Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm42a05p&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM42A-05
Physics
2407 Auroral Ionosphere (2704), 2431 Ionosphere/Magnetosphere Interactions (2736), 2736 Magnetosphere/Ionosphere Interactions, 2752 Mhd Waves And Instabilities
Scientific paper
It is shown that the Atkinson-Sato ionospheric feedback instability stimulates field line resonances in regions of low ionospheric conductivity and high convective drift. The study is based on results of a 2D numerical model in dipole magnetic geometry that includes active ionospheric feedback and high resolution, shear Alfvén dynamics of the magnetospheric response in the context of two-fluid MHD. Strong parallel inhomogeneities of the magnetospheric parameters are included in the numerical model, which permit the simultaneous formation of local Alfvén resonator modes (fast feedback) trapped between the ionosphere and Alfvén speed peak near 1 RE altitude and field line eigenmodes (slow feedback) that stand along the entire field line between northern and southern ionosphere. Although many field line harmonics can be simultaneously generated by the instability, all but the fundamental mode are strongly suppressed by dispersive effects when the meridional length scale of the resonance contracts to the scale of the finite ion Larmor radius in the equatorial magnetosphere. The results provide a new interpretation and causal mechanism for the formation of nearly monochromatic, isolated field line resonances. Diagnostics are presented for the meridional and field-aligned mode structure and dynamic power spectra, which may be compared with measurements made by ionospheric coherent scatter radar and high-altitude magnetospheric satellites. The Fourier spectral analysis determines the relative contribution of fast and slow feedback in the global dynamics of magnetosphere-ionosphere coupling.
Lotko William
Pokhotelov Dimitri
Streltsov Alexander
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