Simulation of Energy Transfer From Magnetosonic Waves to High‐Frequency EMIC Waves via Low‐Energy Protons

Abstract Electromagnetic Ion Cyclotron (EMIC) waves and magnetosonic (MS) waves are frequently observed in the Earth's magnetosphere, playing critical roles in the loss of ring current ions and relativistic electrons. Recent observations suggest a potential energy transfer from MS waves to unusual high‐frequency EMIC waves mediated by low‐energy protons (10–100 eV). Specifically, low‐energy protons are hypothesized to be heated perpendicularly by MS waves, subsequently generating EMIC waves near the local proton cyclotron frequency. However, this hypothesis has not been demonstrated self‐consistently. Here, we employ a 2D particle‐in‐cell (PIC) simulation to investigate this process. Our results show that cold protons can be effectively energized, achieving a large temperature anisotropy during the excitation of MS waves. This finding supports the feasibility of energy transfer from MS waves to EMIC waves. Furthermore, our study highlights the need for further investigations into the key parameters governing the occurrence and efficiency of this energy transfer process.