The effect of magnetic tongues in the determination of Joy's law

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

Congreso; 42nd COSPAR Scientific Assembly; 2018

We study the emergence of 186 bipolar active regions (ARs) to determinethe relation between the tilt angle formed with respect to the E-Wdirection and the latitude of emergence. This relation, known as Joy'slaw, plays a fundamental role to test the ability of dynamo models toexplain, among other things, the equatorial flux cancelation and theinversion of the poloidal magnetic field between solar cycles. Themethods used in recent works to determine this law are based on theautomatic computation of the tilt angle from line-of-sight (LOS)magnetograms (Stenflo & Kosovichev 2012; Wang et al. 2015). However,since those results show a large dispersion, the precise latitudinaldepedence on the tilt is still a topic of discussion. We consider thatan important part of this dispersion can be due to the effect of the socalled magnetic tongues. These are produced by the line of sightprojection of the azimuthal magnetic field of the twisted emergingflux-tubes that form ARs. The tongues are observed in LOS magnetogramsas an elongation of the magnetic polarities. In Poisson et al. (2016,Solar Phys., 291, 1625-1646) we showed that the magnetic tongues affectthe photospheric field distribution observed in LOS magnetograms and,consequently, impact on the determination of the tilt angle. In thiswork we test a novel method to remove the effect of the tongues on thetilt angle determination and we quantify the effect of this correctionon Joy's law. Furthermore, we study the relation of the latitudinaldependence of the corrected tilt with other AR properties such as themagnetic helicity sign, the hemisphere of emergence, and the sense ofrotation of the bipoles.