Active region helicity properties from magnetic tongues

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

Moscú

Congreso; 40th COSPAR Scientific Assembly; 2014

Committee on Space Research

We study photospheric magnetic tongues to infer the magnetic helicity sign of a large set of active regions (ARs) observed during solar cycle 23. The tongues appear during the emergence of twisted toroidal magnetic flux tubes that form ARs due to the the azimuthal component of the magnetic field around the torus axis. The projection of the azimuthal component in the normal direction to the photosphere produces the tongues as observed in photospheric magnetograms. The method to compute the helicity sign is based on the determination and evolution of the polarity inversion line (PIL) and it's relative orientation respect to the direction of the AR main bipolar axis (the AR's tilt). We analyze a set of 150 bipolar ARs observed with SOHO/MDI between 1996 and 2010. The PIL method, as tested in previous works, needs ARs with simple bipolar structures and devoid of backgroud magnetic remnants in order to provide reliable computations. Therefore, the low number of sunspots registered along the minimum of cycle 23 to 24 is a favourable scenario to find simple isolated ARs. We analyze a series of statistical properties of the studied ARs, such as the latitudinal and hemispherical dependence of the magnetic helicity, the tilt, the total unsigned magnetic flux and the presence of asymmetries between the main polarities.