Inferring the Writhe of Emerging Flux Tubes from the Evolution of the Orientation of Bipole Axes

LÓPEZ FUENTES, M.C.; MANDRINI, C.H.; DÉMOULIN, P.; VAN DRIEL-GESZRELYI, L.; PEVTSOV, A.A.

Córdoba

Congreso; X IAU Reunion Regional Latinoamericana de Astronomia; 2001

IAU

We study the long term evolution of 22 bipolar active regions (ARs) in which the main polarities turn one around the other along several solar rotations. We interpret this peculiar evolution as the emergence of distorted magnetic flux tubes. To investigate the relevance of the kink instability as the origin of the deformation, we compare the sign of the twist and the writhe of the flux tubes. Helicity conservation during the development of the kink instability requires that the writhe and the twist have the same sign (necessary but not sucient condition). We infere the handedness of the writhe from the evolution of the tilt angle of the AR bipole axes as observed in magnetic synoptic maps from Kitt Peak National Solar Observatory. We obtain the sign of the twist using vector magnetograms from Haleakala Stokes Polarimeter at Mees Solar Observatory. We find that no more than 32 % of the ARs can plausibly be associated to the kink instability, while 59 % cannot. Then, we suggest that the deformation of the flux tubes is dominantly caused by their interaction with plasma motions during their ascent through the convection zone (in the same way as proposed in Lopez Fuentes et al. 2000, ApJ 544, 540).