Review of coordinated measurements with Swarm and Cluster : multi-scale magnetospheric and ground currents

We review a number of studies, undertaken during the 10 years of Swarm, using distributed, multi-scale measurements arising from the combination with Cluster, MMS and ground based arrays. The scaling, coherence and correlation of field-aligned current sheets (FACs) connecting different regions of the magnetosphere have been explored with associated analysis techniques using these multi-point measurements at both low (LEO) and high altitudes, and in relation to (R1/R2) auroral boundaries. Individual events can map to conjugate current density distributions at the magnetopause and ring current and regions in between; as well as to associated  ground signatures, driven by the external conditions. Large and small-scale (MLT) trends in FAC orientation can be inferred from dual-spacecraft (e.g. the Swarm A&C spacecraft). Conjugate effects seen in ground (dH/dt), ionospheric and magnetospheric magnetic signals show that intense, coherent FA currents can take place in the polar cusp during the main phase of a geomagnetic storm and at near tail local times during substorm activity, at different altitudes. In the former event the mesoscale FACs show vertical scaling and a corresponding geomagnetic disturbance, driven by unsteady magnetic reconnection at the magnetopause. In the latter event, the most intense dH/dt is shown to be associated with FACs driven into the ionosphere by the arrival of bursty bulk flows BBFs at geosynchronous orbit (linked via a modified sub-storm current wedge, SCW). In situ ring current morphology can also be investigated by MMS, THEMIS and Cluster during the Swarm era, and can be compared to distributions of R2-FACs.