Recurrent Tailward-Propagating Auroral Arcs during northward IMF

Auroral arcs in the high latitude are frequently observed during periods of northward interplanetary magnetic field (IMF). However, their generation mechanisms are not yet fully understood, due to the limited availability of simultaneous in-situ and optical auroral observations. In this talk, we present observations of recurrent tailward-propagating auroral arcs in the dawnside during a period of northward IMF.  

THEMIS satellites located near the dawnside magnetopause in the equatorial plane observed strong fluctuations in magnetic field and plasma parameters with periods of 5–7 minutes, suggesting the presence of surface waves or ULF waves. Subsequently, shorter-period fluctuations of 2-3 minutes were observed for an hour, which may indicate the development of Kelvin–Helmholtz instability (KHI). During these intervals, a ground-based all-sky imager detected recurrent auroral arcs detached from the poleward boundary of the auroral oval, with a period of 5–10 minutes, propagating predominantly tailward. DMSP observations revealed multiple auroral arcs on the dawnside, accompanied by electron precipitation associated with paired upward and downward field-aligned currents. Based on these coordinated space- and ground-based observations, we discuss several possible generation mechanisms for the observed auroral arcs, including surface waves, ULF waves, and KHI.