The role of sunspot umbral rotation in triggering solar flares

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 Ha spectroheliograrn data of these active regions were analyzed to identify the flare triggering mechanism. It is found that the umbral rotation in these 6 -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. The primary condition for a solar flare to occur in the sun is the presence of active regions. A sunspot is an active region in the photosphere representing a cross section of the magnetic flux tube. The association of flares with the observed photospheric magnetic fields is in terms of magnetic field configurations and evolutionary changes (Mayfield & Lawrence 1985). The development and decay of sunspots are certainly important indicators on the evolution of active regions, since they represent highest concentration of magnetic flux. If evolutionary changes may provide necessary bnditions for flare8 to occur, then it is quite possible that the sunspot orientation changes indicate WS@ mstions and could be significaat observable factors in the energy buildup of at lea& some solar flares. There are studies canparing the close relationship of sunspot prop glotio~