Simultaneous observations of dayside aurora from Heiss Island and Ny Ålesund

This paper presents the first simultaneous observation of the cusp aurora using two overlapping imagers displaced in longitude by several hundreds of km. The imagers were located at Ny Ålesund, Norway and Heiss Island, Russia. The uniqueness of the case study presented here consists of the rapid response of the entire extension of the cusp‐related aurora to an unsettled IMF. At the start of the event, the IMF Bz component was equal to −5 nT. It was followed by a 10‐min period of positive Bz excursions (∼+2nT), before returning to a −3 nT value. Initially, when Bz was negative, the cusp aurora was located at 73° MLAT, displayed a Bz south‐type ion dispersion signature, and antisunward convection. When the IMF Bz became positive, but under a dominant Bx (−6 nT), the cusp aurora rapidly retreated poleward, and a long single band was seen extending for over 2000 km brightening from east to west. A few minutes later, still during a period of clock angle less than 120°, two bands of red emission, separated in longitude by ∼1000 km, split from the main auroral trace and move equatorward. The data presented here suggest that during a short period of dominant Bx < 0 and a solar wind phase front tilted toward the northern hemisphere the whole cusp‐related aurora responded rapidly to the new solar wind configuration.