Hα observations of flare-productive solar active regions

The development of magnetic shear must be a key factor in understanding the mechanism of energy storage and release in solar flares. Hα monochromatic-image observations of highest spatial-resolution are essential for the study of magnetic shear development in solar active regions. From observations using the Domeless Solar Telescope (DST) of the Hida Observatory, two types of processes are found to be involved in the development of magnetic shear configurations between sunspots: (A) collision of two sunspots of opposite magnetic polarities, and (B) successive emergence of twisted magnetic flux ropes. It is suggested that the latter process is more important for the production of major flares. (author)