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Lavraud B.,CNRS Institute for research in astrophysics and planetology | Zhang Y.C.,CNRS Astrophysics and Planetology Research Institute | Vernisse Y.,CNRS Institute for research in astrophysics and planetology | Gershman D.J.,University of Maryland College Park | And 53 more authors.
Geophysical Research Letters | Year: 2016

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 20eV. 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). ©2016. American Geophysical Union.


Nagai T.,Tokyo Institute of Technology | Kitamura N.,Japan Aerospace Exploration Agency | Hasegawa H.,Japan Aerospace Exploration Agency | Shinohara I.,Japan Aerospace Exploration Agency | And 19 more authors.
Geophysical Research Letters | Year: 2016

The structure of asymmetric magnetopause reconnection is explored with multiple point and high-time-resolution ion velocity distribution observations from the Magnetospheric Multiscale mission. On 9 September 2015, reconnection took place at the magnetopause, which separated the magnetosheath and the magnetosphere with a density ratio of 25:2. The magnetic field intensity was rather constant, even higher in the asymptotic magnetosheath. The reconnected field line region had a width of approximately 540km. In this region, streaming and gyrating ions are discriminated. The large extension of the reconnected field line region toward the magnetosheath can be identified where a thick layer of escaping magnetospheric ions was formed. The scale of the magnetosheath side of the reconnected field line region relative to the scale of its magnetospheric side was 4.5:1. ©2016. American Geophysical Union. All Rights Reserved.


Farrugia C.J.,University of New Hampshire | Lavraud B.,Institut Universitaire de France | Torbert R.B.,University of New Hampshire | Argall M.,University of New Hampshire | And 20 more authors.
Geophysical Research Letters | Year: 2016

We analyze plasma, magnetic field, and electric field data for a flux transfer event (FTE) to highlight improvements in our understanding of these transient reconnection signatures resulting from high-resolution data. The ∼20 s long, reverse FTE, which occurred south of the geomagnetic equator near dusk, was immersed in super-Alfvénic flow. The field line twist is illustrated by the behavior of flows parallel/perpendicular to the magnetic field. Four-spacecraft timing and energetic particle pitch angle anisotropies indicate a flux rope (FR) connected to the Northern Hemisphere and moving southeast. The flow forces evidently overcame the magnetic tension. The high-speed flows inside the FR were different from those outside. The external flows were perpendicular to the field as expected for draping of the external field around the FR. Modeling the FR analytically, we adopt a non-force free approach since the current perpendicular to the field is nonzero. It reproduces many features of the observations. ©2016. American Geophysical Union. All Rights Reserved.

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