A high performance, all-sky, imaging system has provided data on the evolution and drift motions of F-region depletions above the magnetic dip equator at Alca⁁ntara, Brazil, (2.3 ¿S, 44.5 ¿W). Monochromatic images of depletions in the OI(630 nm) nightglow were recorded on eight nights during 1--16 October, 1994, as part of the Guar¿ campaign. The drift motions of the depletions were typically 80--100 m/s eastward prior to local midnight and reduced to a minimum of ~30--50 m/s in the morning hours, in accord with previous observations. However, on October 2--3 and 12--13 the depletions were observed to reverse direction for ~60--90 min, achieving westward speeds of ~30 m/s before the motion reverted to eastward around 0100 LT and accelerated to 35--45 m/s near dawn. Magnetic activity and other evidence suggests that these reversals in the motion of the airglow depletions probably result from reversals in the F-region dynamo rather than from shifts in the altitude of the shear in the nighttime F-region plasma drift.¿ 1997 American Geophysical Union