In the simplest representation of an auroral arc current system, the arc consists of a homogeneous block of increased conductance infinitely extended in longitudinal direction; field-aligned current (FAC) sheets that flow in and out of the ionosphere at the boundaries of the arc are connected through Pedersen current across the arc, while the electrojet (EJ) that flows along the arc as Hall current is divergence-free. To evaluate the deviation of the real arc current system from this ideal configuration, we developed the ALADYN (Auroral Arc Electrodynamics) method, based on a parametric model of the arc, that allows the derivation of the parameters by numerical fit to the experimental data. The method is illustrated with a wide, stable, winter evening arc, for which both Fast Auroral Snapshot (FAST) Explorer measurements at 3850 km altitude and ground optical data are available. We find that in order to obtain consistent results, one has to take into account, as a minimum, the ionospheric polarization, the contribution of the Hall current to the meridional closure of the FAC, and the coupling between the FAC and the EJ.