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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 30, issue 9
Ann. Geophys., 30, 1331–1343, 2012
https://doi.org/10.5194/angeo-30-1331-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 30, 1331–1343, 2012
https://doi.org/10.5194/angeo-30-1331-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 11 Sep 2012

Regular paper | 11 Sep 2012

On the problem of Plasma Sheet Boundary Layer identification from plasma moments in Earth's magnetotail

E. E. Grigorenko1, R. Koleva2, and J.-A. Sauvaud3 E. E. Grigorenko et al.
  • 1Space Research Institute of RAS, Moscow, Russia
  • 2Space Research and Technologies Institute of BAS, Sofia, Bulgaria
  • 3Institute de Recherche en Astrophysique et Planétologie, Toulouse, France

Abstract. The problem of identification of the interface region between the lobe and the Plasma Sheet (PS) – the Plasma Sheet Boundary Layer (PSBL) – using ion moments and magnetic field data often arises in works devoted to statistical studies of various PSBL phenomena. Our experience in the identification of this region based on the analysis of ion velocity distribution functions demonstrated that plasma parameters, such as the ion density and bulk velocity, the plasma beta or the dynamic pressure vary widely depending on the state of magnetotail activity. For example, while field-aligned beams of accelerated ions are often observed propagating along the lobeward edge of the PSBL there are times when no signatures of these beams could be observed. In the last case, a spacecraft moving from the lobe region to the PS registers almost isotropic PS-like ion velocity distribution. Such events may be classified as observations of the outer PS region. In this paper, we attempt to identify ion parameter ranges or their combinations that result in a clear distinction between the lobe, the PSBL and the adjacent PS or the outer PS regions. For this we used 100 crossings of the lobe-PSBL-PS regions by Cluster spacecraft (s/c) made in different periods of magnetotail activity. By eye inspection of the ion distribution functions we first identify and separate the lobe, the PSBL and the adjacent PS or outer PS regions and then perform a statistical study of plasma and magnetic field parameters in these regions. We found that the best results in the identification of the lobe-PSBL boundary are reached when one uses plasma moments, namely the ion bulk velocity and density calculated not for the entire energy range, but for the energies higher than 2 keV. In addition, we demonstrate that in many cases the plasma beta fails to correctly identify and separate the PSBL and the adjacent PS or the outer PS regions.

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