Downstream high-speed plasma jet generation as a direct consequence of shock reformation

Abstract

Shocks are one of nature’s most powerful particle accelerators and have been connected to relativistic electron acceleration and cosmic rays. Upstream shock observations include wave generation, wave-particle interactions and magnetic compressive structures, while at the shock and downstream, particle acceleration, magnetic reconnection and plasma jets can be observed. Here, using Magnetospheric Multiscale (MMS) we show in-situ evidence of high-speed downstream flows (jets) generated at the Earth’s bow shock as a direct consequence of shock reformation. Jets are observed downstream due to a combined effect of upstream plasma wave evolution and an ongoing reformation cycle of the bow shock. This generation process can also be applicable to planetary and astrophysical plasmas where collisionless shocks are commonly found.

On Magnetosheath Jet Kinetic Structure and Plasma Properties

“…This profile consists of a SW‐like velocity and a slightly enhanced density. Our results are therefore particularly consistent with the reformation generation mechanism and its associated observations (Raptis et al., 2022). The presented results are also consistent with the shock ripple mechanism (Hietala et al., 2009), but since there are no upstream measurements or indication of ripples, it is impossible to show any connection directly.…”

“…Overall, the two populations (background and jet) and their interaction result in a net increase in density and velocity, along with variations in the velocity direction. Later, we only see a clear SW-beam-like plasma population, similar to what was expected to occur in the MSH by Raptis et al (2022). Generally, the jet propagates with its front edge consisting of a complex ongoing interaction region, while the rest of the jet (t 2 ) appears to be isolated with a depleted background.…”

“…The origin of jets has been discussed much for several years, and many of the points made in previous studies were based on the properties of jets as shown directly through particle moments (see e.g., . However, recently, as shown by simulations and observations (Raptis et al, 2022;Suni et al, 2021), jets appear to be directly connected to the foreshock dynamics for which a fluid approach and the particle moments may provide quite a limited picture (see e.g., Section 6.6 of Paschmann and Daly (1998)). Here, we show that if we consider the jet as an isolated population and perform a series of fits, it exhibits a SW-like profile.…”

“…Downstream of the Qpar shock, jets have been associated with several other generation mechanisms, from shock ripples (Hietala et al., 2009; Hietala & Plaschke, 2013) to upstream rotational discontinuities (Archer et al., 2012; Dmitriev & Suvorova, 2012) and reconnection (Preisser et al., 2020). More recently, investigations have focused on the connection of jets to upstream foreshock structures (Karlsson et al., 2015; Omelchenko et al., 2021; Sibeck et al., 2021; Suni et al., 2021) and to the reformation of the Qpar shock (Raptis et al., 2022). While the exact generation mechanism of these structures is still under investigation, the connection to SW properties such as the cone angle and transient events has been demonstrated in various recent studies, indicating that there is a direct link between SW conditions and MSH jets (Koller et al., 2022; LaMoury et al., 2021; Plaschke et al., 2013; Tinoco‐Arenas et al., 2022).…”

Investigating the Role of Magnetosheath High‐Speed Jets in Triggering Dayside Ground Magnetic Ultra‐Low Frequency Waves

“…Besides foreshock transients, recent studies show that shock and foreshock processes can trigger supermagnetosonic jets in the magnetosheath, which are named as magnetosheath “high‐speed jets (HSJs)” (Escoubet et al., 2020; Hietala et al., 2009; Koller et al., 2022; Plaschke et al., 2018; Raptis et al., 2022; Suni et al., 2021; Wang et al., 2022). Although magnetosheath HSJs' median spatial scale of about 0.12 $${R}_{E}$$ (Plaschke et al., 2020) is not as large as solar wind structures or foreshock transients, magnetosheath HSJs can also be geoeffective due to their significant dynamic pressure increases and frequent occurrence (Plaschke et al., 2016).…”