Are Cusp‐Aligned Arcs the Equivalent of Auroral Streamers in a Closed Magnetosphere?

Abstract We present the first observations of a 3‐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 localized spot of auroral emission that appears near the pole which subsequently spreads sunward and antisunward 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 southward‐IMF auroral streamers. We further suggest that this process may be responsible for the cusp‐aligned auroral morphology frequently observed when the IMF is directed northward.