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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 7
Ann. Geophys., 19, 687–698, 2001
https://doi.org/10.5194/angeo-19-687-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 19, 687–698, 2001
https://doi.org/10.5194/angeo-19-687-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 Jul 2001

31 Jul 2001

Correlated Interball/ground-based observations of isolated substorm: The pseudobreakup phase

A. G. Yahnin1, V. A. Sergeev2, T. Bösinger3, T. I. Sergienko1, I. A. Kornilov1, N. L. Borodkova4, M. F. Thomsen5, R. D. Belian5, J.-A. Sauvaud6, V. N. Lutsenko4, and A. A. Skalsky4 A. G. Yahnin et al.
  • 1Polar Geophysical Institute, Apatity, Russia
  • 2Institute of Physics, University of St-Petersburg, St-Petersburg, Russia
  • 3Institute of Space Physics, University of Oulu, Oulu, Finland
  • 4Space Research Institute, Moscow, Russia
  • 5Los Alamos National Laboratory, Los Alamos, NM, USA
  • 6CESR/CNRS, Toulouse, France

Abstract. We study the isolated substorm that occurred after a long quiet period, which showed all of the substorm signatures except for the first half hour of the expansion phase, which could be characterized as a pseudobreakup sequence, rather than a full-scale substorm onset. During the considered event, the substorm’s instability leads to a current disruption, which starts at the near-Earth plasma sheet and then propagates tailward. Based on auroral observations, the analysis of geosynchronous plasma injections, and the plasma sheet observations at ~15 RE at the meridian of auroral substorm development we show that (1) before and probably during "pseudobreakup phase", the plasma sheet stayed cold and dense, (2) during the pseudobreakup phase, particle injections at 6.6 RE were only seen in unusually low energy components, and (3) the electron precipitation into the ionosphere was very soft. We conclude that the basic difference between pseudobreakups and "real" substorm activations was found in the low energy of all manifestations. We suggest that high density and low electron temperature in the plasma sheet are the reasons for low energization in the magnetic reconnection operated on closed field lines in the plasma sheet, as well as the weak field-aligned acceleration, as predicted by the Knight’s relationship. The low Hall conductivity could then be the reason for the weak ground magnetic effects observed. This explanation suggests that the role of the ionospheric conductivity is "passive" as the plasma sheet, rather than the ionosphere, controls the development of the magnetospheric instability.

Key words. Ionosphere (particle precipitation) – Magnetospheric physics (auroral phenomena; plasma sheet)

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