Journal Article

Unraveling the Role of Electron Plateau Distributions in the Power Gap Formation of Chorus Waves: Van Allen Probes Observations

Kong, Zhenyu, Ke, Yangguang, Chen, Huayue, Gao, Xinliang, Lu, Quanming, Chen, Rui

2023

Overview

The power gap of chorus waves at ∼0.5fce has been discovered for decades, but its generation mechanism is still under debate. Previous studies have revealed that electron plateau distributions are vitally important for the gap formation. By analyzing over one‐year Van Allen Probes data, we have studied chorus waves with (banded events) and without a power gap (no‐gap events), and their correlations with the electron plateau distribution. Although there is no significant difference in the morphology of velocity distributions in banded and no‐gap events, banded chorus events are typically accompanied by a plateau component with about one order higher number density than no‐gap events. The plateau components can cause severe damping at ∼0.5fce through cyclotron resonance rather than Landau resonance, and the gap frequency is roughly determined by the bulk velocity of plateau components. Our study provides new observational constraints on the generation mechanisms of power gap. Plain Language Summary The generation mechanism of power gap at ∼0.5fce of chorus waves has been a long‐standing problem for decades. Although its generation mechanism is still under debate, there is a consensus that the electron plateau in the parallel velocity distribution is a key factor to solve this problem. Here, we try to find out what role the electron plateau plays in the gap formation based on a statistical analysis of Van Allen Probes data. First of all, we find banded chorus events indeed have a more pronounced plateau shape (about one order higher number density) than no‐gap events, confirming the importance of electron plateau. We further find that the electron plateau can cause the severe wave damping at ∼0.5fce via cyclotron resonance rather than Landau resonance, and the gap frequency is roughly determined by the bulk velocity of electron plateau based on the cyclotron resonance condition. We also compare the morphology of electron velocity distributions in banded and no‐gap events, but do not find an obvious difference between them. Our study provides new observational constraints on the generation mechanisms of the power gap, which may help scientists finally solve this problem. Key Points Banded chorus events typically have a more pronounced plateau shape than no‐gap events in the parallel electron distribution The electron plateau can cause severe damping at ∼0.5fce via cyclotron resonance, and roughly determine the gap frequency There is no significant difference between the normalized electron velocity distributions in banded and no‐gap events

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Chorus waves / Components / Cyclotron resonance / Damping / Density / Distribution / Earth’s inner magnetosphere / electron plateau distribution / Electrons / Morphology / Plateaus / power gap of chorus waves / Probes / Resonance / Sensors / spectrum bite / Statistical analysis / Statistical methods / Velocity / Velocity distribution / Wave damping / wave‐particle interaction