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

Abstract

In this study, 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; andmore » (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.« less

Authors:

Motoba, T. ^[1]; Ohtani, S. ^[2]; Anderson, B. J. ^[2]; Korth, H. ^[2]; Mitchell, D. ^[2]; Lanzerotti, L. J. ^[3]; Shiokawa, K. ^[4]; Connors, M. ^[5]; Kletzing, C. A. ^[6]; Reeves, G. D. ^[7]

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+ Show Author Affiliations

1. The Johns Hopkins Univ. Applied Physics Lab., Laurel, MD (United States); Nagoya Univ., Nagoya (Japan)
2. The Johns Hopkins Univ. Applied Physics Lab., Laurel, MD (United States)
3. New Jersey Institute of Technology, Newark, NJ (United States)
4. Nagoya Univ., Nagoya (Japan)
5. Athabasca Univ., Athabasca, AB (Canada)
6. Univ. of Iowa, Iowa City, IA (United States)
7. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

Tue Oct 27 00:00:00 EDT 2015

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1236775

Report Number(s):

LA-UR-15-27239
Journal ID: ISSN 2169-9380

Grant/Contract Number:  

937836; NAS5-01072; NNX12AJ52G; NAS5-02099; GEO/ATM-110433; AC52-06NA25396

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Space Physics

Additional Journal Information:

Journal Volume: 120; Journal Issue: 10; Journal ID: ISSN 2169-9380

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; growth phase/onset arc; FACs, M-I coupling