Multiple polar auroral arcs – characteristics and magnetospheric source regions

The occasional appearance of auroral arcs far poleward of the latitudes where the aurora usually occurs, gives us a hint on the complicated solar wind –magnetosphere –ionosphere coupling processes during quiet geomagnetic times.

The textbook picture of the polar cap as a region void of aurora and being directly coupled to the solar wind through open magnetic field lines does not hold in such cases.

Different models have been proposed in the last decades to explain the occasional formation of one bright large-scale transpolar arc.Thanks to a new generation of UV imagers onboard low-altitude satellites with a much higher resolution and a better luminosity sensitivity than previous global auroral imagers, a new picture of the quiet polar cap has emerged in recent years.

The simultaneous occurrence of typically cusp-aligned arcs that fill the polar cap during quiet times is far more common than previously understood.

Such cases cannot be explained with the help of standard transpolar arc models, where the formation of one bright polar arc has been linked (in one way or another) to IMF By induced changes in the magnetotail.In the proposed 4-year PhD project we want to address the question of how and why multiple polar auroral arcs emerge and fill the polar cap.In the first part of this work, it is suggested to investigate the polar cap region during multiple polar arc events with the help of DMSP SSUSI images, magnetic field and particle data to find out about characteristics and possible source regions of the arcs.

In addition, SuperDARN plasma flow and AMPERE field-aligned current maps will be examined to understand the global state of the polar cap region during such events.

The identification of typical solar wind conditions will help to understand the global solar wind-magnetosphere coupling when multiple polar arcs occur.In the second part of this work the focus is on (a) possible sources of the filamentation into multiple arcs such as KH-instabilities along the magnetopause flanks, and on (b) the state of the magnetotail lobes during multiple arc events (they should be heavily structured and/or have partly disappeared).

The second part of this work is performed with the help of data from magnetopause and tail orbiting satellite missions such as Cluster and MMS during times when multiple polar arcs are seen in DMSP SSUSI and TIMED GUVI images.