Mirror modes in the Earth's magnetosheath: Results from a global hybrid‐Vlasov simulation

Abstract

We investigate mirror mode structures in the Earth's magnetosheath using our global kinetic Vlasiator simulation, which models ion behavior through their distribution function and treats electrons as a charge‐neutralizing fluid. We follow the evolution of waves as they advect along velocity streamlines through the magnetosheath. We find that mirror mode waves are observed preferentially in the quasi‐perpendicular magnetosheath along velocity streamlines that enter the sheath in the vicinity of the foreshock ULF wave boundary where there are enough initial perturbations in the plasma for the mirror modes to grow, and the plasma properties fulfill the mirror instability condition better than elsewhere in the magnetosheath. We test selection criteria defined by previous studies and show that the spatial extent over which mirror modes occur ranges from much of the magnetosheath on the quasi‐perpendicular side of the subsolar point to very small isolated regions depending on the criteria.

Statistical analysis of mirror mode waves in sheath regions driven by interplanetary coronal mass ejection

“…However, for low Alfvén Mach number shocks, we found MMs more frequently behind quasi-perpendicular shocks than behind quasi-parallel shocks, and the beta anisotropy in the near-shock sub-region was larger in sheaths behind quasiperpendicular shocks, consistent with the observations in the Earth's magnetosheath (e.g., Soucek et al, 2015, see also Hoilijoki et al, 2016).…”

“…MMs also occur more frequently when the Alfvén Mach number (M A ) upstream of the bow shock is large (e.g., Soucek et al, 2015), and when the shock is quasiperpendicular (e.g., Génot et al, 2009b;Hoilijoki et al, 2016). However, MMs have typically larger amplitudes behind quasi-parallel shocks (Génot et al, 2009b).…”

Mirror mode waves in Venus's magnetosheath: solar minimum vs. solar maximum

“…For solar maximum, on the other hand, all fits show positive growth rates 0.003 ≤ γ ≤ 0.018 s −1 , well within the range that Tátrallyay et al (2008) found for the Earth's magnetosheath. Recently, Hoilijoki et al (2016) used a 5-D Vlasov simulation (2-D space and 3-D velocity) to study MM waves in the Earth's magnetosheath. The obtained simulated growth rate for the MM waves was 0.002 ≤ γ ≤ 0.005 s −1 , which does not completely cover the ranges estimated from observations in this paper and in Tátrallyay et al (2008).…”

On the Importance of Spatial and Velocity Resolution in the Hybrid-Vlasov Modeling of Collisionless Shocks

“…A high-density transient wave front travels through the downstream region until it exits the simulation box after approximately 350 s. By that time, the reflected ion population forming the foreshock [44] has propagated upstream and the right-hand resonant beam instability grows, generating typical foreshock ULF waves [30,45]. In the downstream region, the anisotropic heating of the ion population drives the 1D equivalent of mirror mode waves [47]. In the later phases of the simulation, the modulation of the upstream conditions by the foreshock ULF waves influences the evolution of the downstream region, with varying degrees of wave steepening observed in the upstream region.…”