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In this paper, we study low-frequency waves upstream of quasi-parallel shocks by using two-dimensional (2D) hybrid simulations. Simulation results show that reflected particles can backstream and form a superthermal particle component in plasmas in an area just before the shock front. The component interacts with the incident particles and can result in quasi-parallel and quasi-perpendicular fast magnetosonic waves with comparable wave amplitudes, and they have right-hand and linear polarization, respectively. Further upstream, after being scattered by these upstream waves, the backstreaming particles develop a shell-like velocity distribution so that similar waves can be driven by the free energy from this newly formed distribution, and in this area the quasi-perpendicular waves are dominant over the quasi-parallel ones. Linear theory confirms the generation of these two types of upstream waves. [ABSTRACT FROM AUTHOR]

The parametric instabilities of an Alfvén wave in a proton-electron plasma system are found to have great influence on proton dynamics, where part of the protons can be accelerated through the Landau resonance with the excited ion acoustic waves, and a beam component along the background magnetic field is formed. In this paper, with a one-dimensional hybrid simulation model, we investigate the evolution of the parametric instabilities of a monochromatic left-hand polarized Alfvén wave in a proton-electron-alpha plasma with a low beta. When the drift velocity between the protons and alpha particles is sufficiently large, the wave numbers of the backward daughter Alfvén waves can be cascaded toward higher values due to the modulational instability during the nonlinear evolution of the parametric instabilities, and the alpha particles are resonantly heated in both the parallel and perpendicular direction by the backward waves. On the other hand, when the drift velocity of alpha particles is small, the alpha particles are heated in the linear growth stage of the parametric instabilities due to the Landau resonance with the excited ion acoustic waves. Therefore, the heating occurs only in the parallel direction, and there is no obvious heating in the perpendicular direction. The relevance of our results to the preferential heating of heavy ions observed in the solar wind within 0.3 AU is also discussed in this paper. [ABSTRACT FROM AUTHOR]