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Ann. Geophys., 19, 1669-1681, 2001
www.ann-geophys.net/19/1669/2001/
© European Geosciences Union 2001
Cluster EDI convection measurements across the high-latitude plasma sheet boundary at midnight
J. M. Quinn1, G. Paschmann2, R. B. Torbert1, H. Vaith2, C. E. McIlwain3, G. Haerendel4, O. Bauer2, T. M. Bauer2, W. Baumjohann5, W. Fillius3, M. Foerster2, S. Frey2, E. Georgescu2, S. S. Kerr3, C. A. Kletzing6, H. Matsui1, P. Puhl-Quinn2, and E. C. Whipple7
1Space Science Center, Morse Hall University of New Hampshire Durham, NH 03824, USA
2Max-Planck-Institut für extraterrestrische Physik D-87545 Garching, Germany
3Center for Astrophysics and Space Sciences University of California, San Diego La Jolla, CA 92093, USA
4International University Bremen, 28725 Bremen, Germany
5Space Research Institute, 8042 Graz, Austria
6Department of Physics and Astronomy University of Iowa Iowa City, IO 52242, USA
7Geophysics Program University of Washington Seattle, WA 98195, USA
Abstract. 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 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.
Key words. Magnetospheric physics
(electric fields; magnetopause, cusp and boundary layers; instruments and
techniques)
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