HR: 08:00h
AN: SM41A-01    [Abstracts]
TI: Stationary Inertial Alfvén Waves and Auroral Morphology
AU: * Knudsen, D J
EM: knudsen@phys.ucalgary.ca
AF: University of Calgary, Department of Physics and Astronomy, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
AU: Koepke, M E
EM: mkoepke@wvu.edu
AF: West Virginia University, Physics Department, PO Box 6515, Morgantown, WV 26506-6315, United States
AB: Auroral arcs are sometimes observed to oscillate at frequencies related to the field-line resonance frequency of shear-mode dispersive Alfvén waves, indicating that these waves are responsible for the spatial and temporal behavior of such arcs. However, resonant frequencies are not apparent in most arcs. This may be due in part to experimental limitations, yet some arcs are observed to last much longer than the FLR period, indicating that some other mechanism is at play. This talk shows how Alfvén waves can be created in a way which is analogous to time-stationary water waves downstream from a stationary perturbation in a river. Stationary Alfvén waves are predicted by a two-fluid theory of low-beta current sheets with a normal component of plasma flow. The waves manifest as spatially periodic oscillations in field-aligned electron velocity, which can become much larger than the Alfvén speed, and in plasma density, which can vary by tens of percent. Both of these are observed properties of auroral arcs, as is the natural scale of the oscillations direction perpendicular to B: tens of electron inertial lengths, or several to tens of kilometers above the auroral ionosphere. Stationary Alfvén waves offer a mechanism to produce the key features found in FLR arcs, but within a quasi-static structure that can last indefinitely with no time variation.
DE: 7836 MHD waves and instabilities (2149, 2752, 6050)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly