Small and meso-scale properties of a substorm onset auroral arc

Details Small and meso-scale properties of a substorm onset auroral arc Small and meso-scale properties of a substorm onset auroral arc

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010jgra..11510209f&link_type=abstract

Journal of Geophysical Research, Volume 115, Issue A10, CiteID A10209

Physics

1

Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Energetic Particles: Precipitating, Magnetospheric Physics: Field-Aligned Currents And Current Systems (2409), Magnetospheric Physics: Substorms, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions (2431)

Scientific paper

We present small and meso-scale properties of a substorm onset arc observed simultaneously by the Reimei and THEMIS satellites together with ground-based observations by the THEMIS GBO system. The optical observations revealed the slow equatorward motion of the growth-phase arc and the development of a much brighter onset arc poleward of it. Both arcs showed the typical particle signature of electrostatic acceleration in an inverted-V structure together with a strong Alfvén wave acceleration signature at the poleward edge of the onset arc. Two THEMIS spacecraft encountered earthward flow bursts around the times the expanding optical aurora reached their magnetic footprints in the ionosphere. The particle and field measurements allowed for the reconstruction of the field-aligned current system and the determination of plasma properties in the auroral source region. Auroral arc properties were extracted from the optical and particle measurements and were used to compare measured values to theoretical predictions of the electrodynamic model for the generation of auroral arcs. Good agreement could be reached for the meso-scale arc properties. A qualitative analysis of the internal structuring of the bright onset arc suggests the operation of the tearing instability which provides a 'rope-like' appearance due to advection of the current in the sheared flow across the arc. We also note that for the observed parameters ionospheric conductivity gradients due to electron precipitation will be unstable to the feedback instability in the ionospheric Alfvén resonator that can drive structuring in luminosity over the range of scales observed.

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