Flares associated with abnormal rotation rates: Longitudinal minimum separation of leading and following sunspots

Abstract

Using six years (1969-1974) of data of sunspot groups from the white light pictures of the Kodaikanal Observatory, we compute rotation rates of the leading and the following sunspots and the rate of change of longitudinal separation during their life times. We find that (i) the spots that are associated with abnormal rotation rates (i.e, rotation rates that are greater than 1σ from the mean rotation) and that approach at a separation rate of 1-2 deg/day also experience minimum longitudinal separation (~6/sup°-10/sup°) of their foot points during the course of their evolution; (ii) spots that have a minimum separation eventually trigger flares; and (iii) events with abnormal rotation rates and minimum approaching distances of the foot points occur on average during between 50-80% of the life spans, indicating the annihilation of magnetic energy, probably below the surface. These results support the conventional physical scenario of magnetic reconnection that may be responsible for triggering flares.