tokens: 1982 ; Forbes 2000 ; Vršnak 2008 ; Aulanier 2014 ; Janvier et al. 2015 , for reviews). Characterizing coronal currents before and during eruptions is therefore important to develop a comprehensive understanding of the triggering and acceleration of CMEs, especially in the context of a growing need for accurate and quantitative space weather forecasts. In addition, on a more fundamental basis, specifying the spatiotemporal evolution of eruption-related currents at the Sun’s surface would also bring an unprecedented input to the versus debate (e.g., Melrose 1991 ; Parker 1996 , 2001 ; Heikkila 1997 ; Vasyliunas 2005 ), in particular regarding whether the magnetic field or the electric current should be considered as a prime variable and boundary condition in solar eruption models in particular, and in space plasmas in general. All these considerations have recently led to a renewed interest in studying solar electric currents (see, e.g., Melrose 2017 ; Georgoulis 2018 ; Schmieder Aulanier 2018b ). The paradigm regarding the spatial distribution of currents in solar active regions has evolved over the years. For a long time, the geometrical properties of cylindrical flux ropes naturally led to the view that active region magnetic fields ought to be shielded from their surroundings through external return currents, with a magnitude equal to that of the direct currents. This so-called current neutralization of coronal flux ropes was considered to be a natural prediction of the paradigm, in the context of the MHD twisting of coronal flux-tubes (as explained e.g., in Parker 1996 ; Dalmasse et al. 2015 ). Such neutralized currents in the corona, however, are problematic for several eruption models that rely on the existence of net currents (e.g., van Tend Kuperus 1978 ; Forbes Priest 1995 ; Kliem Török 2006 ; Démoulin Aulanier 2010 ). In addition, the most recent observations of sunspots revealed that many flaring active regions carry a non-neutralized (i.e., a net) current (Ravindra et al. 2011 ; Georgoulis et al. 2012 ; Cheng Ding 2016 ; Zhao et al. 2016 ; Vemareddy 2019 ). These observations could have been considered to support the paradigm, with some circuit models associated with net coronal electric currents directly originating from the depths of the Sun’s interior (Alfvén Carlqvist 1967 ; Melrose 1991 ). However, recent numerical MHD models of magnetic fields in the corona driven by magnetic flux emergence (Török et al. 2014 ) or by line-tied motions (Dalmasse et al. 2015 ) have both unveiled that MHD processes could also generate net coronal currents in pre-eruptive active regions, due to the shear component of the magnetic field across polarity inversion lines (PILs). Two different analytical interpretations have been provided to explain this association, either by invoking Lorentz forces (Georgoulis et al. 2012 ) or a simple property of the integral form of Ampère’s law with force-free fields (Dalmasse et al. 2015 ). In both cases, it was
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