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Non-Maxwellianity of electron distributions near Earth's magnetopause
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  • Daniel Bruce Graham,
  • Yuri V. Khotyaintsev,
  • Mats André,
  • Andris Vaivads,
  • Alexandros Chasapis,
  • William H. Matthaeus,
  • Alessandro Retino,
  • Francesco Valentini,
  • Daniel J Gershman
Daniel Bruce Graham
Swedish Institute of Space Physics

Corresponding Author:[email protected]

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Yuri V. Khotyaintsev
Swedish Institute of Space Physics
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Mats André
Swedish Institute of Space Physics
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Andris Vaivads
KTH Royal Institute of Technology, Stockholm, Sweden
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Alexandros Chasapis
University of Colorado
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William H. Matthaeus
University of Delaware
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Alessandro Retino
Laboratoire de Physique des Plasmas - CNRS
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Francesco Valentini
Università della Calabria
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Daniel J Gershman
NASA Goddard Space Flight Center
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Plasmas in Earth’s outer magnetosphere, magnetosheath, and solar wind are essentially collisionless. This means particle distributions are not typically in thermodynamic equilibrium and deviate significantly from Maxwellian distributions. The deviations of these distributions can be further enhanced by plasma processes, such as shocks, turbulence, and magnetic reconnection. Such distributions can be unstable to a wide variety of kinetic plasma instabilities, which in turn modify the electron distributions. In this paper the deviations of the observed electron distributions from a bi-Maxwellian distribution function is calculated and quantified using data from the Magnetospheric Multiscale (MMS) spacecraft. A statistical study from tens of millions of electron distributions shows that the primary source of the observed non-Maxwellianity are electron distributions consisting of distinct hot and cold components in Earth’s low-density magnetosphere. This results in large non-Maxwellianities in at low densities. However, after performing a stastical study we find regions where large non-Maxwellianities are observed for a given density. Highly non-Maxwellian distributions are routinely found are Earth’s bowshock, in Earth’s outer magnetosphere, and in the electron diffusion regions of magnetic reconnection. Enhanced non-Maxwellianities are observed in the turbulent magnetosheath, but are intermittent and are not correlated with local processes. The causes of enhanced non-Maxwellianities are investigated.
Oct 2021Published in Journal of Geophysical Research: Space Physics volume 126 issue 10. 10.1029/2021JA029260