Transpolarlichtbogen

Transpolarlichtbogen, also known as a transpolar auroral arc, is a relatively rare auroral phenomenon that stretches across the polar cap, connecting the auroras seen on the dayside with those seen on the nightside. Unlike typical auroras that form along the oval-shaped auroral zones, transpolar arcs can extend from the dayside magnetospheric cusp region directly over the geomagnetic pole to the nightside magnetosphere.

These arcs are typically observed during periods of relatively low geomagnetic activity, which is somewhat counterintuitive given that auroras are generally associated with strong geomagnetic storms. They are often faint and diffuse, appearing as broad, greenish-white bands. The exact mechanisms responsible for their formation are still a subject of research, but they are believed to be related to the transport of plasma from the dayside magnetosphere across the polar cap to the nightside.

One proposed mechanism involves the merging of magnetic field lines from the solar wind with the Earth's magnetic field at the dayside magnetopause. This process can inject plasma into the magnetosphere, and under specific conditions, this plasma can be guided along magnetic field lines over the pole. Another theory suggests that they are caused by the convection of plasma within the polar cap itself, driven by electric fields.

The observation of transpolar auroral arcs provides valuable insights into the dynamics of the Earth's magnetosphere and the processes by which energy and particles are transferred from the solar wind into the space surrounding our planet. They serve as a visible indicator of large-scale plasma transport pathways.