Asymmetric braking and dawnward deflection of dipolarization fronts: Effects of ion reflection

Zhou, X.‐Z.; Angelopoulos, V.; Liu, Jiang; Pan, Dong‐Xiao

doi:10.1002/2014gl061794

Cited by 20 publications

(23 citation statements)

References 29 publications

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“…In contrast, the pressure enhancement is much larger (up to five to six times the original value) and is confined to the central portion (30 y/d i 38) and extends much further downstream than does the There are also considerably weaker enhancements in both P ixx and the density immediately ahead of the secondary front. Some of these pressure and density features are consistent with the calculations of Zhou et al 2014aZhou et al , 2014b regarding the role of ion reflection in the asymmetric breaking and dawnward deflection of dipolarization fronts. However, as shown in Fig.…”

Section: Overview Of Jet Expansionsupporting

confidence: 83%

Reconnection flow jets in 3D as a source of structured dipolarization fronts

Pritchett

2015

Earth Planet Sp

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Three-dimensional electromagnetic particle-in-cell simulations are used to investigate the propagation and breakup of a reconnection flow jet of initial cross-tail extent 24d i (∼ 1.5R E ; d i is the ion inertial length). Such a front is found to separate into two segments, with the dawnward portion propagating ahead of the duskward one. Both segments expand duskward, reaching separate lengths of 18-25d i , and both segments develop internal structures on east-west scales of 1-2d i . The currents responsible for the ramp up of B z at the fronts are confined to narrow ( d i ) ribbons whose localization is primarily associated with the electron U ey flow. The incoming ion flow is slowed down and deflected duskward at the front, and ambient ions are reflected back from the moving front. These processes create regions of enhanced T ixx both downstream and upstream of the front, while there is a local minimum at the front itself. These results help to explain the prevalence of ∼ 1R E flow jets in the plasma sheet.

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Section: Overview Of Jet Expansionsupporting

confidence: 83%

Reconnection flow jets in 3D as a source of structured dipolarization fronts

Pritchett

2015

Earth Planet Sp

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“…[] also found FAC pairs thinner than 0.2 h of MLT; these are likely caused by very small DFBs that were difficult for two THEMIS probes to observe simultaneously and thus rare in our DFB width statistics.) The dawnward drift of both wedgelets and ground FAC sheets further supports the relationship between them [ Forsyth et al ., ; Zhou et al ., ]. Asymmetric wedgelets seem counterintuitive because a wedgelet cannot close its FAC loop within itself.…”

Section: Discussionmentioning

confidence: 99%

Substorm current wedge composition by wedgelets

Liu

Angelopoulos

Chu

et al. 2015

Geophysical Research Letters

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Understanding how a substorm current wedge (SCW) is formed is crucial to comprehending the substorm phenomenon. One SCW formation scenario suggests that the substorm time magnetosphere is coupled to the ionosphere via “wedgelets,” small building blocks of an SCW. Wedgelets are field‐aligned currents (FACs) carried by elemental flux transport units known as dipolarizing flux bundles (DFBs). A DFB is a magnetotail flux tube with magnetic field stronger than that of the ambient plasma. Its leading edge, known as a “dipolarization front” or “reconnection front,” is a product of near‐Earth reconnection. Dipolarizing flux bundles, and thus wedgelets, are localized—each is only <3 RE wide. How these localized wedgelets combine to become large‐scale (several hours of magnetic local time) region‐1‐sense SCW FACs is unclear. To determine how this occurs, we investigated wedgelets statistically using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. The results show wedgelet asymmetries: in the dawn (dusk) sector of the magnetotail, a wedgelet has more FAC toward (away from) the Earth than away from (toward) the Earth, so the net FAC is toward (away from) the Earth. The combined effect of many wedgelets is therefore the same as that of large‐scale region‐1‐sense SCW, supporting the idea that they comprise the SCW.

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“…Before 16 April 2012, MESSENGER crossed the plasma sheet at a distance of ~ −2 R M to −3 R M downtail during hot seasons, which is consistent with the location of Near‐Mercury Neutral Line (NMNL) [ Slavin et al ., ; DiBraccio et al ., ]. Previous studies at Earth have revealed that the distributions of flux ropes [ Imber et al ., ] and reconnection fronts [ Zhou et al ., ] earthward of the Near‐Earth Neutral Line (NENL, > −20 R E ) is different to that in the NENL region. In order to remove this effect, we therefore only study the flux ropes and reconnection fronts in the NMNL region and also investigate the feature of Mercury's near tail reconnection site.…”

Section: Data Sourcesmentioning

confidence: 99%

Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations

et al. 2016

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We perform a statistical study of flux ropes and reconnection fronts based on MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma observations to study the implications for the spatial distribution of reconnection sites in Mercury's near magnetotail. The results show important differences of temporal and spatial distributions as compared to Earth. We have surveyed the plasma sheet crossings between −2 RM and −3 RM downtail from the planet, i.e., the location of Near‐Mercury Neutral Line (NMNL). Plasma sheets were defined to be regions with β ≥ 0.5. Using this definition, 39 flux ropes and 86 reconnection fronts were identified in the plasma sheet. At Mercury, the distributions of flux ropes and reconnection fronts show clear dawn‐dusk asymmetry with much higher occurrence rate on the dawnside plasma sheet than on the duskside. This suggests that magnetic reconnection in Mercury's magnetotail occurs more frequently in the dawnside than in the duskside plasma sheet, which is different than the observations in Earth's magnetotail showing more reconnection signatures in the duskside plasma sheet. The distribution of plasma sheet thickness shows that plasma sheet near the midnight is the thinnest part and does not show obvious asymmetry. Thus, the reasons that cause magnetic reconnection to preferentially occur on the dawnside of the magnetotail at Mercury may not be the plasma sheet thickness and require further study. The peak occurrence rates of flux ropes and reconnection fronts in Mercury's plasma sheet are ~ 60 times higher than that of Earth's values, which we interpret to be due to the highly variable magnetospheric conditions at Mercury. Such higher occurrence rate of magnetic reconnection would generate more plasma flows in the dawnside plasma sheet than in the duskside. These plasma flows would mostly brake and initiate the substorm dipolarization on the postmidnight sector at Mercury rather than the premidnight susbtorm onset location at Earth.

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Asymmetric braking and dawnward deflection of dipolarization fronts: Effects of ion reflection

Cited by 20 publications

References 29 publications

Reconnection flow jets in 3D as a source of structured dipolarization fronts

Reconnection flow jets in 3D as a source of structured dipolarization fronts

Substorm current wedge composition by wedgelets

Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations

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