Global Occurrence Morphology of Higher Band ECH Waves in the Magnetosphere Derived From MMS Observations

Abstract

Electron cyclotron harmonic (ECH) waves, which are electrostatic emissions outside the plasmasphere, are of great interest because of their essential role in producing diffuse auroras. Since they are commonly observed in the first band, the global distributions of those waves in higher bands remain unknown in the magnetosphere. Using Magnetospheric Multiscale satellite data, we present the global occurrence morphology of higher band ECH waves in the magnetosphere. Higher band ECH waves are widespread in the pre-midnight to post-noon magnetosphere with occurrence rates slightly lower and spatial distribution narrower than the first band. They predominantly occur near the magnetic equator at L = 4–9 on the nightside but are more prevalent and extend to the duskside at high latitudes at L = 9–12 on the dayside. As the geomagnetic activity intensifies, their occurrence rates show an increasing tendency and their spatial coverage expands radially and azimuthally. Our results potentially contribute to understanding the magnetospheric electron dynamics driven by ECH waves.