Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm33a1881j&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM33A-1881
Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2753] Magnetospheric Physics / Numerical Modeling
Scientific paper
The ionospheric feedback is considered to be one of the major mechanisms responsible for a generation of small-scale, intense electric fields and currents in the low-altitude magnetosphere at high latitudes. The main idea of this mechanism is that when magnetic field-aligned currents (FACs) carried by ultra-low-frequency, shear Alfvén waves interact with the ionosphere and change its density/conductivity, these variations in the conductivity feed back on structure and amplitude of the currents. If FAC is carried by shear Alfvén wave standing along the closed magnetic field line between magnetically conjugate locations in the ionosphere, then it can be amplified via ''positive" feedback from the ionosphere, if conditions for the instability are favorable. The favorable conditions include low ionospheric conductivity and large-amplitude perpendicular electric field in the ionosphere. The instability has been studied extensively in many theoretical papers assuming homogeneous plasma density and the electric field in the direction perpendicular to the ambient magnetic field. We present results from a numerical study of the instability inside the ionospheric cavity (and the enhanced electric field), which we expect to see in locations where the large-scale downward FAC interacts with the ionosphere. Our study demonstrates that the cavity 1) localizes the development of the instability in the direction across the ambient magnetic field and 2) changes spatial and temporal parameters of the feedback unstable waves inside the cavity. We investigate how parameters of the feedback unstable waves (e.g., frequency and the perpendicular wavenumber) depend on the size of the cavity, its location (magnetosphere/ionosphere), and the amplitude of the density and the electric field inside the cavity. We discuss relations between these numerical results and observations.
Jia Ning
Streltsov Anatoly V.
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