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Found 4 entries in the Bibliography.
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2021 
Abstract We study packages of VLF whistlermode waves observed by the Van Allen Probes satellites in the equatorial plasmasphere. We demonstrate that the main mechanism providing localization of these waves inside relatively broad (>1 RE across the ambient magnetic field) magnetospheric regions is a combined effect of the transverse gradients in the plasma density and the ambient magnetic field. The criterion for the wave trapping by these gradients is the same as for the wave trapping inside a highdensity duct with a symmetric, Gaussianlike profile of the density in the uniform magnetic field. This criterion can be used to determine the parallel wavelength of the wave with a known frequency trapped by the density and magnetic field inhomogeneities with known parameters. The developed theoretical approach demonstrates a good, quantitative agreement with the observations. The analytical results have been confirmed with comprehensive, timedependent simulations of the electronMHD model. Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028933 density inhomogeneity; duct; Plasmapause; plasmasphere; VLF waves; whistler; Van Allen Probes 
2017 
Bayesian Spectral Analysis of Chorus SubElements from the Van Allen Probes We develop a Bayesian spectral analysis technique that calculates the probability distribution functions of a superposition of wavemodes each described by a linear growth rate, a frequency and a chirp rate. The Bayesian framework has a number of advantages, including 1) reducing the parameter space by integrating over the amplitude and phase of the wave, 2) incorporating the data from each channel to determine the model parameters such as frequency which leads to high resolution results in frequency and time, 3) the ability to consider the superposition of waves where the waveparameters are closely spaced, 4) the ability to directly calculate the expectation value of wave parameters without resorting to ensemble averages, 5) the ability to calculate error bars on model parameters. We examine one risingtone chorus element in detail from a disturbed time on November 14, 2012 using burst mode waveform data of the three components of the electric and magnetic field from the EMFISIS instrument on board NASA\textquoterights Van Allen Probes. The results demonstrate that subelements are likely composed of almost linear waves that are nearly parallel propagating with continuously changing wave parameters such as frequency and wavevector. Between subelements the wave parameters of the dominant mode undergoes a discrete change in frequency and wavevector. Near the boundary of subelements multiple waves are observed such that the evolution of the waves is reminiscent of wavewave processes such as parametric decay or nonlinear induced scattering by particles. These nonlinear processes may affect the saturation of the whistlermode chorus instability. Crabtree, Chris; Tejero, Erik; Ganguli, Gurudas; Hospodarsky, George; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023547 
2016 
We present observations of higherfrequency (~50\textendash2500 Hz, ~0.1\textendash0.7 fce) wave modes modulated at the frequency of colocated lower frequency (0.5\textendash2 Hz, on the order of fci) waves. These observations come from the Van Allen Probes Electric Field and Waves instrument\textquoterights burst mode data and represent the first observations of coupling between waves in these frequency ranges. The higherfrequency wave modes, typically whistler mode hiss and chorus or magnetosonic waves, last for a few to a few tens of seconds but are in some cases observed repeatedly over several hours. The higherfrequency waves are observed to be unmodulated before and after the presence of the electromagnetic ion cyclotron (EMIC) waves, but when the EMIC waves are present, the amplitude of the higherfrequency waves drops to the instrument noise level once every EMIC wave cycle. Such modulation could significantly impact waveparticle interactions such as acceleration and pitch angle scattering, which are crucial in the formation and depletion of the radiation belts. We present one case study with broadband, highfrequency waves observed to be modulated by EMIC waves repeatedly over a 2 h time span on both spacecraft. Finally, we show two additional case studies where other highfrequency wave modes exhibit similar modulation. Colpitts, C.; Cattell, C.; Engebretson, M.; Broughton, M.; Tian, S.; Wygant, J.; Breneman, A.; Thaller, S.; Published by: Geophysical Research Letters Published on: 11/2016 YEAR: 2016 DOI: 10.1002/2016GL071566 EMIC; Modulation; precipitation; Radiation belt; Van Allen Probes; wave; whistler 
2015 
Most previous work on nonlinear waveparticle interactions between energetic electrons and VLF waves in the Earth\textquoterights magnetosphere has assumed parallel propagation, the underlying mechanism being nonlinear trapping of cyclotron resonant electrons in a parabolic magnetic field inhomogeneity. Here nonlinear waveparticle interaction in oblique whistlers in the Earth\textquoterights magnetosphere is investigated. The study is nonselfconsistent and assumes an arbitrarily chosen wave field. We employ a \textquotedblleftcontinuous wave\textquotedblright wave field with constant frequency and amplitude, and a model for an individual VLF chorus element. We derive the equations of motion and trapping conditions in oblique whistlers. The resonant particle distribution function, resonant current, and nonlinear growth rate are computed as functions of position and time. For all resonances of order n, resonant electrons obey the trapping equation, and provided the wave amplitude is big enough for the prevailing obliquity, nonlinearity manifests itself by a \textquotedbllefthole\textquotedblright or \textquotedbllefthill\textquotedblright in distribution function, depending on the zeroorder distribution function and on position. A key finding is that the n = 1 resonance is relatively unaffected by moderate obliquity up to 25\textdegree, but growth rates roll off rapidly at high obliquity. The n = 1 resonance saturates due to the adiabatic effect and here reaches a maximum growth at ~20 pT, 2000 km from the equator. Damping due to the n = 0 resonance is not subject to adiabatic effects and maximizes at some 8000 km from the equator at an obliquity ~55\textdegree. Nunn, David; Omura, Yoshiharu; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020898 Chorus; nonlinear process; oblique propagation; simulation; Waveparticle interaction; whistler 
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