The Dawn-Dusk Tail Lobe Magnetotail Configuration and the Formation of Aurora Transpolar Arc

The magnetotail configuration includes a northern tail lobe, a southern tail lobe, and a plasma sheet when IMF directs southward, as a result of the Dungey cycle. However, it is little known about the magnetotail configuration for northward IMF (NIMF) conditions. Using in situ data and corresponding simulations, we show that the magnetotail forms into a dawnside tail lobe and a duskside tail lobe under NIMF with significant By conditions. The data shows signatures related to magnetotail reconnection under such conditions. Cusp reconnection and such magnetotail reconnection may form a dawn-dusk tail lobe configuration and its version of Dungey cycle. Simulation results also show that aurora transpolar arc may be caused by a process of reconfiguration of the dawn-dusk tail lobe structure as a result of an IMF By reversal.