Journal article
Chorus Wave Within Wavelength‐Scale Density Irregularities
Journal of geophysical research. Space physics, Vol.131(1), e2025JA034573
01/2026
DOI: 10.1029/2025JA034573
Abstract
We present observations from the Van Allen Probes of lower band chorus waves interacting with wavelength‐scale density irregularities and gradients on the order of a few kilometers—comparable to the wavelength of the chorus waves themselves. High‐resolution electron density is derived from the upper hybrid resonance line in the High‐Frequency Receiver (HFR) merged spectrum, with a time resolution of 0.5 s. These observations show that density fluctuations modulate both the amplitude and wave normal angles of lower band chorus. High‐amplitude, quasi‐parallel waves are associated with regions of enhanced density, whereas very oblique waves with lower amplitude are found in regions of density depletion. The very oblique chorus waves are not generated locally by anisotropic electrons or shaped solely by propagation effects. One‐dimensional wave field calculations in a multilayered plasma demonstrate that wavelength‐scale density irregularities can scatter incident quasi‐parallel waves and produce very oblique waves at density depletions. Lower band chorus waves play an important role in the dynamics of energetic electrons in near‐Earth space. The angle between wave vector and background magnetic field, known as the wave normal angle, strongly influences how they interact with electrons. In this study, we use observations from NASA's Van Allen Probes to show two events where both the wave normal angle and amplitude of lower band chorus waves are influenced by small‐scale fluctuations in background plasma density. These density fluctuations have spatial scales comparable to the wavelength of the chorus waves—just a few kilometers. We find that chorus waves tend to be nearly parallel to the magnetic field in high‐density regions, and become very oblique in low‐density regions. The very oblique waves observed in low‐density regions cannot be explained by the usual generation mechanism involving anisotropic electrons. Instead, we use one‐dimensional wave modeling to show that these oblique waves result from scattering of the initially quasi‐parallel waves by the density irregularities. Van Allen Probes observe two cases of chorus waves with amplitude and wave normal angle modulated by wavelength‐scale density fluctuations Quasi‐parallel waves are found in density enhancements while oblique waves are in density depletions One‐dimensional wave field calculation shows oblique waves in these cases are produced by scattering effect of density irregularities
Details
- Title: Subtitle
- Chorus Wave Within Wavelength‐Scale Density Irregularities
- Creators
- Wenyao Gu - The University of Texas at DallasLunjin Chen - The University of Texas at DallasDavid P. Hartley - University of IowaXu Liu - The University of Texas at DallasZhiyang Xia - The University of Texas at DallasJiabei He - The University of Texas at Dallas
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.131(1), e2025JA034573
- DOI
- 10.1029/2025JA034573
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Publisher
- Wiley
- Grant note
- National Aeronautics and Space Administration: 80NSSC20K1324, 80NSSC24K0263, 80NSSC24K0558, 80NSSC22K1637, 80NSSC25K7749, 80NSSC21K0519 National Science Foundation: 2040708, 2350235
WG, LC, and DPH are supported by NASA Grant 80NSSC20K1324. Work in UT Dallas is supported by NASA Grants 80NSSC24K0263, 80NSSC24K0558, 80NSSC22K1637, and 80NSSC25K7749. DPH also acknowledges NASA Grant 80NSSC21K0519 and NSF-GEM Grants 2040708 and 2350235.
- Language
- English
- Date published
- 01/2026
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9985130055202771
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