Evolution of Solar Magnetic Flux Ropes with Significant Non-neutralized Electric Current toward Eruption

It is generally accepted that magnetic flux ropes (MFRs) are a critical component of many coronal mass ejections. However, the nature of the pre-eruptive magnetic configuration of CMEs is still under debate. A more crucial question is how the pre-eruptive magnetic configuration forms in the Sun and further evolves toward eruptions. In our previous statistical studies, we investigated pre-eruptive magnetic properties of 80 erupting MFRs whose feet are well identified by conjugate coronal dimmings. An interesting finding from our previous study is that 17 out of 80 MFRs carried significant non-neutralized electric currents prior to their eruption.  Here we investigate the entire evolution of these MFRs from birth to eruption. Impressively, the significant non-neutralized electric current appeared several hours ahead of the formation of coronal MFRs. The buildup of coronal MFRs were simultaneous with evolution of the non-neutralized electric current in the photosphere. The preflare brightening with two ribbon-like structures always observed among the coronal MFRs. Quantitative measurements indicate that the significant non-neutralized electric current also flows through the footpoints of the erupting MFRs. The asymmetric distributions of electric current and magnetic twist were found in these MFRs. The evolution of the photospheric non-neutralized electric current is demonstrated to signal the buildup of the pre-eruptive structure and the imminent eruption.