Local field-aligned currents in the magnetotail and ionosphere as observed by a Cluster, Double Star, and MIRACLE conjunction

During a fortuitous conjunction event observed by Cluster, Double Star TC1, and Magnetometers-Ionospheric Radars-All-Sky Cameras Large Experiment ( MIRACLE) magnetometer stations at almost the same local time, crossings of the plasma sheet boundary layer (PSBL) are observed with a 45-50 s delay between the two spacecraft located approximately 6 RE apart in X. Taking into account the different polarity of BY, Cluster curlometer current density, and the curl of the equivalent current on the ground, the associated current system resembles that of a bubble model, i.e., the propagation of a bursty bulk flow (BBF) with field-aligned currents (FACs) on each side of the flow. The presence of such local FACs associated with BBFs is supported by the time delays of PSBL crossings, corresponding weak auroral brightening, and enhancement of the ionospheric equivalent current pattern. The Cluster observation also shows different signatures between inbound and outbound crossings, i.e., electron beam direction. Such differences are considered to be caused by the relative location of the observation point from the beam ejection region, such as reconnection, and may suggest that the beam ejection region is approaching during the PSBL crossing.