Journal article
Unraveling the Formation Region and Frequency of Chorus Spectral Gaps
Geophysical research letters, Vol.49(19), e2022GL100385
10/16/2022
DOI: 10.1029/2022GL100385
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
Details
- Title: Subtitle
- Unraveling the Formation Region and Frequency of Chorus Spectral Gaps
- Creators
- Jinxing Li - University of California, Los AngelesJacob Bortnik - University of California, Los AngelesWen Li - Boston UniversityXin An - University of California, Los AngelesLarry R. Lyons - University of California, Los AngelesWilliam S. Kurth - University of IowaGeorge B. Hospodarsky - University of IowaDavid P. Hartley - University of IowaGeoffrey D. Reeves - Los Alamos National LaboratoryHerbert O. Funsten - New Mexico ConsortiumJ. Bernard Blake - The Aerospace CorporationHarlan Spence - University of New HampshireDaniel N. Baker - Laboratory for Atmospheric and Space Physics
- Resource Type
- Journal article
- Publication Details
- Geophysical research letters, Vol.49(19), e2022GL100385
- DOI
- 10.1029/2022GL100385
- ISSN
- 0094-8276
- eISSN
- 1944-8007
- Number of pages
- 8
- Grant note
- National Aeronautics and Space Administration (NASA) (LWS‐ 80NSSC20K0201; NNX14AI18G; 80NSSC18K1227; 80NSSC21K0522; 80NSSC20K0917; 80NSSC20K1506; 80NSSC19K0845; 80NSSC20K0698; NAS5‐01072) Alfred P. Sloan Research Fellowship (FG‐2018‐10936) National Science Foundation (NSF) (AGS‐1923126; AGS‐1847818) DOE Idaho Operations Office, U.S. Department of Energy (DOE‐ID) (DE‐SC0010578)
- Language
- English
- Date published
- 10/16/2022
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984455266002771
Metrics
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