Azimuthal Evolution of Substorm Exapansive Phase Onset

Details Azimuthal Evolution of Substorm Exapansive Phase Onset Azimuthal Evolution of Substorm Exapansive Phase Onset

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm53b..08d&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SM53B-08

Physics

2704 Auroral Phenomena (2407), 2716 Energetic Particles: Precipitating, 2740 Magnetospheric Configuration And Dynamics, 2764 Plasma Sheet, 2788 Magnetic Storms And Substorms (7954)

Scientific paper

Digital all-sky imagers are being deployed across Canada and into Alaska as part of the upcoming NASA THEMIS mission. The fields of view of these instruments come together to form what is effectively a continent- scale high time (3 seconds) and space (~1 km) resolution auroral imager. For the first time we have the capability to follow the spatio-temporal evolution of the aurora at these scales with contiguous coverage across several or more hours of local time. In this paper, we present observations of the late growth phase and early expansive phase aurora from these imagers. Our results, while preliminary, show that the initial brightening occurs along an extended region of the onset arc. For several minutes, brightness in that region increases while its extent along the arc remains more or less unchanged. Furthermore, periodic enhancements in the brightness along the arc suggest wave activity related to the onset mechanism. These results, taken together with recent work with riometers and the lack of dynamics in the aurora poleward of the onset arc during the initial brightening lead us to the following conclusions: (1) in at least these few events the initial brightening of the aurora that constitutes the "onset" occurs on field lines that map to the inner Central Plasma Sheet; (2) this brightening most likely corresponds in time and space to the onset of dispersionless injection; (3) the onset occurs along an azimuthally extended but radially limited region in the magnetosphere corresponding; (4) the onset region grows azimuthally in steps rather than smoothly. We conclude by briefly discussing how different theories of substorm onset are consistent or inconsistent with these observations.

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