# Solar Active Region Electric Currents Before and During Eruptive Flares

## TL;DR

This paper reviews how electric currents in solar active regions evolve before and during eruptions, combining observations, models, and simulations to explain current behaviors and their relation to solar flares.

## Contribution

It demonstrates that MHD models can explain non-neutralized currents and replicate observed current patterns during solar eruptions, confirming previous observational findings.

## Key findings

- MHD models explain non-neutralized currents via magnetic shear.
- Current densities increase in QSLs during eruptions.
- Observed current patterns match model predictions.

## Abstract

The chapter "Solar Active Region Electric Currents Before and During Eruptive Flares" is a discussion on electric currents in the pre-eruption state and in the course of eruptions of solar magnetic structures, using information from solar observations, nonlinear force-free field extrapolations relying on these observations, and three-dimensional magnetohydrodynamic (MHD) models. The discussion addresses the issue of neutralized vs. non-neutralized currents in active regions and concludes that MHD models are able to explain non-neutralized currents in active regions by the existence of strong magnetic shear along the polarity inversion lines, thus confirming previous observations that already contained this result. The models have also captured the essence of the behavior of electric currents in active regions during solar eruptions, predicting current-density increases and decreases inside flare ribbons and in the interior of expanding flux ropes respectively. The observed photospheric current density maps, inferred from vector magnetic field observations, exhibit similar whirling ribbon patterns to the MHD model results, that are interpreted as the signatures of flux ropes and of quasi-separatrix layers (QSLs) between the magnetic systems in active regions. Enhancement of the total current in these QSLs during the eruptions and decreasing current densities at the footpoint of erupting flux ropes, has been confirmed in the observations.