Journal article
Propagation of Very Oblique Chorus Waves Near a Plasmaspheric Plume Boundary
Journal of geophysical research. Space physics, Vol.129(2), e2023JA032151
02/01/2024
DOI: 10.1029/2023JA032151
Abstract
In a case study using Van Allen Probe B, we investigate chorus wave observations near the western edge of a plasmaspheric plume characterized by steep density gradients. Initially, wave vectors are oriented anti-Earthward, but they become very oblique and eastward as the probe approaches the plume boundary. Treating the plume boundary as an azimuthal density gradient, ray tracing can reproduce the observed wave vector directions. Ray tracing shows that the azimuthal density gradient strongly inclines the wave vectors eastward. Consequently, waves are reflected upon reaching the Gendrin angle and cannot enter the plume. We establish an analytical criterion for the azimuthal density enhancement, determining the condition for chorus waves to enter plumes near the equatorial region. Our results partly explain the oblique chorus near plumes observed by Hartley, Chen et al. (2022, https://doi.org/10.1029/2022GL098710), offering insight into wave-particle interactions by chorus waves with the influence of azimuthal density structures.
In near-Earth space, whistler-mode chorus waves are typically observed in the plasma trough. The wave vector direction of chorus waves, which is an important parameter in quantifying wave-particle interactions, has been shown to become oblique near the boundaries of plasmaspheric plumes. In this study, we explain this phenomenon by using ray tracing to simulate an observation of chorus waves near a plume boundary with a steep density gradient. Ray tracing shows that the density gradient at the plume boundary can strongly refract the chorus wave, contributing to oblique wave vectors. With a steep density gradient, the wave can be reflected at the plume boundary and thus cannot enter the plume. Our ray-tracing results reproduce the observed wave power distribution in different wave vector directions. We also established an analytical criterion to determine if the chorus wave can enter the plume region near the equatorial region. Our results give insight into wave-particle interactions by chorus waves with the influence of azimuthal density structures such as plume boundaries.
Chorus waves with very oblique, eastward-oriented $k$ vectors are observed at the westward edge of a plasmaspheric plume Ray tracing shows chorus wave vectors are affected by steep azimuthal density gradients, with results being consistent with observations A general criterion is established to determine whether chorus can enter plumes, which reveals that entry is not possible in this case
Details
- Title: Subtitle
- Propagation of Very Oblique Chorus Waves Near a Plasmaspheric Plume Boundary
- Creators
- Wenyao Gu - The University of Texas at DallasDavid Hartley - University of IowaXu Liu - The University of Texas at DallasLunjin Chen - The University of Texas at DallasJacob Bortnik - University of California, Los AngelesRichard B. Horne - British Antarctic Survey
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.129(2), e2023JA032151
- DOI
- 10.1029/2023JA032151
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Publisher
- Amer Geophysical Union
- Number of pages
- 12
- Grant note
- 80NSSC22K1637 / National Aeronautics and Space Administration; National Aeronautics & Space Administration (NASA) NASA; National Aeronautics & Space Administration (NASA)
- Language
- English
- Date published
- 02/01/2024
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984560424002771
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