Articles | Volume 27, issue 5
Ann. Geophys., 27, 1935–1940, 2009

Special issue: Ninth International Conference on Substorms (ICS9)

Ann. Geophys., 27, 1935–1940, 2009

  04 May 2009

04 May 2009

Longitudinal development of a substorm brightening arc

K. Shiokawa1, A. Ieda1, A. Nakajima1, K. Sakaguchi1, R. Nomura1, T. Aslaksen2, M. Greffen3, E. Spanswick3, E. Donovan3, S. B. Mende4, J. McFadden4, K.-H. Glassmeier5,6, V. Angelopoulos7, and Y. Miyashita8 K. Shiokawa et al.
  • 1Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan
  • 2Department of Physics and Technology, University of Tromsø, Tromsø, Norway
  • 3Department of Physics and Astronomy, University of Calgary, Calgary, Canada
  • 4Space Science Laboratory, University of California Berkeley, CA, USA
  • 5Institut of Geopyhsics and extraterrtestrial Physics, TU Braunschweig, Germany
  • 6Max Planck Institut of Solar System Reserach, Katlenburg-Lindau, Germany
  • 7Institute of Geophysics and Planetary Physics, University of California at Los Angeles, Los Angeles, CA, USA
  • 8Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan

Abstract. We present simultaneous THEMIS-ground observations of longitudinal (eastward) extension of a substorm initial-brightening arc at Gillam (magnetic latitude: 65.6°) at 08:13 UT on 10 January 2008. The speed of the eastward arc extension was ~2.7 km/s. The extension took place very close to the footprints of the longitudinally separated THEMIS E and D satellites at ~12 RE. The THEMIS satellites observed field dipolarization, weak earthward flow, and pressure increase, which propagated eastward from E to D at a speed of ~50 km/s. The THEMIS A satellite, located at 1.6 RE earthward of THEMIS E, observed fluctuating magnetic field during and after the dipolarization. The THEMIS E/D observations suggest that the longitudinal extension of the brightening arc at substorm onset is caused by earthward flow braking processes which produce field dipolarization and pressure increase propagating in longitude in the near-earth plasma sheet.