EOMF-06. Exploring near-Earth magnetospheric field asymmetries

We present a new study of the near-Earth magnetospheric field variations. This study is particularly focused on local-time variations. The magnetospheric field is well known to be highly asymmetric with local time during periods of high geomagnetic activity. Moreover, this field could also be significantly asymmetric during periods of low and moderate geomagnetic activity, although such an asymmetry has not been properly quantified yet. This asymmetry is not well taken into account in current geomagnetic field models which usually rely on global indices of the geomagnetic field. Our approach is to take advantage of the full ground magnetic observatory network to derive a new local-time dependent geomagnetic index. The data are preprocessed by removing the main, local crustal and E-region ionospheric fields using a priori geomagnetic field models. The new index is used to investigate the local time asymmetry for all geomagnetic activity. We also discuss potential improvements of our index when using Swarm satellite data. In the future, this index will be used to build more refined magnetospheric field models which remains one of today's main limitation to build accurate models of the Earth's magnetic field.