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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1171-1182, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 07 Sep 2018

Regular paper | 07 Sep 2018

Magnetosheath jet properties and evolution as determined by a global hybrid-Vlasov simulation

Minna Palmroth1,2, Heli Hietala3,4, Ferdinand Plaschke5,6, Martin Archer7,8, Tomas Karlsson9, Xóchitl Blanco-Cano10, David Sibeck11, Primož Kajdič10, Urs Ganse1, Yann Pfau-Kempf1, Markus Battarbee1, and Lucile Turc1 Minna Palmroth et al.
  • 1Department of Physics, University of Helsinki, Helsinki, Finland
  • 2Space and Earth Observation Centre, Finnish Meteorological Institute, Helsinki, Finland
  • 3Department of Physics and Astronomy, University of Turku, Turku, Finland
  • 4Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, USA
  • 5Institute of Physics, University of Graz, Graz, Austria
  • 6Space Research Institute, Austrian Academy of Sciences, Graz, Austria
  • 7The Blackett Laboratory, Imperial College London, London, UK
  • 8School of Physics and Astronomy, Queen Mary University of London, London, UK
  • 9School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
  • 10Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico City, Mexico
  • 11Code 674, NASA Goddard Space Flight Center, Greenbelt, MD, USA

Abstract. We use a global hybrid-Vlasov simulation for the magnetosphere, Vlasiator, to investigate magnetosheath high-speed jets. Unlike many other hybrid-kinetic simulations, Vlasiator includes an unscaled geomagnetic dipole, indicating that the simulation spatial and temporal dimensions can be given in SI units without scaling. Thus, for the first time, this allows investigating the magnetosheath jet properties and comparing them directly with the observed jets within the Earth's magnetosheath. In the run shown in this paper, the interplanetary magnetic field (IMF) cone angle is 30°, and a foreshock develops upstream of the quasi-parallel magnetosheath. We visually detect a structure with high dynamic pressure propagating from the bow shock through the magnetosheath. The structure is confirmed as a jet using three different criteria, which have been adopted in previous observational studies. We compare these criteria against the simulation results. We find that the magnetosheath jet is an elongated structure extending earthward from the bow shock by  ∼ 2.6RE, while its size perpendicular to the direction of propagation is  ∼ 0.5RE. We also investigate the jet evolution and find that the jet originates due to the interaction of the bow shock with a high-dynamic-pressure structure that reproduces observational features associated with a short, large-amplitude magnetic structure (SLAMS). The simulation shows that magnetosheath jets can develop also under steady IMF, as inferred by observational studies. To our knowledge, this paper therefore shows the first global kinetic simulation of a magnetosheath jet, which is in accordance with three observational jet criteria and is caused by a SLAMS advecting towards the bow shock.

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Short summary
Magnetosheath jets are high-velocity plasma structures that are commonly observed within the Earth's magnetosheath. Previously, they have mainly been investigated with spacecraft observations, which do not allow us to infer their spatial sizes, temporal evolution, or origin. This paper shows for the first time their dimensions, evolution, and origins within a simulation whose dimensions are directly comparable to the Earth's magnetosphere. The results are compared to previous observations.
Magnetosheath jets are high-velocity plasma structures that are commonly observed within the...