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Generated by interplanetary shocks or solar wind pressure pulses, shock aurora has transient, global, and dynamic significances and provides a direct manifestation of the solar wind‐magnetosphere‐ionosphere interaction. As a part of a series of studies of the shock aurora, this paper focuses on the interaction at the morning magnetopause and its auroral manifestation at ~06 magnetic local time, where the velocity and magnetic field shears dominate the interaction. Flow shears can generate wave‐like structures inside a viscous boundary layer or even larger‐scale vortices. These structures couple to the ionosphere via quasi‐static field‐aligned currents or via kinetic Alfvén waves. Potential drops along field‐aligned filaments may be generated accelerating electrons to form auroral manifestations of the structures. A shock aurora event at dawnside is used to test this scenario. The findings include moving auroral streaks/rays that have a vertical profile from red (at ~250 km altitude) to purple (at ~100 km). The streaks moved antisunward along the poleward boundary of the oval at an ionospheric speed of ~3 km s−1. It was mapped to the magnetopause flank at ~133 km s−1, which was consistent with the observed speed of the magnetopause surface waves generated by the Kelvin‐Helmholtz instability. The calculated field‐aligned potential drop using Haerendel's analytic model was ~5 kV that reasonably explained the observations. The results support the above scenario and reveal that magnetic and velocity shears at the flanks of the magnetospause may be the main cause of the fast moving shock aurora streaks. © 2017 American Geophysical Union

We report a study of ionospheric signatures of plasma entry and momentum transfer at the dayside magnetopause during northward oriented interplanetary magnetic field (IMF), combining ground observations of the dayside aurora and ionospheric ion drift (CUTLASS HF radar) with simultaneous particle precipitation data obtained from three overflights by the Defence Meteorological Satellite Program (DMSP) F12, F13 and F14 spacecraft. The observations were taken during a 37-min long interval of strongly northward IMF (Bz=7 nT; clock angle ∼10°–15°) after a rapid northward turning. The meridan scanning photometer at the ground station recorded a long stepwise poleward retraction and latitudinal widening of the band of auroral emission in the cusp region. Thus the activity includes a series of episodes which are characterized by an initial 1–2 min poleward “step” of the auroral poleward boundary, followed by a ∼3–4 min period of relatively steady auroral latitude. The auroral events were accompanied by bursts of “reverse” two-cell convection characterized by equatorward flow across the cusp poleward boundary. The three DMSP spacecraft, which traversed the poleward boundary of the cusp aurora from north to south, entered into a region of auroral precipitation where electrons and ions of magnetosheath origin were present, together with equatorward convection. The observations are found to be consistent with a theoretical description of a sequence of bursts of lobe reconnection involving both hemispheres. This process results in the capture of magnetosheath flux tubes and thereby closed flux is added to the dayside magnetosphere.