Preprints
https://doi.org/10.5194/angeo-2020-89
https://doi.org/10.5194/angeo-2020-89

  01 Feb 2021

01 Feb 2021

Review status: this preprint is currently under review for the journal ANGEO.

Ion distribution functions in magnetotail reconnection: Global hybrid-Vlasov simulation results

Andrei Runov1, Maxime Grandin2, Minna Palmroth2,3, Markus Battarbee2, Urs Ganse2, Heli Hietala4,5, Sanni Hoilijoki6, Emilia Kilpua2, Yann Pfau-Kempf2, Sergio Toledo-Redondo7,8, Lucile Turc2, and Drew Turner9 Andrei Runov et al.
  • 1Institute of Geophysics and Planetary Physics, University of California at Los Angeles, Los Angeles, USA
  • 2University of Helsinki, Department of Physics, Helsinki, Finland
  • 3Space and Earth Observation Centre, Finnish Meteorological Institute, Helsinki, Finland
  • 4The Blackett Laboratory, Imperial College, London, UK
  • 5Department of Physics and Astronomy, University of Turku, Turku, Finland
  • 6Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, USA
  • 7Department of Electromagnetism and Electronics, University of Murcia, Murcia, Spain
  • 8Institut de Recherche en Astrophysique et Planétologie, Toulouse, France
  • 9The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA

Abstract. We present results of noon–midnight meridional plane global hybrid-Vlasov simulations of the magnetotail ion dynamics under steady southward interplanetary magnetic field using the Vlasiator model. The simulation results show magnetotail reconnection and formation of earthward and tailward fast plasma outflows. The hybrid-Vlasov approach allows us to study ion velocity distribution functions (VDFs) that are self-consistently formed during the magnetotail evolution. We examine the VDFs collected by virtual detectors placed along the equatorial magnetotail within earthward and tailward outflows and around the quasi-steady X-line formed in the magnetotail at X ≈ −14 RE. This allows us to follow the evolution of VDFs during earthward and tailward motion of reconnected flux tubes as well as study signatures of unmagnetized ion motion in the weak magnetic field near the X-line. The VDFs indicate actions of Fermi-type and betatron acceleration mechanisms, ion acceleration by the reconnection electric field, and Speiser-type motion of ions near the X-line. The simulated VDFs are compared and show good agreement with VDFs observed in the magnetotail by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. We find that the VDFs become more gyrotropic but retain transverse anisotropy and counter-streaming ion beams when being convected earthward. The presented global hybrid-Vlasov simulation results are valuable for understanding physical processes of ion acceleration during magnetotail reconnection, interpretation of in-situ observations, and for future mission development by setting requirements on pitch-angle and energy resolution of upcoming instruments.

Andrei Runov et al.

Status: open (until 15 Mar 2021)

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  • RC1: 'Comment on angeo-2020-89', Anonymous Referee #1, 28 Feb 2021 reply

Andrei Runov et al.

Andrei Runov et al.

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Short summary
In collisionless systems like space plasma, particle velocity distributions contain fingerprints of undergoing physical processes. However, it is challenging to decode this information from observations. We used hybrid-Vlasov simulations to obtain ion velocity distribution functions at different locations and at different stages of the Earth's magnetosphere dynamics. The obtained distributions provide valuable examples that may be directly compared with the observations by satellites in space.