Abstract This letter presents the first observation of banded Electron Cyclotron Harmonic (ECH) waves by Magnetospheric Multiscale (MMS) satellites near the Earth’s subsolar magnetopause. The observation shows the fundamental mode (n=1 $n=1$) and its higher harmonics (n=2 $n=2$–6), each with distinct lower and upper bands separated by a spectral gap at nfce $n{f}{ce}$, where fce ${f}{ce}$ is the electron cyclotron frequency and n $n$ is the mode number. Our analysis shows that the observed electron distribution during the wave event exhibits a loss cone and weak beam, modeled using a subtracted bi‐Maxwellian distribution. The linear dispersion analysis shows the growth only for the upper bands (>nfce ${ >} n{f}_{ce}$), suggesting banded ECH as‐yet‐unknown processes. These findings offer new insights into electron‐scale plasma dynamics and highlight the need for further work to understand the generation of banded ECH waves in the Earth’s magnetosphere.
Observations from the Little Bunker
Last updated: February 24, 2026 10:22 PM
Atmospheric CO₂
429.9 ppm
+17.3
ppm/year
Atmospheric CH₄
1946.47 ppb
+6.49
ppb/year
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Peak: +1.73°C
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