Modelling the Time-Variability of the Ionospheric Electric Field (TiVIE)

We present a statistical model of the ionospheric electric field derived from line-of-sight plasma velocity measurements from the Super Dual Auroral Radar Network (SuperDARN). Electric potential patterns are produced using an established technique that models the electric field as a spherical harmonic expansion of the ionospheric electric field. Improvements over existing models are achieved by the use of novel parameterisations that capture three major sources of time-variability of the coupled solar wind-magnetosphere-ionosphere system. The first source of variability relates directly to the time-dependence of the system to the upstream solar wind conditions, specifically the strength and orientation of the interplanetary magnetic field. The magnetosphere-ionosphere system is not static under continuous driving by the solar wind but evolves with time, even if the solar wind conditions themselves remain steady. We account for this by defining a solar wind steadiness timescale with which we parameterise the electric field. The second source of variability relates to the storage and release of energy in the magnetosphere that is associated with magnetospheric substorms. The electric field evolves throughout the substorms cycle, and its morphology is strongly influenced by the location of substorm onset. We therefore parameterise by substorm onset location and the time relative to substorm onset. Lastly we account for the variability introduced by geomagnetic storms. The ionospheric electric field evolves differently through each phase of a storm, so we parameterise by storm phase. We discuss the details of the model, and assess its performance by comparison to other models and to observations.