Influence of upstream turbulence on plasma stability at a perpendicular shock: hybrid simulations

Collisionless shock waves and plasma turbulence play fundamental roles in particle acceleration and energy dissipation in space plasmas. In the heliosphere, the inherently turbulent solar wind continuously interacts with planetary bow shocks and interplanetary shocks. Such pre-existing turbulence can modulate the shock front, influence particle acceleration and transport, and modify the plasma conditions and plasma stability in the vicinity of the shock. We present a novel modelling setup in which we use MHD simulations to generate turbulent fields that are dynamically input to our hybrid shock simulations. This allows us to study the interaction between realistic plasma turbulence and a shock wave. Here we report results on the influence of upstream turbulence on plasma stability against ion kinetic instabilities downstream of a perpendicular shock. We find that while turbulence can locally drive plasma towards an unstable configuration, it generally makes the downstream plasma more stable against proton cyclotron and mirror mode instabilities. We also find that a sharp low limit in β_parallel–T_perp/T_parallel “Brazil plots”, sometimes also seen in observations, can be caused by tracks representing adiabatic evolution of plasma in magnetic islands.