Parametric Study of Magnetosheath Jets in 2D Local Hybrid Simulations

Abstract

We perform 2D local hybrid simulations of collisionless shocks in order to study the properties of simulated magnetosheath jets as a function of shock properties, namely their Alfvénic Mach number (MA) and geometry (angle between the upstream magnetic field and the shock normal, θBN). In total we perform 15 simulations with inflow speeds of Vin = 3.3 CA (Alfvén velocity), 4.5 CA and 5.5 CA and θBN = 15°, 30°, 45°, 50°, and 65°. Under these conditions, the shock MA varied between 4.28 and 7.42. In order to identify magnetosheath jets in the simulation outputs, we use four different criteria, equivalent to those utilized to identify subsets of magnetosheath jets, called high-speed jets (Plaschke and Hietala and Angelopoulos, Ann. Geophys., 2013, 31, 1877–1889), transient flux enhancements (Němeček et al., Geophys. Res. Lett., 1998, 25, 1273–1276), density plasmoids (Karlsson et al., J. Geophys. Res., 2012, 117, a–n; Karlsson et al., J. Geophys. Res., 2015, 120, 7390–7403) and high-speed plasmoids (Gunell et al., Ann. Geophys., 2014, 32, 991–1009). In our simulations, the density plasmoids were produced only by shocks with MA ≥5.7, while the high-speed plasmoids only formed downstream of shocks with MA ≥6.97. We show that higher MA shocks tend to produce faster jets that tend to have larger surface area, mass, linear momentum and kinetic energy, while these quantities tend to be anticorrelated with θBN. In general, the increase of θBN to up to 45° results in increased jet formation rates. In the case of high-speed jets in runs with Vin = 3.3 CA and high-speed plasmoids, the jet formation anticorrelates with θBN. The jet production all but ceases for θBN = 65° regardless of the shock’s MA. The maximum distances of the magnetosheath jets from the shocks were ≲140 di (upstream ion intertial lengths), which, estimating 1 di ∼100–150 km at Earth, corresponds to 2.4–3.3 Earth radii. Thus, none of the simulated jets reached distances equivalent to the average extension of the Earth’s subsolar magnetosheath, which would make them the equivalents of geoeffective jets. Higher MA shocks are probably needed in order to produce such jets.

Magnetosheath Jet Formation Influenced by Parameters in Solar Wind Structures

“…Our findings regarding the jet occurrence in relation to SW conditions are further supported by simulation results done recently by Tinoco‐Arenas et al. ( 2022 ). The appearance of jets ceased at shocks with very low Alfvén Mach numbers.…”

“…They also discuss that the shock rippling may occur at smaller scales as well, which directly connects to proposed jet generation mechanisms. Our findings regarding the jet occurrence in relation to SW conditions are further supported by simulation results done recently by Tinoco-Arenas et al (2022). The appearance of jets ceased at shocks with very low Alfvén Mach numbers.…”

On Magnetosheath Jet Kinetic Structure and Plasma Properties

“…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).…”

Solar Wind Parameters Influencing Magnetosheath Jet Formation: Low and High IMF Cone Angle Regimes

“…Tinoco‐Arenas et al. (2022) studied 2D local hybrid simulations of shocks with parameters close to these threshold values. They used β = 0.5 and varied θ Bn and M A .…”