Use of twenty years CLUSTER/FGM data to observe the mean behavior of the
magnetic field and current density of Earth’s magnetosphere
Abstract
The data from the CLUSTER FGM magnetometer, recorded for 20 years at
ESA’s Cluster Science Archive, have been used to form a database aligned
in time. It allows the calculation of curl(B) over all the life of the
mission. The ̵⃗B and J⃗ data are then averaged, as a function of the
dipole tilt angle, to form a 3D grid of spatial extend of 20 RE, and for
any spatial resolution. From these data grids, maps of the direction of
the magnetic field and of the current density are produced, allowing the
observation of the average behavior of the magnetic field and the
current density on a large scale. The validity of the calculation of J⃗
is discussed. By means of spatial interpolation, the grids are used to
provide a measurement of the magnetic field at any point in space where
the grid is filled. This allows possibility of ray tracing to obtain
empirical plots of the magnetic field lines, i.e. not theoreti-cal, but
from experimental data. Field lines near the cusp are visualized, even
if they are very smoothed by the averaging of IMF and solar wind
parameters. In a future work it would be possible to add other
classification than just the dipole tilt angle, such as various activity
indicese and solar wind parameters. The prospect of adding data from
other missions would extend the regions that have been covered by
Cluster, and in-crease the spatial extent of the 3D grid and its
resolution.