Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm

Varsani, A.; Nakamura, R.; Сергеев, В. А.; Baumjohann, W.; Owen, C. J.; Petrukovich, A. A.; Yao, Zhonghua; Nakamura, Takuma; Kubyshkina, M. V.; Sotirelis, T.; Burch, J. L.; Genestreti, K. J.; Vörös, Z.; Andriopoulou, M.; Gershman, D. J.; Avanov, L. A.; Magnes, W.; Russell, C. T.; Plaschke, Ferdinand; Khotyaintsev, Yuri V.; Giles, B. L.; Coffey, V. N.; Dorelli, J.; Strangeway, R. J.; Torbert, R. B.; Lindqvist, Per‐Arne; Ergun, R. E.

doi:10.1002/2017ja024547

Cited by 20 publications

(47 citation statements)

References 53 publications

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“…We have indeed confirmed that these electrons are originally accelerated near the EDR and experience no additional significant acceleration and drifting during their propagation to the probe (not shown). This is a typical feature of the first contact of reconnection signatures at the reconnection boundary at a location sufficiently far away from the X‐line as very recently observed by MMS at the near‐Earth PSBL (Varsani et al, ). The P4 probe observes similar signatures Δ t = 2Ω i −1 later than P3 (see the time difference between two vertical lines in Figures g–l).…”

Section: Resultssupporting

confidence: 70%

“…After the first contact of the highest energy electrons, the lower energy electrons are sequentially observed and form the energy dispersion (see the time after the first vertical line in Figure g). This dispersion is caused mainly by the time‐of‐flight effect in which slower electrons reach the probe later than the faster electrons when these electrons are coming from a close location near the X‐line along the same field line and experience almost no additional acceleration during their flights (Varsani et al, ). We have indeed confirmed that these electrons are originally accelerated near the EDR and experience no additional significant acceleration and drifting during their propagation to the probe (not shown).…”

Section: Resultsmentioning

confidence: 99%

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Remote Sensing of the Reconnection Electric Field From In Situ Multipoint Observations of the Separatrix Boundary

Nakamura

Varsani

et al. 2018

Geophysical Research Letters

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A remote sensing technique to infer the local reconnection electric field based on in situ multipoint spacecraft observation at the reconnection separatrix is proposed. In this technique, the increment of the reconnected magnetic flux is estimated by integrating the in-plane magnetic field during the sequential observation of the separatrix boundary by multipoint measurements. We tested this technique by applying it to virtual observations in a two-dimensional fully kinetic particle-in-cell simulation of magnetic reconnection without a guide field and confirmed that the estimated reconnection electric field indeed agrees well with the exact value computed at the X-line. We then applied this technique to an event observed by the Magnetospheric Multiscale mission when crossing an energetic plasma sheet boundary layer during an intense substorm. The estimated reconnection electric field for this event is nearly 1 order of magnitude higher than a typical value of magnetotail reconnection.Plain Language Summary Magnetic reconnection is an important phenomenon in space plasmas that explosively releases the accumulated magnetic energy. In the Earth's magnetotail, it is known that the released energy by this process leads to aurora substorms. The rate of reconnection, which defines how efficiently the magnetic flux is transferred at the central reconnection region called the diffusion region, is a key parameter to explore such reconnection physics. However, it is very challenging to directly measure this parameter by observing the small-scale diffusion region in situ. Thus, in this paper, we propose a new remote sensing technique that infers the reconnection rate along the boundary of the whole reconnection region called the separatrix from in situ measurements. In this technique, by observing how rapidly the magnetic flux passes through the separatrix, the rate can be remotely inferred even outside the diffusion region. We confirmed the adequacy of this technique by testing it in a kinetic simulation, and then applied it to a latest observation event by the MMS spacecraft during an intense substorm. The result shows a remarkably high rate. This indicates the positive correlation between the reconnection rate and the substorm strength and strongly motivates future survey using the technique proposed in this paper.

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Section: Resultssupporting

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Remote Sensing of the Reconnection Electric Field From In Situ Multipoint Observations of the Separatrix Boundary

Nakamura

Varsani

et al. 2018

Geophysical Research Letters

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“…Most of the time shown in Figure 2, MMS spent in the southern lobe as indicated by recordings of~100-eV polar rain electrons (Figure 2c) and by a spectacular trace of the cold ions in Figure 2a showing the lobe population, which is known from previous studies (e.g., Varsani et al, 2017). As in those previous papers, at the top of spectrogram (a) we overplotted the trace of kinetic energy due to the proton convective transport (Ep = m p VE 2 /2, VE = (E × B)/B 2 ).…”

Section: Observationssupporting

confidence: 66%

Substorm‐Related Near‐Earth Reconnection Surge: Combining Telescopic and Microscopic Views

Сергеев

Apatenkov

Nakamura

et al. 2019

Geophysical Research Letters

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A strong ~11‐min‐long surge of the lobe reconnection was observed during a substorm on the tailward side of the near‐Earth neutral line. In the southern lobe near the reconnection separatrix the MMS spacecraft observed short‐duration earthward electron beams providing the local Hall current, tailward propagating Alfven wave (AW) bursts with Poynting flux up to 10−4 W/m2, and large‐amplitude E field spikes (e‐holes) and low hybrid waves. The reconnection surge was accompanied by substorm current wedge formation and fast poleward expansion of auroral bulge‐related westward electrojet in the conjugate ionosphere. During its meridional crossing above the expanding bulge the Metop‐2 spacecraft observed an intense energetic precipitation spike near the expected X line foot point and confirmed the dipolarized character of magnetic field lines inside of the bulge. Globally the observed average reconnection rate ( ~3.3 mV/m) was sufficient to produce the magnetic flux increase in the bulge, associated with observed fast poleward expansion (about 6° latitude in 5 min).

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“…These flows are earthward at THEMIS and tailward at ARTEMIS, that is, magnetic reconnection occurs somewhere between the spacecraft positions (presumably around ∼30 R E , where the reconnection occurrence rate is highest; see Genestreti et al, ; Nagai et al, ). Because the THEMIS spacecraft are some distance from the equatorial plane (| B x | is large; see panels b1–b3), the significant part of the observed plasma flows is field‐aligned and can be attributed to the parallel propagating ions accelerated in the reconnection region (e.g., Nakamura et al, ; Varsani et al, ), whereas plasma flows observed by ARTEMIS are mostly transverse (i.e., these are typical reconnection tailward ejecta; see Kiehas et al, ; Runov et al, , and references therein). Thus, spacecraft (THEMIS and ARTEMIS) are located at different regions (not only different sides) of the middle‐tail reconnection.…”

Section: Spatial Localizationmentioning

confidence: 99%

Global View of Current Sheet Thinning: Plasma Pressure Gradients and Large‐Scale Currents

et al. 2019

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The formation of a thin magnetotail current sheet is a key process in magnetic energy accumulation before magnetic reconnection during substorms. Although the 3‐D configuration of a thinning current sheet has been well reproduced in many numerical simulations, observational details of this configuration have been less thoroughly studied. To investigate the global and local 3‐D structure of a thinning current sheet, we use a data set collected by three spacecraft of the Time History of Events and Macroscale Interactions during Substorms mission, two spacecraft of the Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun mission, and the Geostationary Operational Environmental Satellite 15. We demonstrate that near‐Earth current sheet thinning is accompanied by the formation of equatorial plasma pressure gradients directed from the flanks toward midnight. These gradients are associated with an intensification of the dawn‐dusk current (during current sheet thinning) and field‐aligned currents of opposite polarity at the dawn and dusk flanks. Simultaneous Time History of Events and Macroscale Interactions during Substorms and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun observations show that current sheet thinning occupies a large portion of the tail, from the near‐Earth region to lunar orbit. An increase in the equatorial plasma pressure (and the lobe magnetic field pressure) is provided by a cold plasma density increase in the near‐Earth tail and likely by a plasma temperature increase in the distant tail. We discuss plasma convection patterns that are consistent with observed properties of the current sheet thinning.

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Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm

Cited by 20 publications

References 53 publications

Remote Sensing of the Reconnection Electric Field From In Situ Multipoint Observations of the Separatrix Boundary

Remote Sensing of the Reconnection Electric Field From In Situ Multipoint Observations of the Separatrix Boundary

Substorm‐Related Near‐Earth Reconnection Surge: Combining Telescopic and Microscopic Views

Global View of Current Sheet Thinning: Plasma Pressure Gradients and Large‐Scale Currents

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