  Electric currents play a critical role in the triggering of solar flares and
their evolution. The aim of the present paper is to test whether the surface
electric current has a surface or subsurface fixed source as predicts the
circuit approach of flare physics, or is the response of the surface magnetic
field to the evolution of the coronal magnetic field as the MHD approach
proposes. Out of all 19 X-class flares as observed by SDO from 2011 to 2016
near the disk center, we analyzed the only 9 eruptive flares for which clear
ribbon-hooks were identifiable. Flare ribbons with hooks are considered to be
the footprints of eruptive flux ropes in MHD flare models. For the first time,
fine measurements of time-evolution of electric currents inside the hooks in
the observations as well as in the OHM 3D MHD simulation are performed. Our
analysis shows a decrease of the electric current in the area surrounded by the
ribbon hooks during and after the eruption. We interpret the decrease of the
electric currents as due to the expansion of the flux rope in the corona during
the eruption. Our analysis brings a new contribution to the standard flare
model in 3D.
