The effect of magnetic tongues on the determination of the tilt angle of active regions

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

Cartagena de Indias

Simposio; IAUS 327: Fine Structure and Dynamics of the Solar Atmosphere; 2016

International Astronomical Union

p { margin-bottom: 0.21cm; }We studythe evolution of solar active regions (ARs) to determine how theirmagnetic helicity properties affect the evolution of the photosphericflux observed in SOHO/MDI magnetograms. The amount of magnetichelicity accumulated in the solar atmosphere is one the main triggersfor solar flares and other active phenomena. Several proxies toestimate the magnetic helicity of ARs have been used in recentdecades (Pevtsov et al., 2014, Space Sci. Rev., 186, 285?324).Poisson et al. (2015, Solar Phys., 290, 727-751) used, as a proxy ofthe twist in emerging ARs, the so-called magnetic tongues that areobserved in line-of-sight magnetograms. These tongues are due to theline-of-sight projection of the azimuthal component of the magneticfield in toroidal emerging flux-tubes that form ARs. Analysing seriesof observed magnetograms, in this work we study the effect of thetongues on the evolution of the tilt angle and the polarity inversionline. In bipolar ARs the tilt is defined as the angle that thesegment that joins the main centers (or barycenters) of positive andnegative polarities forms with the solar Equator. The retraction ofthe tongues during the emergence of ARs can produce a spuriousapparent evolution of the tilt. Previous works have used AR tiltevolutions to infer a large torsions of the main axis of emergingmagnetic flux-tubes (the writhe helicity component). We show that theapparent rotation of the AR polarities is not necessarily due to thetorsion of the main flux-rope axis but to the effect of the tongues.We test several methods to reduce this effect on the tilt angledetermination.