Some occurrence characteristics of plasma bubbles based on data from the ion drift meter aboard the Atmosphere Explorer E satellite are presented. Of 5200 bubbles detected between 250 and 475 km altitude, 65% had ion density depletions of less than 1 order of magnitude below the ambient ion density, and the occurrence frequency decreased with increasing depletion depth. Depletion depth decreased with local time, probably due to diffusive decay of bubbles. Bubble activity above 300 km altitude had its onset around 1900 and peaked around 2130 LT. Late, shallow bubbles appeared to be associated with frequency spread F, and early, deep bubbles with range spread F. Increase in magnetic activity inhibits bubble generation except near sunrise, at which time bubble activity has been found to increase with magnetic disturbance. Bubble activity is restricted largely to a belt within about ¿20¿ dip latitude.¿ 1997 American Geophysical Union