Helical Shape and Twisting Motion as Intrinsic Properties of Penumbral Filaments

A wealth of high resolution data obtained with advanced ground based telescopes and the SOT instrument on HINODE have led to new findings in the properties of penumbral filaments and controversies in their interpretation. Here we address one such issue, namely the question of whether the apparent twist of filaments is real or is just a viewing effect. We show that the helical shape and twisting motions of penumbral filaments follow from first principles and represent an integral part of penumbra formation and dynamics. As such, these properties link together other observed features of filaments including their magnetic and thermal substructure and their impact on the overlying atmosphere. At all stages of penumbral dynamics, qualitative agreement of theory and observations is supported by quantitative analysis as well.