Inferring the writhe of magnetic flux tubes from the evolution of active solar regions

We study the long-term evolution of bipolar active regions in which the main polarities are observed to rotate one about the other along several solar rotations. We propose that this peculiar evolution is due to the emergence of distorted magnetic flux tubes. We are able to infer the sign of the writhe helicity of the flux tubes from the rotation of the axis joining the main positive and negative polarities. The origin of the deformations may be explained by the development of a kink instability. Another possibility is the interaction with plasma motions during the ascent of the flux tubes in the Convective Zone. We discuss the role of the Coriolis force, convective turbulence and other large-scale motions in this process.