Distinct Global Distribution of Electrostatic Electron Cyclotron Harmonic Waves in Earth's Magnetosphere Revealed by Multi‐Satellite Observations

Electrostatic electron cyclotron harmonic (ECH) waves have been analyzed using different satellite data. However, single‐mission studies prevent a systematic understanding of the emissions in Earth's magnetosphere. We perform a comprehensive survey of ECH waves using observations from Van Allen Probes, Arase, and MMS satellites spanning over 2012–2023. Our results indicate that these waves cover a broad spatial region of L = 3–15, |MLAT| < ∼40°, and nearly all magnetic local time sectors, showing a pronounced regional dependence. In the inner magnetosphere ( L < ∼6), ECH wave power peaks in the premidnight‐to‐noon sectors, while the waves in outer regions ( L > 6) exhibit dayside‐maximized occurrence rates. Wave amplitudes are strongest on the nightside but display a secondary pre‐noon peak at L > 8. In addition, ECH waves are predominantly confined near the equator (|MLAT| < 5°) at L < ∼8, in contrast to the much broader latitudinal distribution (|MLAT| < 35°) at higher L .