Simultaneous Mesoscale Polar Cusp Field-Aligned Currents Measured on Mid- and Low-Altitude Satellites

Using a conjunction of Cluster in the mid-altitude dayside magnetosphere and Swarm in the low-altitude ionosphere, we show, by employing multi-spacecraft analysis, that matched, strong magnetic perturbations and the corresponding mesoscale field-aligned current (FAC) structures are measured in the high latitude polar cusp region during the 7 October 2015 storm. Two pairs of opposite (positive/negative) FACs are observed by both Cluster and Swarm, which may relate to pulsed magnetic reconnection at the dayside magnetopause. Furthermore, the current intensity of these matched FACs decreases from high to low latitude, consistent with the time elapsed since reconnection. Corresponding geomagnetic disturbances are also observed by ground stations. Our observations provide direct evidence for the coupling of mesoscale FACs between the magnetosphere, ionosphere and ground in the polar cusp region, where the signatures are driven in this case by conditions suitable for inducing reconnection.