Space Technology 5 Multipoint Observations of Transpolar Arc Related Field-aligned Currents

Transpolar arcs are often observed during northward interplanetary magnetic field (IMF) and their formation and motion is dependent on IMF By. For northward IMF and a By sign change transpolar arcs (theta aurorae) are almost always formed in both hemispheres, regardless of IMF Bx and dipole tilt. In the present study we use the Space Technology 5 (ST5) mission consisting of three microsatellites which provide the first multipoint magnetic field measurements in low Earth orbit. We use this unique data set to study the variability of transpolar arc associated field-aligned currents. These high-latitude arcs are identified by DMSP F13 SSJ4 particle data. In addition, some of the arcs can be identified as transpolar arcs in the TIMED GUVI images. We analyze several cases of transpolar arc and auroral oval associated field-aligned currents where the currents are expected to change both temporally and spatially corresponding to changes in the interplanetary magnetic field.