New properties of whistler modes

Stenzel, R. L.; Urrutia, J. M.

doi:10.1002/2016gl072446

Cited by 5 publications

(4 citation statements)

References 26 publications

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“…This indicates that the transverse propagation direction of the reflected whistler waves may depend on their initial wave properties, such as wave frequency and wave normal angle (Bortnik et al, 2008; Bortnik et al, 2011; He et al, 2015). It should also be mentioned that a strong standing wave pattern and linear polarization in the LHR reflection region, which are shown in our simulation results in sections 3.1 and 3.2, are similar to the observation in a laboratory plasma experiment on the new reflection mechanism of whistler mode waves by Stenzel and Urrutia (2017). The signatures from simulated magnetospheric reflection can be compared with observation evidence from satellites near the LHR reflection region in the magnetosphere, which is left as a future study.…”

Section: Conclusion and Discussionsupporting

confidence: 90%

Two‐Dimensional Full‐Wave Simulation of Whistler Mode Wave Propagation Near the Local Lower Hybrid Resonance Frequency in a Dipole Field

Chen

Zhou

et al. 2020

JGR Space Physics

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We investigate the propagation of whistler mode waves near the local lower hybrid resonance (LHR) frequency in a dipole field with a two-dimensional full-wave model. First, we run a simulation in which a parallel whistler with frequency above the local LHR frequency is launched at the equatorial region in electron plasma. We find that whistler emission propagates along the dipole field line to a high latitude, turns quasi-electrostatic where the wave frequency is close to the local LHR frequency, and continues to propagate until being absorbed. Then, the proton response is considered. We find that (1) a quasi-electrostatic whistler reflects where the wave frequency is below the local LHR frequency and propagates to a larger L-shell and lower latitude, (2) a strong standing-wave pattern is formed in the LHR reflection region, and (3) the whistler emission turns from right-hand circularly polarized to linearly polarized near the reflection region. Finally, we run a simulation in which a quasi-electrostatic whistler is launched at a high latitude with a small-scale density irregularity added as a depletion to the background plasma. We find that a small portion of quasi-electrostatic whistler energy can be coupled to a parallel whistler, which can propagate to a much lower altitude while most of the wave energy experiences LHR reflection. Moreover, the mode coupling depends on the transverse and longitudinal sizes of the density irregularity. This makes a possible explanation of ground observations of nonducted whistler emission, which could have been reflected in the high-latitude ionosphere and magnetosphere.

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Section: Conclusion and Discussionsupporting

confidence: 90%

Two‐Dimensional Full‐Wave Simulation of Whistler Mode Wave Propagation Near the Local Lower Hybrid Resonance Frequency in a Dipole Field

Chen

Zhou

et al. 2020

JGR Space Physics

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“…This effect has been shown and explained in a recent letter. 48 In the present work, we observe in detail the motion of the incident phase front in an ambient magnetic field whose curvature changes on a scale smaller than a wavelength. The off-axial field lines bend faster than the phase front such that the incident wave changes from oblique to perpendicular and beyond.…”

Section: Wave Reflection Mechanism In Highly Nonuniform Magnetic Fmentioning

confidence: 81%

Whistler modes in highly nonuniform magnetic fields. III. Propagation near mirror and cusp fields

Stenzel

Urrutia

2018

Physics of Plasmas

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The properties of helicon modes in highly nonuniform magnetic fields are studied experimentally. The waves propagate in an essentially unbounded uniform laboratory plasma. Helicons with mode number m ¼ 1 are excited with a magnetic loop with dipole moment across the dc magnetic field. The wave fields are measured with a three-component magnetic probe movable in three orthogonal directions so as to resolve the spatial and temporal wave properties. The ambient magnetic field has the topology of a mirror or a cusp, produced by the superposition of a uniform axial field B 0 and the field of a current-carrying loop with the axis along B 0. The novel finding is the reflection of whistlers by a strong mirror magnetic field. The reflection arises when the magnetic field changes on a scale length shorter than the whistler wavelength. The simplest explanation for the reflection mechanism is the strong gradient of the refractive index which depends on the density and magnetic field. More detailed observations show that the incident wave splits when the k vector makes an angle larger than 90 with respect to B 0 which produces a parallel phase velocity component opposite to that of the incident wave. The reflection coefficient has been estimated to be close to unity. Interference between reflected and incident waves creates nodes in which the whistler mode becomes linearly polarized. When the magnetic field topology is that of a reversed field configuration (FRC), the incident wave is absorbed near the three-dimensional (3D) magnetic null point which prevents wave reflections. However, waves outside the separatrix are not absorbed and continue to propagate around the null point. When waves are excited inside the FRC, their polarization and helicon mode are reversed. Implications of these observations on research in space plasmas and helicon sources are pointed out.

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“…It is thus suggested that a majority of whistler mode waves in the Martian magnetosphere are almost linearly polarized and propagating obliquely with respect to the background magnetic field. Linear polarization may be due to the interference of the circular polarized waves while propagating in opposite directions, and oblique propagating waves may be caused by wave refraction during propagation away from source regions (Chen et al., 2013; Stenzel & Urrutia, 2017; Yu & Yuan, 2022). However, the reason why linearly polarized and oblique propagating waves dominate is not yet conclusive, which will be further explored in the future work.…”

Section: Statistical Resultsmentioning

confidence: 99%

Statistical Distribution of Whistler Mode Waves in the Martian Induced Magnetosphere Based on MAVEN Observations

Du,

Cao,

et al. 2024

JGR Space Physics

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Whistler mode waves are a common type of electromagnetic waves in the Martian induced magnetosphere. Using high‐resolution magnetic field data from the Magnetometer (MAG) instrument onboard Mars Atmosphere and Volatile Evolution (MAVEN) from October 2014 to November 2022, we perform a detailed analysis of the statistical distribution of the occurrence rate, averaged amplitude, peak frequency, wave normal angle and ellipticity of left‐hand and right‐hand polarized whistler mode waves in the Martian induced magnetosphere. Our results show that whistler mode waves are mainly observed in the subsolar and magnetic pileup region, with the occurrence rate of right‐hand mode waves higher than that of left‐hand mode waves. The averaged wave amplitude ranges from 0.02 to 0.13 nT and peak wave frequency ranges from 2 to 9 Hz. We also find that the wave normal angles for both left‐hand and right‐hand polarized whistler waves are relatively larger in the subsolar region and magnetic pileup region where the corresponding wave ellipticity is closer to the linear polarization. Our results are valuable to in‐depth understanding of the generation mechanism of whistler mode waves as well as their contributions to the electron dynamics in the Martian induced magnetosphere.

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New properties of whistler modes

Cited by 5 publications

References 26 publications

Two‐Dimensional Full‐Wave Simulation of Whistler Mode Wave Propagation Near the Local Lower Hybrid Resonance Frequency in a Dipole Field

Two‐Dimensional Full‐Wave Simulation of Whistler Mode Wave Propagation Near the Local Lower Hybrid Resonance Frequency in a Dipole Field

Whistler modes in highly nonuniform magnetic fields. III. Propagation near mirror and cusp fields

Statistical Distribution of Whistler Mode Waves in the Martian Induced Magnetosphere Based on MAVEN Observations

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