In the Earth's auroral zone, currents flow along magnetic field lines in both
upward and downward direction. In the upward current region, the field-aligned
current (FAC) is often associated with a field-aligned potential drop (FAPD) and,
within certain limits, the current-voltage relationship (CVR) can be approximated as
linear (Knight, 1973; Lyons et al., 1979). As a preliminary step towards a
systematic examination of the CVR based on Cluster and FAST data, we use multipoint
measurements of the electric and magnetic fields, combined with particle
measurements, to investigate temporal and spatial variations of the upward currents.
The influence of different magnetic field models is checked. We also estimate the
FAPD and explore its association with ion beams as inferred from Cluster and FAST
observations - above and below the FAPD region, respectively.