| 1. |
- Chen, Li-Jen, et al.
(författare)
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Earth's Alfvén Wings Driven by the April 2023 Coronal Mass Ejection
- 2024
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 51:14
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Tidskriftsartikel (refereegranskat)abstract
- We report a rare regime of Earth's magnetosphere interaction with sub-Alfvénic solar wind in which the windsock-like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low-beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter-streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic-cloud and Alfvén-wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub-Alfv & eacute;nic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars.
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| 2. |
- Richard, Louis, et al.
(författare)
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Fast Ion Isotropization by Current Sheet Scattering in Magnetic Reconnection Jets
- 2023
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 131:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a statistical analysis of ion distributions in magnetic reconnection jets using data from the Magnetospheric Multiscale spacecraft. Compared with the quiet plasma in which the jet propagates, we often find anisotropic and non-Maxwellian ion distributions in the plasma jets. We observe magnetic field fluctuations associated with unstable ion distributions, but the wave amplitudes are not large enough to scatter ions during the observed travel time of the jet. We estimate that the phase-space diffusion due to chaotic and quasiadiabatic ion motion in the current sheet is sufficiently fast to be the primary process leading to isotropization.
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| 3. |
- Richard, Louis, et al.
(författare)
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Fast Ion Isotropization by Current Sheet Scattering in Magnetic Reconnection Jets
- 2023
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a statistical analysis of ion distributions in magnetic reconnection jets using data from the Magnetospheric Multiscale spacecraft. Compared with the quiet plasma in which the jet propagates, we often find anisotropic and non-Maxwellian ion distributions in the plasma jets. We observe magnetic field fluctuations associated with unstable ion distributions, but the wave amplitudes are not large enough to scatter ions during the observed travel time of the jet. We estimate that the phase-space diffusion due to chaotic and quasiadiabatic ion motion in the current sheet is sufficiently fast to be the primary process leading to isotropization.
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| 4. |
- Roberts, Owen Wyn, et al.
(författare)
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Sub-ion Scale Compressive Turbulence in the Solar Wind : MMS Spacecraft Potential Observations
- 2020
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 250:2
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Tidskriftsartikel (refereegranskat)abstract
- Compressive plasma turbulence is investigated at sub-ion scales in the solar wind using both the Fast Plasma Investigation (FPI) instrument on the Magnetospheric MultiScale mission (MMS), as well as using calibrated spacecraft potential data from the Spin Plane Double Probe (SDP) instrument. The data from FPI allow the sub-ion scale region (f(sc) greater than or similar to 1 Hz) to be investigated before the instrumental noise becomes significant at a spacecraft frame frequency off(sc) 3 Hz. Whereas the calibrated spacecraft potential allows a measurement up tof(sc) 40 Hz. In this work, we give a detailed description of density estimation in the solar wind using the spacecraft potential measurement from the SDP instrument on MMS. Several intervals of solar wind plasma have been processed using the methodology described and are made available. One of the intervals is investigated in more detail and the power spectral density of the compressive fluctuations is measured from the inertial range to the sub-ion range. The morphology of the density spectra can be explained by either a cascade of Alfven waves and slow waves at large scales and kinetic Alfven waves at sub-ion scales or more generally by the Hall effect. Using electric field measurements, the two hypotheses are discussed.
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| 5. |
- Toledo-Redondo, Sergio, et al.
(författare)
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Cold ion demagnetization near the X-line of magnetic reconnection
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6759-6767
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Tidskriftsartikel (refereegranskat)abstract
- Although the effects of magnetic reconnection in magnetospheres can be observed at planetary scales, reconnection is initiated at electron scales in a plasma. Surrounding the electron diffusion region, there is an Ion-Decoupling Region (IDR) of the size of the ion length scales (inertial length and gyroradius). Reconnection at the Earth's magnetopause often includes cold magnetospheric (few tens of eV), hot magnetospheric (10keV), and magnetosheath (1keV) ions, with different gyroradius length scales. We report observations of a subregion inside the IDR of the size of the cold ion population gyroradius (approximate to 15km) where the cold ions are demagnetized and accelerated parallel to the Hall electric field. Outside the subregion, cold ions follow the E x B motion together with electrons, while hot ions are demagnetized. We observe a sharp cold ion density gradient separating the two regions, which we identify as the cold and hot IDRs.
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| 6. |
- Toledo-Redondo, Sergio, et al.
(författare)
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Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 122:9, s. 9396-9413
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Tidskriftsartikel (refereegranskat)abstract
- Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10-25% of the energy spent by reconnection into ion heating went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely helium and oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization. Plain Language Summary The magnetic field of Earth creates a natural shield that isolates and protects us from the particles and fields coming from our star, the Sun. This natural shield is called the magnetosphere and is filled by plasma. The particles coming from the Sun form another plasma called the solar wind and are usually deviated around the magnetosphere. However, under certain circumstances these two plasmas can reconnect (magnetic reconnection), and part of the energy and mass of the two plasmas is interchanged. Magnetic reconnection is the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs to particles of very low energy (cold ions) of ionospheric origin when they reach the reconnecting boundary of the magnetosphere. It is found that they are energized and take an important part of the energy spent in reconnecting the plasmas. The plasma boundary develops spatial structures and emits waves that are able to heat the cold ions. Once heated, these cold ions irreversibly will escape the Earth's magnetosphere to never come back to Earth.
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| 7. |
- Wang, Shan, et al.
(författare)
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Lower-Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:5
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Tidskriftsartikel (refereegranskat)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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| 8. |
- André, Mats, et al.
(författare)
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Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6705-6712
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Tidskriftsartikel (refereegranskat)abstract
- Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
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| 9. |
- Breuillard, H., et al.
(författare)
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New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data
- 2018
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Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 859:2
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Tidskriftsartikel (refereegranskat)abstract
- The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i. e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f > 1Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves.
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| 10. |
- Breuillard, H., et al.
(författare)
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The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:1, s. 93-103
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Tidskriftsartikel (refereegranskat)abstract
- Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency similar to 100Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05-0.2f(ce) by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.
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