Observations and electrodynamics of an omega band aurora at Tromsø, Norway

Omega bands are a dawn-sector phenomena which appear as wave-like structures in the aurora, which often look like a chain of the Greek letter Ω. Omega bands have recently been shown to be responsible for large variations in dB/dt which can trigger geomagnetically induced currents (GICs), which are a significant space weather hazard. Signatures of an omega band event are visible in the European Incoherent SCATter (EISCAT) data at Tromsø, Norway (69.6 °N, 19.2 °E), alongside observations from multiple instruments situated near Tromsø. The omega band is clearly identifiable in the Tromsø all sky camera data from 00:00 – 03:00 UT as it propagates eastward. This event is of interest for several reasons. During this event, the polar cap and field aligned current systems are expanded, and there are multiple intensifications in the AL index. These features are often misidentified as substorms, however in this case the fluctuations in the westward electrojet result from the omega band. Large ground-based magnetic perturbations are visible, and associated ‘spikes’ in dB/dt are identified in the auroral dawn sector. Data from the EISCAT UHF and VHF radars allow us to see enhancements in the ionospheric electron density which occurred as the upwards field aligned current and luminous aurora passed overhead. Additional electron density enhancements in the D region ionosphere were observed, which correspond to enhancements in cosmic noise absorption measured by nearby riometers. We present an overview of the electrodynamics of this omega band event at Tromsø.