Systematics of discrete hard X ray enhancements detected using the Army Background Experiment between April 1990 and October 1992 are presented. A total of 822 enhancement events were detected, most often within two bands of geomagnetic latitude that overlay (1) the inner trapped radiation belt and (2) the slot between inner and outer radiation belts. Local hour and seasonal variations are strongest for the inner-zone events, which occur preferentially just after local dawn and during the northern summer months. ¿ American Geophysical Union 1996