The relation of solar flares to the evolution and proper motions of magnetic fields

The second Action Interval of the FBS coincided with an extended period of gradual evolution in a large complex of activity which served as the target for a coordinated space-ground study. The complex produced a multitude of subflares, half of which were clustered around just a few sites, each with a distinctive magnetic character. The essential flare-producing conditions at these preferred sites were preserved for many hours, even days, despite disruptions by flares and despite the eroding effects that accompany the disintegration of sunspot groups. Three preferred sites were active for the entire Interval, 22–27 May 1980. A comparison of flaring with non-flaring sites which also contained strong concentrations of flux demonstrates the importance of magnetic complexity, flux emergence, and motions at the photospheric level. The most energetic events by far, a chain of five closely homologous flares, erupted within 13 hours at a site where all these factors were conspicuously combined. The incessant activity preceding and during these flares of the fine chromospheric fibrils that covered and surrounded this particularly energetic site indicates reconfiguration of flux tubes in the chromosphere in a matter of minutes. These rapid (2–5 minutes), small (～10 arc-sec) changes are identified with emerging flux and with pores moving rapidly (≥200 m/s) very close to a magnetic neutral line.