Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jgra..11312208s&link_type=abstract
Journal of Geophysical Research, Volume 113, Issue A12, CiteID A12208
Physics
12
Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Instruments And Techniques, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions (2431), Magnetospheric Physics: Mhd Waves And Instabilities (2149, 6050, 7836), Magnetospheric Physics: Magnetic Storms And Substorms (7954)
Scientific paper
An analysis of multiscale observations of a substorm auroral breakup are presented which clarify the role of wave dispersion in the formation of elemental (<100 m) auroral structure. At coarse resolution (all-sky white light camera, 1 frame/s), observations fit the established substorm morphology-namely, arc brightening, formation of spatial distortions, and breakup into multiple ``rayed'' structures. At fine-scale resolution (electron multiplying charge-coupled device [EMCCD] camera, 9-degree field of view, prompt emission filter, 30 frames/s), an entirely different type of coherence is observed. The ``arc,'' as identified at lower resolution, is observed to be a dynamic structure composed of bifurcating elemental arcs that propagate outward from the center of an ``arc packet.'' This dynamic process is well captured in time-brightness histories (keograms) along a cut bisecting the structure. The observations are interpreted with respect to theoretical predictions for inertial Alfvén wave dispersion. Specifically, the arc packets are interpreted as the B $\perp$ projection of the parallel electric field within the Alfvén resonant cone. Prebreakup observations are found to be qualitatively consistent with this model. However, some difficulties are encountered for the more active postbreakup period. The article includes a discussion of perspective considerations in interpreting small-scale auroral features; in particular, it is shown that the ``rayed'' appearance of discrete breakup aurora is, in fact, a consequence of sharply kinked sheets viewed obliquely.
Díaz Marco
Mende Stephen
Semeter Joshua
Zettergren M.
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