Electrodynamics of transpolar aurorae

Polar UV image and Astrid-2 electric and magnetic field data are used to study the evolution of the electrodynamical configuration of the high-latitude ionosphere during a 5-h transpolar arc event. During the course of the event we observe Sunward convection in narrow regions associated with pairs of upward and downward transpolar arc-related field-aligned currents. We also observe Sunward convection deriving from more remotely located field-aligned currents as well as stagnant convection in the centre of the polar region associated with a decoupling of the dawn and dusk side current systems. Schematic pictures of the current closure and convective flows are presented for a variety of configurations. The different states evolve naturally into each other and do not represent fundamentally different magnetospheric configurations.