An empirical model of high-latitude ionospheric conductances based on EISCAT observations

Abstract. Conductances are key properties of the ionospheric electrodynamics and the difficulty of measuring them directly is a significant limitation to the usefulness of many analysis techniques. We have utilized all available field-aligned observations from the EISCAT incoherent scatter ultra-high frequency (UHF) radar since 2001 and from the 42 m EISCAT Svalbard Radar (ESR) since 1998 to develop a new empirical model for estimating the high-latitude ionospheric Hall and Pedersen conductances. The solar radiation component of the model is parametrized with the solar zenith angle and the F_10.7 index, and the auroral precipitation component is parametrized with the magnetic local time and the divergence-free part of the horizontal ionospheric current density, which is obtained from ground-based magnetic field observations. We have also derived a new technique based on spherical elementary current systems that can be used to solve for the ionospheric potential electric field and field-aligned current density from known ionospheric conductances and ground-based magnetic field observations, taking into account induction in the ionosphere and in the ground. The new empirical conductance model and solver were applied to IMAGE magnetometer network observations. Comparison of the results with Swarm satellite observations showed reasonable agreement in the electric field profile and direction of the field-aligned current, but in the post-midnight sector the amplitudes tended to be weaker than those observed by Swarm. The combination of the new conductance model and analysis technique allows estimating the key properties of ionospheric electrodynamics from ground-based magnetic field observations.