The influence of out‐of‐plane shear flow on Hall magnetic reconnection and FTE generation

Chen, Yangao; Xiao, Chijie; Wang, Xiaogang; Wang, Jiaqi; Zhang, Hui; Pu, Z. Y.; W., Z.; Guo, Zhifang

doi:10.1002/jgra.50417

Cited by 5 publications

(5 citation statements)

References 51 publications

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“…The magnetosheath flow along the flanks is greater than the flow speed near the subsolar point, making the flanks more conducive to KHIs that can then have localized regions of reconnection within the resulting vortices [ Eriksson et al ., ; Li et al ., ]. High flow shear has also been suggested to play a role in forming FTEs [ Chen et al ., ], and so may be related to the observations on the flanks in this study. The thickness of the current sheet at the reconnection site may also be an important factor for producing magnetic islands [ Zelenyi et al ., ], and could be related to the prevalence of magnetic island signatures observed for antiparallel reconnection sites.…”

Section: Discussionsupporting

confidence: 65%

Occurrence frequency and location of magnetic islands at the dayside magnetopause

et al. 2017

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Simulations of magnetic reconnection often predict the formation of magnetic islands forming and propagating out through the reconnection exhaust region. However, to date, only a few observations of magnetic islands at the Earth's magnetopause have been identified and analyzed. Crossings near reconnection sites at the dayside magnetopause by Cluster from 2001 to 2009 are examined in a systematic effort to determine the frequency and location of magnetic islands. Using the maximum magnetic shear model as a guide for the distance to the reconnection site, 47 magnetopause crossings within 3 RE of the predicted reconnection site are examined. The occurrence of island structures in the reconnection exhaust is investigated in the context of how the type of reconnection, antiparallel or component, affects the frequency of formation of the islands. For Cluster magnetopause crossings confirmed to be near reconnection sites, island signatures, primarily bidirectional streaming electrons in the magnetosheath boundary layer, are seen for approximately 85% of the crossings and are common features for both antiparallel and component reconnection.

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Section: Discussionsupporting

confidence: 65%

Occurrence frequency and location of magnetic islands at the dayside magnetopause

et al. 2017

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“…The guide field is important because, when coupled with a gas pressure gradient across the inflow direction at the dissipation region, it can set up diamagnetic effects which also have been shown to cause the X-line to convect in the outflow direction [Swisdak et al, 2003;Beidler and Cassak , 2011], and therefore either reinforce or oppose the convection caused by flow shear [Tanaka et al, 2010]. The analysis and simulations also do not include upstream flows in the out-of-plane direction [Wang et al, 2012;Chen et al, 2013;Wang et al, 2014;Tassi et al, 2014]. Also, the simulations used the fluid model, which does not self-consistently capture plasma mixing in the exhaust for systems with asymmetric density [Cassak and Shay, 2009]; this would be fixed using simulations employing the particle-in-cell technique [Roytershteyn and Daughton, 2008;Tanaka et al, 2010].…”

Section: Discussionmentioning

confidence: 99%

Asymmetric magnetic reconnection with a flow shear and applications to the magnetopause

et al. 2015

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We perform a systematic theoretical and numerical study of anti-parallel two-dimensional magnetic reconnection with asymmetries in the plasma density and reconnecting magnetic field strength in addition to a bulk flow shear across the reconnection site in the plane of the reconnecting fields, which commonly occurs at planetary magnetospheres. We analytically predict the speed at which an isolated X-line is convected by the flow, the reconnection rate, and the critical flow speed at which reconnection no longer takes place for arbitrary reconnecting magnetic field strengths, densities, and upstream flow speeds, and we confirm the results with two-fluid numerical simulations. The predictions and simulation results counter the prevailing model of reconnection at Earth's dayside magnetopause which says reconnection occurs with a stationary X-line for sub-Alfvénic magnetosheath flow, reconnection occurs but the X-line convects for magnetosheath flows between the Alfvén speed and double the Alfvén speed, and reconnection does not occur for magnetosheath flows greater than double the Alfvén speed. In particular, we find that X-line motion is governed by momentum conservation from the upstream flows, which are weighted differently in asymmetric systems, so the X-line convects for generic conditions including sub-Alfvénic upstream speeds. For the reconnection rate, as with symmetric reconnection, it drops with increasing flow shear and there is a cutoff speed above which reconnection is not predominant. However, while the cutoff condition for symmetric reconnection is that the difference in flows on the two sides of the reconnection site is twice the Alfvén speed, we find asymmetries cause the cut-off speed for asymmetric reconnection to be higher than twice the asymmetric form of the Alfvén speed. The stronger the asymmetries, the more the cutoff exceeds double the asymmetric Alfvén speed. This is due to the fact that in asymmetric reconnection, the plasma with the smaller mass flux into the dissipation region contributes a smaller mass to the dissipation region, so the effect of its flow on opposing the release of energy by the reconnected magnetic fields is diminished and the reconnection is not suppressed to the extent previously thought. The results compare favorably with an observation of reconnection at Earth's polar cusps during a period of northward interplanetary magnetic field, where reconnection occurs despite the magnetosheath flow speed being more than twice the magnetosheath Alfvén speed, the previously proposed suppression condition. These results are expected to be of broad importance for magnetospheric physics of Earth and other planets; particular applications are discussed.

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“…Determining whether these observations are due to relative motion of secondary magnetic islands or to temporally intermittent local reconnection event occurring during this period requires further analysis with observations from all four MMS spacecraft. The main effects on reconnection and X line motion, then, of these magnetosheath conditions probably arise from the asymmetry in density, and quite a few theoretical and modeling studies have undertaken this particular topic in reconnection [e.g., Tanaka et al, 2008;2010;Malakit et al, 2010;Chen et al, 2013;Doss et al, 2015]. A more common feature of the Earth's magnetopause, which is observed in this crossing, is a sharp density gradient, with much higher densities in the magnetosheath.…”

Section: Discussionmentioning

confidence: 95%

“…A more common feature of the Earth's magnetopause, which is observed in this crossing, is a sharp density gradient, with much higher densities in the magnetosheath. The main effects on reconnection and X line motion, then, of these magnetosheath conditions probably arise from the asymmetry in density, and quite a few theoretical and modeling studies have undertaken this particular topic in reconnection [e.g., Tanaka et al, 2008;2010;Malakit et al, 2010;Chen et al, 2013;Doss et al, 2015]. However, to what extent the effect of the larger magnetic field with the larger densities may have on asymmetric reconnection merits further investigation.…”

Section: Discussionmentioning

confidence: 99%

Stable reconnection at the dusk flank magnetopause

Gomez

Vines

Fuselier

et al. 2016

Geophysical Research Letters

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The dusk flank magnetopause was surveyed with instruments on board the Magnetospheric Multiscale (MMS) spacecraft on 28 August 2015 between 13:55 UT and 14:15 UT during a period of persistent southward interplanetary magnetic field (IMF) with varying dawn‐dusk component. Plasma measurements (500 eV electrons, > 2 keV ions) revealed the existence of at least one active reconnection region that persisted throughout the interval. The reconnection region convected equatorward despite the poleward and tailward magnetosheath flow, which ranged from slightly sub‐Alfvénic to slightly super‐Alfvénic throughout the interval. These results suggest that magnetic reconnection moved in response to changes in the IMF clock angle rather than the magnetosheath flow, which is corroborated using predictions of the maximum magnetic shear model.

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The influence of out‐of‐plane shear flow on Hall magnetic reconnection and FTE generation

Cited by 5 publications

References 51 publications

Occurrence frequency and location of magnetic islands at the dayside magnetopause

Occurrence frequency and location of magnetic islands at the dayside magnetopause

Asymmetric magnetic reconnection with a flow shear and applications to the magnetopause

Stable reconnection at the dusk flank magnetopause

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