15:45 〜 16:00
[PEM10-12] Nonlinear simulation of the feedback instability in a non-local model of the magnetosphere-ionosphere coupling
キーワード：オーロラ、磁気流体力学
Auroral formation in the magnetosphere-ionosphere (M-I) coupling system has long been investigated in terms of observations and theories. Previous of simulation studies of auroral formation through the feedback instability have focused on fine structure formation under the local approximation or global characteristics of the auroral arcs structure formation. The nonlinear simulation under the local approximation has revealed deformation of auroral arc structures due to the Kelvin-Helmholtz like secondary instability, where fine vortex structures are formed spontaneously. However, the fine structure formation has never been discussed in the case of global simulations because of the lack of spatial resolution.
We have performed nonlinear simulations of the feedback instability in the dipole field configuration by means of the dipole flux coordinates adapted to the spherical boundary in order to investigate the auroral fine structure formation in the non-local M-I coupling system. In the simulation results, we have observed that the feedback instability leads to spontaneous growth of the ionospheric density, field-aligned current density, and the electric field perturbations elongated in the east-west direction. In addition, we have found that the longitudinally elongated arc-like structures of these evolved perturbations are distorted due to nonlinear growth of high wave number components in the east-west direction through the secondary instability. Growth rate of the secondary instability agrees well with that ofthe Kelvin-Helmholtz instability induced by the perturbed E×B flow sheer. Moreover, the sense of rotation and the scale of these fine vortex structures are consistent with observation of the auroral curl structures.
We have performed nonlinear simulations of the feedback instability in the dipole field configuration by means of the dipole flux coordinates adapted to the spherical boundary in order to investigate the auroral fine structure formation in the non-local M-I coupling system. In the simulation results, we have observed that the feedback instability leads to spontaneous growth of the ionospheric density, field-aligned current density, and the electric field perturbations elongated in the east-west direction. In addition, we have found that the longitudinally elongated arc-like structures of these evolved perturbations are distorted due to nonlinear growth of high wave number components in the east-west direction through the secondary instability. Growth rate of the secondary instability agrees well with that ofthe Kelvin-Helmholtz instability induced by the perturbed E×B flow sheer. Moreover, the sense of rotation and the scale of these fine vortex structures are consistent with observation of the auroral curl structures.