Fundamental Understanding of Magnetic Reconnection via Spiral CT Scan. V. Ion Demagnetization, Electron Demagnetization, and Hall Effect

Abstract For the first time, we reveal the distribution of ion demagnetization, electron demagnetization, and Hall effect around a reconnection X-line by using the spiral CT scan technique, which is a novel technique analogous to that in the hospital. This X-line was detected by the Magnetospheric Multiscale mission and has been widely believed to host a non-guide-field reconnection. With the help of such an advanced technique, we find that: (1) the ion demagnetization is prominent everywhere at scale <1 d i , with a clear enhancement corresponding to the out-of-plane electron jet near the X-point; (2) the Hall electric field is large in both the magnetosheath-side and magnetosphere-side inflow regions, but is small at the current sheet center; (3) the electron demagnetization is strong in the magnetosheath-side inflow region and at the out-of-plane electron jet, but is weak in the magnetosphere-side inflow region and at the separatrix; (4) there is a good correlation between the ion demagnetization and Hall electric field at scale 0.25 d i < Δ < 1 d i , indicating that at such scale the Hall electric field is responsible for the breaking of the ion frozen-in law; (5) there is a good correlation between the electron demagnetization and whistler-wave power around the whole X-line, meaning that whistler waves lead to the electron demagnetization; (7) apparently, there is no correlation between the electron demagnetization and Hall electric field, so that the Hall effect does not contribute to electron demagnetization; and (8) at scale <0.25 d i , the ion demagnetization should be attributed to other effects, rather than the Hall electric field. The exact mechanism for whistler waves to cause electron demagnetization is the anomalous resistivity. All these results clearly demonstrate that magnetic reconnection is triggered (electron demagnetization) by whistler waves and is developed (ion demagnetization) by Hall effects in space.