Two-dimensional Hybrid Simulations of Filamentary Structures and Kinetic Slow Waves Downstream of a Quasi-parallel Shock

Abstract

In this paper, with two-dimensional hybrid simulations, we study the generation mechanism of filamentary structures downstream of a quasi-parallel shock. The results show that in the downstream both the amplitude of magnetic field and number density exhibit obvious filamentary structures, and the magnetic field and number density are anticorrelated. Detailed analyses find that these downstream compressive waves propagate almost perpendicular to the magnetic field, and the dominant wave number is around the inverse of the ion kinetic scale. Their parallel and perpendicular components roughly satisfy (where and represent the parallel and in-plane perpendicular components of magnetic field, is the wave number in the perpendicular direction, and ρ i in the ion gyroradius), and their Alfvén ratio also roughly agrees with the analytical relation (where R Ai and β indicate the Alfvén ratio and plasma beta, respectively), while the corresponding cross helicity and compressibility show good agreement with previous theoretical calculations. All of these properties are consistent with those of kinetic slow waves (KSWs). Therefore, we conclude that the filamentary structures downstream of a quasi-parallel shock are produced by the excitation of KSWs.