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Electron Dynamics Within the Electron Diffusion Region of Asymmetric Reconnection.

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Title: Electron Dynamics Within the Electron Diffusion Region of Asymmetric Reconnection.
Authors: Argall, M. R.1 matthew.argall@unh.edu, Paulson, K.1, Alm, L.1, Rager, A.2, Dorelli, J.2, Shuster, J.2, Wang, S.2, Torbert, R. B.1,3, Vaith, H.1, Dors, I.1, Chutter, M.1, Farrugia, C.1, Burch, J.3, Pollock, C.2, Giles, B.2, Gershman, D.2, Lavraud, B.4, Russell, C. T.5, Strangeway, R.5, Magnes, W.6
Source: Journal of Geophysical Research. Space Physics. Jan2018, Vol. 123 Issue 1, p146-162. 17p.
Abstract: Abstract: We investigate the agyrotropic nature of electron distribution functions and their substructure to illuminate electron dynamics in a previously reported electron diffusion region (EDR) event. In particular, agyrotropy is examined as a function of energy to reveal detailed finite Larmor radius effects for the first time. It is shown that the previously reported ∼66 eV agyrotropic “crescent” population that has been accelerated as a result of reconnection is evanescent in nature because it mixes with a denser, gyrotopic background. Meanwhile, accelerated agyrotropic populations at 250 and 500 eV are more prominent because the background plasma at those energies is more tenuous. Agyrotropy at 250 and 500 eV is also more persistent than at 66 eV because of finite Larmor radius effects; agyrotropy is observed 2.5 ion inertial lengths from the EDR at 500 eV, but only in close proximity to the EDR at 66 eV. We also observe linearly polarized electrostatic waves leading up to and within the EDR. They have wave normal angles near 90°, and their occurrence and intensity correlate with agyrotropy. Within the EDR, they modulate the flux of 500 eV electrons travelling along the current layer. The net electric field intensifies the reconnection current, resulting in a flow of energy from the fields into the plasma. [ABSTRACT FROM AUTHOR]
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Abstract:Abstract: We investigate the agyrotropic nature of electron distribution functions and their substructure to illuminate electron dynamics in a previously reported electron diffusion region (EDR) event. In particular, agyrotropy is examined as a function of energy to reveal detailed finite Larmor radius effects for the first time. It is shown that the previously reported ∼66 eV agyrotropic “crescent” population that has been accelerated as a result of reconnection is evanescent in nature because it mixes with a denser, gyrotopic background. Meanwhile, accelerated agyrotropic populations at 250 and 500 eV are more prominent because the background plasma at those energies is more tenuous. Agyrotropy at 250 and 500 eV is also more persistent than at 66 eV because of finite Larmor radius effects; agyrotropy is observed 2.5 ion inertial lengths from the EDR at 500 eV, but only in close proximity to the EDR at 66 eV. We also observe linearly polarized electrostatic waves leading up to and within the EDR. They have wave normal angles near 90°, and their occurrence and intensity correlate with agyrotropy. Within the EDR, they modulate the flux of 500 eV electrons travelling along the current layer. The net electric field intensifies the reconnection current, resulting in a flow of energy from the fields into the plasma. [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1002/2017JA024524