Active regions twist from magnetic tongues and force-free coronal models

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

Cuzco

Congreso; X Conferencia Latinoamericana de Geofísica Espacial; 2014

Asociación Latinoamericana de Geofísca Espacial - International Space Weather Initiative

The magnetic flux distribution observed in photospheric magnetograms provide valuable information about the characteristics of the magnetic structures that originate active regions (ARs). This is the case of the so-called magnetic tongues, that appear in bipolar AR magnetograms as deformations of the main polarities. They are due to the projection, in the direction normal to the photosphere, of the azimuthal component of the magnetic field around the main axis of twisted toroidal flux-tubes that emerge from the solar interior. In a recent work, we developed a new method to characterize the effect of magnetic tongues in bipolar ARs by computing and analizing the evolution of the AR polarity inversion line (PIL). Here, we use the PIL technique to infer the twist of a set of ARs observed with SOHO/MDI, assuming that they are formed by twisted toroidal magnetic flux-tubes. We use as a proxy of the twist the number of turns of the magnetic field lines around the tube´s axis. To test the procedure we compare our findings with the twist obtained from linear force-free field models of the AR coronal structures observed in EUV. From our results we confirm that the the method based on the PIL is a robust and reliable way to obtain an early indicator of the twist content in ARs. (See also the poster "Statistical analysis of magnetic twist properties of ARs from magnetic tongues" by Poisson et al., presented in this meeting).