A Statistical Study of Electron Cyclotron Harmonic Waves in the Lunar Plasma Environment

Electron cyclotron harmonic (ECH) waves, a subset of electron Bernstein modes, are characterized by their distinct harmonic frequency structures. In the outer magnetosphere of the Earth, these waves play a vital role in electron scattering, pitch‐angle diffusion, and the subsequent precipitation of particles into the ionosphere. In contrast, their properties in the vicinity of the Lunar surface remain relatively poorly understood. In this study, we investigate the statistical characteristics of ECH waves using 8 years of observations from the ARTEMIS mission, with the objective of systematically characterizing their behavior across diverse Lunar plasma environments. Our analysis indicates that the overall occurrence rate of ECH waves within the region is approximately 0.099%, but this rate rises to more than 1% on the anti‐sun side in close proximity to the Moon. Moreover, the majority of ECH wave events are detected when the Moon resides within the Earth's magnetotail. On the anti‐sun side, enhanced ECH wave amplitudes are most pronounced in the near Lunar surface region. These results demonstrate that the local Lunar plasma environment strongly influences ECH wave activity, with Lunar magnetic field anomalies significantly modulating the occurrence rate of ECH waves while exerting no substantial influence on their amplitude. Collectively, these findings provide new insights into the plasma processes operating near the Lunar surface.