On the nature of precursor flows upstream of advancing dipolarization fronts

Zhou, X.‐Z.; Angelopoulos, V.; Сергеев, В. А.; Runov, A.

doi:10.1029/2010ja016165

Cited by 78 publications

(168 citation statements)

References 45 publications

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“…Our test particle results on precursor protons of tens of keV are essentially consistent with conclusions of Zhou et al [2010Zhou et al [ , 2011, involving the reflection of preexisting plasma sheet ions at the dipolarization front. However, our orbits also show commonly multiple encounters with the DF, enabling larger energy gain than from a single reflection.…”

Section: Summary and Discussionsupporting

confidence: 76%

“…Figure 5 also shows the flux enhancements at 21 keV, which precede the dipolarization, involving mainly phase angles near 0 ∘ , that is, earthward moving ions. These precursor ions originate mainly from the near-tail plasma sheet, consistent with the model of Zhou et al [2010Zhou et al [ , 2011; they will be discussed further in section 7. The flux increases at higher energy (81.5 keV) after the dipolarization are largely associated with particles of PSBL origin.…”

Section: Temporal Variations Of Energetic Ion Fluxesmentioning

confidence: 56%

“…Our MHD and test particle simulations showed the presence of earthward flowing accelerated ions, as well as plasma flow ahead of the dipolarization front, as seen in observations [e.g., Zhou et al, 2010Zhou et al, , 2011. We have investigated the properties of these precursors by tracing both fluid elements and ions backward in time from such locations.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…In a number of papers, Zhou et al [2010Zhou et al [ , 2011Zhou et al [ , 2012aZhou et al [ , 2014 have emphasized observations of energetic ions of a few tens of keV preceding the arrival of dipolarization fronts, coincident with an increase of the plasma density and flow velocity. They attributed these observations to ion reflection and acceleration at the propagating front and supported this view with test particle investigations in a simplified model.…”

Section: Precursor Ionsmentioning

confidence: 99%

“…The major simplifications of the Zhou et al [2011] model were the assumption of uniform speed of the propagating front and the neglect of variations across the tail. (The latter was modified by Zhou et al [2014], who assumed a circular shape of the DF in the equatorial plane.)…”

Section: Precursor Ionsmentioning

confidence: 99%

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Energetic ions in dipolarization events

2015

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We investigate ion acceleration in dipolarization events in the magnetotail, using the electromagnetic fields of an MHD simulation of magnetotail reconnection and flow bursts as basis for test particle tracing. The simulation results are compared with “Time History of Events and Macroscale Interactions during Substorms” observations. We provide quantitative answers to the relative importance of source regions and source energies. Flux decreases at proton energies up to 10–20 keV are found to be due to sources of lobe or plasma sheet boundary layer particles that enter the near tail via reconnection. Flux increases result from both thermal and suprathermal ion sources. Comparable numbers of accelerated protons enter the acceleration region via cross‐tail drift from the dawn flanks of the near‐tail plasma sheet and via reconnection of field lines extending into the more distant tail. We also demonstrate the presence of earthward plasma flow and accelerated suprathermal ions ahead of a dipolarization front. The flow acceleration stems from a net Lorentz force, resulting from reduced pressure gradients within a pressure pile‐up region ahead of the front. Suprathermal precursor ions result from, typically multiple reflections at the front. Low‐energy ions also become accelerated due to inertial drift in the direction of the small precursor electric field.

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Section: Summary and Discussionsupporting

confidence: 76%

Section: Temporal Variations Of Energetic Ion Fluxesmentioning

confidence: 56%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Precursor Ionsmentioning

confidence: 99%

Section: Precursor Ionsmentioning

confidence: 99%

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Energetic ions in dipolarization events

2015

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On the role of pressure and flow perturbations around dipolarizing flux bundles

et al. 2013

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[1] As a dipolarizing flux bundle (DFB) moves earthward, it creates pressure and flow perturbations. These perturbations may play a significant role in controlling DFB motion and generating field-aligned currents (FACs) which render the DFB a "wedgelet", a traveling building block of the substorm current wedge. To investigate this hypothesis, we use DFB observations from the Time History of Events and Macroscale Interactions during Substorms mission to reconstruct the spatial profiles of the thermal and total (thermal plus magnetic) pressures and of the plasma flow near the DFB. The total pressure reaches maximum inside the dipolarization front (DF, the leading edge of the DFB). The resultant pressure gradient force pushes ambient plasma in the direction normal to the front and exerts a gradient force density of~0.15 nPa/R E against the DFB motion. The thermal pressure in the equatorial plane is strongest immediately ahead of the DFB's leading point; it decreases with distance from that peak: toward the ambient plasma, toward the DFB interior, and toward the DFB flanks. Combining our estimate of the flux tube volume distortion with the measured equatorial thermal pressure distribution, we obtain a region-1-sense FAC inside the DF layer and region-2-sense FAC in the~1 R E thick region immediately ahead of it. This system of FACs is indeed consistent with a wedgelet.

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Open boundary particle‐in‐cell simulation of dipolarization front propagation

et al. 2014

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[1] First results are presented from an ongoing open boundary 2½D particle-in-cell simulation study of dipolarization front (DF) propagation in Earth's magnetotail. At this stage, this study is focused on the compression, or pileup, region preceding the DF current sheet. We find that the earthward acceleration of the plasma in this region is in general agreement with a recent DF force balance model. A gyrophase bunched reflected ion population at the leading edge of the pileup region is reflected by a normal electric field in the pileup region itself, rather than through an interaction with the current sheet. We discuss plasma wave activity at the leading edge of the pileup region that may be driven by gradients, or by reflected ions, or both; the mode has not been identified. The waves oscillate near but above the ion cyclotron frequency with wavelength several ion inertial lengths. We show that the waves oscillate primarily in the perpendicular magnetic field components, do not propagate along the background magnetic field, are right handed elliptically (close to circularly) polarized, exist in a region of high electron and ion beta, and are stationary in the plasma frame moving earthward. We discuss the possibility that the waves are present in plasma sheet data, but have not, thus far, been discovered.

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On the nature of precursor flows upstream of advancing dipolarization fronts

Cited by 78 publications

References 45 publications

Energetic ions in dipolarization events

Energetic ions in dipolarization events

On the role of pressure and flow perturbations around dipolarizing flux bundles

Open boundary particle‐in‐cell simulation of dipolarization front propagation

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