Abstract A long-lived sunspot group (AR 9604) on the south hemisphere that lasted five solar rotations and produced some strong bursts is analyzed. The focus is on its evolving features. Its whole life was successfully maintained by four Emerging Flux Regions (EFRs). Apart from the one that lasted only a short time and did not produce any bursts, the other three EFRs have the following common features: (1) A positive writhe of magnetic flux tubes and a twist of the field lines of the same sign, indicating kink instability. (2) A clockwise rotation and a high tilt because the writhe was right-handed. (3) A compact ``island δ'' structure of the sunspot group indicating concentrated kink instability. Since magnetic reconnection easily occurs at the kinked point of a very kink-unstable flux tube, these features should be the inducement of the strong bursts.
Keywords Sun --- active region evolution
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