Electron‐Driven Dissipation in a Tailward Flow Burst

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Electrostatic solitary waves (ESWs) have been reported inside reconnection jets, but their source and role remain unclear hitherto. Here we present the first observational evidence of ESWs generation by cold ion beams inside the jet, by using high‐cadence measurements from the Magnetospheric Multiscale spacecraft in the Earth's magnetotail. Inside the jet, intense ESWs with amplitude up to 30 mV m−1 and potential up to ~7% of the electron temperature are observed in association with accelerated cold ion beams. Instability analysis shows that the ion beams are unstable, providing free energy for the ESWs. The waves are observed to thermalize the beams, thus providing a new channel for ion heating inside the jet. Our study suggests that electrostatic turbulence can play an important role in the jet dynamics.

Section: Introductionmentioning

confidence: 99%

Ion‐Beam‐Driven Intense Electrostatic Solitary Waves in Reconnection Jet

Liu

Vaivads

Graham

et al. 2019

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“…DFs are usually suggested to be the leading edge of the reconfigured magnetic field after reconnection (e.g., Fu, Cao, et al, ; Sitnov et al, ). They are structures with a typical thickness comparable to the ion inertial length (e.g., Fu et al, ; Lu, Lu, et al, ), and usually embedded inside bursty bulk flows (e.g., Angelopoulos et al, ; Cao et al, , ; Chen et al, ). DFs play an important role in the Earth's magnetotail plasma sheet dynamics, contributing to the particles acceleration (e.g., Birn et al, ; Duan et al, ; Fu, Khotyaintsev, et al, ; Liu, Fu, Cao, Xu, et al, ; Liu & Fu, ; Zhou et al, , ), energy conversion (e.g., Angelopoulos et al, ; Huang et al, ; Khotyaintsev et al, ; Yang et al, ; Yao et al, ), and magnetic flux transport (e.g., Liu et al, ; Nakamura et al, ) during substorms.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric Cold Ions Detected by MMS Behind Dipolarization Fronts

Norgren

et al. 2019

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Traditionally, dipolarization front (DF) is a discontinuity at the leading edge of the high‐speed plasma jets, separating hot tenuous plasma from the denser ambient plasma. The particles behind the DF are usually hot population resulting from various heating and acceleration processes therein. Here, using Magnetospheric Multiscale (MMS) observations, we report that cold ions of ionospheric origin can be found behind the DFs. These cold ions move along the reconnected magnetic field lines directly from lobe during substorm, forming counter‐streaming cold ion flows behind the DFs. We find that cold ionospheric ions, as an additional population behind the DF, could increase ion density by ~50%. This indicates that the cold ions can change the gradients in the plasma density, such as the density‐driven instabilities near the DFs, and further affect the DF dynamics.

“…During crossing of the reconnection exhaust region, MMS detected reversal of B L (from −20 to 40 nT; Panel b), guide field (~10 nT) in B M (Panel c), generally negative B N (Panel d), and negative plasma flow (Panel e). Moreover, MMS detected energy dissipation (Panel g), supporting that reconnection exhaust region can be an important dissipation region (Chen, Fu, Liu, et al, ; Liu, Fu, Xu, et al, ; Liu, Fu, Vaivads, et al, ; Yang et al, ). We apply the FOTE method to investigate magnetic nulls in this reconnection exhaust region.…”

Section: Observationsmentioning

confidence: 77%

“…Regarding the third point, we investigate electron heating/acceleration near the X‐line. During reconnection in the shock transition region, simulations found electron acceleration by magnetic islands (Bessho et al, ; Matsumoto et al, ), suggesting the importance of O‐line structures (Chen, Fu, Liu, et al, ). However, it is unknown whether radial nulls contribute to electron heating in shock transition regions.…”

Section: Discussionmentioning

confidence: 99%

“…The method we use is the FOTE method, which was initially developed by Fu et al (), later validated by Fu et al (), and hitherto has been extensively applied to the analyses of reconnection events in the Earth's magnetosphere (e.g., Chen et al, ; Chen, Fu, Liu, et al, ; Chen, Fu, Wang, et al, ; Fu et al, ; Fu, Cao, et al, ; Huang et al, ; Liu, Fu, Cao, et al, ; Liu et al, ; Man et al, ; Wang et al, ; Wang, Fu, et al, ). This method, based on four‐spacecraft measurements, can position a magnetic null both inside and outside the spacecraft tetrahedron and can also reconstruct the magnetic topology of the null.…”

Section: Methodsmentioning

confidence: 99%

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Evidence of Magnetic Nulls in the Reconnection at Bow Shock

Chen

Wang

et al. 2019

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Magnetic nulls are believed to play important roles in the energy dissipation during reconnection. Such nulls have been observed in reconnection at the magnetopause, magnetosheath, and magnetotail but have never been observed in reconnection at the bow shock. Recently, four reconnection events were reported at the terrestrial bow shock, by utilizing Magnetospheric Multiscale (MMS) data. We examine whether the magnetic nulls exist in these events. We successfully find radial nulls in three of the events, meaning that spacecraft were close to X points in these events; we, however, cannot find radial nulls in another event, which was actually a crossing of the reconnection exhaust region. The minimum distance between radial nulls and spacecraft is 8 km, about 0.3 ion inertial length. We reconstruct topologies of these nulls and subsequently resolve the reconnection rates in these events. We find that the resolved reconnection rates are comparable with those at the magnetopause and magnetotail. Surprisingly, we do not find electron heating at the radial nulls. Our results are useful to understand the reconnection at bow shock.