Rapid rotation of a sunspot associated with flares

Context. Active region NOAA 10424 observed on August 5, 2003 is studied in detail by using TRACE, SOHO/MDI, BBSO H alpha monograph, and GOES data. This investigation focuses on the sunspot rotation and its relation with the eruptive phenomena by analyzing the magnetic configuration that the rotation results in. Aims. It is shown that there is a close relationship between the sunspot rotation and the emerging kinked magnetic Omega-loops, where the flares occur. Methods. Through tracing the traceable features motion by using the TRACE white-light images, one can get the rotation velocities of the umbra, the penumbra, the area near the penumbra, and the area far from the penumbra. Furthermore, the evolution of the emerging kinked magnetic Omega-loops and magnetic fields were studied. Results. For the sunspot with positive polarity, the umbra, the penumbra, and the area near the penumbra exhibit a conspicuous counterclockwise rotation. Moreover, the velocities decrease from the umbra through the penumbra to the area near the penumbra. It is interesting that the rotation of the umbra, the penumbra, and the area near the penumbra are opposite to that of the area far from penumbra. The rotation velocities of the umbra, the penumbra, polarity separation, and total magnetic flux increase with time. During the largest event (M1.7/Sn flare), emerging kinked magnetic Omega-loops are observed from TRACE 171 angstrom images. Conclusions. The different rotation speeds of the different parts of the sunspot cause twist, and then the twist is injected through the chromosphere into the corona to trigger the flares.