Case study of a transpolar arc during high geomagnetic activity

We examine a transpolar arc recorded by the FUV-WIC camera onboard IMAGE satellite on 15 May 2005 around 5.45 UT. The arc was observed at the onset of a geomagnetic storm, following a significant increase of the IMF By-component and a strong positive excursion of IMF Bz before the arrival of a magnetic cloud that drove a major storm. Surprisingly, the transpolar arc did not vanish after southward turning of the IMF, but persisted for few tens of minutes into the cloud arrival. The transpolar arc appears within a peak in AE-activity of about 1300 nT, and persists until nearly 6:30 UT at which time the AE-activity had reached about 1800 nT and Dst was already at the level of -100 nT. In this study, we examine the topology of the global magnetic field configuration during the transpolar arc event using the Space Weather Modeling Framework (SWMF) global geospace simulation. While such studies have been conducted before, the persistence of the arc through the storm onset combined with our ability to include a dynamic inner magnetosphere ring current reacting to the storm onset provide a unique opportunity to examine the interplay between the solar wind driver, the inner and outer magnetosphere response, and their respective signatures in the auroral precipitation patterns in the ionosphere.