Browsing by Subject "Bow shock"

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  • Suni, Jonas (Helsingin yliopisto, 2021)
    Magnetosheath jets are a class of structures in the Earth's magnetosheath usually defined by an enhancement of the dynamic pressure of the plasma. Magnetosheath jets have been observed by several different spacecraft over the past few decades, but their origin and formation mechanism have remained unclear. The aim of this thesis is to use data from a global simulation to investigate the origin of magnetosheath jets. We defined two different kinds of structures, magnetosheath jets and foreshock compressive structures (FCS), and collected a database of individual jets and FCSs from 4 Vlasiator global hybrid-Vlasov simulation runs, all of which simulate only the ecliptic plane. We then conducted a statistical analysis of the properties of jets and FCSs, and their occurrence rates as a function of the definition of the FCS criterion. Jets were separated into two categories: jets that form in contact with FCSs (FCS-jets), and those that do not (non-FCS-jets). We found that up to 75% of magnetosheath jets form in association with an FCS impacting the Earth's bow shock. We also found that FCS-jets penetrate deeper into the magnetosheath than non-FCS-jets. Finally, we found no conclusive explanation for the formation of non-FCS-jets. The properties of both jets and FCSs agree qualitatively and to some extent quantitatively with spacecraft observations and other simulations in the literature. The formation of jets from FCSs impacting the bow shock is similar to the proposed theory that jets are linked to Short Large-Amplitude Magnetic Structures (SLAMS). In the future, we will study magnetosheath jets and FCSs in polar plane simulation runs as well, and ultimately in full 3D simulation runs. If made possible by new simulations, the effects of electron kinetic effects on jets and FCSs will also be studied. Comparison studies with spacecraft observations of jet formation from FCSs will also be conducted, if and when such observations are found and become available.
  • Plaschke, Ferdinand; Hietala, Heli; Archer, Martin; Blanco-Cano, Xochitl; Kajdic, Primoz; Karlsson, Tomas; Lee, Sun Hee; Omidi, Nojan; Palmroth, Minna; Roytershteyn, Vadim; Schmid, Daniel; Sergeev, Victor; Sibeck, David (2018)
    The magnetosheath flow may take the form of large amplitude, yet spatially localized, transient increases in dynamic pressure, known as "magnetosheath jets" or "plasmoids" among other denominations. Here, we describe the present state of knowledge with respect to such jets, which are a very common phenomenon downstream of the quasi-parallel bow shock. We discuss their properties as determined by satellite observations (based on both case and statistical studies), their occurrence, their relation to solar wind and foreshock conditions, and their interaction with and impact on the magnetosphere. As carriers of plasma and corresponding momentum, energy, and magnetic flux, jets bear some similarities to bursty bulk flows, which they are compared to. Based on our knowledge of jets in the near Earth environment, we discuss the expectations for jets occurring in other planetary and astrophysical environments. We conclude with an outlook, in which a number of open questions are posed and future challenges in jet research are discussed.