Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers

Abstract Nightside auroral zone localized flow channels, typically associated with auroral poleward boundary intensifications and streamers, are an important component of high‐latitude ionospheric plasma dynamics. We investigate the structure of these flow channels using two‐dimensional line‐of‐sight flow observations from the Super Dual Auroral Radar Network (SuperDARN) radars and auroral images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground‐based all‐sky imager (ASI) array. Radar echoes captured <~500 km horizontal distance from the radars were mainly used to detect small‐scale flow structures that would otherwise be missed or poorly resolved in long‐range radar echoes. After identifying 135 auroral streamers in the ASI images at close‐radar capture locations, we examined the associated ionospheric flow data in the radar echoes. Flow bursts and streamers are invariably correlated in all events. The flow bursts are often directed equatorward and appear simultaneously with the streamers. Equatorward flows are located just to the east of the streamers. Less frequently (~10% of the time), a poleward flow enhancement was detected even when a streamer propagated equatorward, the poleward flow enhancement being located to the west of the auroral streamer, or to the east of the equatorward flow enhancement, consistently with the spatial relationship between flow shear and upward field‐aligned currents in plasma sheet flow bursts. The azimuthal width of the flow channel is, on average, ~75 km, and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is ~57 km eastward. This study demonstrates the capability of radar‐imager pairs for identifying the 2‐D structure of localized flows associated with plasma sheet flow bursts. Key Points Structure of flow channels using SuperDARN radars and THEMIS ASI is investigated Simultaneous flow bursts and streamers are invariably correlated in all events 3‐D structure of flows consistent with plasma flow shears around a BBF channel