Global Distribution of Electrostatic Electron Cyclotron Harmonic Waves from Over-10-year Multi-Satellite Observations

To obtain a comprehensive global morphology of the ECH waves, we combine the high-quality observations from the recent satellites of Van Allen Probes, Arase, and Magnetospheric Multiscale from 2012 to 2022. With the well-accumulated data, we find that ECH waves can be observed over a broad spatial region with significant asymmetry. Primarily, ECH waves can be observed from L= ~2.5 and extend to L = ~15 on the nightside while dayside waves are compressed closer to the Earth. On the nightside, the waves are observed more frequently at low L with strong wave strength. As L increases, both wave occurrence and amplitude decline. It is noteworthy that ECH waves exhibit a double peak pattern at L = ~4-6 and 8-12 on the dayside, and a dip of occurrence at L = 6-8, which might indicate two dominant driving mechanisms of ECH waves on the inner and outer magnetosphere, respectively. At low L, ECH waves are observed near the equator, while they can be observed extensively over the magnetic latitude of ~-40° — 40° at higher L. Compared with the nightside, the magnetic latitude sensitivity to the increase of L is more dramatic on the dayside. Furthermore, at low latitudes, ECH waves can be observed with broad MLT coverage and have strong wave amplitude at low L. For high latitudes, the waves occur at higher L, with higher occurrence on the dayside while stronger wave strength on the nightside. Our results provide a new insight into the generating and propagating mechanism of ECH waves.