The dynamics and spatial scale of auroral absorption events, named 'spikes', have been investigated with a new multi-narrow-beam riometer experiment. Measurements of the components of the ionospheric electric field perpendicular to the geomagnetic field at the time of a spike were made with the auroral radar system Stare. An absorption spike is caused by a ribbon-shaped enhancement in the ionospheric electron density causing maximum absorption at an altitude near 90 km. The velocity of a ribbon is generally poleward directed and of magnitude between 300 and 3000 m/s. The half width at falf maximum and the length of a ribbon are characterized by dimensions of 10 to 50 km and >400 km, respectively. The electric field within a ribbon is so weak that its polward motion cannot be explained as E¿B drift in the ionosphere. Equatorward of the ribbon the meridional component of the electric field points equatorward. The height of maximum absorption suggest an effective mean energy of the precipitating electrons of about 30 keV. Finally, we find that these events typically occurred during dusk to midnight in magnetic local time. Events which occurred at early local times were associated with high values of Kp.