Magnetic Helicity properties in Solar Active Regions

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

Córdoba

Congreso; Friends of Friends; 2014

Observatorio Astronómico de Cordoba

p { margin-bottom: 0.25cm; line-height: 120%; }We study the effectof the so called magnetic tongues on the photospheric magnetic fluxdistribution of observed bipolar active regions (ARs). The tonguesappear during the emergence of twisted toroidal magnetic flux tubesthat form ARs due to the the azimuthal component of the magnetic fieldaround the torus axis. The projection of the azimuthal component inthe normal direction to the photosphere produces the tongues asobserved in photospheric magnetograms. We present a new method tocharacterize the tongues based on the determination and evolution of the polarityinversion line (PIL). In particular, we define and compute the angleparameter (τ ) that measures the relative orientation of the PILwith respect to the direction of the AR main bipolar axis. In the wayit is defined, the sign of τ provides a proxy for the AR helicitysign. We apply the method to a set ofARs observed with SOHO/MDI and SDO/HMI and compare the results withthe computation of the parameters for model ARs based on theemergence of flux tubes with prescribed twists. We also compare thenew procedure with previous methods to characterize the tongues. Ourresults demonstrate that the PIL evolution is a robust indicator ofthe presence of tongues and that the τ parameter is a very goodearly proxy of the helicity content in ARs.