Comparison of ionospheric drift and magnetic deflections on the ground

Resolute Bay, Canada, with an almost vertical geomagnetic field and the associated simplicity of ionospheric current system, is an optimal location to determine the relationship between the ionospheric electric field and the magnetic deflections on the ground. Considering uniform current sheets in a plane geometry, the magnetic deflection direction on the ground is expected to be (1) the same as the ionospheric electric field direction for the Hall current only or (2) lag the electric field direction 0-to-90° in the clockwise sense looking down when the Pedersen current is included. However, our analysis of Resolute incoherent scatter radar and magnetometer data shows that the magnetic deflection angle is leading in a range 30-70° depending on the magnetic local time. Additional magnetometers at Thule and Cambridge Bay observatories were used to investigate the effect of auroral zone currents, however, a simple deconvolution using these stations did not change the results significantly. Furthermore, inclusion of the neutral winds only slightly changed the offset angle. We conclude that a sunward magnetic contribution on the order of 50 nT caused by magnetospheric currents is needed to explain the offset.