The Effect of Current on Magnetic Null Topology during Turbulent Reconnection

Using data from the Cluster mission and the First-Order Taylor Expansion method, we investigate the spiral magnetic nulls nested in the diffusion region of turbulent reconnection in the magnetotail. We particularly focus on the relation between the magnetic null topologies and currents, which can be decomposed into a component perpendicular to spine ( j ⊥ ) and a component parallel to spine ( j ∥ ). We find that (1) the currents surrounding the spiral nulls are mainly contributed by j ∥ ; (2) the null with large ( j ⊥ ) and small spine-fan angle ( θ ), which are predicted by traditional linear theory, does not exist in the turbulent diffusion region; (3) the background current j b plays an important role in determining the direction of the currents around spiral nulls and consequently the orientation of the magnetic null structures; and (4) the spiral nulls with strong current (large magnitude j ) tend to degenerate into 2D configurations, whereas the nulls with weak currents retain the 3D features. Since the spiral magnetic nulls are crucial for the energy dissipation during the turbulent reconnection process, all of these results can provide important information for better understanding 3D turbulent reconnection.