Bibliography

Electromagnetic characteristics of fast magnetosonic waves in the inner magnetosphere

Abstract In evaluating the effects of fast magnetosonic (MS) waves on magnetospheric particles, their magnetic spectra are often obtained from satellite observations, while electric field components are usually derived under the cold plasma approximation. However, such an approximation has not been verified with in situ observations yet. In this paper, we report the electromagnetic characteristic for MS waves in various plasma environments with observations of the Van Allen Probe A. It is found that a considerable number of observed MS waves consist of dominated electrostatic components, which also suggest the importance of inspecting the estimation algorithm for the electric field components. Moreover, the comparison between results from statistical and theoretical analysis shows that electromagnetic characteristics of the observed MS waves can be well predicted by cold plasma theory. Our result indicates the validation of cold plasma approximation to estimate the electric field components of MS waves from their magnetic counterparts in the inner magnetosphere.

Yu, Xiongdong; Yuan, Zhigang; Yao, Fei; Ouyang, Zhihai; Wang, Dedong;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2021

YEAR: 2021     DOI: https://doi.org/10.1029/2021JA029759

Fast Magnetosonic Waves; Electromagnetic characteristics; Van Allen Probes; Cold plasma approximation

Effects of the plasmapause on the radial propagation of fast magnetosonic waves: An Analytical Approach

Abstract In this paper, analytical approximation is used to solve the wave equations near the plasmapause boundary layer in order to examine the validity of ray tracing approach for fast magnetosonic (MS) wave propagations, and then analytical solutions for electromagnetic fields of MS waves through the plasmapause boundary layer are provided for the first time. Both theoretical calculations from the analytical expressions and observations of Van Allen Probes have indicated that electric fields of MS waves decrease rapidly but magnetic fields increase rapidly when propagating across the plasmapause boundary layer from the outside. Considering effects of width of the plasmapause and wave frequency, parameter analysis has shown that when the width of the plasmapause boundary layer is narrow in comparison with the wavelength of MS waves, a significant part of waves will be reflected. In these circumstances, the WKB approximation and then ray tracing method might become invalid, and analytical approach provided in this paper could be utilized to solve the wave equation.

Yu, Xiongdong; Yuan, Zhigang; Ouyang, Zhihai; Yao, Fei;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2021

YEAR: 2021     DOI: https://doi.org/10.1029/2020JA028330

MS waves; Radial propagation; Analytical approach; WKB approximation; Van Allen Probes

Narrowband Magnetosonic Waves Near the Lower Hybrid Resonance Frequency in the Inner Magnetosphere: Wave Properties and Excitation Conditions

In this study, the excitation of narrowband fast magnetosonic (MS) waves near the lower hybrid resonance frequency (fLHR) has been investigated with observations from Van Allen Probes mission and linear growth theory. A typical wave event is first examined to show that these waves can be excited through linear instabilities driven by partial shell distributions of protons. Then it is found that these narrowband MS waves from 188 wave events observed by the Van Allen Probe A between January 1, 2013 to December 31, 2015 have central frequencies around 0.7fLHR with a bandwidth of 0.2fLHR. In addition, these waves are observed mainly in the dayside and dusk sectors outside the plasmapause, which is different from previously reported results. Moreover, the simultaneously observed energetic protons during wave activities show that the ratios of the ring speed Vr to the Alfvén speed VA mainly fall into the range of 0.8 < Vr/VA < 1, and this preferred condition for excitations of narrowband MS waves near fLHR is also verified by a parameter analysis of calculating linear wave growth rates combined with wave observations.

Ouyang, Zhihai; Yuan, Zhigang; Yu, Xiongdong; Yao, Fei;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028158

central frequencies; linear growth rates; lower hybrid resonance frequency; narrowband fast magnetosonic wave; Proton rings; Van Allen Probes

Analytical Fast Magnetosonic Wave Model Based on Observations of Van Allen Probe

Based on observations of Van Allen Probe-A during the period from 19 September 2012 to 28 February 2016, the relations of the fast magnetosonic (MS) wave amplitude Bw with kp index, the wave normal angle (WNA), and the wave normalized frequency (norF) are presented. Then, we establish an analytical regression model for MS wave amplitude as a function of geomagnetic storm activity (presented by kp index), L-shell (L), magnetic local time (MLT), magnetic latitude (λ), and the characteristics of MS wave, that is, wave norF and WNA. From the analytical Bw models, we found MS wave amplitude Bw has a positive relation with the intensity of geomagnetic activities both inside and outside the plasmapause, while the Bw can reach higher values inside the plasmapause than it does outside the plasmapause as the kp index increases. The Bw distribution on the norF demonstrates that most of the wave energies are concentrated on the lower harmonics part, which results from the excitation mechanism of MS waves. In addition, the Bw distribution on the WNA shows that the waves with larger normal angles have higher values of wave amplitude. Our analytic MS wave model agrees with the observed distribution in 3-D space of L, MLT, and λ well with high value of determine coefficient R2. The extended λ dimension will help us to calculate the more accurate bounced averaged diffusion coefficients during particles transit time.

Yao, Fei; Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Ouyang, Zhihai;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028527

fast magnetosonic wave; Van Allen Probe; analytical regression model; wave normal angle; Plasmapause; Van Allen Probes

Ionospheric Signatures of Ring Current Ions Scattered by Magnetosonic Waves

In this letter, we present unique conjugated satellite observations of ionospheric signatures of ring current (RC) ions scattered by fast magnetosonic (MS) waves. In the plasmasphere, the Van Allen Probe in situ observed MS waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen Probe simultaneously observed obvious enhancements of mirroring RC ions, but no obvious variations of precipitating RC ions at subauroral latitudes. Theoretical calculations of pitch angle diffusion coefficients for RC ions confirm that observed MS waves can lead to flux enhancements only for mirroring but not for precipitating RC ions, which is in agreement with the observations of NOAA 16. Our result provides a direct link between in situ inner magnetospheric observations of MS waves and conjugated ionospheric observations of flux enhancements for mirroring RC ions caused by MS waves so as to reveal the ionospheric signature of RC ions scattered by MS waves.

Yuan, Zhigang; Yao, Fei; Yu, Xiongdong; Ouyang, Zhihai; Huang, Shiyong;

Published by: Geophysical Research Letters      Published on: 08/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089032

magnetosonic waves; mirroring ions; pitch angle scatter; precipitating ions; Van Allen Probes; Ring current ions

An Automatic Detection Algorithm Applied to Fast Magnetosonic Waves With Observations of the Van Allen Probes

Fast magnetosonic (MS) waves can play an important role in the evolution of the inner magnetosphere. However, there is still not an effective method to quantitatively identify such waves for observations of the Van Allen Probes reasonably. In this paper, we used Van Allen Probes data from 18 September 2012 to 30 September 2014 to find a more comprehensive automatic detection algorithm for fast MS waves through statistical analysis of the major properties, including the planarity, ellipticity, and wave normal angle of whole fluctuations using the singular value decomposition method. According to a control variate method, we find an obvious difference between fast MS waves and other waves in the statistical distribution of their major properties. After eliminating the influence of background noises, by excluding fluctuations at L < 1.8, we set up an automatic detection algorithm applied to fast MS waves, that is, smaller than 0.2 for the absolute value of wave ellipticity, larger than 70\textdegree for the wave normal angle, with frequency range of 2 Hz to 1.5 fLHR (fLHR is the local lower hybrid resonance frequency). Finally, we have checked the planarity to verify availability of this method and tested this completely automatic method on the Van Allen Probes data and found some results consistent with previous studies. Inside the plasmapause, we found that there is a more obviously favorable occurrence of MS waves at dusk sector with increasing magnetic latitudes.

Yuan, Zhigang; Yao, Fei; Yu, Xiongdong; Huang, Shiyong; Ouyang, Zhihai;

Published by: Journal of Geophysical Research: Space Physics      Published on: Apr-05-2021

YEAR: 2019     DOI: 10.1029/2018JA026387

ellipticity; magnetosonic wave; normalized distribution; planarity; Van Allen Probes; wave normal angle

Simultaneous trapping of EMIC and MS waves by background plasmas

Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low density regions. Theoretical analysis based on Snell\textquoterights law and linear growth theory have been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from a conservation of the parameter Q during their propagation. Here Q = nrsinψ, with n the refractive index, r the radial distance, and ψ the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference between different plasma density regions. Our results indicate the alternative mechanism for simultaneous appearance of electromagnetic ion cyclotron waves and fast magnetosonic waves (rather than wave excitations of both two wave emissions), which might take combined effects on the evolution of radiation belt electrons.

Yuan, Zhigang; Yu, Xiongdong; Ouyang, Zhihai; Yao, Fei; Huang, Shiyong; Funsten, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2019

YEAR: 2019     DOI: 10.1029/2018JA026149

EMIC waves; MS waves; Ring current ions; Van Allen Probes; Wave trapping

Precipitation of radiation belt electrons by EMIC waves with conjugated observations of NOAA and Van Allen satellites

In this letter, we present unique conjugated satellite observations of MeV relativistic electron precipitation caused by electromagnetic ion cyclotron (EMIC) waves. On the outer boundary of the plasmasphere, the Van Allen probe observed EMIC waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen probe simultaneously detected obvious flux enhancements for precipitating >MeV radiation belt electrons, but not for precipitating MeV radiation belt electrons. Our result provides a direct magnetic conjugated observational link between in-situ inner magnetospheric EMIC waves and precipitation of MeV relativistic electrons at ionospheric altitudes so as to reveal that EMIC waves can solely scatter MeV radiation belt electrons into the loss cone so as to precipitate into the atmosphere.

Yuan, Zhigang; Liu, Kun; Yu, Xiongdong; Yao, Fei; Huang, Shiyong; Wang, Dedong; Ouyang, Zhihai;

Published by: Geophysical Research Letters      Published on: 11/2018

YEAR: 2018     DOI: 10.1029/2018GL080481

Chorus; EMIC waves; Particle precipitation; Radiation belt; ring current; Van Allen Probes; Wave-particle interaction

Global distribution of proton rings and associated magnetosonic wave instability in the inner magnetosphere

Using the Van Allen Probe A observations, we obtained the global distribution of proton rings and calculated the linear wave growth rate of fast magnetosonic (MS) waves in the region L ~ 3-6. Our statistical and calculated results demonstrate that MS waves can be locally excited on the dayside outside the plasmapause, as well as in the dusk sector inside the plasmapause. The frequency range of unstable MS waves is strongly modulated by the ratio of the proton ring velocity (Vr) to the local Alfv\ en speed (VA). High harmonic MS waves (ω>20ΩH+) can be excited outside the plasmapause where Vr/VA<1 while low harmonic MS waves (ω<10ΩH+) with frequencies less than ~30 Hz are found to be excited both outside and inside the plasmapause where 1

Yuan, Zhigang; Ouyang, Zhihai; Yu, Xiongdong; Huang, Shiyong; Yao, Fei; Funsten, H.;

Published by: Geophysical Research Letters      Published on: 09/2018

YEAR: 2018     DOI: 10.1029/2018GL079999

Fast Magnetosonic Waves; linear growth rates; locally excited; low harmonic magnetosonic waves; Proton rings; Van Allen Probes