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

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

Research output: Contribution to journalJournal Articlepeer-review

22 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)8707-8722
Number of pages16
JournalJournal of Geophysical Research: Space Physics
Volume120
Issue number10
DOIs
Publication statusPublished - 1 Oct. 2015

Keywords

  • FACs
  • M-I coupling
  • growth phase/onset arc

Fingerprint

Dive into the research topics of 'On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations'. Together they form a unique fingerprint.

Cite this