MMS Measurements of the Vlasov Equation: Probing the Electron Pressure Divergence Within Thin Current Sheets
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Shuster, J. R., D. J. Gershman, L.-J. Chen, S. Wang, N. Bessho, J. C. Dorelli, D. E. da Silva, et al. “MMS Measurements of the Vlasov Equation: Probing the Electron Pressure Divergence Within Thin Current Sheets.” Geophysical Research Letters 46, no. 14 (2019): 7862–72. https://doi.org/10.1029/2019GL083549.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
We investigate the kinetic structure of electron-scale current sheets found in the vicinity of the magnetopause and embedded in the magnetosheath within the reconnection exhaust. A new technique for computing terms of the Vlasov equation using Magnetospheric Multiscale (MMS) measurements is presented and applied to study phase space density gradients and the kinetic origins of the electron pressure divergence found within these current sheets. Crescent-shaped structures in ∇⊥2fe give rise to bipolar and quadrupolar signatures in v·∇fe measured near the maximum ∇·Pe inside the current layers. The current density perpendicular to the magnetic field is strong (J⊥∼2 μA/m²), and the thickness of the current layers ranges from 3 to 5 electron inertial lengths. The electron flows supporting the current layers mainly result from the combination of E×B and diamagnetic drifts. We find nonzero J·E′ within the current sheets even though they are observed apart from typical diffusion region signatures.