Electric space currents in the polar regions consist of one part which flows almost radially along magnetic field lines, one part which close these currents horizontally, and one part which circulates horizontally in closed loops. Karl M. LaundalOnly the latter can be measured from ground, and only the two former can be measured from high up in space. Only a few satellites, in very low orbits, can be used to detect all three parts.
Laundal et al. show that significant differences exist between sunlit and dark conditions: While significant currents appear practically everywhere in sunlight, there are almost no currents poleward of the aurora when it is dark. In the figure below Laundal et al. provide estimates of horizontal currents in the ionosphere. The northern hemisphere is shown on top. In the left column, it is dark in the north, and sunlit in the south, and it is opposite in the right column. In darkness, the currents are confined to the auroral oval. Estimates of horizontal currents in the ionosphere.