Short-wavelength instabilities in the shock transition region and their influence of the shock structure and energy partition

Short-wavelength, high-frequency fluctuations are routinely detected in spacecraft traversals of supercritical shocks. The amplitude of electric field perturbations associated with these fluctuations significantly exceeds (by order of magnitude or more) motional electric field and the electric field associated with quasi-stationary shock potential. Such observations have long motivated the question of whether the fluctuations significantly affect the overall structure of the shock and/or its energetics. We present results of large-scale, high-resolution particle-in-cell simulations of quasi-perpendicular collisionless shocks with realistic mass ratio and parameters typical of observed interplanetary shocks at 1au. The simulations exhibit most of the fluctuations typically observed, such as (steepening) whistler/magnetosonic precursors, short-wavelength field aligned whistlers, ion acoustic fluctuations, and solitary electrostatic structures. We discuss both the origin of the instabilities in highly non-Maxwellian particle populations and their effect on the evolution of such distributions through the shock transition. Specific attention is paid to interrelation between local and global effects, which are hard to assess from spacecraft data. Results from simulations with purely Maxwellian upstream distributions and from those accounting for the presence of non-thermal electron populations are compared.