Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm22c..02s&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM22C-02
Physics
2704 Auroral Phenomena (2407), 2736 Magnetosphere/Ionosphere Interactions, 2752 Mhd Waves And Instabilities, 3230 Numerical Solutions
Scientific paper
Results from a numerical investigation of a three-dimensional dynamics of intense electric fields and currents frequently observed by polar-orbiting satellites above the auroral ionosphere are presented. A causal explanation of these electromagnetic structures is given in terms of small-scale Alfvén waves generated below the auroral acceleration region in a process of ULF magnetosphere-ionosphere interaction mediated by large-scale Alfvén waves. These waves curry the electromagnetic power from the nightside plasmasheet boundary layer or equatorial magnetosphere where various energy sources reside to the ionosphere. The field-aligned current in the wave causes a microinstability at about 1 RE altitude. The instability leads to the formation of a collisionless resistive layer (auroral auroral acceleration region), which serves as an effective upper boundary for the resonator cavity (the lower boundary is formed by the ionospheric E-layer). Inside the cavity small-scale, intense electromagnetic structures can be formed by the ionospheric feedback instability when the ionospheric conductivity is low. This study focuses on a three-dimensional aspects of this process. In particular, we consider effects of the finite Hall conductivity and strong convective nonlinearities of a three-dimensional solution on structure and dynamics of the resonant Alfvén waves. Dependency of these nonlinear effects on parameters of the waves (frequency, amplitude, transverse wavelength) and ionospheric plasma is investigated. Relevance of the numerical results to selected auroral observations and recent theoretical studies is discussed.
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