The three Swarm satellites provide an optimum, low Earth orbit (LEO) and multi-spacecraft platform, to explore for the first time the local correlation between field-aligned currents (FACs), auroral electrojets, and magnetic perturbations at the Earth’s surface. By Swarm and ground magnetic field data together, one can investigate systematically the full correlation chain, whose final link controls the ground induced currents and related space weather effects. We introduce an integrated FAC product, the Sheet FAC (SFAC) index, as a convenient measure of the in-situ FAC data, and check the correlations SFAC-AE, SFAC-PEJ and SFAC-dH, with AE the standard auroral electrojet index, PEJ the local, Swarm based, polar electrojet index, and dH the horizontal magnetic field perturbation at the Earth’s surface. Given the good SFAC-dH correlation, we also suggest an extension of SFAC to higher LEO satellites, which cannot observe any more the electrojet currents, but are fully capable to monitor SFAC.

The conjunction of different spacecraft missions provide the opportunity to investigate the multiple scale of the magnetospheric current system. In our work, we use the data from MMS, Cluster and Swarm to study the characteristics of both the dayside current, including the magnetopause, and other current systems connected by the field aligned currents. Using the MMS four spacecraft data, we investigated the small-scale physical process of the magnetopause current, e.g. current carriers and current sources, which show features beyond the classic Chapman-Ferraro model. We compare MMS crossings to simultaneous crossings at different locations on the MP current layer observed by Cluster. Cluster is an order of magnitude lower than MMS and cannot reveal the detailed current structure due to its large separation. However, we find that the MP at the above two locations can have similar magnetic field structure. This may suggest that the MP has similar current structure across wide region during specific IMF conditions. We also used the conjunction of MMS and Swarm and Cluster and Swarm to investigate the behaviour of field-aligned currents. MMS and Swarm can calculate the current in the dayside inner low latitude boundary and the mapped ionospheric region simultaneously. Comparing the observed current signatures, we can investigate the correlation between them, which may reveal the nature of the magnetopause-ionosphere coupling between the field aligned current systems.