Relationship Between Each FAC Component and Auroral Electron Precipitation During Substorms

It is traditionally assumed that upward currents correspond to electron precipitation, suggesting that electron precipitation should align with Region 2 (R2) Field-Aligned Currents (FACs) in the dawn sector and Region 1 (R1) FACs in the dusk sector. However, some previous studies have indicated systematic discrepancies between the locations of auroral electron precipitation and R1/R2 FACs, a topic that remains controversial and lacks an adequate explanation. This study aims to investigate and explain these differences. We conducted a detailed analysis of the relationship between FACs and auroral electron precipitation throughout the substorm phases, including the growth, expansion, and recovery phases. It is shown that (a) the region of large energy flux in auroral electron precipitation corresponds to the transition zone between R1 and R2 FACs, (b) auroral electron precipitation enhances height-integrated conductances, which combine with downward vorticities to be associated with upward magnetospheric-origin FACs, and (c) auroral electron precipitation also strengthens the gradient of height-integrated conductances and this enhanced gradient, together with drift velocities, contributes to the formation of downward ionospheric-origin FACs. The interplay between downward ionospheric-origin FACs and upward magnetospheric-origin FACs shifts the transition zone to poleward, resulting in the observed correlation between the region of large energy flux and the transition zone. This is similar to the mechanism of feedback instability. Specifically, the height-integrated conductance gradients due to auroral electron precipitation drive polarized currents, fed by downward and upward FACs. These FACs shift the transition zone poleward and enhance auroral electron precipitation energy flux, forming a closed feedback loop.