Properties of Magnetic tongues over a Solar Cycle

DÉMOULIN, P.; POISSON, M.; MANDRINI, C.H.; POISSON, M.; MANDRINI, C.H.; LÓPEZ FUENTES, M.C.; LÓPEZ FUENTES, M.C.; DÉMOULIN, P.

SOLAR PHYSICS

SPRINGER

Lugar: Berlin; Año: 2016 vol. 291 p. 1625 - 1646

0038-0938

The photospheric spatial distribution of the main magnetic polarities of bipolar active regions (ARs) presents during their emergence deformations thatare known as magnetic tongues. They are attributed to the presence of twist intthe toroidal magnetic flux-tubes that form the ARs. The aim of this article is tostudy the twist of newly emerged ARs from the evolution of magnetic tonguesobserved in photospheric line-of-sight magnetograms. We apply the proceduredescribed by Poisson et al. (2015, Solar Phys. 290, 727) to ARs observed overthe full Solar Cycle 23 and the beginning of Cycle 24. Our results show thatthe hemispherical rule obtained using the tongues as a proxy of the twist has aweak sign-dominance (53 % in the southern hemisphere and 58 % in the northernhemisphere). By defining the variation of the tongue angle, we characterize thestrength of the magnetic tongues during different phases of the AR emergence.We find that there is a tendency of the tongues to be stronger during the beginning of the emergence and to become weaker as the AR reaches its maximummagnetic flux. We compare this evolution with the emergence of a toroidal flux-rrope model with non-uniform twist. The variety of evolutions of the tongues inthe analyzed ARs can only be reproduced when using a broad range of twistprofiles, in particular having a large variety of twist gradient in the directionvertical to the photosphere. Although the analytical model used is a specialcase, selected to minimize the complexity of the problem, the results obtained set new observational constraints to theoretical models of flux-rope emergencet   that  form bipolar ARs.