Solar Wind Influence on Dual-Lobe Reconnection and Horse-Collar Aurora

Horse-collar aurora (HCA) are an auroral formation generated by the geomagnetic reconfiguration during prolonged periods of northward-directed interplanetary magnetic field (IMF). HCA formation has been linked to dual-lobe reconnection (DLR) closing open flux at the dayside magnetopause, resulting in a reversal of the typical ionospheric twin-cell convection pattern and a poleward motion of the dawn and dusk portions of the open/closed field line boundary (OCB). This morphology gives rise to a horse-collar or teardrop-shaped polar cap.

We aim to investigate two key aspects of HCA: a) whether the dim region within the HCA is open flux, and b) whether there exists a correlation between the DLR rate and upstream solar wind parameters. This study uses HCA arc velocity as a proxy measurement for DLR rate, allowing us to infer correlation between IMF parameters and DLR rate.

Far-ultraviolet spectral images from the Special Sensor Ultraviolet Spectrographic Imager instrument on-board the Defense Meteorological Satellite Program spacecraft were used to measure the location of HCA in successive polar passes. At the current stage of the study we find a linear relation between HCA closing velocity and the total IMF magnitude and Bz magnitude. No relation was found between HCA closing velocity and solar wind flow speed or IMF By. The timescale for a full closure of the magnetosphere by DLR was also estimated for the events.