Abstract
Electron flux in the Earth’s outer radiation belt is highly variable due to a delicate balance between competing acceleration and loss processes. It has been long recognized that Electromagnetic Ion Cyclotron (EMIC) waves may play a crucial role in the loss of radiation belt electrons. Previous theoretical studies proposed that EMIC waves may account for the loss of the relativistic electron population. However, recent observations showed that while EMIC waves are responsible for the significant loss of ultra-relativistic electrons, the relativistic electron population is almost unaffected. In this study, we provide a theoretical explanation for this discrepancy between previous theoretical studies and recent observations. We demonstrate that EMIC waves mainly contribute to the loss of ultra-relativistic electrons. This study significantly improves the current understanding of the electron dynamics in the Earth’s radiation belt and also can help us understand the radiation environments of the exoplanets and outer planets.
Highlights
Gyro-frequency and νA is the Alfvén velocity
In order to understand this discrepancy between previous theoretical studies and recent observations, we incorporate the hot plasma effects in evaluations of electron minimum cyclotron resonant energy, which denotes the minimum energy of electrons that can undergo cyclotron resonance with Electromagnetic Ion Cyclotron (EMIC) waves for scattering into the loss cone
We demonstrate that for all reasonable combinations of input parameters, EMIC waves mainly contribute to the loss of ultra-relativistic electrons, while the relativistic electron population is practically unaffected
Summary
Gyro-frequency and νA is the Alfvén velocity. Red and black lines denote the results for H+. When the anisotropy is very large and the electron density is unusually high (above one standard deviation), electron resonant energies for interactions with H+ band EMIC waves can fall below 1.5 MeV.
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