NOAA 7926: A Kinked Ω-Loop?

摘要

Using vector magnetograms and X-ray images, we study the evolution of the decaying active region NOAA AR 7926. The active region had bipolar structure with a leading sunspot of positive (northern [N]) polarity—non-Hale polarity of cycle 22. Observations suggest that the following (southern [S]) polarity of this active region was in fact the leading (S) polarity of Active Region 7918 (AR 7918) of the previous solar rotation. Analyzing the rotation rate of both active regions and their magnetic field topology, we conclude that they form a single magnetic system resembling a kinked Ω-loop. During the first rotation, the upper part of the loop was exposed, forming a bipolar active region of normal (Hale) polarity. The rest of the Ω-loop had emerged by the time of the second rotation, giving the appearance of non-Hale polarity.