Results from the numerical experiments. Top panel: macroscopic variables calculated from the hybrid simulations at t = 5τ_A. In this plot β_e = 6 × 10⁻² and β_p = 10⁻². Bottom panel: same as the top panel, but at a later stage, t = 36.25τ_A. A standing ion-acoustic mode is excited in system. In this simulation L = 20 d_i (d_i is the ion-inertial length) and k = 2 × 2π/L. The magnetic field is normalised as B = B_units/B₀ and the electric field as E = cE_units/v_AB₀, where c is the speed of light and v_A the equilibrium Alfvén speed. The density is normalised to the equilibrium density. For visualisation purposes a smoothing of the macroscopic variables has been applied over ten grid cells. The temporal evolution is available as an online movie.