We rated the auroral activity in 749 southen hemisphere DMSP images taken during 1972 and 1973 on a qualitative scale with active (A), moderate (M) quiet (Q), and no aurora (N) categories. The overall occurrence rates of images with A, M, Q, and N ratings are 0.17, 0.55, 0.16, and 0.11, respectively. After one DMSP orbit (102 min), both A and Q conditions recur in about one half of the cases. Thus successive images showning A conditions and successive images showing Q conditions occur more often than expected from the overall rates of A and Q images. The difference between the recurrence rate and overall occurrence rate of M images is much smaller (0.63 versus 0.55), suggesting that moderate auroral activity, as seen in a series of DMSP images, occurs essentially randomly. Nearly random, short-period (15--30 min) bursts of auroral activity has been observed by Krukonis and Whalen (1980) in montages of all-sky photographs taken 1 min apart. Our results, which cover a much longer time span, are consistent with this behavior and confirm that auroral activity occurs on time scales that differ from the full duration of the classic substorm pattern.