Unraveling the Formation Region and Frequency of Chorus Spectral Gaps

Journal Article · Thu Sep 29 00:00:00 EDT 2022 · Geophysical Research Letters

DOI:https://doi.org/10.1029/2022GL100385· OSTI ID:1996042

Li, Jinxing ^[1]; Bortnik, Jacob ^[1]; Li, Wen ^[2]; An, Xin ^[3]; Lyons, Larry R. ^[1]; Kurth, William S. ^[4]; Hospodarsky, George B. ^[4]; Hartley, David P. ^[4]; Reeves, Geoffrey D. ^[5]; Funsten, Herbert O. ^[6]; Blake, J. Bernard ^[7]; Spence, Harlan ^[8]; Baker, Daniel N. ^[9]

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1. Department of Atmospheric and Oceanic Sciences University of California, Los Angeles Los Angeles CA USA
2. Center for Space Physics Boston University Boston MA USA
3. Department of Earth, Planetary and Space Sciences University of California, Los Angeles Los Angeles CA USA
4. Department of Physics and Astronomy University of Iowa Iowa City IA USA
5. Space Science and Applications Group Los Alamos National Laboratory Los Alamos NM USA, Los Alamos National Laboratory Los Alamos NM USA
6. New Mexico Consortium Los Alamos NM USA
7. Space Science Applications Laboratory The Aerospace Corporation El Segundo CA USA
8. Institute for the Study of Earth, Oceans, and Space University of New Hampshire Durham NH USA
9. Laboratory for Atmospheric and Space Physics University of Colorado, Boulder Boulder CO USA

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 f _ce ( f _ce : 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 f _ce 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 f _ce by suppressing wave excitation.

• Sponsoring Organization: USDOE
• Grant/Contract Number: NONE; SC0010578
• OSTI ID: 1996042
• Journal Information: Geophysical Research Letters, Journal Name: Geophysical Research Letters Journal Issue: 19 Vol. 49; ISSN 0094-8276
• Publisher: American Geophysical Union (AGU)
• Country of Publication: United States
• Language: English