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

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Tetsuo Motoba1, Shinichi Ohtani2, Brian J Anderson3, Haje Korth2, Donald G Mitchell4, Louis J Lanzerotti5, Kazuo Shiokawa6, Martin G Connors7, Craig Kletzing8 and Geoffrey D Reeves9, (1)STEL/Nagoya University, Nagoya, Japan, (2)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (3)Johns Hopkins University, Baltimore, MD, United States, (4)JHU/APL, Laurel, MD, United States, (5)New Jersey Institute of Technology, Edison, NJ, United States, (6)Nagoya University, Nagoya, Japan, (7)Athabasca University, Athabasca, AB, Canada, (8)University of Iowa, Iowa City, IA, United States, (9)Los Alamos National Laboratory, Los Alamos, NM, United States
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 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. The observations strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via a local upward FAC.