Omega Band Magnetospheric Source Location: A Statistical Model-Based Study.

Auroral omega bands have been observed since the 1960s and their ionospheric electrodynamic properties are well established. At the same time magnetospheric source is poorly investigated leaving a room for few competing hypotheses on how the omega band forms. Here we present the statistical study of the projections of about 400 omega bands from the ionosphere to magnetosphere to investigate the location and properties of a possible omega source region in the magnetosphere. We used the Magnetometers--Ionospheric Radars--All-sky Cameras Large Experiment all-sky images on the list of individual omega structures (Partamies et al., 2017, http://doi.org/10.5194/angeo-35-1069-2017) which were observed in the Fennoscandian Lapland in the period of 1997-2007, and a new empirical magnetic field model (Tsyganenko & Andreeva, 2016, https://doi.org/10.1002/2016ja023217) to identify the magnetospheric equatorial projection of the observed omegas. We found that 90% of the auroral omega structures map to the radial distances of 6-14 RE from the Earth, coinciding with the bursty bulk flow braking region. An average magnetic field configuration in the vicinity of magnetospheric omega projections corresponds approximately to the transition region between tail- and dipole-like magnetic configuration. Velocity estimates for omega projections reveal the dawnward as well as the radial propagation in the magnetosphere with a typical speed of up to few tens of km/s. It is shown that the source of omega structures propagates earthward in most of the events. [ABSTRACT FROM AUTHOR]