SA034-01
Nonlinear Magnetosphere-Ionosphere Interactions in the Auroral and Subauroral Geospace
Nonlinear Magnetosphere-Ionosphere Interactions in the Auroral and Subauroral Geospace
Tuesday, 15 December 2020: 19:00
Virtual
Abstract:
Intense ULF waves and the ionospheric density disturbances frequently observed in the auroral and subauroral geospace can be produced by strongly nonlinear interactions between the magnetospheric field-aligned currents and the ionospheric plasma. The essence of these interactions is the fact that the currents change the ionospheric conductivity and changes in the conductivity “feedback” on structure and amplitude of the currents. Under certain conditions these currents can be trapped in the magnetospheric resonator and amplified by the positive feedback interactions with the ionosphere. The necessary condition for this amplification is the electric field in the ionosphere. The goal of our presentation is to demonstrate that this mechanism works in the auroral and subauroral zones and produces waves and currents with similar characteristics in both regions.
We show with simulations of a two-fluid MHD model, that the active, nonlinear ionospheric feedback can lead to a generation of a system of small-scale, intense field-aligned currents with a significant difference in size and amplitude between the upward and downward currents. In both hemispheres, the downward currents (where the electrons are flowing from the ionosphere) become narrower and more intense than the adjacent upward currents. In the auroral zone such configuration of currents explains so-called “black” auroral arcs, appearing as narrow, dark strips embedded in the broad luminous background. In the subauroral zone the ionospheric feedback mechanism reproduces in quantitative details structure and amplitude of ULF waves observed at different altitudes near the plasmapause by the Van Allen Probes, CREES, and DMSP satellites. Specifically, the nonlinear stage of the ionospheric feedback instability explains a “spiky” character of the electric field detected by the DMSP above the subauroral ionosphere. The structure of these small-scale fields is like the structure of the fields observed above the black aurora.
We show with simulations of a two-fluid MHD model, that the active, nonlinear ionospheric feedback can lead to a generation of a system of small-scale, intense field-aligned currents with a significant difference in size and amplitude between the upward and downward currents. In both hemispheres, the downward currents (where the electrons are flowing from the ionosphere) become narrower and more intense than the adjacent upward currents. In the auroral zone such configuration of currents explains so-called “black” auroral arcs, appearing as narrow, dark strips embedded in the broad luminous background. In the subauroral zone the ionospheric feedback mechanism reproduces in quantitative details structure and amplitude of ULF waves observed at different altitudes near the plasmapause by the Van Allen Probes, CREES, and DMSP satellites. Specifically, the nonlinear stage of the ionospheric feedback instability explains a “spiky” character of the electric field detected by the DMSP above the subauroral ionosphere. The structure of these small-scale fields is like the structure of the fields observed above the black aurora.