The dynamics of NBZ auroras

We present the first observations of a three-hour quasi-periodic intensification of the polar auroras during a prolonged interval of strongly-northward interplanetary magnetic field (IMF).  This takes the form of a localised spot of auroral emission that appears near the pole which subsequently spreads sunwards and antisunwards to produce a sun-aligned auroral arc.  This arc eventually merges with the dayside and nightside auroral zones.  Twin reverse-cell convection in the noon-sector ionosphere suggests that this occurs during on-going dual-lobe magnetic reconnection which has closed the magnetosphere.  We propose that the polar auroral dynamics are an indication of reconnection in the magnetotail, bearing similarities to southwards-IMF substorms.  We further suggest that this process may be responsible for the cusp-aligned auroral morphology frequently observed when the IMF is directed northwards.