Alfv¿n waves transfer field-aligned currents, momentum and energy from the source region in the equatorial magnetosphere along Earth's magnetic field lines to the polar ionosphere and play therefore an important role in auroral electrodynamics. The parallel potential drop of some kV in the auroral acceleration region (AAR) at altitudes of some 1000 km has considerable effect on the propagation of these waves. The purpose of this report is to investigate the reflection and transmission properties of the AAR in the frame of a thin sheet approximation. Combining key relations of auroral electrodynamics with the requirement of current continuity results in an easy-to-handle physical description of the problem. The model provides an opportunity to study different acceleration mechanisms. It turns out that the reflection properties of the auroral zone depends strongly on the perpendicular scale length of the incident wave. ¿ 1998 American Geophysical Union