Observations of Magnetic Reconnection in the Transition Region of Quasi‐Parallel Shocks

et al. 2019

Magnetic reconnection in a quasi‐parallel bow shock is investigated with two‐dimensional local particle‐in‐cell simulations. In the shock transition and downstream regions, large amplitude magnetic fluctuations exist, and abundant current sheets form. In some current sheets, reconnection occurs, and ion‐scale and electron‐scale magnetic islands are generated. In electron‐scale island regions, only electron outflow jets are observed, producing a quadrupolar out‐of‐plane magnetic field pattern, while in ion‐scale islands, both ions and electrons are involved and energized in reconnection. Normalized reconnection rates are obtained to be between around 0.1 to 0.2, and particle acceleration signatures are seen in distribution functions.

Section: 1029/2019gl083397mentioning

confidence: 99%

“…In one event, an ion‐scale sheet showed only electron jets, while in another current sheet whose thickness is several ion skin depths, both electron and ion jets were observed. Gingell et al () studied two quasi‐parallel shocks and showed reconnecting current sheets with only electron outflow jets in the transition region.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Reconnection in a Quasi‐Parallel Shock: Two‐Dimensional Local Particle‐in‐Cell Simulation

Bessho

et al. 2019

“…Evidence of reconnection has been reported to occur in the magnetosheath downstream of the Earth's bow shock Phan et al, 2018;Retinò et al, 2007;Vörös et al, 2017;Wilder et al, 2017Wilder et al, , 2018. Features of current sheet structures consistent with magnetic reconnection were identified in the transition region of a quasi-parallel shock in a recent study (Gingell et al, 2018). The role of reconnection in energy conversion in the shock and differences and similarities between the reconnection features at the shock and those in magnetotail and magnetopause are yet to be investigated.…”

Section: Introductionmentioning

confidence: 99%

Observational Evidence of Magnetic Reconnection in the Terrestrial Bow Shock Transition Region

Bessho

et al. 2019

Self Cite

We report evidence of magnetic reconnection in the transition region of the Earth's bow shock when the angle between the shock normal and the immediate upstream magnetic field is 65°. An ion‐skin‐depth‐scale current sheet exhibits the Hall current and field pattern, electron outflow jet, and enhanced energy conversion rate through the nonideal electric field, all consistent with a reconnection diffusion region close to the X‐line. In the diffusion region, electrons are modulated by electromagnetic waves. An ion exhaust with energized field‐aligned ions and electron parallel heating are observed in the same shock transition region. The energized ions are more separated from the inflowing ions in velocity above the current sheet than below, possibly due to the shear flow between the two inflow regions. The observation suggests that magnetic reconnection may contribute to shock energy dissipation.

“…In this study, we analyze four reconnection events, which were observed recently at the terrestrial bow shock by Gingell et al () and Wang, Chen, et al (), using the FOTE method. We find radial nulls (X‐line) in three events, which were identified as diffusion regions.…”

Section: Discussionmentioning

confidence: 99%

“…The third event, detected by MMS at about 06:07:02 UT on 31 December 2016, has been analyzed by Gingell et al (2019) and identified as a reconnection diffusion region at the quasi-parallel bow shock. Figure 2C is in the same format as Figure 2A (Panels b and d), indicating the existence of "inplane" magnetic nulls in this event.…”

Section: Observationsmentioning

confidence: 99%

Evidence of Magnetic Nulls in the Reconnection at Bow Shock

et al. 2019

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.