| 1. |
- Ling, Yiming, et al.
(author)
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Observations of Kelvin-Helmholtz Waves in the Earth's Magnetotail Near the Lunar Orbit
- 2018
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:5, s. 3836-3847
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Journal article (peer-reviewed)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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| 2. |
- Tian, Anmin, et al.
(author)
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Reconstruction of Plasma Structure with Anisotropic Pressure : Application to Pc5 Compressional Wave
- 2020
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In: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 889:1
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Journal article (peer-reviewed)abstract
- The conventional Grad-Shafranov (GS) method is designed to reconstruct a two-dimensional magnetohydrostatic structure with isotropic pressure. In this work, we developed a new GS solver (GS-like) that includes the effect of pressure anisotropy based on reduced equations from Sonnerup et al. The new GS solver is benchmarked, and the results are compared with two other GS solvers based on the conventional GS method and that from Teh. This solver is applied to reconstruct a Pc5 compressional wave event, which has mirror-like features and includes a significant pressure anisotropy (p/p(parallel to) similar to 1.5, where p and p(parallel to) are the thermal pressures perpendicular and parallel to the magnetic field), observed by the Magnetospheric Multiscale mission in the duskside outer magnetosphere on 2015 September 19. The recovered maps indicate that, within some model constraints, the wave in the selected time interval consists of two magnetic bottle-like structures, each with an azimuthal size of about 9000 km (wavenumber similar to 44) and a larger field-aligned size. The spacecraft passed through the bottles at similar to 1600 km southward of the bottle centers. Further multispacecraft measurements revealed that the Pc5 compressional wave propagates sunward along with the background plasma and retains the bottle-like structures, driven mainly by the ion diamagnetic currents. The reconstructed magnetic topology is similar to that described in previous empirical or theoretical antisymmetric standing wave models. This Pc5 compressional wave is possibly driven by drift-mirror-like instabilities.
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| 3. |
- Tian, Anmin, et al.
(author)
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Structure of Pc 5 Compressional Waves Observed in the Duskside Outer Magnetosphere: MMS Observations
- 2022
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In: Journal of Geophysical Research - Space Physics. - : John Wiley & Sons. - 2169-9380 .- 2169-9402. ; 127:3
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Journal article (peer-reviewed)abstract
- The geometrical structure of the Pc 5 compressional wave is important in judging its generation mechanism and the wave-particle interaction process. In this work, 117 magnetic troughs (where magnetic field strength transiently decreases) identified from 50 Pc 5 compressional wave events in the duskside (15.5–18.5 local time) magnetosphere are studied based on the Magnetospheric Multiscale (MMS) data. We derived the three dimensional geometry of the magnetic trough by including the normal and velocity information at its boundaries from the multi-spacecraft analysis method. The magnetic trough has a magnetic bottle shape along the magnetic field line with the most probable center (with weakest magnetic field) located at θ = (Formula presented.), while the widest part of the magnetic bottle located around θ (Formula presented.) (θ denotes the angle between spacecraft position vector and the ambient magnetic field). The cross section of the magnetic trough is eccentric and has a “wedge-like” shape whose average open angle is ∼23° toward radial outward. It is found that the radial component of the current density is the dominant one at the boundaries, and the value is generally proportional to the depth of the magnetic trough. The generation of these Pc 5 compressional waves can be attributed to the drift Alfvén ballooning mirror instability. This work reveals the possible changes of magnetic field configuration caused by the Pc 5 compressional wave in the magnetosphere and may bring new ideas to the interaction way between wave field and ring current particles.
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| 4. |
- Wang, Mengmeng, et al.
(author)
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Statistical analysis of whistler precursors upstream of foreshock transient shocks : MMS observations
- 2024
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 51:8
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Journal article (peer-reviewed)abstract
- Using the high-time-resolution data from the Magnetospheric Multiscale mission, precursor waves upstream of foreshock transient (FT) shocks are statistically investigated using the four-spacecraft timing method. The wave frequencies and wave vectors determined in the plasma rest frame (PRF) are shown to follow the cold plasma dispersion relation for whistler waves. Combining with the feature of the right-hand polarization in the PRF, the precursors are identified as whistler-mode waves around the lower hybrid frequency. The occurrence of whistler precursors is independent of the Alfvén Mach number and the FT shock normal angle. More importantly, all the whistler precursors have group velocities pointing upstream in the shock frame, suggesting the dispersive radiation to be a possible generation mechanism. The study improves the understanding of not only the whistler precursors but also the overall FT shock dynamics.
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| 6. |
- Zhang, Shuangshuang, et al.
(author)
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Discovery of carbon-based strongest and hardest amorphous material
- 2022
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In: National Science Review. - : Oxford University Press. - 2095-5138 .- 2053-714X. ; 9:1
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Journal article (peer-reviewed)abstract
- Carbon is one of the most fascinating elements due to its structurally diverse allotropic forms stemming from its bonding varieties (sp, sp2, and sp3). Exploring new forms of carbon has always been the eternal theme of scientific research. Herein, we report the amorphous (AM) carbon materials with high fraction of sp3 bonding recovered from compression of fullerene C60 under high pressure and high temperature previously unexplored. Analysis of photoluminescence and absorption spectra demonstrates that they are semiconducting with a bandgap range of 1.5–2.2 eV, comparable to that of widely used amorphous silicon. Comprehensive mechanical tests demonstrate that the synthesized AM-III carbon is the hardest and strongest amorphous material known so far, which can scratch diamond crystal and approach its strength. The produced AM carbon materials combine outstanding mechanical and electronic properties, and may potentially be used in photovoltaic applications that require ultrahigh strength and wear resistance.
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