6D hybrid-Vlasov simulation of a high-resolution foreshock during quasi-radial IMF: First Vlasiator results

The foreshock is a large region of space upstream of a collisionless shock characterised by the presence of particles of solar wind origin that have been reflected at the shock. The interaction between these particles and the pristine solar wind can also generate ultra-low frequency (ULF) waves that are advected toward the quasi-parallel bow shock, that is, the part of the bow shock where the interplanetary magnetic field (IMF) and shock normal are almost parallel. The interaction between the ULF waves and the shock cause the quasi-parallel bow shock and the magnetosheath downstream of it to become turbulent and dynamic, which in turn can lead to the formation of transient structures such as magnetosheath jets. During intervals of quasi-radial IMF at Earth, the quasi-parallel bow shock is upstream of the dayside magnetosheath, and the dynamics of the quasi-parallel bow shock and magnetosheath have larger potential to have geoeffective consequences. Understanding the properties of the foreshock is therefore important, but studying the overall structure of this extended region using point measurements by spacecraft is difficult.

In this study, we present the first ever global 6D (3D+3V) hybrid-Vlasov simulation of near-Earth space with quasi-radial IMF conditions, featuring a high-resolution foreshock. We introduce the new criterion that was used to identify the foreshock for the purpose of applying adaptive mesh refinement, and elaborate on some of the technical challenges that needed to be overcome to make the simulation possible. We investigate the effects of ULF waves on the velocity distributions in different parts of the foreshock. Finally, we probe the velocity distributions inside magnetosheath jets in order to study their kinetic nature.