Modeling the photospheric magnetic field distribution of emerging solar active regions

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

Boulder

Conferencia; Applications of Statistical Methods and Machine Learning in the Space Sciences; 2021

Space Science Institute

Active regions (ARs) appear in the solar atmosphere as a consequence of the emergence of magnetic flux tubes. It has been shown that in order to survive their transit through the convective zone, these flux tubes should be twisted, forming so-called magnetic flux-ropes (FR) and transporting with them magnetic helicity from the solar interior. This quantity plays a key role in the production of energetic events such as flares and coronal mass ejections. Photospheric observations of the line-of-sight (LOS) component of the magnetic field reveal that during the emergence of ARs the presence of twisted field lines around the FR axis produces an elongation of the main AR magnetic polarities known as magnetic tongues. In this work we aim to estimate the intrinsic geometrical properties of FRs, by comparing LOS magnetograms of emerging ARs with synthetic magnetograms derived from a toroidal magnetic flux tube model. In particular, we estimate the tilt angle, defined as the inclination of the AR main bipolar axis with respect to the solar equator, which is strongly affected by magnetic tongues. Our method uses a probabilistic scheme based on the Bayes theorem to infer the most probable intrinsic parameters of an emerging flux tube, assuming a normal departure between the model and the observations. Open access python 3 packages, pymc3 and Theano are used to optimize the sampling of the model 8-dimensional parameter space. Analyzing a sequence of 66 magnetograms, we are able to infer the most probable values of the intrinsic parameters for AR 10268, including its magnetic helicity content and its intrinsic tilt angle.