Efficient Scattering Loss of Energetic Electrons by Enhanced Higher‐Band ECH Waves Observed by Van Allen Probes

Abstract

AbstractElectron cyclotron harmonic (ECH) waves, which are responsible for the diffuse aurora, are usually observed with the strongest intensity in the first band. Here, we present observations of enhanced higher‐band ECH with wave intensities above 10−3 mV2m−2 Hz−1 by Van Allen Probes. Fully thermal simulation results indicate that these waves can be locally excited by the observed electron distributions, and higher plasma density and lower magnetic strength are favorable for generating the enhanced higher‐band ECH. The pitch angle diffusion coefficient of the higher‐band ECH can exceed 10−5 s−1 inside the loss cone for energetic electrons (300 eV–∼15 keV), greater than the momentum diffusion coefficient by ∼100 times. It is suggested that the enhanced higher‐band ECH can also efficiently scatter these electrons into the loss cone and contribute to the diffuse aurora.