Possible signatures of an auroral arc's root in the central plasma sheet

Details Possible signatures of an auroral arc's root in the central plasma sheet Possible signatures of an auroral arc's root in the central plasma sheet

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm33a2127l&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM33A-2127

Physics

[2704] Magnetospheric Physics / Auroral Phenomena, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2744] Magnetospheric Physics / Magnetotail

Scientific paper

While the auroral arc is among the most commonly visible and extensively studied phenomenon in space science, one fundamental question pertinent to the arc physics, namely "where a pre-existing auroral arc maps to the equatorial magnetosphere", remains to be answered. Recent study by Jiang et al. suggests that the preexisting arc is located at an interface between the large-scale region-1 and region-2 field-aligned current (FAC) systems. In this study, we investigate a few events when THEMIS probes mainly moved in radial direction in the near-Earth plasma sheet in the premidnight sector, while the NORSTAR ground optical observations in conjugate sector revealed long-standing arc existence without major geomagnetic disturbance. We illustrate several candidate signatures that might hint the traverse of an arc's magnetospheric source by the in-situ probe. Those magnetospheric signatures include: (1) the large-scale spatial variation of magnetic fields that is consistent with the FAC configuration associated with the arc proposed by Jiang et al.; (b) the large-scale flow shear that is consistent with the arc's FAC system assuming an electrostatic mapping between the ionosphere and the magnetosphere; (c) most interestingly, the appearance of intense, bi-directional, quasi-field-aligned electron beam at energies of ~100 eV which is likely contributed by the upward-accelerated ionospheric electrons often observed in close vicinity of the auroral arc by lower-altitude satellites such as FAST. We also find that the estimated location of the arc's magnetospheric source is slightly tailward of the region of peak parallel proton fluxes, consistent with the notion that an auroral arc is usually located at the poleward edge of intense proton precipitation. When the above features are consistently organized, we suggest that they may be used to delimit the arc's source in the near-Earth central plasma sheet.

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