Logo image
Back
Unraveling the Formation Region and Frequency of Chorus Spectral Gaps
Journal article   Open access   Peer reviewed

Unraveling the Formation Region and Frequency of Chorus Spectral Gaps

Jinxing Li, Jacob Bortnik, Wen Li, Xin An, Larry R. Lyons, William S. Kurth, George B. Hospodarsky, David P. Hartley, Geoffrey D. Reeves, Herbert O. Funsten, …
Geophysical research letters, Vol.49(19), e2022GL100385
10/16/2022
DOI: 10.1029/2022GL100385
url
https://doi.org/10.1029/2022GL100385View
Published (Version of record) Open Access

Abstract

The present study addresses two basic questions related to banded chorus waves in the Earth’s magnetosphere: 1) are chorus spectral gaps formed near the equatorial source region or during propagation away from the equator? and 2) why are chorus spectral gaps usually located below 0.5 fce (fce: electron gyro‐frequency)? By analyzing Van Allen Probes data, we demonstrate that chorus spectral gaps are observed in the source region where chorus waves propagate both in the parallel and anti‐parallel directions to the magnetic field. Chorus spectral gaps below 0.5 fce are associated with electron parallel acceleration at energies above the equatorial Landau resonant energies. We explain that initially generated chorus waves quickly isotropize the electron distribution through Landau resonant acceleration, and the isotropization occurs for higher energies at higher latitudes. The isotropized population, after returning to the magnetic equator, leads to a chorus gap typically below 0.5 fce by suppressing wave excitation. Plain Language Summary Chorus waves are naturally occurring electromagnetic waves in the Earth’s magnetized space known as the magnetosphere, and they typically have two frequency bands. A previous study proposed that the banded characteristics is produced by two anisotropic electron populations. This study aims to address two basic questions about banded chorus waves: 1) are chorus frequency gaps formed near the equatorial source region or during propagation away from equator? and 2) why are chorus frequency gaps usually located below 0.5 fce (fce: electron gyro‐frequency)? Van Allen Probe spacecraft data reveals that chorus frequency gaps are formed in the equatorial source region where the waves propagate both in the parallel and anti‐parallel directions to the magnetic field. By showing the electron distribution in association with banded chorus waves, we explain that initially generated chorus waves quickly accelerate electrons as they propagate away from equator, and the electrons being accelerated at high latitudes lead to a chorus gap below 0.5 fce when they bounce back to the equatorial source region. Key Points Chorus spectral gaps are formed near the equatorial source region where parallel and anti‐parallel emissions are interleaved Landau resonance causes electron parallel acceleration and phase space density isotropization around half electron Alfven velocity, which increases with latitudes Chorus spectral gaps are usually found below 0.5 fce due to electron anisotropy reduction caused by Landau resonance at high latitudes
 chorus spectral gaps chorus waves isotropization Landau resonance radiation belt wave‐particle interactions

Details

Metrics

9 Record Views
10 Times Cited - Web of Science
Logo image