ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-19-1567-2001 Four point measurements of electrons using PEACE in the high-altitude cusp Taylor M. G. G. T. 1 Fazakerley A. 1 Krauklis I. C. 1 Owen C. J. 1 Travnicek P. 2 1 Dunlop M. 3 Carter P. 1 Coates A. J. 1 Szita S. 1 Watson G. 1 Wilson R. J. 1 Mullard Space Science Laboratory, University College London, UK Institute of Atmospheric Physics, The Academy of Sciences of the Czech Republic Imperial College of Science Technology and Medicine, UK 30 09 2001 19 10/12 1567 1578 Copyright: © 2001 M. G. G. T. Taylor et al. 2001 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/19/1567/2001/angeo-19-1567-2001.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/19/1567/2001/angeo-19-1567-2001.pdf

We present examples of electron measurements from the PEACE instruments on the Cluster spacecraft in the high-latitude, high-altitude region of the Earth’s magnetosphere. Using electron density and energy spectra measurements, we examine two cases where the orbit of the Cluster tetrahedron is outbound over the northern hemisphere, in the afternoon sector approaching the magnetopause. Data from the magnetometer is also used to pinpoint the position of the spacecraft with respect to magnetospheric boundaries. This preliminary work specifically highlights the benefit of the multipoint measurement capability of the Cluster mission. In the first case, we observe a small-scale spatial structure within the magnetopause boundary layer. The Cluster spacecraft initially straddle a boundary, characterised by a discontinuous change in the plasma population, with a pair of spacecraft on either side. This is followed by a complete crossing of the boundary by all four spacecraft. In the second case, Cluster encounters an isolated region of higher energy electrons within the cusp. The characteristics of this region are consistent with a trapped boundary layer plasma sheet population on closed magnetospheric field lines. However, a boundary motion study indicates that this region convects past Cluster, a characteristic more consistent with open field lines. An interpretation of this event in terms of the motion of the cusp boundary region is presented.<br><br><b>Key words. </b>Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions)