ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-19-1669-2001 Cluster EDI convection measurements across the high-latitude plasma sheet boundary at midnight Quinn J. M. 1 Paschmann G. 2 Torbert R. B. 1 Vaith H. 2 McIlwain C. E. 3 Haerendel G. 4 Bauer O. 2 Bauer T. M. 2 Baumjohann W. 5 Fillius W. 3 Foerster M. 2 Frey S. 2 Georgescu E. 2 Kerr S. S. 3 Kletzing C. A. 6 Matsui H. 1 Puhl-Quinn P. 2 Whipple E. C. 7 Space Science Center, Morse Hall University of New Hampshire Durham, NH 03824, USA Max-Planck-Institut für extraterrestrische Physik D-87545 Garching, Germany Center for Astrophysics and Space Sciences University of California, San Diego La Jolla, CA 92093, USA International University Bremen, 28725 Bremen, Germany Space Research Institute, 8042 Graz, Austria Department of Physics and Astronomy University of Iowa Iowa City, IO 52242, USA Geophysics Program University of Washington Seattle, WA 98195, USA 30 09 2001 19 10/12 1669 1681 Copyright: © 2001 J. M. Quinn 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/19/1669/2001/angeo-19-1669-2001.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/19/1669/2001/angeo-19-1669-2001.pdf

We examine two crossings of three Cluster satellites from the polar cap into the high-latitude plasma sheet at midnight local time, using data from the Electron Drift Instrument (EDI). EDI measures the full electron drift velocity in the plane perpendicular to the magnetic field for any field and drift directions. The context of the measured convection velocities is established by their relation to the intense enhancements in 1 keV electrons, also measured by EDI, as the satellites move from the polar cap into the plasma sheet boundary. In both cases presented here, the cross <b><i>B</i></b> convection in the polar cap is anti-sunward (toward the nightside plasma sheet) with a small duskward component. As the satellites enter the plasma sheet boundary region, the dawn-dusk convective flow component reverses its sign, and the flow in the meridianal plane (toward the center of the plasma sheet) drops substantially. The relatively stable convection in the polar cap becomes highly variable as the PSBL is encountered. The timing and sequence of the boundary crossings by the Cluster satellites are consistent with a relatively static structure on a time scale of the few minutes in satellite separations. In one of the two events, the plasma sheet boundary has a spatially separate structure that is crossed by the satellites before entering the plasma sheet.<br><br><b>Key words. </b>Magnetospheric physics (electric fields; magnetopause, cusp and boundary layers; instruments and techniques)