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How neutral is quasi-neutral: Charge Density in the Reconnection Diffusion Region Observed by MMS
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  • Matthew Argall,
  • Jason Shuster,
  • Ivan Dors,
  • Kevin Genestreti,
  • Takuma Nakamura,
  • Roy Torbert,
  • James Webster,
  • Narges Ahmadi,
  • Robert Ergun,
  • Robert Strangeway,
  • Barbara Giles,
  • James Burch
Matthew Argall
University of New Hampshire

Corresponding Author:matthew.argall@unh.edu

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Jason Shuster
NASA Goddard Space Flight Center
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Ivan Dors
University of New Hampshire
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Kevin Genestreti
Southwest Research Institute
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Takuma Nakamura
Austrian Academy of Sciences
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Roy Torbert
University of New Hampshire
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James Webster
Rice University
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Narges Ahmadi
University of Colorado, Boulder
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Robert Ergun
University of Colorado, Boulder
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Robert Strangeway
University of California, Los Angeles
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Barbara Giles
NASA Goddard Space Flight Center
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James Burch
Southwest Research Institute
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Abstract

Magnetic reconnection is responsible for the major reconfigurations of the magnetosphere that lead to energy transport and deposition into the ionosphere. The fast rate at which magnetic energy is converted to plasma kinetic energy is likely enabled by the polarization Hall electric field that results from the separation of ions and electrons at small scales. Signatures of Hall fields have played a key role in identifying and studying reconnection, but the density of accumulated charge has not been quantified. We use the 4-point measurements of the Magnetospheric Multiscale mission to compute the divergence of the electric field and present the first observations of charge density in the diffusion region of magnetic reconnection. We show how it ties into the Hall system, discuss measurement uncertainties, analyze quality estimates, and make comparisons to 2D simulations. Charge density is briefly presented for other phenomena, and ranges from 2% or less of the background plasma density for magnetic reconnection and electron-scale magnetic holes and peaks to upwards of 4% for electron phase space holes.