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Evidence for Alfvén wave dispersion identified in high‐resolution auroral imagery
Author(s) -
Semeter J.,
Blixt E. M.
Publication year - 2006
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl026274
Subject(s) - physics , alfvén wave , amplitude , envelope (radar) , computational physics , wave packet , dispersion (optics) , plasma , phase (matter) , geophysics , plane wave , plane (geometry) , phase velocity , dispersion relation , magnetohydrodynamics , optics , geometry , atomic physics , quantum mechanics , telecommunications , radar , mathematics , computer science
The two‐fluid theory of inertial Alfvén waves predicts that wave energy spreads azimuthally across the background magnetic field, and that phase‐ and group‐ velocities in the B ⊥ plane are oppositely directed. These features have been observed in laboratory plasmas but have yet to be identified in the natural auroral plasma. Using narrow‐field video recorded at 50 images/s, we have identified a time dependent morphology that is consistent with these predictions. The aurora at issue is best modeled as an expanding amplitude envelope within which periodic auroral structure evolves. If luminous structure is interpreted as a projection of the parallel wave electric field into the B ⊥ plane, then successive images reveal the cross‐sectional structure of the resonant cone at increasing distance from the wave source. Phase‐ and group‐velocities extracted under this interpretation were found to be consistent with theoretical predictions for a dispersing inertial Alfvén wave packet.