Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause
B. LavraudY. C. ZhangY. VernisseD. J. GershmanJ. DorelliP. A. CassakJ. DargentC. J. PollockB. L. GilesN. AunaiM. R. ArgallL. A. AvanovA. C. BarrieJ. L. BurchM. O. ChandlerLi‐Jen ChenG. ClarkI. J. CohenV. N. CoffeyJ. P. EastwoodJ. EgedalS. ErikssonR. E. ErgunC. J. FarrugiaS. A. FuselierV. GénotD. B. GrahamЕ. Е. ГригоренкоH. HasegawaC. JacqueyI. KacemY. V. KhotyaintsevE. MacDonaldW. MagnesA. MarchaudonB. H. MaukT. E. MooreT. MukaiR. NakamuraW. R. PatersonE. PenouT. D. PhanA. C. RagerAlessandro RetinòZhaojin RongC. T. RussellY. SaitoJ. A. SauvaudS. J. SchwartzChao ShenS. E. SmithR. J. StrangewaySergio Toledo‐RedondoR. B. TorbertD. L. TurnerS. WangShoichiro Yokota
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Abstract Based on high‐resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field‐aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field‐aligned potentials).Keywords:
Pitch angle
Current sheet
Guiding center
Electron scattering
[1] Early magnetopause observations revealed that the magnetic field can rotate across tangential current sheets in the form of C-and S-shaped hodograms. We use the four-spacecraft magnetopause crossings by Cluster in order to study the structure of the C- and S-sheets. We show that both current sheets can be described by analytical equilibria. We employ a force-free current sheet equilibrium for description of the C-sheet and develop a new equilibrium to describe the S-sheet. We suggest that both equilibria be used for setting up initial conditions in the next generation of current sheet simulations.
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Abstract One of the major questions about magnetic reconnection is how specific solar wind and interplanetary magnetic field conditions influence where reconnection occurs at the Earth’s magnetopause. There are two reconnection scenarios discussed in the literature: a) anti-parallel reconnection and b) component reconnection. Early spacecraft observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection X-line location with respect to the spacecraft. An improved view of the reconnection location at the magnetopause evolved from ionospheric emissions observed by polar-orbiting imagers. These observations and the observations of accelerated ion beams revealed that both scenarios occur at the magnetopause. Improved methodology using the time-of-flight effect of precipitating ions in the cusp regions and the cutoff velocity of the precipitating and mirroring ion populations was used to pinpoint magnetopause reconnection locations for a wide range of solar wind conditions. The results from these methodologies have been used to construct an empirical reconnection X-line model known as the Maximum Magnetic Shear model. Since this model’s inception, several tests have confirmed its validity and have resulted in modifications to the model for certain solar wind conditions. This review article summarizes the observational evidence for the location of magnetic reconnection at the Earth’s magnetopause, emphasizing the properties and efficacy of the Maximum Magnetic Shear Model.
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