| 1. |
|
|
| 2. |
- Li, Xing-Yu, et al.
(författare)
-
Comparative Study of Dayside Pulsating Auroras Induced by Ultralow-Frequency Waves
- 2023
-
Ingår i: Universe. - : MDPI AG. - 2218-1997. ; 9:6
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsating auroras are usually observed with ultralow-frequency (ULF) waves in the Pc 3-5 band (period 10-600 s). These auroras are thought to result from interactions between energetic electrons and chorus waves, but their relationship with ULF waves remains an open question. In this study, we investigated this question by conducting a comparative study on two ULF wave events with pulsating auroras observed near the magnetic footprints. Conjugate observations from the Magnetospheric Multiscale mission and the Chinese Yellow River Station were used. In both events, lower-band chorus waves were observed, which were suggested to be connected with the auroral pulsations by wavelet analysis. The intensity of these waves oscillates at the period of the ULF waves, but the physics laid behind them differs by events. During the event of 22 January 2019, compressional ULF waves changed the threshold for the whistler anisotropy instability periodically, affecting the emission of chorus waves. In the event on 10 January 2016, poloidal ULF waves modulated the chorus wave generation by regulating electron temperature anisotropy through drift resonance. ULF waves in these events may originate from perturbations in the solar wind. We highlight the role of ULF waves in the solar wind-magnetosphere-ionosphere coupling, which requires further study.
|
|
| 3. |
- Li, Xing Yu, et al.
(författare)
-
Ion Acceleration and Corresponding Bounce Echoes Induced by Electric Field Impulses: MMS Observations
- 2024
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 129:2
-
Tidskriftsartikel (refereegranskat)abstract
- Dayside magnetosphere interactions are essential for energy and momentum transport between the solar wind and the magnetosphere. In this study, we investigate a new phenomenon within this regime. Sudden enhancements of ion fluxes followed by repeating dropouts and recoveries were observed by Magnetospheric Multiscale on 5 November 2016, which is the very end of the recovery phase from a moderate geomagnetic storm. These repetitive flux variations display energy-dispersive characteristics with periods relevant to ion bounce motion, suggesting they are corresponding echoes. Alongside the flux variations, bipolar electric field impulses originating from external sources were detected. We traced the source region of the initial injection and found it is located near the spacecraft's position. To elucidate the underlying physics, a test-particle simulation is conducted. The results reveal that radial transport resulting from impulse-induced acceleration can give rise to these echoes. Observations demonstrate dayside magnetosphere interactions are more common than we previously considered, which warrants further research.
|
|
| 4. |
- Li, Xing-Yu, et al.
(författare)
-
Off-Equatorial Minima Effects on ULF Wave-Ion Interaction in the Dayside Outer Magnetosphere
- 2021
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:18
-
Tidskriftsartikel (refereegranskat)abstract
- The ultra-low frequency wave-particle drift-bounce resonance in the inner magnetosphere has been studied in detail, due to its important role in particle energization. However, it remains an open question how drift-bounce resonance manifests in the dayside outer magnetosphere, where particles' orbits show bifurcations because of off-equatorial magnetic field minima. In this study, we investigate this question, by analyzing Magnetospheric Multiscale observations of the January 20, 2017 event. A test-particle simulation is conducted to help us understand the observations. The observed pitch angle-time spectrograms show "pawtrack-like" structures. We find there are more than two resonant pitch angles at fixed energy, since off-equatorial minima change the relationship between the bounce (drift) frequency and pitch angle from unimodal function to trimodal function. These results reveal a new drift-bounce acceleration mechanism in the dayside outer magnetosphere, which potentially affects the efficiency of particle energization during geomagnetic activities like geomagnetic storms.
|
|
| 5. |
- Li, Xing-Yu, et al.
(författare)
-
ULF Wave-Induced Ion Pitch Angle Evolution in the Dayside Outer Magnetosphere
- 2022
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:8
-
Tidskriftsartikel (refereegranskat)abstract
- Drift-bounce resonance between ultralow frequency (ULF) waves and ions is essential for ion energization in the magnetosphere. Here, we present the first comprehensive study of drift-bounce resonance in the dayside outer magnetosphere, where off-equatorial magnetic field minima would strongly distort ions' bounce and drift motion. A generalized theory is proposed, in which the effects of off-equatorial minima, time-evolving fields and ion bounce motion are taken into account. In consequence of these effects, ion pitch angle distributions undergo dramatic changes. In the presence of off-equatorial minima, the time-of-flight effect of ion bounce motion forms latitude-dependent dispersions besides "paw-track shaped" structures, while evolving wave fields cause time-dependent phase shifts in "paw-tracks." All the predicted signatures have been confirmed by 5 years of Magnetospheric Multiscale spacecraft data and numerical simulations. These results allow us to better understand the interactions between ULF waves and thermal ion species in global magnetospheric dynamics.
|
|
| 6. |
- Li, Yu-Xuan, et al.
(författare)
-
Quantification of Cold-Ion Beams in a Magnetic Reconnection Jet
- 2021
-
Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media S.A.. - 2296-987X. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Cold (few eV) ions of ionospheric origin are widely observed in the lobe region of Earth's magnetotail and can enter the ion jet region after magnetic reconnection is triggered in the magnetotail. Here, we investigate a magnetotail crossing with cold ions in one tailward and two earthward ion jets observed by the Magnetospheric Multiscale (MMS) constellation of spacecraft. Cold ions co-existing with hot plasma-sheet ions form types of ion velocity distribution functions (VDFs) in the three jets. In one earthward jet, MMS observe cold-ion beams with large velocities parallel to the magnetic fields, and we perform quantitative analysis on the ion VDFs in this jet. The cold ions, together with the hot ions, are reconnection outflow ions and are a minor population in terms of number density inside this jet. The average bulk speed of the cold-ion beams is approximately 38% larger than that of the hot plasma-sheet ions. The cold-ion beams inside the explored jet are about one order of magnitude colder than the hot plasma-sheet ions. These cold-ion beams could be accelerated by the Hall electric field in the cold ion diffusion region and the shrinking magnetic field lines through the Fermi effect.
|
|
| 7. |
- Ling, Yiming, et al.
(författare)
-
Observations of Kelvin-Helmholtz Waves in the Earth's Magnetotail Near the Lunar Orbit
- 2018
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:5, s. 3836-3847
-
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.
|
|
| 8. |
- Park, Jong-Sun, et al.
(författare)
-
Transpolar Arcs During a Prolonged Radial Interplanetary Magnetic Field Interval
- 2021
-
Ingår i: Journal of Geophysical Research - Space Physics. - : John Wiley & Sons. - 2169-9380 .- 2169-9402. ; 126:6
-
Tidskriftsartikel (refereegranskat)abstract
- Transpolar arcs (TPAs) are believed to predominantly occur under northward interplanetary magnetic field (IMF) conditions with their hemispheric asymmetry controlled by the Sun-Earth (radial) component of the IMF. In this study, we present observations of TPAs that appear in both the northern and southern hemispheres even during a prolonged interval of radially oriented IMF. The Defense Meteorological Satellite Program (DMSP) F16 and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellites observed TPAs on the dawnside polar cap in both hemispheres (one TPA structure in the southern hemisphere and two in the northern hemisphere) during an interval of nearly earthward-oriented IMF on October 29, 2005. The southern hemisphere TPA and one of the northern hemisphere TPAs are associated with electron and ion precipitation and mostly sunward plasma flow (with shears) relative to their surroundings. Meanwhile, the other TPA in the northern hemisphere is associated with an electron-only precipitation and antisunward flow relative to its surroundings. Our observations indicate the following: (a) the TPA formation is not limited to northward IMF conditions; (b) the TPAs can be located on both closed field lines rooted in the polar cap of both hemispheres and open field lines connected to the northward field lines draped over one hemisphere of the magnetopause. We believe that the TPAs presented here are the result of both indirect and direct processes of solar wind energy transfer to the high-latitude ionosphere.
|
|
| 9. |
- Wang, Shan, et al.
(författare)
-
Electrostatic Waves Around a Magnetopause Reconnection Secondary Electron Diffusion Region Modulated by Whistler and Lower-Hybrid Waves
- 2023
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:18
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate electrostatic waves in a magnetopause reconnection event around a secondary electron diffusion region. Near the current sheet mid-plane, parallel electron beam-mode waves are modulated by whistler waves. We conclude that the anisotropy of energized electrons in the reconnection exhaust excites whistler waves, which produce spatially modulated electron beams through nonlinear Landau resonance, and these beams excite beam-mode electrostatic waves. In the separatrix region, parallel propagating electrostatic waves associated with field-aligned electron beams and perpendicular propagating electron cyclotron harmonic waves with loss cone distributions exhibit modulation frequencies in the lower-hybrid wave (LHW) frequency range. We infer that LHWs scatter electrons to produce beams and alter loss cones to modulate electrostatic waves. The results advance our understanding about the regimes and mechanisms of electrostatic waves in reconnection, with an emphasis on their coupling with lower-frequency electromagnetic waves. Magnetic reconnection is an important energy dissipation process at the Earth's dayside magnetopause. In its central region, plasmas deviate from the thermal equilibrium and form structured distribution functions, which excite plasma waves. We investigate high-frequency electrostatic waves in an event, where the waves are associated with electron beam-plasma interaction or anisotropy of distribution functions. We find that electrostatic waves are driven and modulated by lower-frequency waves, as the latter alters the particle distribution functions. The results help us understand how various processes couple with each other to achieve the energy dissipation. Parallel electron beam-mode waves are modulated by whistler near the current sheet mid-plane, by driving beams through Landau resonanceElectron beam-mode and cyclotron waves are modulated by lower-hybrid waves near separatrices, with beam and loss cone distributions
|
|
| 10. |
- Xie, Zi Kang, et al.
(författare)
-
Electron scale coherent structure as micro accelerator in the Earth's magnetosheath
- 2024
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1, s. 886-
-
Tidskriftsartikel (refereegranskat)abstract
- Turbulent energy dissipation is a fundamental process in plasma physics that has not been settled. It is generally believed that the turbulent energy is dissipated at electron scales leading to electron energization in magnetized plasmas. Here, we propose a micro accelerator which could transform electrons from isotropic distribution to trapped, and then to stream (Strahl) distribution. From the MMS observations of an electron-scale coherent structure in the dayside magnetosheath, we identify an electron flux enhancement region in this structure collocated with an increase of magnetic field strength, which is also closely associated with a non-zero parallel electric field. We propose a trapping model considering a field-aligned electric potential together with the mirror force. The results are consistent with the observed electron fluxes from ~50 eV to ~200 eV. It further demonstrates that bidirectional electron jets can be formed by the hourglass-like magnetic configuration of the structure.
|
|
