Ion distributions upstream and downstream of the Earth's bow shock: first results from Vlasiator

D Pokhotelov,S Von Alfthan,M Palmroth,H E J Koskinen,R Vainio,Y Kempf

doi:10.5194/angeo-31-2207-2013

D Pokhotelov, S Von Alfthan + Show 4 more

Open Access

https://doi.org/10.5194/angeo-31-2207-2013

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Abstract

Abstract. A novel hybrid-Vlasov code, Vlasiator, is developed for global simulations of magnetospheric plasma kinetics. The code is applied to model the collisionless bow shock on scales of the Earth's magnetosphere in two spatial dimensions and three dimensions in velocity space retrieving ion distribution functions over the entire foreshock and magnetosheath regions with unprecedented detail. The hybrid-Vlasov approach produces noise-free uniformly discretized ion distribution functions comparable to those measured in situ by spacecraft. Vlasiator can reproduce features of the ion foreshock and magnetosheath well known from spacecraft observations, such as compressional magnetosonic waves generated by backstreaming ion populations in the foreshock and mirror modes in the magnetosheath. An overview of ion distributions from various regions of the bow shock is presented, demonstrating the great opportunities for comparison with multi-spacecraft observations.

Highlights

Global modeling of the Earth’s magnetosphere became feasible with rapidly increasing computational power
Many large-scale magnetospheric processes cannot be successfully reproduced in MHD models. One such example is a complex waveparticle interaction pattern observed in the ion foreshock region in front of the Earth’s bow shock, which emerges due to resonant interactions between the solar wind and backstreaming particles that are reflected and energized by the collisionless bow shock (Scholer et al, 1993; Eastwood et al, 2005a)
We demonstrate that the new code, Vlasiator, is able to reproduce the key features of solar wind– magnetosphere interactions such as ion reflection and energization at the collisionless bow shock and to simulate associated wave-particle interaction processes taking place in the ion foreshock and in the magnetosheath

Summary

Introduction

Global modeling of the Earth’s magnetosphere became feasible with rapidly increasing computational power. The first approach is based on coupling kinetic and MHD models for respective magnetospheric regions (e.g., Tóth et al, 2012), while the second approach is focused on solving the kinetic equations throughout the entire system The former approach was successfully applied in modeling the inner magnetosphere and ring current region (Glocer et al, 2013) where collisional processes and multi-ion plasma composition become significant. The latter approach is typically based on hybrid particle-in-cell (PIC) simulations, where electrons are modeled as fluid while ions are modeled as macroparticles for which plasma kinetic equations are solved (Winske et al, 2003). The newly developed global hybrid-Vlasov code, Vlasiator (Sandroos et al, 2013; Palmroth et al, 2013), has been utilized in this study to model the kinetic behavior of the collisionless bow shock, mainly focusing on ion distribution functions upstream and downstream of the Earth’s bow shock

Numerical model

Global magnetospheric simulation

Findings

Conclusions and summary