Nonlinear simulation of feedback instability using gyrofluid model of magnetosphere

Abstract

The feedback instability occurs in a coupling system of the magnetosphere and the ionosphere and is a theoretical model explaining spontaneous structure formation of the quiet aurora. In this study, we perform a nonlinear simulation of the feedback instability using a gyrofluid model of the magnetosphere. Using the gyrofluid model makes it possible to properly discuss kinetic effects, such as the finite Larmor radius effect and the electron Landau damping, on nonlinear evolution of the feedback instability. In simulation results, it is observed that nonlinear saturation is reached when linearly unstable modes grow sufficiently. In a nonlinear saturation phase, vorticity in a plane perpendicular to a magnetic field has a complex structure, changing every moment. In addition, an energy flux from the ionosphere and energy dissipation due to the electron Landau damping are balanced in the nonlinear saturation phase. It is newly found that the process where generation of various modes by nonlinear coupling and dissipation of them by the electron Landau damping is indispensable for the nonlinear saturation of the feedback instability.