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Ann. Geophys., 20, 311-320, 2002
www.ann-geophys.net/20/311/2002/
© European Geosciences Union 2002
Cusp-like plasma in high altitudes: a statistical study of the width and location of the cusp from Magion-4
J. Mĕrka, J. Šafránková, and Z. Nĕmeček
Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic
Correspondence to: J. M.erka (jan.merka@mff.cuni.cz)
Abstract. The width of the cusp
region is an indicator of the strength of the merging process and the degree of
opening of the magnetosphere. During three years, the Magion-4 satellite, as
part of the Interball project, has collected a unique data set of cusp-like
plasma observations in middle and high altitudes. For a comparison of high- and
low-altitude cusp determination, we map our observations of cusp-like plasma
along the magnetic field lines down to the Earth’s surface. We use the
Tsyganenko and Stern 1996 model of the magnetospheric magnetic field for the
mapping, taking actual solar wind and IMF parameters from the Wind
observations. The footprint positions show substantial latitudinal dependence
on the dipole tilt angle. We fit this dependence with a linear function and
subtract this function from observed cusp position. This process allows us to
study both statistical width and location of the inspected region as a function
of the solar wind and IMF parameters. Our processing of the Magion-4
measurements shows that high-altitude regions occupied by the cusp-like plasma
(cusp and cleft) are projected onto a much broader area (in magnetic local time
as well as in a latitude) than that determined in low altitudes. The trends of
the shift of the cusp position with changes in the IMF direction established by
low-altitude observations have been confirmed.
Key words. Magnetospheric physics
(magnetopause, cusp and boundary layer; solar wind – magnetosphere
interactions)
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