Kelvin-Helmholtz Vortices in the Low-latitude Boundary Layer Associated with Auroral Beads: Conjunction Observations from MMS and DMSP

We report a Kelvin-Helmholtz vortex (KHV) event observed at the dusk-side low-latitude boundary layer by the Magnetospheric Multiscale (MMS) satellites, in conjunction with auroral beads detected in the high-latitude ionosphere by the Defense Meteorological Satellite Program (DMSP) on 27 September 2016. During this KHV event, MMS traversed the low-latitude boundary layer (LLBL), magnetically mapping to the DMSP auroral footprint. MMS revealed small-scale substructures embedded within the KHVs. These structures are associated with intense field-aligned currents (FACs) connecting the magnetospheric boundary layer to the ionosphere. These FACs are capable of driving aurora precipitations, forming discrete auroral beads. The ~1200 km KHV scale and ~50 km auroral electron precipitation scale are consistent with magnetosphere-ionosphere flux tube mapping. These observations provide evidence that small-scale auroral beads are ionospheric signatures of mesoscale KHVs, highlighting the role of boundary layer instabilities in regulating magnetosphere-ionosphere coupling.