@article{921baf2a6d934d6f8cd0cc948f506335,
title = "On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations",
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.",
keywords = "FACs, growth phase/onset arc, M-I coupling",
author = "T. Motoba and S. Ohtani and Anderson, {B. J.} and H. Korth and D. Mitchell and Lanzerotti, {L. J.} and K. Shiokawa and M. Connors and Kletzing, {C. A.} and Reeves, {G. D.}",
note = "Funding Information: Work at JHU/APL was supported by JHU/APL subcontract 937836 under NASA prime contract NAS5-01072 for the Van Allen Probes mission and also partially by a NASA grant (NNX12AJ52G) and an NSF grant (GEO/ATM-110433). The research at NJIT was supported in part by Van Allen Mission subcontract 937836 under NASA prime contract NAS5-01072. The authors thank all of the Van Allen Probes teams for operating the spacecraft and providing each instrument''s data. Most of the data from the Van Allen Probe B spacecraft used in this study are publicly available at CDAWeb (http://cdaweb.gsfc.nasa. gov/). RBSPICE data are also archived on the RBSPICE Science Data Center web site: http://rbspice.ftecs.com/Data.html. We would also like to thank the AMPERE team and the AMPERE Science Center for providing the processed AMPERE data products that are publicly available on the AMPERE website: http://ampere.jhuapl.edu/. In addition, the AMPERE raw δB vector data are provided by H. Korth of the JHU/APL on request. We also thank V. Angelopoulos, S. Mende, and E. Donovan for use of the THEMIS ASI data. Deployment and data retrieval of the THEMIS ASIs were supported primarily by NASA contract NAS5-02099 and partly by the Canadian Space Agency. Data from the THEMIS GBO measurements are publicly available on the THEMIS mission website: http://themis.ssl.berkeley.edu/index. shtml. The SuperMAG ground-based magnetometer and geomagnetic index data were downloaded from the SuperMAG website: http://supermag. jhuapl.edu/. We gratefully acknowledge not only all of the organizations and national agencies that operate the ground-based magnetometers but also all of the PIs for willingly providing these data to SuperMAG. The OMTIs (http://stdb2.stelab.nagoya-u.ac.jp/omti/) have been developed and operated by Y. Katoh, M. Satoh, T. Katoh, Y. Haraguchi, Y. Yamamoto, and T. Adachi of the STEL, Nagoya University, and I. Schofield and K. Reiter of the Athabasca University. The OMTI data at Athabasca are provided by the PI (K. Shiokawa of the STEL, Nagoya University) on request. Athabasca ground facilities were installed and operated with financial support from the Canada Foundation for Innovation. The SYM-H index data were obtained from WDC for geomagnetism, Kyoto. The OMNI solar wind data were obtained from the GSFC/SPDF OMNIWeb interface at http://omniweb.gsfc.nasa.gov. Publisher Copyright: {\textcopyright}2015. American Geophysical Union. All Rights Reserved.",
year = "2015",
month = oct,
day = "1",
doi = "10.1002/2015JA021676",
language = "English",
volume = "120",
pages = "8707--8722",
number = "10",
}