Abstract
Abstract. Kinetically driven plasma waves are fundamental for a description of the thermodynamical properties of the Earth's magnetosheath. The most commonly observed ion-scale instabilities are generated by temperature anisotropy of the ions, such as the mirror and proton cyclotron instabilities. We investigate here the spatial resolution dependence of the mirror and proton cyclotron instabilities in a global hybrid-Vlasov simulation using the Vlasiator model; we do this in order to find optimal resolutions and help future global hybrid-Vlasov simulations to save resources when investigating those instabilities in the magnetosheath. We compare the proton velocity distribution functions, power spectra and growth rates of the instabilities in a set of simulations with three different spatial resolutions but otherwise identical set-up. We find that the proton cyclotron instability is absent at the lowest resolution and that only the mirror instability remains, which leads to an increased temperature anisotropy in the simulation. We conclude that the proton cyclotron instability, its saturation and the reduction of the anisotropy to marginal levels are resolved at the highest spatial resolution. A further increase in resolution does not lead to a better description of the instability to an extent that would justify this increase at the cost of numerical resources in future simulations. We also find that spatial resolutions between 1.32 and 2.64 times the inertial length in the solar wind present acceptable limits for the resolution within which the velocity distribution functions resulting from the proton cyclotron instability are still bi-Maxwellian and reach marginal stability levels. Our results allow us to determine a range of spatial resolutions suitable for the modelling of the proton cyclotron and mirror instabilities and should be taken into consideration regarding the optimal grid spacing for the modelling of these two instabilities, within available computational resources.
Highlights
The Earth’s magnetosheath is permeated with several kinds of ion-kinetic waves, which are an important source of energy transfer and dissipation within the magnetosheath plasma (Schwartz et al, 1997)
The mirror instability gives rise to compressional, linearly polarised waves characterised by zero frequency in the plasma frame, anticorrelation between the plasma density and the magnetic field, and magnetic perturbations which are mostly parallel to the background magnetic field (Tsurutani et al, 1982; Price et al, 1986)
The proton cyclotron instability has maximum growth rate around the ion cyclotron frequency, and it produces waves propagating in the direction parallel to the background magnetic field
Summary
The Earth’s magnetosheath is permeated with several kinds of ion-kinetic waves, which are an important source of energy transfer and dissipation within the magnetosheath plasma (Schwartz et al, 1997). The mirror instability gives rise to compressional, linearly polarised waves characterised by zero frequency in the plasma frame, anticorrelation between the plasma density and the magnetic field, and magnetic perturbations which are mostly parallel to the background magnetic field (Tsurutani et al, 1982; Price et al, 1986). They create magnetic mirrorlike structures trapping particles (Soucek et al, 2008). The magnetic perturbations of the waves are perpendicular to the background magnetic field and produce left-
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