Foreshock compressive structure-magnetosheath jet coupling in a global hybrid-Vlasov simulation

<p>Magnetosheath jets are a class of phenomena usually defined as pulses of high dynamic pressure in the magnetosheath, but the details of their origins are currently unclear. Many theories on the origin of magnetosheath jets have been developed, such as bow shock rippling and foreshock structures. The usefulness of spacecraft data in studying some of them is limited, due to the transient and localised nature of jets. We use the 5D global hybrid-Vlasov simulation Vlasiator in a statistical study to investigate the relationship between compressive structures in the foreshock and magnetosheath jets. Foreshock compressive structures and magnetosheath jets are identified and their evolution over time is tracked. We find that up to 75% of magnetosheath jets forming at the bow shock are associated with foreshock compressive structures impacting the bow shock at the same location. Furthermore, magnetosheath jets that are associated with foreshock compressive structures penetrate deeper into the magnetosheath than jets that are not associated with foreshock compressive structures.</p>

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

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 ∼2.6 RE, while its size perpendicular to the direction of propagation is ∼0.5 RE. 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.

A Method for Producing Extra-High Dynamic Pressure Due to the Efficient Use of High Explosive

In the material processing such as shock synthesis and powder consolidation by shock waves the method for generating dynamic pressure is a vital factor for the quality of the final recovered materials. A general and convenient way for producing shock wave demanded in such applications is to take advantage of the explosion effect from high explosive. Under normal conditions, a given high explosive can only provide some kind of magnitude of dynamic pressure after its explosion. Therefore, it is whether possible to obtain the higher dynamic pressure by adequately changing the form of the explosion of high explosive. Starting from this motivation, we put forward a new method for producing high dynamic pressure from the use of the overdriven detonation of high explosive. The proposed device consists of the following configurations. A metal flyer accelerated by the high explosive is used to impact another layer of high explosive to incur an overdriven detonation in this layer of explosive. The overdriven detonation of high explosive acts on the powder materials, bringing out high dynamic pressures to the materials studied. To examine the efficiency of this combination on the improvement of dynamic pressure, a numerical computation is performed on this system. The details on the illustration of this method as well as the results of numerical investigation will be given.