Computing the tilt angle of solar active regions

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

San Juan

Congreso; Towards Future Research on the Drivers of Space Weather; 2019

Instituto de Astronomía y Física del Espacio

Thetilt angle of an active region (AR) is defined as the acute anglebetween the segment that joints the magnetic barycenters of the mainAR polarities and E-W solar direction. Current methods to estimatethe tilt angle rely on the magnetic flux distribution of the ARobtained from line-of-sight (LOS) magnetograms. However, the LOSprojection of magnetic field in twisted emerging structures formingARs produces an elongation of the magnetic polarities known asmagnetic tongues. In Poisson et al. (2016, Solar Phys., 291,1625-1646) we have shown that magnetic tongues affect thephotospheric field distribution in LOS magnetograms and,consequently, impact on the determination of the tilt angle. Asa first approach, we use a simple flux emergence model to test amethod to isolate and remove the flux associated with the tonguesfrom the tilt angle estimation. Then, with our experience gained fromthe model, wedevelop a new procedure to determine the tilt angle of solar ARs. Weapply this method to 150 ARs observed by the Michelson DopplerImager. We compute the evolution of the corrected tilt during theemergence the ARs and we quantify the effect of the magnetic tonguesin the determination of the tilt. Finally, using this method wecorrect the mean size of the ARs and we estimate the intrinsicrotation of the emerging bipoles. Knowledge of an AR intrinsicrotation can be a good proxy for the free magnetic energy storedduring the AR emergence. p { margin-bottom: 0.25cm; line-height: 120%; }