An image intensified, all-sky, 6300-¿ airglow imaging system operating on Ascension Island is early 1981 has been used to assemble a photographic data base of several hundred airglow depletion patterns. By mapping the airglow depletion features along geomagnetic field lines to the equatorial plane, the geometrical characteristics of plasma depleted regions may be described over the 400- to 1200-km altitude region above the equator. Such an analysis revealed that single or linear depletions tilted toward the west with an average skewness of 0.6¿ longitude west/100-km altitude, corresponding to a zenith angle tilt of ~40¿ at a height of 80 km. The tilts increased with local time during the evening hours, showing that an effective velocity shear of ~0.05 m/s/km is required to account for the observed evolution. In several cases, the depletion geometry showed a ''wishbone'' or bifurcated pattern. Such features had a mean height of bifurcation of 740 km and tilt factors very similar to those found for linear depletions observed during the same local time periods.