20 research outputs found
Kinetic signatures of the region surrounding the X-line in asymmetric (magnetopause) reconnection
Kinetic particle-in-cell simulations are used to identify signatures of the
electron diffusion region (EDR) and its surroundings during asymmetric magnetic
reconnection. A "shoulder" in the sunward pointing normal electric field (EN >
0) at the reconnection magnetic field reversal is a good indicator of the EDR,
and is caused by magnetosheath electron meandering orbits in the vicinity of
the x-line. Earthward of the X-line, electrons accelerated by EN form strong
currents and crescent-shaped distribution functions in the plane perpendicular
to B. Just downstream of the X-line, parallel electric fields create
field-aligned crescent electron distribution functions. In the immediate
upstream magnetosheath, magnetic field strength, plasma density, and
perpendicular electron temperatures are lower than the asymptotic state. In the
magnetosphere inflow region, magnetosheath ions intrude resulting in an
Earthward pointing electric field and parallel heating of magnetospheric
particles. Many of the above properties persist with a guide field of at least
unity.Comment: Submitted to Geophysical Research Letter
Ion Larmor radius effects near a reconnection X line at the magnetopause: THEMIS observations and simulation comparison
We report a Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) spacecraft crossing of a magnetopause reconnection exhaust ~9 ion skin depths (di) downstream of an X line. The crossing was characterized by ion jetting at speeds substantially below the predicted reconnection outflow speed. In the magnetospheric inflow region THEMIS detected (a) penetration of magnetosheath ions and the resulting flows perpendicular to the reconnection plane, (b) ion outflow extending into the magnetosphere, and (c) enhanced electron parallel temperature. Comparison with a simulation suggests that these signatures are associated with the gyration of magnetosheath ions onto magnetospheric field lines due to the shift of the flow stagnation point toward the low-density magnetosphere. Our observations indicate that these effects, ~2â3 di in width, extend at least 9 di downstream of the X line. The detection of these signatures could indicate large-scale proximity of the X line but do not imply that the spacecraft was upstream of the electron diffusion region
Magnetic Reconnection inside a Flux Transfer Eventâlike structure in Magnetopause KelvinâHelmholtz Waves
This is the final version. Available from the American Geophysical Union via the DOI in this recordMMS data are available from https://lasp.colorado.edu/mms/sdc/public/Magnetopause KelvinâHelmholtz (KH) waves are believed to mediate solar wind plasma transport via smallâscale mechanisms. Vortexâinduced reconnection (VIR) was predicted in simulations and recently observed using NASA's Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations but detailed observations were still lacking. Here we report MMS observations of an FTEâtype structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterised by (1) bipolar magnetic B Y variation with enhanced core field (B Z ) and (2) enhanced total pressure with dominant magnetic pressure. The crossâsection size of the FTE is found to be consistent with vortexâinduced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (V Y ), electron parallel heating, ion and electron density enhancements, and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTEâtype structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Ăieroset et al. (2019). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves.Science and Technology Facilities Council (STFC)Thailand Science Research and InnovationNAS
Electron heating during magnetic reconnection: A simulation scaling study
Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfv en speed c Ar based on the reconnecting magnetic field through the relation DT e ÂŒ 0:033 m i c 2 Ar , where DT e is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature T tot ÂŒ T i ĂŸ T e or plasma b. An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al., Geophys. Res. Lett. 40, 4475, 2013), which also found that DT e was proportional to the inflowing Alfv en speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating proportional to m i c 2 Ar ; (3) at most a weak dependence on electron mass; and (4) an exhaust electron temperature that varies little with distance from the x-line. V C 2014 AIP Publishing LLC. [http://d
Electron Heating During Magnetic Reconnection: A Simulation Scaling Study
Electron bulk heating during magnetic reconnection with symmetric inflow
conditions is examined using kinetic particle-in-cell (PIC) simulations. The
degree of electron heating is well correlated with the inflowing Alfv\'en speed
based on the reconnecting magnetic field through the relation , where is the increase in electron
temperature. For the range of simulations performed, the heating shows almost
no correlation with inflow total temperature or plasma
. An out-of-plane (guide) magnetic field of similar magnitude to the
reconnecting field does not affect the total heating, but it does quench
perpendicular heating, with almost all heating being in the parallel direction.
These results are qualitatively consistent with a recent statistical survey of
electron heating in the dayside magnetopause, which also found that was proportional to the inflowing Alfv\'en speed. The net electron heating
varies very little with distance downstream of the x-line. The simulations show
at most a very weak dependence of electron heating on the ion to electron mass
ratio. In the antiparallel reconnection case, the largely parallel heating is
eventually isotropized downstream due a scattering mechanism such as stochastic
particle motion or instabilities. The study highlights key properties that must
be satisfied by an electron heating mechanism: (1) Preferential heating in the
parallel direction; (2) Heating proportional to ; (3) At most a
weak dependence on electron mass; and (4) An exhaust electron temperature that
varies little with distance from the x-line.Comment: 27 pages, 1 table, 7 figures. Submitted to Physics of Plasma
Ion-scale secondary flux-ropes generated by magnetopause reconnection as resolved by MMS
New Magnetospheric Multiscale (MMS) observations of small-scale (~ 7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10 km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multi-spacecraft techniques, allowing them to be identified as flux ropes, whose flux content is small (~22 kWb). The current density, calculated using plasma and magnetic field measurements independently, is found to be filamentary. Inter-comparison of the plasma moments with electric and magnetic field measurements reveals structured non-frozen-in ion behavior. The data are further compared with a particle-in-cell simulation. It is concluded that these small-scale flux ropes, which are not seen to be growing, represent a distinct class of FTE which is generated on the magnetopause by secondary reconnection