Abstract:
The evolution of large active regions NOAA 9393 and NOAA 9433 observed during March and April 2001 respectively on their successive rotation and the active region NOAA 10069 that appeared during August 2002 were studied. Kodaikanal photoheliogram and Hα Spectroheliogram data of these active regions were analyzed to identify the flare triggering mechanism. It is found that the umbral rotation in these δ -type sunspots plays an important role for the occurrence of flares. The flare locations were generally near sites where the umbrae of the sunspot underwent more rotation.
