Low frequency (&ohgr;100 mV/m) Alfv¿n waves occur in the auroral zone. Such waves have a ponderomotive effect on both ions and electrons. In the region between the large wave field and the ionosphere, the ponderomotive force accelerates electrons downward and ions upward, which produces an ambipolar electric field. The combined effect is to produce a differential acceleration between O+ and H+ with the O+ accelerated more out of the ionosphere. The typical resulting energization for O+ is tens of eV, which is sufficient for the ions to escape the ionosphere. We demonstrate this by means of analysis and test-particle calculation. ¿ American Geophysical Union 1993