Detection of High‐Latitude Magnetic Reconnection Between the Northward Interplanetary Magnetic Field and a Closed Magnetic Field Wedge Linked to a Transpolar Arc

Abstract Transpolar arcs (TPAs) describe a subset of auroral emissions observed poleward of the Earth's main auroral ovals when the interplanetary magnetic field (IMF) is northward. These emissions are thought to align with a “wedge” of closed magnetic field lines extending to the high‐latitude boundary of the Earth's magnetosphere, where they are postulated to interact with the IMF through magnetic reconnection. Such an instance of “high‐latitude TPA wedge reconnection” is expected to open the Earth's magnetic field lines, but the event has never been verified by in situ observations. Here we report a detection of a high‐latitude TPA wedge reconnection site within one ion gyroradius distance on 18 March 2002, which manifests in the ionosphere as colocation of the TPA and a cusp spot. The result may explain previously reported cases of remotely detected “non‐lobe” high‐latitude magnetic reconnection, with implications for future understanding of TPAs and northward‐IMF global magnetospheric dynamics.