| 1. |
- Li, Tongkuai, et al.
(författare)
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Kelvin-Helmholtz Waves and Magnetic Reconnection at the Earth's Magnetopause Under Southward Interplanetary Magnetic Field
- 2023
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:20
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale (MMS) observations of a K-H wave event under southward IMF conditions, accompanied by ongoing magnetic reconnection. The nonlinear K-H waves are characterized by quasi-periodic fluctuations, the presence of low-density and high-speed ions, and variations in the boundary normal vectors at both the leading and trailing edges. Our observations reveal clear evidence of on-going magnetic reconnection through the identification of Alfvenic ion jets and the escape of energetic magnetospheric electrons. Among the 36 magnetopause current-sheet crossings in this event, 19 exhibit unambiguous signatures of reconnection at both the leading (7) and trailing (12) edges. Notably, the estimated current-sheet thicknesses at both edges are comparable to the ion-inertial scale, confirming the compression effect resulting from the large-scale evolution of the K-H waves. The reconnection jets potentially contribute to the suppression of K-H growth through boundary-layer broadening and the development of complex flow and magnetic field patterns.
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| 2. |
- Ling, Yiming, et al.
(författare)
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Observations of Kelvin-Helmholtz Waves in the Earth's Magnetotail Near the Lunar Orbit
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:5, s. 3836-3847
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Tidskriftsartikel (refereegranskat)abstract
- Kelvin‐Helmholtz waves (KHWs), which have been widely observed at the magnetopause in the region near the Earth, play an essential role in the transport of solar wind plasma and energy into the magnetosphere under dominantly northward interplanetary magnetic field (IMF) conditions. In this study, we present simultaneous observations of KHWs under the northward IMF observed by both the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft in the Earth's magnetotail around the lunar orbit (at X ~ −50RE, Y ~ 30RE, dusk side) and the Geotail in the near‐Earth space (at X ~ −5RE, Y ~ −10RE, dawn side). The KHWs are quantitatively characterized by their dominant period, phase velocity, and wavelength, utilizing wavelet analysis and an approximation of their center‐of‐mass velocity. Our results suggest that the phase velocity and spatial scale of KHWs may increase as they propagate along the boundary layer toward the tail. Alternatively, the differences between the ARTEMIS and Geotail observations may indicate the possibility of dawn‐dusk asymmetry in the excited KHWs in this study. Our results strongly evidence the existence of the development of KHWs in terms of their wave frequency and scale size in the magnetotail and provide insight to the time evolution of KHWs along the magnetopause.
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| 3. |
- Tang, Binbin, et al.
(författare)
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Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin-Helmholtz waves
- 2018
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Ingår i: Annales Geophysicae. - : COPERNICUS GESELLSCHAFT MBH. - 0992-7689 .- 1432-0576. ; 36:3, s. 879-889
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Tidskriftsartikel (refereegranskat)abstract
- We report an ion-scale magnetic flux rope (the size of the flux rope is similar to 8.5 ion inertial lengths) at the trailing edge of Kelvin-Helmholtz (KH) waves observed by the Magnetospheric Multiscale (MMS) mission on 27 September 2016, which is likely generated by multiple X-line reconnection. The currents of this flux rope are highly filamentary: in the central flux rope, the current flows are mainly parallel to the magnetic field, supporting a local magnetic field increase at about 7 nT, while at the edges the current filaments are predominantly along the antiparallel direction, which induce an opposing field that causes a significant magnetic depression along the axis direction (> 20 nT), meaning the overall magnetic field of this flux rope is depressed compared to the ambient magnetic field. Thus, this flux rope, accompanied by the plasma thermal pressure enhancement in the center, is referred to as a crater type. Intense lower hybrid drift waves (LHDWs) are found at the magnetospheric edge of the flux rope, and the wave potential is estimated to be similar to 17% of the electron temperature. Though LHDWs may be stabilized by the mechanism of electron resonance broadening, these waves could still effectively enable diffusive electron transports in the cross-field direction, corresponding to a local density dip. This indicates LHDWs could play important roles in the evolution of crater flux ropes.
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| 4. |
- Xin, Tongzheng, et al.
(författare)
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Phase transformations in an ultralight BCC Mg alloy during anisothermal ageing
- 2022
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- Mg-Li-Al alloys with a body-centred cubic (BCC) structure can exhibit exceptional specific strengths in combination with excellent ductility and corrosion resistance. In general, the strength of these alloys is very sensitive to the processing temperature due to the occurrence of various phase transformations. Although different phases have been identified in these alloys, their corresponding transformation mechanisms and unique role played in controlling the mechanical properties have never been studied in depth. In this work, we identified the phase transformation sequence by in-situ synchrotron X-ray diffraction. Moreover, we investigated the evolution of precipitation and their morphology using transmission and scanning electron microscopy, together with simulations based on the phase field modelling and first-principles calculations. Phase transformation sequence of Al-rich zone?->?theta (D0(3)(-)Mg(3)Al)?->?AlLi was confirmed during anisothermal ageing. A braided structure resulting from spinodal decomposition was found to be the optimized microstructure for achieving the peak strength. Nanocrystalline alpha-Mg phase at the interface between theta and the matrix was identified as the main reason for softening in the alloy. The core-shell model for theta?->?AlLi transformation is observed and verified. Our findings deepen the understanding of BCC Mg-Li-Al alloys and pave a pathway to develop new generation of ultralight alloys with stronger strength and better stability. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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