| 1. |
- Wang, Shan, et al.
(author)
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Lower-Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions
- 2022
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In: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:5
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Journal article (peer-reviewed)abstract
- We investigate waves close to the lower-hybrid frequency in 12 magnetotail reconnection electron diffusion region (EDR) events with guide field levels of near-zero to 30%. In about half of the events, the wave vector has a small component along the current sheet normal, consistent with known lower-hybrid drift wave properties, but the perpendicular magnetic field fluctuations can be comparable or greater than the parallel component, a feature unique to the waves inside and adjacent to EDRs. Another new wave property is that the wave vector has a significant component along the current sheet normal in some events and completely along the normal for one event. In 1/4 of the events, the backward difference center dot Pe $\nabla \cdot {\boldsymbol{P}}_{e}$ term has a significant contribution to the wave electric field, possibly a feature of lower-hybrid waves more likely to exist in the diffusion region than further away from the X-line. Electron temperature variations are correlated with the wave potential, due to wave electric field acceleration and crossings at the corrugated separatrix region with different amounts of mixing between reconnection inflowing and outflowing populations. The latter also leads to the anti-correlation between parallel and perpendicular temperature components. Using four-spacecraft measurements, the magnetic field line twisting is demonstrated by the correlated fluctuations in backward difference xVExB|| ${\left(\nabla \times {\boldsymbol{V}}_{E\times B}\right)}_{\vert \vert }$ and ( backward difference xB)|| ${(\nabla \times \mathbf{B})}_{\vert \vert }$. The lower-hybrid wave in the EDR of weak guide field reconnection may be generated near separatrices and penetrate to the mid-plane or locally generated, and the latter possibility is beyond the prediction of previous reconnection simulations.
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| 2. |
- Lindberg, Martin, et al.
(author)
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Electron Kinetic Entropy across Quasi-Perpendicular Shocks
- 2022
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In: Entropy. - : MDPI AG. - 1099-4300. ; 24:6, s. 745-
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Journal article (peer-reviewed)abstract
- We use Magnetospheric Multiscale (MMS) data to study electron kinetic entropy per particle Se across Earth's quasi-perpendicular bow shock. We have selected 22 shock crossings covering a wide range of shock conditions. Measured distribution functions are calibrated and corrected for spacecraft potential, secondary electron contamination, lack of measurements at the lowest energies and electron density measurements based on plasma frequency measurements. All crossings display an increase in electron kinetic entropy across the shock Delta S-e being positive or zero within their error margin. There is a strong dependence of Delta S-e on the change in electron temperature, Delta T-e, and the upstream electron plasma beta, beta(e). Shocks with large Delta T-e have large Delta S-e. Shocks with smaller beta(e) are associated with larger Delta S-e. We use the values of Delta S-e, Delta Te and density change Delta n(e) to determine the effective adiabatic index of electrons for each shock crossing. The average effective adiabatic index is = 1.64 +/- 0.07.
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| 3. |
- Norgren, C., et al.
(author)
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Millisecond observations of nonlinear wave-electron interaction in electron phase space holes
- 2022
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 29:1
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Journal article (peer-reviewed)abstract
- Electron phase space holes (EHs) associated with electron trapping are commonly observed as bipolar electric field signatures in both space and laboratory plasma. Until recently, it has not been possible to resolve EHs in electron measurements. We report observations of EHs in the plasma sheet boundary layer, here identified as the separatrix region of magnetic reconnection in the magnetotail. The intense EHs are observed together with an electron beam moving toward the X line, showing signs of thermalization. Using the electron drift instrument onboard the satellites of the Magnetospheric Multiscale mission, we make direct millisecond measurements of the electron particle flux associated with individual electron phase space holes. The electron flux is measured at a millisecond cadence in a narrow parallel speed range within that of the trapped electrons. The flux modulations are of order unity and are direct evidence of the strong nonlinear wave-electron interaction that may effectively thermalize beams and contribute to transforming directed drift energy to thermal energy.
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