A METHOD TO CORRECT THE EFFECT OF MAGNETIC TONGUES AND ITS APPLICATION TO MEASURE ACTIVE-REGION TILT ANGLES

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

Reunión virtual

Congreso; Committee on Space Research General Assembly; 2021

COSPAR

The presence of elongated magnetic polarities in active-region (AR) line-of-sight (LOS) magnetogramsindicates the existence of twist in the flux tube forming them. These elongations,called magnetic tongues, which are mostly visible during the emergence phase of ARs, affectthe measurement of several AR characteristics; in particular, their tilt angles. Tilt angleshave been measured thoroughly using LOS magnetograms and, historically speaking, long-termwhite-light (WL) databases, sometimes combined with magnetic field information. Since theinfluence of magnetic tongues on tilt measurements has not yet been taken into account in thesemeasurements, we aim to investigate their impact on the different methods used to compute tiltvalues. We apply standard methods to WL data and LOS magnetograms, some developed byus and others used in long-term databases, and show that the computed tilt values are affectedby the presence of magnetic tongues. Therefore, we apply the newly developed Core Field FitEstimator (CoFFE) method to separate the magnetic flux in the tongues from that in the ARcore when using LOS magnetograms. We compare all the determined tilt-angle values and findthat, for ARs with low magnetic flux tongues, all of them report consistent values. But for ARswith high flux tongues, there are noticeable discrepancies between all methods, indicating thatthese features affect differently WL and magnetic data. However, in general, CoFFE achievesa better estimation of the main bipole tilt because it removes the effect of tongues, as well asthe influence of the emergence of secondary bipoles.