencies and band widths have a sensitive dependence on the Alfven speed profile. The behavior of eigenmode structures related to the deformation of the profile is clearly shown, which can be used for obtaining the time series of the trapped modes in a certain radial location by the inverse Fourier transform and can be compared with the observations. We show how the time histories at each location appear for some different Alfven speed profiles. We also present a new feature of the mode excited in a certain frequency regime, which is similar to discrete Alfven eigenmode or global Alfven eigenmode.