Magnetic helicity properties of emerging active regions determined from longitudinal photospheric magnetograms

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

Niza

Workshop; Flux Emergence Workshop 2013; 2013

We study the emergence of solar active regions (ARs) to determine how their magnetic helicity properties affect the evolution of the photospheric flux observed in SOHO/MDI magnetograms. We characterize the so called magnetic tongues (Luoni et al. 2011, Solar Phys. 270, 45), which are produced by the line of sight projection of the azimuthal component of the magnetic field in ARs formed by twisted emerging flux-tubes. We analyze a set of 25 ARs observed between 2004 and 2010. We only select regions for which the full emergence process is observed on the solar disk. In order to minimize the background magnetic field contribution, we select cases that emerge in areas devoid of remnant flux from older ARs. From the magnetograms we determine and study the evolution of relevant parameters, in particular the tilt angle, the relative direction of the polarity inversion line (defined as the PIL angle), and the magnetic flux of the ARs. Modeling the emergence of twisted magnetic flux-tubes, we demonstrate that the PIL angle is a direct proxy for the evolution of the tongues. To further characterize this evolution we compute and analyze weighted averages of the PIL angle and the magnetic flux. We find that in 22 ARs from our set the presence of magnetic tongues has a direct effect on the evolution of the PIL angle. For these cases, we are able to infer the magnetic helicity sign from the obtained measurements and their computed averages. Since ARs with high contents of magnetic helicity are, in general, the most productive in term of flares and CMEs, the possible determination of their magnetic helicity properties from the very beginning of the emergence can be a powerful forecast tool for solar activity.