First Report of Rising‐Tone EMIC Waves Driven by the Magnetosheath High‐Speed Jet

Magnetosheath high‐speed jets (HSJs) are pervasive transient structures with enhanced dynamic pressure in the terrestrial magnetosheath and can exert notable local impacts on the magnetopause. Although various geoeffects have been reported to be associated with HSJs, whether HSJs can drive the generation of electromagnetic ion cyclotron (EMIC) waves remains unknown. Using coordinated observations from THEMIS‐A and THEMIS‐E, we report the first observation of magnetospheric EMIC waves driven by a HSJ. Two rising‐tone EMIC wave elements are detected during the “Rebounce” phase of the magnetopause's response to the HSJ impact, exhibiting distinct chirping rates and magnetic amplitudes. During this phase, higher‐energy protons with larger pitch angles efficiently replenish the magnetic equatorial region, leading to a significant increase in proton flux and temperature anisotropy. Both linear and nonlinear theoretical models confirm that these energetic protons account for the excitation of the observed rising‐tone EMIC waves.