Articles | Volume 29, issue 11
Ann. Geophys., 29, 2117–2130, 2011

Special issue: Cluster 10th anniversary workshop

Ann. Geophys., 29, 2117–2130, 2011

Regular paper 24 Nov 2011

Regular paper | 24 Nov 2011

THEMIS observations of earthward convected flux ropes triggering field dipolarization/substorm expansion and associated particle energization

I. I. Vogiatzis1,2, O. E. Malandraki3, Q.-G. Zong1,7, X.-Z. Zhou4, T. E. Sarris2, E. T. Sarris2, H. Zhang5, and T. A. Fritz6 I. I. Vogiatzis et al.
  • 1Institute of Space Physics and Applied Technology, Peking University, Beijing, China
  • 2Department of Electrical and Computer Engineering, Democritus University of Thrace, Xanthi, Greece
  • 3Institute of Astronomy and Astrophysics, National Observatory of Athens, Athens, Greece
  • 4Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA
  • 5Physics Department and Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA
  • 6Center for Space Physics, Department of Astronomy, Boston University, Boston, MA, USA
  • 7Center for Atmospheric Research, University of Massachusetts Lowell, Lowell, MA, USA

Abstract. We investigated a number of substorm events during major conjunctions of the THEMIS spacecraft for the tail seasons of the mission. We present simultaneous observations from various instruments onboard the THEMIS spacecraft during the events. We focus particularly on events when at least one of the THEMIS spacecraft is adjacent to the neutral sheet where convectional plasma flows are observed. The events demonstrate clear dipolarization signatures accompanied by high-speed earthward plasma flows and intense wave activity. We present evidence that flux ropes are embedded within the high-speed earthward convective plasma sheet flows. This fact has important implications since the leading edge of the flux rope having south polarity can impulsively merge with the north polarity field of the stretched magnetotail leading to mutual erosion of both magnetic structures. The merging of the vertically oriented oppositely-directed field lines can lead to local cross-tail current reduction and flux rope dissipation. These observations are very important in explaining the mechanism triggering near-Earth dipolarization and particle acceleration to supra-thermal energies, since they can be associated with non-adiabatic conditions and breakdown of the frozen-in condition in the near-Earth magnetotail similar to that taking place during magnetic reconnection in the mid-tail.