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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 2 | Copyright
Ann. Geophys., 36, 655-677, 2018
https://doi.org/10.5194/angeo-36-655-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 23 Apr 2018

Regular paper | 23 Apr 2018

Investigating the anatomy of magnetosheath jets – MMS observations

Tomas Karlsson1, Ferdinand Plaschke2, Heli Hietala3, Martin Archer4, Xóchitl Blanco-Cano5, Primož Kajdič5, Per-Arne Lindqvist1, Göran Marklund1, and Daniel J. Gershman6 Tomas Karlsson et al.
  • 1Space and Plasma Physics, School of Electrical Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
  • 2Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
  • 3Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, 603 Charles E. Young Drive East, Slichter Hall 6844D, Los Angeles, CA 90095-1567, USA
  • 4School of Physics & Astronomy, Queen Mary University of London, London, E1 4NS, UK
  • 5Instituto de Geofísica Universidad Nacional Autónoma de México, Ciudad Universitaria, CDMX, México
  • 6NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Abstract. We use Magnetosphere Multiscale (MMS) mission data to investigate a small number of magnetosheath jets, which are localized and transient increases in dynamic pressure, typically due to a combined increase in plasma velocity and density. For two approximately hour-long intervals in November, 2015 we found six jets, which are of two distinct types. (a) Two of the jets are associated with the magnetic field discontinuities at the boundary between the quasi-parallel and quasi-perpendicular magnetosheath. Straddling the boundary, the leading part of these jets contains an ion population similar to the quasi-parallel magnetosheath, while the trailing part contains ion populations similar to the quasi-perpendicular magnetosheath. Both populations are, however, cooler than the surrounding ion populations. These two jets also have clear increases in plasma density and magnetic field strength, correlated with a velocity increase. (b) Three of the jets are found embedded within the quasi-parallel magnetosheath. They contain ion populations similar to the surrounding quasi-parallel magnetosheath, but with a lower temperature. Out of these three jets, two have a simple structure. For these two jets, the increases in density and magnetic field strength are correlated with the dynamic pressure increases. The other jet has a more complicated structure, and no clear correlations between density, magnetic field strength and dynamic pressure. This jet has likely interacted with the magnetosphere, and contains ions similar to the jets inside the quasi-parallel magnetosheath, but shows signs of adiabatic heating. All jets are associated with emissions of whistler, lower hybrid, and broadband electrostatic waves, as well as approximately 10s period electromagnetic waves with a compressional component. The latter have a Poynting flux of up to 40µWm−2 and may be energetically important for the evolution of the jets, depending on the wave excitation mechanism. Only one of the jets is likely to have modified the surrounding magnetic field into a stretched configuration, as has recently been reported in other studies. None of the jets are associated with clear signatures of either magnetic or thermal pressure gradient forces acting on them. The different properties of the two types also point to different generation mechanisms, which are discussed here. Their different properties and origins suggest that the two types of jets need to be separated in future statistical and simulation studies.

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We have studied fast plasma jets outside of Earth’s magnetic environment. Such jets are small-scale structures with a limited lifetime, which may be important in determining the properties of the near-Earth space environment, due to their concentrated kinetic energy. We have used data from the NASA Magnetospheric MultiScale (MMS) satellites to study their properties in detail, to understand how these jets are formed. We have found evidence that there are at least two different types of jets.
We have studied fast plasma jets outside of Earth’s magnetic environment. Such jets are...
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