Physics
Scientific paper
Apr 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993jgr....98.5839r&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 98, no. A4, p. 5839-5853.
Physics
49
Auroras, Earth Magnetosphere, Field Aligned Currents, Magnetohydrodynamic Waves, Resonance Lines, E Region, Earth Ionosphere, F Region, Kelvin-Helmholtz Instability, Vorticity
Scientific paper
MHD field line resonances in the Earth's magnetosphere can have very large velocity shears and field-aligned currents. The velocities associated with the resonances in the E and F regions are often much greater than 1 km/s, with frequencies in the interval of 1-4 mHz. Assuming that these resonances are oscillating at the fundamental mode frequency, and mapping these velocity fields along magnetic field lines to the equatorial plane, shows that the velocity shears in the equatorial plane are of the order of 200 km/s over a radial distance of less than 2000 km. Using a 3D MHD computer simulation code, resonances are shown to evolve through the development of Kelvin-Helmholtz (K-H) instabilities near the equatorial plane. Within this framework, the instability is taking place on dipole magnetic field lines, and the resonances form a standing shear Alfven wave field due to the boundary conditions which must be satisfied at the polar ionospheres. The nonlinear evolution of the K-H instability leads to the propagation of vorticity from the equatorial plane to the polar ionosphere, and the vorticity leads to the dissipation of the resonance within a quarter wave period of the shear Alfven field associated with the resonances.
Frycz P.
Harrold B. G.
Rankin Robert
Samson John C.
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