Abstract
Abstract[1] Magnetopause Kelvin‐Helmholtz (KH) waves are rich in complex magnetic and flow structures which are key to understand the role of these waves in facilitating the solar wind plasma transport into the Earth's magnetosphere. Four spacecraft in tetrahedral configuration provide the tools necessary for characterizing in situ magnetic geometry and vortical flow. We apply the tools on KH waves observed by Cluster inside an electron boundary layer on the duskside magnetopause. Magnetic curvature and flow vorticity properties of the KH waves are obtained for various solar wind conditions. Smaller curvature radius and higher‐positive vorticity are found for longer wavelength. Changes in KH wavelengths observed with relatively fixed tetrahedron size allow us to resolve magnetic curvature in multiscales. For the first time in a space plasma, we report the dependence of the curvature radius measurement on the ratio of the tetrahedron size to the wavelength, consistent with nonlinear spatial variations of magnetic structures that would be resolved by nested cross‐scale spacecraft tetrahedrons. Negative vorticity is found to develop in the rolled‐up vortex, adjacent to positive vorticity in the vortex core. The strength of negative vorticity is found to increase with the solar wind proton density and proton bulk flow speed. This study provides observational evidence of multiscale magnetic structures and is useful for understanding the development of rolled‐up vortex signatures during various stages of solar wind‐controlled KH wave evolution.
Highlights
Four-spacecraft analyses allow us to resolve in situ spatial and temporal dimensions of space plasmas
For the first time in a space plasma, we report the dependence of the curvature radius measurement on the ratio of the tetrahedron size to the wavelength, consistent with nonlinear spatial variations of magnetic structures that would be resolved by nested cross-scale spacecraft tetrahedrons
We found the smaller radius of magnetic curvature and larger positive flow vorticity for lower interplanetary magnetic field (IMF) clock angle
Summary
Four-spacecraft analyses allow us to resolve in situ spatial and temporal dimensions of space plasmas. This was demonstrated in K18, who found that the measures of four-spacecraft signatures of the magnetopause KH waves are depending on the tetrahedron size This is because plasma structures have nonlinear variations in the spatial dimension (e.g., see Figure 1c). Some qualitative features of the magnetopause KH waves are shown to be less sensitive to the tetrahedron size such as magnetic curvature direction and flow vorticity polarity (as those sketched in Figures 1a and 1b). With these simulated preliminaries in mind, we are looking for observational confirmation of nonlinear spatial variations of plasma structures associated with the Earth's flank magnetopause KH waves. We compare four-spacecraft analysis results for different scales of KH waves subjected to various IMF clock angle conditions, as characterized in F08
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