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  • 1
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    The Relationship of Ion Beams and Fast Flows in the Plasma Sheet Boundary Layer (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We report new findings on the behavior of plasmas in the vicinity of the plasma sheet boundary layer (PSBL). A large geometrical factor detector on WIND (3D plasma experiment) has discovered a unidirectional ion beam streaming in the tailward direction missed by previous observations. This tailward beam is as intense as the earthward streaming beam and it is found just inside the outer edge of the PSBL where earthward streaming beams are observed. The region where this tailward beam is observed includes an isotropic plasma component which is absent in the outer edge where earthward streaming beams are found. When these different distributions are convolved to calculate the velocity moments, fast flows (greater than 400 km/s) result in the earthward direction and much slower flows (less than 200 km/s) in the tailward direction. These new findings are substantially different from previous observations. Thus, the interpretation of fast flows and earthward and counterstreaming ion beams in terms of a neutral line model must be reexamined.
    Keywords: Geophysics
    Type: International Conference on Substorms; United States
    Format: text
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  • 2
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    Electron Bulk Acceleration and Thermalization at Earth's Quasiperpendicular Bow Shock (2018)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observedacceleration and thermalization is essential to the cross-shock electron heating.
    Keywords: Solar Physics
    Type: GSFC-E-DAA-TN60656 , Physical Review Letters (ISSN 0031-9007) (e-ISSN 1079-7114); 120; 22; 225101
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  • 3
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    Magnetic Reconnection in a QuasiParallel Shock: TwoDimensional Local ParticleinCell Simulation (2019)
    In:  Other Sources
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    Publication Date: 2020-01-03
    Description: Magnetic reconnection in a quasiparallel bow shock is investigated with twodimensional local particleincell simulations. In the shock transition and downstream regions, large amplitude magnetic fluctuations exist, and abundant current sheets form. In some current sheets, reconnection occurs, and ionscale and electronscale magnetic islands are generated. In electronscale island regions, only electron outflow jets are observed, producing a quadrupolar outofplane magnetic field pattern, while in ionscale islands, both ions and electrons are involved and energized in reconnection. Normalized reconnection rates are obtained to be between around 0.1 to 0.2, and particle acceleration signatures are seen in distribution functions.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN76654 , Geophysical Research Letters (ISSN 0094-8276) (e-ISSN 1944-8007); 46; 16; 9352-9361
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  • 4
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    Electron Distribution Functions in the Diffusion Region of Asymmetric Magnetic Reconnection (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We study electron distribution functions in a diffusion region of antiparallel asymmetric reconnection by means of particle-in-cell simulations and analytical theory. At the electron stagnation point, the electron distribution comprises a crescent-shaped population and a core component. The crescent-shaped distribution is due to electrons coming from the magnetosheath toward the stagnation point and accelerated mainly by electric field normal to the current sheet. Only a part of magnetosheath electrons can reach the stagnation point and form the crescent-shaped distribution that has a boundary of a parabolic curve. The penetration length of magnetosheath electrons into the magnetosphere is derived. We expect that satellite observations can detect crescent-shaped electron distributions during magnetopause reconnection.
    Keywords: Solar Physics
    Type: GSFC-E-DAA-TN31210 , Geophysical Research Letters (ISSN 0094-8276); 43; 5; 1828-1836
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  • 5
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    Coincident POLAR/UVI and WIND Observations of Pseudobreakups (2000)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: Using POLAR/UVI global images, we have identified a period of successive minor auroral activations during which WIND was making a perigee pass (X approx. - 11Re). These auroral brightenings are interpreted to be pseudobreakups due to the lack of global expansion. Large magnetic field fluctuations and high earthward ion velocity moments measured by the WIND spacecraft show a nearly one-to-one correspondence with the auroral intensifications. Analysis of the plasma parameters indicates that there is no difference in the behavior of the plasma during pseudobreakups as compared to substorm expansive phase onset. Inspection of the ion distribution functions during high velocity moment events reveals the presence of a two component plasma. The particles contributing to the large mean velocities are energetic ions from approx. 2-27 keV. We conclude that pseudobreakups are the ionospheric signature of high velocity moment events.
    Keywords: Geophysics
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  • 6
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    Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E (sub parallel)) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E (sub parallel) events near the electron diffusion region have amplitudes on the order of 100 millivolts per meter, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E (sub parallel) events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E (sub parallel) events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN41303 , Physical Review Letters (ISSN 0031-9007) (e-ISSN 1079-7114); 116; 23; 235102
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  • 7
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    Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields (2019)
    In:  CASI
    Details
    Publication Date: 2019-11-08
    Description: Kinetic structures of electron diffusion regions (EDRs) under finite guide fields in magnetotail reconnection are reported. The EDRs with guide fields 0.140.5 (in unit of the reconnecting component) are detected by the Magnetospheric Multiscale spacecraft. The key new features include the following: (1) cold inflowing electrons accelerated along the guide field and demagnetized at the magnetic field minimum while remaining a coherent population with a low perpendicular temperature, (2) wave fluctuations generating strong perpendicular electron flows followed by alternating parallel flows inside the reconnecting current sheet under an intermediate guide field, and (3) gyrophase bunched electrons with high parallel speeds leaving the Xline region. The normalized reconnection rates for the three EDRs range from 0.05 to 0.3. The measurements reveal that finite guide fields introduce new mechanisms to break the electron frozenin condition.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN73675 , Geophysical Research Letters (ISSN 0094-8276) (e-ISSN 1944-8007); 46; 12; 6230–6238
    Format: application/pdf
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  • 8
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    Magnetospheric Multiscale Mission Observations of the Outer Electron Diffusion Region (2017)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper presents Magnetospheric Multiscale mission (MMS) observations of the exhaust region in the vicinity of the central reconnection site in Earth's magnetopause current sheet. High-time-resolution measurements of field and particle distributions enable us to explore the fine structure of the diffusion region near the X line. Ions are decoupled from the magnetic field throughout the entire current sheet crossing. Electron jets flow downstream from the X line at speeds greater than the E by B drift velocity. At or around the magnetospheric separatrix, large-amplitude electric fields containing field-aligned components accelerate electrons along the magnetic field toward the X line. Near the neutral sheet, crescent-shaped electron distributions appear coincident with (1) an out-of-plane electric field whose polarity is opposite to that of the reconnection electric field and (2) the energy transfer from bulk kinetic to field energy. The observations indicate that MMS passed through the edge of an elongated electron diffusion region (EDR) or the outer EDR in the exhaust region.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN51475 , Geophysical Research Letters (ISSN 0094-8276) (e-ISSN 1944-8007); 44; 5; 2049-2059
    Format: text
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