The normal, thickness, and speed of the dusk magnetopause from Cluster Electric Field and Wave experiment measurements
Bale, S D
EM: bale@ssl.berkeley.edu
Space Sciences Laboratory, University of California , Berkeley, CA 94720 United States
Mozer, F S
Space Sciences Laboratory, University of California , Berkeley, CA 94720 United States
Andre, M
Swedish Institute of Space Physics, Uppsala Division, Uppsala, SE-75121 Sweden
Ericsson, A
Swedish Institute of Space Physics, Uppsala Division, Uppsala, SE-75121 Sweden
Gustafsson, G
Swedish Institute of Space Physics, Uppsala Division, Uppsala, SE-75121 Sweden
Holmgren, G
Swedish Institute of Space Physics, Uppsala Division, Uppsala, SE-75121 Sweden
Lindqvist, P
Royal Institute of Technology, Royal Institute of Technology, Stockholm, Sweden
Holtet, J
Department of Physics, University of Oslo, Oslo, N-0316 Norway
Lybekk, B
Department of Physics, University of Oslo, Oslo, N-0316 Norway
Pedersen, A
Department of Physics, University of Oslo, Oslo, N-0316 Norway
Grard, R
Solar System Division, ESTEC, Noordwijk, Netherlands
Laakso, H
Solar System Division, ESTEC, Noordwijk, Netherlands
Mursula, K
Department of Physical Sciences, University of Oulu, Oulu, Finland
Tanskanen, P
Department of Physical Sciences, University of Oulu, Oulu, Finland
Yerby, K
ACSE, University of Sheffield, Sheffield, United Kingdom
AB: We present a measurement of the normal, thickness, and speed of the dusk magnetopause using data from Electric Field and Wave (EFW) experiment at 39 magnetopause encounters by the four Cluster satellites during a single event. EFW measures the potential between spherical probe sensors and the body of the spacecraft. This spacecraft potential is related functionally to the ambient thermal electron current; as such, it gives a primary signature of the magnetopause. We use a timing analysis on the 4 spacecraft data and obtain a system of equations which is solved by regression for the boundary normal vector and speed. This analysis assumes a locally planar magnetopause with its velocity vector colinear with the normal. Magnetopause speeds range from 20 to 200 km/s and current layer thicknesses from 200 to 1200 km. The characteristic time between successive magnetopause encounters suggests a relationship to magnetospheric Pc-5 modes and we discuss the results in the context of an operative Kelvin-Helmholtz instability on the flank magnetopause.