3D Topology of the Transient Bifurcation on the Verge of Substorm Onset

This paper reports a transient bifurcation in a 3D terrestrial magnetospheric topology on the verge of the substorm onset in a 3D global MHD simulation. The 2D manifolds of the separatrices are determined using the Geodesic Level Set method. The separatrices are determined starting from the magnetic nulls or critical points near Earth’s north and south poles and magnetotail. We visualize the Earth magnetospheric topologies at different times near the substorm onset and identify a particular pair of saddle-connected separatrices that include two separator lines. They are both bifurcated toward north and south, thus, and allows the southward IMF to connect to the Earth magnetic field. This special topology appears on the verge of the substorm onset.