Omega Bands as a Source of Large dB/dt in the Dawn Sector
By Rosie Hodnett (University of Leicester)
Omega bands are a type of aurora which occur in the dawn sector and drift eastwards. They are often described as having a morphology similar to that of the Greek letter Ω. Omega bands have been shown to have the potential to cause geomagnetically induced currents, which are an important area of research as they are recognised as a hazard to our infrastructure, such as power grids.
In this study, we have examined an omega band event which occurred from 23 – 04 UT on 2012-11-13—14 using multiple instruments around Tromsø, Norway (69.6°N, 19.2°E). The first two panels (a-b) of the figure show EISCAT UHF/VHF electron density measurements, panel (c) shows a keogram of all-sky camera (ASC) data. It is clear that when the luminous aurora passes over head, enhancements in electron density are observed.
Panel (d) shows the magnetic field perturbations as measured by the IMAGE magnetometer and (e) shows dB/dt. For this event, we saw large perturbations in the Y component of the magnetic field, with a maximum peak of approx. 915 nT. The rapid motion of the omega bands leads to large dB/dt of above 10 nT/s.
Panel (f) shows AMPERE data, where the yellow dashed line is the location of EISCAT, where red is upward field aligned current (FAC) and blue is downward FAC. The auroral signatures and large dB/dt are evident when EISCAT is located between the boundary of region 1 and 2 current systems.
Panel (g) shows AL, where negative excursions due to the ground based magnetic perturbations of the omega bands are apparent. It is important that these rapid variations in AL are not misidentified as substorms, because as well as substorms, we have shown that omega band activity in the dawn sector causes drops in AL.

See publication for details:
Hodnett, R. M., Milan, S. E., Nozawa, S., Raita, T., Gjerloev, J. W., Vines, S. K., & Paxton, L. J. (2025). Omega bands as a source of large dB/dt in the dawn sector. Journal of Geophysical Research: Space Physics, 130, e2025JA034342. https://doi.org/10.1029/2025JA034342