Interaction between a fast rotating sunspot and ephemeral regions as the origin of the major solar event on 2006 December 13

TL;DR

This study investigates how the interaction between a rapidly rotating sunspot and ephemeral regions in active region NOAA AR 10930 led to a major solar event on December 13, 2006, highlighting the role of sunspot rotation and magnetic shear.

Contribution

It reveals that a fast-rotating sunspot interacting with ephemeral regions can trigger major solar eruptions, with a record rotation angle of at least 240 degrees.

Findings

The sunspot rotated at least 240 degrees, the largest reported.

Interaction between the rotating sunspot and ephemeral regions triggered the flare.

Major solar event occurred after the sunspot rotated approximately 200 degrees.

Abstract

The major solar event on 2006 December 13 is characterized by the approximately simultaneous occurrence of a heap of hot ejecta, a great two-ribbon flare and an extended Earth-directed coronal mass ejection. We examine the magnetic field and sunspot evolution in active region NOAA AR 10930, the source region of the event, while it transited the solar disk centre from Dec. 10 to Dec. 13. We find that the obvious changes in the active region associated with the event are the development of magnetic shear, the appearance of ephemeral regions and fast rotation of a smaller sunspot. Around the area of the magnetic neutral line of the active region, interaction between the fast rotating sunspot and the ephemeral regions triggers continual brightening and finally the major flare. It is indicative that only after the sunspot rotates up to 200$^{\circ}$ does the major event take place. The sunspot rotates at least 240$^{\circ}$ about its centre, the largest sunspot rotation angle which has been reported.