Multi-scale Magnetosonic Whistler Waves Induced by SLAMS in the Earth's Foreshock

Short large‐amplitude magnetic structures (SLAMS) are common magnetic field structures in the terrestrial foreshock and play an important role in particle dynamics, often leading to the formation of unstable ion and electron velocity distributions. Consequently, the presence of SLAMS can naturally excite plasma waves at various scales. This study integrated MMS observations with instability theories to investigate the local excitation of multi-scale magnetosonic whistler waves associated with SLAMS. The findings revealed that low-frequency magnetosonic whistler waves appear in the tailing region of SLAMS, where solar wind ions and low-energy ions coexist. Within SLAMS, counter-streaming high-frequency magnetosonic whistler waves (also known as whistlers) are characterized by an anisotropic electron temperature, where the perpendicular temperature exceeds the parallel temperature. Based on instability theory analysis, we proposed that the excitation of low-frequency magnetosonic whistler waves results from two-stream instability, driven by the relative drift between low-energy ions and electrons, while the excitation of whistler waves arises from electron temperature anisotropy instability. These results indicated that SLAMS significantly influence (and may even determine) the dynamic properties of particles and the excitation of certain types of plasma waves.