Internal and external reconnection in a series of homologous solar flares

Using data from the extreme ultraviolet imaging telescope (EIT) on SOHO and the soft X-ray telescope (SXT) on Yohkoh, we examine a series of morpholog ically homologous solar flares occurring in National Oceanic and Atmospheri c Administration (NOAA) active region 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coro nal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X rays. In EIT each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities similar to 20 km s(-1). A shrinking and ex pansion of the width of the coronal hole coincides with the crinkle activit y, and generation and evolution of a postflare loop system begins near the time of crinkle formation. Using a schematic based on magnetograms of the r egion, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions but are modified by the presen ce of the additional magnetic fields of the sunspot and coronal hole. In th e schematic, internal reconnection begins inside of the EFR-associated fiel ds, unleashing a flare, postflare loops, and a coronal mass ejection (CME). External reconnection, first occurring between the escaping CME and the co ronal hole field and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting i n morphologically homologous eruptions. Our inferred magnetic topology is s imilar to that suggested in the "breakout model" of eruptions [Antiochos, 1 998], although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, primar ily by the internal reconnection.