Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsm41a..01k&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #SM41A-01
Other
7836 Mhd Waves And Instabilities (2149, 2752, 6050)
Scientific paper
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.
Knudsen David J.
Koepke Mark E.
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