Modeling the Magnetic Field in Active Regions: LFFF versus NLFFF

NUEVO, FEDERICO A.; LÓPEZ FUENTES, MARCELO; VALORI, G.; VÁSQUEZ, ALBERTO M.; MANDRINI, CRISTINA. H

San Juan

Conferencia; Towards Future Research on Space Weather Drivers (FRESWED); 2019

The knowledge of the three-dimensional coronal magnetic field ($mathbf{B}$) at high-resolution is key to better understand the physical mechanisms that trigger eruptive phenomena in the inner corona, the ultimate drivers of space weather conditions. High-resolution, direct coronal measurements of $mathbf{B}$ are not available, so we must rely on suitable coronal field models based on the available photospheric field measurements (magnetograms). For active regions´ (ARs) field, where $etall 1$, the force-free regime ($ abla imesmathbf{B} = alpha mathbf{B}$) is the simplest approximation. If $alpha$ is taken to be constant across field lines, then the model field is called a linear force-free field (LFFF), while if $alpha$ depends on position, then the model field is a non-linear force free field (NLFFF). While LFFF models are fully determined by the line-of-sight magnetograms as boundary condition, NLFFF models require information from the full vector magnetogram. In ARs with a high degree of non-potentiality, currents are observed to be concentrated in limited region of coronal space. The observational determination of $alpha$ using vector magnetograms confirms that this quantity is not constant in complex ARs. In such cases, large variations of $alpha$ are expected that cannot be accomodated for by LFFF models. In this work we test and compare specific numerical implementations of both LFFF and NLFFF models applied to two ARs exhibiting different levels of non-potentiality. We first compare the small-scale and the large-scale structure of the field, using observed coronal loops as proxies for the field-line tracing. Then, we compare the amount of magnetic free energy and helicity obtained with both models for the same integration box, and discuss the implications of our results for the determination of the characteristics of active phenomena with impact on Space Weather conditions. We also analyze the convenience of using one method over the other for different applications.