Transients associated with recurrent storms

From August 1993, to April 1994, in the declining phase of solar cycle 22, a broken series of eight storms recurred with successive passages of the same sector boundary in the course of 10 Solar rotations. Three of the strongest of these storms, on November 3-4, 1993, February 21, 1994, and April 17, 1994, are the subjects of recent community studies. All three have been associated with X ray events in Yohkoh data signaling the launch of coronal mass ejections (CMEs). Because of the clear morphology of these events, the associations are more obvious than past associations with flares. We find additional X ray events that can be associated with the remaining five storms in the sequence. The associations range from nearly certain for three of the four strongest storms to doubtful for the weakest storm. No X ray events occurred on the two rotations with no storms. Of the eight storms in total, four were associated with large arcades near the south polar crown, three with smaller-scale events in active regions bordering the northern coronal hole extension, and one with a medium arcade equatorward of the north polar crown. These sites apparently map out to the same sector boundary at 1 AU. Although recurrent storms are usually associated with high-speed streams from coronal holes, we infer that the southward interplanetary magnetic field responsible for peak activity is often brought by CMEs from the base of the sector boundary between coronal holes. Coupled with corotating interaction regions (CIRs) created by any oncoming high-speed flow from the following coronal hole, the transient CMEs fall into the recurrence pattern and can account for the unpredictably wide range of recurrent storm strengths.