Multi-Scale Observations of the Magnetopause Kelvin-Helmholtz Waves During Southward IMF

The energy transfer across Earths magnetopause is caused by a variety of different plasma processes. One such process is the Kelvin-Helmholtz instability (KHI), excited by the velocity shear between the fast-flowing magnetosheath plasma and the relatively stagnant magnetosphere. It has been frequently observed during periods of northward interplanetary magnetic field (IMF), however much less is known about its behaviour during southward IMF conditions.We present the first Magnetospheric Multiscale (MMS) observations of KH waves and vortices at the dusk-flank magnetopause during southward IMF conditions on September 23, 2017. The instability criterion for the KHI was fulfilled during this event. The boundary normal vectors, obtained by using multi-point methods, are consistent with the predicted structures of the KH waves. A comparison to results from a 2D fully kinetic PIC simulation, performed for the plasma parameters observed during this MMS event, demonstrated quantitative consistencies with the MMS data in many aspects such as the flow and total pressure variations in the KH waves, and the signatures of the non-linearly rolled up KH vortices including the Low Density Faster Than Sheath (LDFTS) plasma. Furthermore, the high time resolution of MMS enabled us to study kinetic-scale plasma waves, which are observed on the low-density side of the edges of the KH waves. A comparison to 3D fully kinetic simulation results suggests, that these waves can be interpreted as being generated by the Lower-Hybrid Drift Instability (LHDI). The observed waves form due to the strong density gradient between the two sides of the boundary layer and can lead to a flattening of the edge layers.In this presentation, we will show these multi-scale properties of the observed KH waves during southward IMF.