| 1. |
- Hwang, K.-J., et al.
(author)
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Bifurcated Current Sheet Observed on the Boundary of Kelvin-Helmholtz Vortices
- 2021
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In: Frontiers in Astronomy and Space Sciences. - : Frontiers Media S.A.. - 2296-987X. ; 8
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Journal article (peer-reviewed)abstract
- On May 5, 2017 MMS observed a bifurcated current sheet at the boundary of Kelvin-Helmholtz vortices (KHVs) developed on the dawnside tailward magnetopause. We use the event to enhance our understanding of the formation and structure of asymmetric current sheets in the presence of density asymmetry, flow shear, and guide field, which have been rarely studied. The entire current layer comprises three separate current sheets, each corresponding to magnetosphere-side sunward separatrix region, central near-X-line region, and magnetosheath-side tailward separatrix region. Two off-center structures are identified as slow-mode discontinuities. All three current sheets have a thickness of ∼0.2 ion inertial length, demonstrating the sub-ion-scale current layer, where electrons mainly carry the current. We find that both the diamagnetic and electron anisotropy currents substantially support the bifurcated currents in the presence of density asymmetry and weak velocity shear. The combined effects of strong guide field, low density asymmetry, and weak flow shear appear to lead to asymmetries in the streamlines and the current-layer structure of the quadrupolar reconnection geometry. We also investigate intense electrostatics waves observed on the magnetosheath side of the KHV boundary. These waves may pre-heat a magnetosheath population that is to participate into the reconnection process, leading to two-step energization of the magnetosheath plasma entering into the magnetosphere via KHV-driven reconnection.
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| 2. |
- Hwang, K-J, et al.
(author)
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Magnetic Reconnection Inside a Flux Rope Induced by Kelvin-Helmholtz Vortices
- 2020
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 125:4
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Journal article (peer-reviewed)abstract
- On 5 May 2017, MMS observed a crater-type flux rope on the dawnside tailward magnetopause with fluctuations. The boundary-normal analysis shows that the fluctuations can be attributed to nonlinear Kelvin-Helmholtz (KH) waves. Reconnection signatures such as flow reversals and Joule dissipation were identified at the leading and trailing edges of the flux rope. In particular, strong northward electron jets observed at the trailing edge indicated midlatitude reconnection associated with the 3-D structure of the KH vortex. The scale size of the flux rope, together with reconnection signatures, strongly supports the interpretation that the flux rope was generated locally by KH vortex-induced reconnection. The center of the flux rope also displayed signatures of guide-field reconnection (out-of-plane electron jets, parallel electron heating, and Joule dissipation). These signatures indicate that an interface between two interlinked flux tubes was undergoing interaction, causing a local magnetic depression, resulting in an M-shaped crater flux rope, as supported by reconstruction.
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| 3. |
- Hwang, K. -J, et al.
(author)
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Microscale Processes Determining Macroscale Evolution of Magnetic Flux Tubes along Earth's Magnetopause
- 2021
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In: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 914:1
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Journal article (peer-reviewed)abstract
- An important process affecting solar wind-Earth's magnetosphere coupling is nonsteady dayside magnetic reconnection, observationally evidenced by a flux transfer event (FTE) that shows a bipolar variation of the magnetic field component normal to the magnetopause. FTEs often consist of two interlinked flux tubes, but, local kinetic processes between the flux tubes are not understood in the context of the FTE structuring, evolution, and impact. An FTE observed by the Magnetospheric Multiscale mission on 2017 December 18 consisted of two flux tubes of different topology. One includes field lines with ends connected to the northern and southern hemispheres while the other includes field lines with both ends connected to the magnetosheath. Reconnection occurring at the flux-tube interface indicates how interacting flux tubes evolve into a flux rope with helical magnetic topology that is either closed or open. This study demonstrates a new aspect of how micro- to meso-scale dynamics occurring within FTEs determines their macroscale characteristics and evolution.
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