The magnetic twist of solar active regions from photospheric tongues and force-free coronal models

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

Córdoba

Congreso; Friends of Friends; 2015

Observatorio Astronómico de Cordoba

In a recent paper (Poisson et al. 2015, Solar Phys., 290, 727) we showedthat the effect of magnetic tongues in line-of-sight magnetograms can beused as a proxy of the magnetic helicity of bipolar active regions (ARs).Using a twisted toroidal magnetic flux-tube to model the emergence of ARs, we relate the number of turns ($N_t$) of the magnetic field lines around the main axis of the tube with the evolution of the polarity inversion line (PIL) of observed ARs. In this work we compare the twist inferred from the $N_t$ parameter with linear force-free field models of the ARs coronal  structures observed in EUV. We use the force-free parameter ($alpha$) obtained from the best model to compute a "coronal" number of turns, $N_h$. For our set of ARs observed between 2003 and 2010 we find a good agreement between both procedures. These results confirm that PIL evolution method is a reliable way to obtain an early indicator of the twist in ARs.