On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations

T Motoba; C. A Kletzing; B. J Anderson; S Ohtani; H Korth; D Mitchell; L. J Lanzerotti; K Shiokawa; M Connors; G. D Reeves

doi:10.1002/2015JA021676

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On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations

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On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations

T Motoba, C. A Kletzing, B. J Anderson, S Ohtani, H Korth, D Mitchell, L. J Lanzerotti, K Shiokawa, M Connors and G. D Reeves

Journal of geophysical research. Space physics, Vol.120(10), pp.8707-8722

10/2015

DOI: 10.1002/2015JA021676

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Abstract

Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at ~780 km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of ~5.0–5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1) at the early stage of the growth phase the quiet auroral arc emerged ~4.3° equatorward of the boundary between the downward Region 2 (R2) and upward Region 1 (R1) currents; (2) shortly before the auroral breakup (poleward auroral expansion) the latitudinal separation between the arc and the R1/R2 demarcation narrowed to ~1.0°; (3) RBSP-B observed a magnetic field signature of a local upward field-aligned current (FAC) connecting the arc with the near-Earth tail when the spacecraft footprint was very close to the arc; and (4) the upward FAC signature was located on the tailward side of a local plasma pressure increase confined near L ~5.2–5.4. These findings strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via the local upward FAC.

FACs

growth phase/onset arc

M-I coupling

Details

Title: Subtitle: On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations
Creators: T Motoba - Nagoya University
C. A Kletzing - University of Iowa
B. J Anderson - Johns Hopkins University Applied Physics Laboratory
S Ohtani - Johns Hopkins University Applied Physics Laboratory
H Korth - Johns Hopkins University Applied Physics Laboratory
D Mitchell - Johns Hopkins University Applied Physics Laboratory
L. J Lanzerotti - New Jersey Institute of Technology
K Shiokawa - Nagoya University
M Connors - Athabasca University
G. D Reeves - Los Alamos National Laboratory
Resource Type: Journal article
Publication Details: Journal of geophysical research. Space physics, Vol.120(10), pp.8707-8722
DOI: 10.1002/2015JA021676
ISSN: 2169-9380
eISSN: 2169-9402
Publisher: Blackwell Publishing Ltd
Number of pages: 16
Grant note: DOI: 10.13039/100000104, name: National Aeronautics and Space Administration, award: NAS5–01072, NNX12AJ52G, NAS5‐01072, NAS5–02099; DOI: 10.13039/100000001, name: National Science Foundation, award: GEO/ATM‐110433; DOI: 10.13039/501100000016, name: Canadian Space Agency
Language: English
Date published: 10/2015
Academic Unit: Physics and Astronomy
Record Identifier: 9984199741002771

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