The spectral dependence in the equatorward cutoff of diffuse auroral electron and ion precipitation is investigated using the Defense Meteorological Satellite Program F6 and F7 low-altitude polar-orbiting satellites. These equatorward boundaries are determined at 100, 1000, and 3000 eV during very quiet conditions and during normal conditions (low-level magnetic activity) in the dawn, dusk, premidnight, and prenoon sectors. We find that under normal conditions the low-energy ions cut-off equatorward of the higher energy ions at all local times, with the largest effect at dawn and the smallest at dusk. Electrons exhibit greater variability; however, at premidnight, low-energy electrons cut-off equatorward of higher energy electron, while at dawn the electron cutoff-ordering becomes &lgr;100>>&lgr;3000>&lgr;1000, where the subscripts are energies in electron volts. During times of prolonged and profoundly quiet conditions, the dispersion, particularly for ions, disappears; that is, the cutoffs at all three energies coincide. It is argued that these observations provide evidence against the predictions of the often considered model of steady-state Alfv¿n layers arising from a constant source in the magnetotail convected earthward by a Stern-Volland cross-tail electric field toward a magnetic dipole. For example, the predicted ion dispersion is never observed. Investigating the response to magnetic disturbances following times of profound quiet, we find prompt, near simultaneous reaction over a wide local time range, including dawn and dusk. Following a return to quiet magnetic conditions, the precipitation relaxes to predisturbance patterns in the premidnight region within 1 to 2 hours but takes several hours longer at dawn. The electron precipitation cutoffs are equatorward of the ion precipitation cutoffs in all magnetic local time sectors except dusk, where the ion precipitation extends further equatorward. ¿ American Geophysical Union