Electron inertia effects on Alfvénic turbulence in the feedback magnetosphere-ionosphere coupling

Feedback instability is one of the possible mechanisms which describes quiet auroral arcs formation and their dynamics, where resonant interactions between the Alfvén waves in the magnetosphere and the plasma density waves in the ionosphere play an essential role. In previous studies, it was shown that initial linear growth of feedback instability resulted in nonlinear turbulence phase after the secondary growth of the Kelvin-Helmholtz instability. The energy equipartition was also confirmed in the turbulent phase, that is, a typical feature of the Alfvénic turbulence. In this study, we have added the electron inertia effect to the magnetospheric reduced-MHD model so that the electric field along magnetic field line (W parallel) can be generated even with no resistivity.

In our present simulation, we have found that the initial growth rate is reduced by the electron inertia effect, which was also confirmed by the linear dispersion relation. Depression of the feedback instability is observed not only in the initial growth phase, but also in the turbulent phase. Through the nonlinear simulation, furthermore, we found local production of E parallel as well as J parallel due to the electron inertia effect, leading to enhancement of the fluctuation spectrum in the high wavenumber region as well. The attached figure shows E parallel distribution when the secondary instability grows (where Z=0 and Z=1000 correspond the ionosphere and the magnetospheric equator, respectively). The obtained results provide us a unique theoretical model to discuss the auroral arc growth and the electron acceleration simultaneously.