EVOLUTION OF MAGNETIC NONPOTENTIALITY IN NOAA AR 10486

摘要

The active region NOAA 10486 was one of the most flare-productive regions during solar cycle 23. In this paper, we focus our analysis on the daily evolution of magnetic nonpotentiality for this region from 2003 October 26 to October 30. Daily averaged values of three nonpotential parameters: magnetic shear angle, line-of-sight current, and current helicity of the selected regions along the main neutral lines are calculated using the vector magnetograms obtained at Huairou Solar Observing Station. The magnetic flux evolution and proper motion of magnetic features are also studied in detail for the initial brightening regions of the two large X-class flares (X17 on October 28 and X10 on October 29). The main results are as follows. (1) Three parameters of the magnetic nonpotentiality in the photosphere obviously increased at the impulsively brightening flare sites from at least 1 day before the two large X-class flares, and most of the three parameters decreased after the flares around the main flare regions. (2) The increase of magnetic flux and complex proper motions of the magnetic knots were found to be simultaneously occurring at the non-potentiality developing sites along the main neutral lines. Such increases and motions of the magnetic flux can be explained by the model of emerging twisted flux ropes, and we conclude that the emergence of twisted magnetic flux ropes are a main reason for the development of nonpotentiality along the neutral line and for the production of strong X-class flares.