Identification of substorm onset location and pre-onset sequence using Reimei, THEMIS GBO, PFISR and Geotail (Invited)

Details Identification of substorm onset location and pre-onset sequence using Reimei, THEMIS GBO, PFISR and Geotail (Invited) Identification of substorm onset location and pre-onset sequence using Reimei, THEMIS GBO, PFISR and Geotail (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm54b..02z&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM54B-02

Physics

[2407] Ionosphere / Auroral Ionosphere, [2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2455] Ionosphere / Particle Precipitation, [2790] Magnetospheric Physics / Substorms

Scientific paper

One of the most important questions puzzling the substorm community is the location of the breakup arc relative to general auroral morphology, ionospheric convection, and particle precipitation, which are ionospheric signatures of dynamic processes in the magnetosphere. We present a state-of-the-art ground and space-based imaging study of a substorm that occurred on 12 October 2007. The auroral breakup was observed simultaneously by the Reimei satellite, THEMIS all-sky imager and PFISR radar. The magnetic field footprint of the Geotail spacecraft was also near the ionospheric location of the substorm onset. We report unique spaceborne high-spatial and temporal resolution images of a portion of a breakup arc and of a wave-like auroral enhancement captured by cameras onboard Reimei. This substorm was isolated and occurred in a thin, only ~1.5° wide, auroral oval. Observations from PFISR and Geotail suggest a sudden plasma sheet thinning initiated ~10 min prior to the onset. Wave-like auroral enhancements were observed twice along the most equatorward preexisting auroral arc about 3 min and 1 min before the auroral expansion. This most equatorward wavy arc did not initiate the auroral spatial expansion, but remained almost stable until being engulfed after onset by auroral equatorward expansion from slightly higher latitudes. The wave-like auroral enhancement was associated with three fine inverted-V structures and fully embedded within energetic ion precipitation and westward flows. Following this enhancement, an arc formed at higher latitude just adjacent to the PSBL, and was likely a poleward boundary intensification (PBI). This arc then extended southwestward and initiated the spatial expansion. The breakup arc, i.e., the arc initiated the spatial expansion, was located poleward of and separated from the wave-like auroral enhancement. Assuming longitudinal homogeneity of proton precipitation over one degree in geographic longitude, this breakup arc was located within a region without ion precipitation just poleward of the energetic ion precipitation, and near the center of the Harang reversal. We discuss the possible existence of a low-entropy flow channel associated with the arc adjacent to the PSBL, which might be associated with instability in the near-Earth plasma sheet responsible for the auroral breakup.

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