Collisionless Electron Heat Flux for the Nonequilibrium Solar Wind Plasma: Revisiting Hollweg’s Parameter

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Abstract
Here, we discuss an extension of the modelling of the collisionless heat flux and the related parameter α , derived by Hollweg for a truncated Maxwellian to distributions with suprathermal tails. In the collisionless solar wind plasma, electrons and ions are described by a multitude of non-Maxwellian (nonequilibrium) velocity distributions, such as the standard, regularized κ , and Druyvesteyn distributions. We show that for these nonidealized distributions, the heat flux and the related parameter α can deviate significantly from the Maxwellian values derived by Hollweg. It is also shown that the heat flux is best described using a form that does not directly involve the truncation speed. Furthermore, we discuss the applicability of these distribution models for the nonrelativistic case, which constrains the κ values for the standard κ distribution to values above 4. In addition, we provide the possibility to easily obtain the heat flux parameter for a given solar wind environment.
Funding Information
  • KU Leuven (G002523N-WEAVE)
  • ESA (Podex)
  • Deutsche Forschungsgemeinschaft (WEAVE FI 706/31-1)
  • Stiftung Begabtenförderung Cusanuswerk (scholarship program)

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