Stabilization mechanism of the feedback instability with height-resolved ionosphere and Alfvén resonator models

Abstract

Eigenvalue analysis of feedback instability in a magnetosphere–ionosphere (M–I) coupling model has been extended to study the stabilization mechanism of high-frequency shear Alfvén modes by introducing both an inhomogeneous conductivity profile and an ionospheric Alfvén resonator. Stabilization of high-frequency modes is attributed to change of the effective impedance due to the non-uniform ionospheric conductivity along the field line rather than the collision-induced flow shear, while low-frequency modes relevant to auroral arc excitation remain unstable. An effective impedance model incorporating the inhomogeneous conductivity profile is also developed as an extension of the height-integrated ionosphere model.