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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A11, 1363, doi:10.1029/2001JA000134, 2002

Harmonic structure of field line eigenmodes generated by ionospheric feedback instability

Dimitri Pokhotelov

Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA


William Lotko

Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA


Anatoly V. Streltsov

Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA


Abstract

Ionospheric feedback instability generates field line eigenmodes under favorable conditions of low ionospheric conductivity and high electric convection. A numerical study has been performed using a two-dimensional model in dipole magnetic field geometry that includes active ionospheric feedback and shear Alfvén wave dynamics of the magnetospheric response. Strong parallel inhomogeneities of the magnetospheric parameters included in the numerical model permit the simultaneous development of local ionospheric resonator modes (fast feedback) trapped between the ionosphere and Alfvén speed maximum above it and field line eigenmodes (slow feedback) that stand along the entire magnetic field line between two conjugate ionospheres. Fourier analysis of the numerical solution has been used to investigate the relative contribution of fast and slow feedback in the global dynamics of magnetosphere–ionosphere coupling. While many harmonics of the global magnetospheric resonator can be simultaneously generated by the ionospheric feedback instability, all modes above the fundamental eigenmode are strongly suppressed by Alfvén wave dispersion. The numerical results suggest that ionospheric feedback is a generating mechanism for the formation of narrow field line resonances.

Published 14 November 2002.

Index Terms: 2704 Magnetospheric Physics: Auroral phenomena (2407); 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2752 Magnetospheric Physics: MHD waves and instabilities; 2753 Magnetospheric Physics: Numerical modeling.

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Citation: Pokhotelov, D., W. Lotko, and A. V. Streltsov (2002), Harmonic structure of field line eigenmodes generated by ionospheric feedback instability, J. Geophys. Res., 107(A11), 1363, doi:10.1029/2001JA000134.