Two-dimensional Ionospheric Flow Pattern Associated with Auroral Streamers

We present direct flow observations and auroral images from the SuperDARN radar and IMAGE WIC imager to investigate the ionospheric flow pattern associated with auroral streamers. For all four cases studied, streamers were ejected from east-west (EW) arcs that initiated from bead-like or small-scale auroral intensifications around the auroral poleward boundary. We find a vortex-like flow pattern with clockwise sense surrounding both the initial auroral forms and the ensuing streamers. The initial eastward flows poleward of the auroral forms and westward flows equatorward of the forms evolved to be roughly equatorward within and to the east of the streamers, and primarily poleward or toward a more poleward direction to the west of the streamers. We also found in three cases signatures of flow bifurcations at the equatorward end of the streamers, which suggests a double vortex-like flow pattern with the counterclockwise one further east of the clockwise one. Our results are consistent with the double-vortex flow structure due to interchange convection associated with a plasma sheet bubble predicted by different numerical simulations, and also provide solid evidence to several previous studies, especially Sergeev et al. [2004]. This indicates that the observed flow pattern may be the ionospheric manifestation of interchange instability in the plasma sheet.