Abstract
Quiet auroral arcs formation has been investigated theoretically and numerically in a self‐consistent dynamic way. By using a three‐dimensional magneto‐hydro‐dynamics simulation of a dipole magnetosphere‐ionosphere coupling system, it is shown that multiple longitudinally striated structures of the ionospheric plasma density and the field‐aligned current are formed, resulting from nonlinear feedback instability. The areas where these structures appear are consistent with the prediction by the integrated feedback theory that includes the effects of the spatially non‐uniform electric field and non‐uniform plasma density. Effects of the difference of the field line lengths between the ionosphere and the magnetospheric equator over the auroral latitudes are also discussed on the feedback instability.
Highlights
Integrated these studies and concluded that a quiet auroral arc is formed by a feedback instability that arises spontaneously between the inductive magnetosphere and the dissipative ionosphere
Lysak [1986, 1988, 1991] showed that the gradient in the Alfvén speed profile has an influence on the propagation of the Alfvén waves and that a locally resonant feedback instability is produced by the inhomogeneity of the Alfvén speed, which was not considered by Sato [1978]
[28] We study the quiet auroral arc formation by the feedback instability in such a realistic system as has a dipole geomagnetic field by means of a three‐dimensional MHD
Summary
[2] Formation of quiet auroral arcs was investigated theoretically based on different models of the magnetosphere‐. The region 1 current system between the magnetosphere and the ionosphere [Iijima and Potemra, 1976; Sato and Iijima, 1979] is expected to be formed by the electric charges (electric potential) which are induced by the magnetospheric plasma convection flow In such a global convection‐current system, a feedback instability can be produced as a result of the resonance of the ionospheric electrostatic wave with the magnetospheric Alfvén wave. In the work of Watanabe and Sato [1988], by using the same code, it is shown that longitudinally striated structures of the field‐aligned current and the ionospheric plasma density were generated by the feedback instability.
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