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\begin{document}

\title{Use of twenty years CLUSTER/FGM data to study the global behavior of the
magnetic field and current density of Earth's magnetosphere}



\author[1]{Patrick Jean-François Robert}%
\author[2]{Dunlop Wray Malcolm}%
\affil[1]{LPP/CNRS Ecole Polytechnique}%
\affil[2]{RAL}%


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  \date{May 23, 2024}


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\begin{abstract}
The data from the CLUSTER FGM magnetometer, recorded for 20 years at
ESA's Cluster Science Archive, as well as the position of the
spacecraft, have been used to form a database aligned in time, the 4 s/c
flying in formation has allowed the calculation of curl(B) over all the
life of the mission.

The data of B and J are then averaged, as a function of the dipole tilt
angle, to form a 3D grid of spatial extend of about 20 Re.

From these data grids, maps of the direction of the magnetic field and
of the current density are produced, allowing the study of the average
behavior of the magnetic field and the current density on a large scale.

The validity of the calculation of J is discussed. The direction of B is
used to determine the position and shape of the polar cusps, both in
latitude and longitude. A simple model of the day-side magnetopause is
proposed.

By means of spatial interpolation, the grid is used to provide a digital
model of the magnetic field at any point in space where the grid is
filled. This model allows ray tracing so as to obtain empirical plots of
the magnetic field lines, i.e. not theoreti-cal, but from experimental
data. In particular, field lines near the cusp bring a direct view of
the shape of the cusps. The results are discussed.The prospect of adding
data from other missions would extend the regions that have been covered
by Cluster.%
\end{abstract}%



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