Horizontal currents and their divergences in the northern polar region. The colour-scale indicates the size of the divergence. Note that a positive divergence implies a downward current, corresponding to the south–north current in the equatorial plane. The solid line is a contour of zero divergence, and because the divergences in the Southern hemisphere are negligible, this is, to a very good approximation, magnetically connected to the equivalent solid line in Fig. 8. The arrows show the size and direction of the height-integrated Pedersen and Hall currents at each location. The longest arrow represents a current of ∼1 mA m⁻¹. The dashed, dotted, dot–dashed and triple dot–dashed lines have the same meaning as in Fig. 4.