Figure - available from: Journal of Geophysical Research: Space Physics
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Sketch of (a) magnetic curvature directions and (b) flow vorticity of a rolled‐up Kelvin‐Helmholtz vortex developed on the duskside magnetopause; and (c and d) illustrations of the magnetic curvature analysis technique. (a) Curvature directions (colored vectors) point in opposite directions across the wave trailing edge and turn in a clockwise sense around the vortex center. (b) Vorticity is positive and strong around the vortex core, while it is negative and weak between the vortex core and the original shear layer. (c) Magnetic curvature ( C→) of the local magnetic field is resolved at the center of tetrahedron. (d) The corresponding curvature radius (Rc) is retrieved from 1/|C→| which is equal to the radius of a circle that can be fitted into the curved magnetic field line.
Source publication
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 vor...
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Citations
... At the Earth's magnetopause, the solar wind brings a large sheared flow as well as a strong tailward net momentum. Thus, the KH vortex is expected to have a sharp tailward leading edge (Kieokaew et al., 2018;Kieokaew & Foullon, 2019). However, it has been demonstrated that due to the fast corotational flow, the large sheared flow with a small net momentum on Jupiter's and Saturn's dawn side magnetopause boundary will generate an active KH vortex without a sharp tailward leading edge, resulting in a uniform distribution of angles between the perturbed normal direction and the unperturbed normal direction . ...
The interaction between the solar wind and giant magnetospheres (i.e., Jupiter's and Saturn's magnetospheres) is fundamentally important for magnetospheric physics, in which the viscous interaction (presumably driven by the Kelvin‐Helmholtz (KH) instability) is often expected to play an important role. Previous simulation and theory studies suggested that Jupiter's low‐latitude dawn side flank region is KH unstable due to the large sheared flow between the fast tailward solar wind and magnetospheric sunward corotational flow. The onset of the KH instability can strongly modify the magnetopause boundary layer, which is consistent with the identification of 194 boundary crossings during Juno's first 14 orbits. We applied four different boundary normal analysis methods to illustrate that there is always a wide range of local normal directions, suggesting Jupiter's dawn‐side flank region is often highly perturbed. The distribution of local normal directions is insensitive to the upstream solar wind dynamic pressure, Juno's inward/outward boundary crossing direction, and the location along the z direction of the boundary crossing. We also used a 2‐D magnetohydrodynamic simulation to demonstrate that such a wide distribution can be formed by the KH instability even at the beginning of the nonlinear stage.
... These velocity shears can lead to the generation of the Kelvin-Helmholtz (KH) instability (Coleman 1968;Helmholtz 1868;Kelvin 1871;Chandrasekhar 1961). Many observations show that KH waves frequently appear in various space plasma domains, including where the solar wind interacts with the Earthʼs magnetosphere (e.g., Fairfield et al. 2000;Hasegawa et al. 2004;Eriksson et al. 2016;Kieokaew & Foullon 2019), at magnetopauses of other planets like Mercury and Saturn (Slavin et al. 2008;Masters et al. 2010), on the flanks of CMEs (e.g., Foullon et al. 2011;Möstl et al. 2013;Johnson et al. 2014), and where magnetic flux interacts with solar prominences (e.g., Berger et al. 2010Berger et al. , 2017Ryutova et al. 2010;Hillier & Polito 2018). Recently, Solar Orbiter observed KH waves in the inner heliosphere at 0.69 au for the first time (Kieokaew et al. 2021). ...
The Kelvin–Helmholtz instability (KHI) can be generated at velocity shears in plasmas. While shears are abundant in the solar wind, whether they generate KHI in situ remains an open question, because of the lack of models that can simultaneously resolve the global structure of the expanding solar wind and the local structure of much smaller-scale velocity shears. In this paper, we use the Grid Agnostic MHD for Extended Research Applications model whose high resolving power, in combination with a highly refined spatial grid, allowed us to extend the simulation from global scales roughly into the first decade of the inertial range (∼1.5 × 10 ⁵ km, which we refer to as mesoscale). We employ this computational capability to extract from the simulation the local properties of radial and azimuthal solar wind velocity shears and investigate their KH stability using a linear dispersion relation, which includes both the finite width of the shear and plasma compressibility. We find that radial shears, which dominate the global structure of the inner heliosphere, are stabilized by compressibility. However, depending on the local Alfvén speed, sound speed, shear thickness, and the strength of the stabilizing azimuthal magnetic field, the azimuthal shears generated inside stream interaction regions could be KH-unstable. While our highly resolved simulation allowed us to analyze the local properties of the velocity shears, its resolution was still insufficient to confirm the instability. We argue that even higher resolution simulations are required to reproduce in situ generation of KHI at velocity shears in the solar wind.
... Magnetic curvature has been resolved in Cluster observations of various plasma structures such as current sheets (Shen et al., 2003), magnetic reconnection (Runov et al., 2003(Runov et al., , 2005, magnetic flux ropes (Yang et al., 2014), and MMS observations of electron diffusion regions . It has also been applied to investigate KH wave structures in MHD simulations (Kieokaew et al., 2018) and Cluster observations (Kieokaew & Foullon, 2019). Figure 4m shows magnetic curvature components; the component C m (red) is dominant, indicating that the magnetic fields are mainly curved in the ±m direction (sunward or tailward direction). ...
Magnetopause Kelvin‐Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small‐scale mechanisms. Vortex‐induced reconnection (VIR) was predicted in simulations and recently observed using NASA's Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations, but detailed observations were still lacking. Here we report MMS observations of an FTE‐type structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterized by (1) bipolar magnetic BY variation with enhanced core field (BZ) and (2) enhanced total pressure with dominant magnetic pressure. The cross‐section size of the FTE is found to be consistent with vortex‐induced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (VY); electron parallel heating, ion, and electron density enhancements; and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTE‐type structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Øieroset et al. (2019s). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves.
Calculating the pressure‐strain terms has recently been performed to quantify energy conversion between the bulk flow energy and the internal energy of plasmas. It has been applied to numerical simulations and satellite data from the Magnetospheric MultiScale Mission. The method requires spatial gradients of the velocity and the use of the full pressure tensor. Here we present a derivation of the errors associated with calculating the pressure‐strain terms from multi‐spacecraft measurements and apply it to previously studied examples of magnetic reconnection at the magnetopause and the magnetotail. The errors are small in a dense magnetosheath event but much larger in the more tenuous magnetotail. This is likely due to larger counting statistics in the dense plasma at the magnetopause than in the magnetotail. The propagated errors analyzed in this work are important to understand uncertainties of energy conversion measurements in space plasmas and have applications to current and future multi‐spacecraft missions.
