scholarly journals Magion 5 observations of chorus-like emissions and their propagation features as inferred from ray-tracing simulation

2003 ◽  
Vol 21 (12) ◽  
pp. 2293-2302 ◽  
Author(s):  
J. Chum ◽  
F. Jiříček ◽  
J. Šmilauer ◽  
D. Shklyar
Keyword(s):  
Wave Propagation ◽  
Satellite Observation ◽  
Particle Interactions ◽  
Discrete Elements ◽  
Inner Magnetosphere ◽  
Different Types ◽  
Generation Region ◽  
Electron Gyrofrequency ◽  
Wave Normal ◽  
Ray Tracing Simulation

Abstract. After reviewing briefly the present state of knowledge about chorus-like emissions, we present an overview of Magion 5 satellite observations of these emissions in the inner magnetosphere of the Earth. From the extensive VLF data recorded on board the Magion 5 satellite, we show examples of different types of discrete elements, representing rising and falling tones, and discuss their spectral properties, such as the bandwidth and the characteristic frequency as compared to the equatorial electron gyrofrequency. We analyse the possibility of satellite observation of discrete elements, assuming nonducted wave propagation from the source. As for the characteristic dimension of the generation region, we apply the figures obtained from the recently published correlation analysis of chorus emission recorded by four satellites in the Cluster experiment. We conclude that different frequencies in the chorus element should be emitted in a certain span of wave normal angles, so that the whole element could be observed far from the generation region.Key words. Magnetospheric physics (plasmasphere; plasma waves and instabilities) – Space plasma physics (wave-particle interactions) – Ionosphere (wave propagation)

scholarly journals Subpacket Structure in Strong VLF Chorus Rising Tones: Characteristics and Consequences for Radiation Belt Acceleration

2021 ◽  
Author(s):  
John C. Foster ◽  
Philip J. Erickson ◽  
Yoshiharu Omura
Keyword(s):  
Low Frequency ◽  
Phase Variation ◽  
Continuous Phase ◽  
Inner Magnetosphere ◽  
Equatorial Wave ◽  
Generation Region ◽  
Electron Gyrofrequency ◽  
Wave Normal ◽  
Local Value

Abstract Van Allen Probes in situ observations are used to examine detailed subpacket structure observed in strong VLF (very low frequency) rising tone chorus elements observed at the time of a rapid MeV electron energization in the inner magnetosphere. Analysis of the frequency gap between lower and upper chorus-band waves identifies fceEQ, the electron gyrofrequency in the equatorial wave generation region. Initial subpackets in these strong chorus rising-tone elements begin at a frequency near 1/4 fceEQ, exhibit smooth gradual frequency increase across their > 10 ms temporal duration. A second much stronger subpacket is seen at frequencies around the local value of 1/4 fce with small wave normal angle (< 10 deg) and steeply rising df/dt. Smooth frequency and phase variation across and between the initial subpackets supports continuous phase trapping of resonant electrons and increased potential for MeV electron acceleration. The total energy gain for seed electrons with energies between 100 keV and 3 MeV ranges between 2 % and 15 %, in their nonlinear interaction with a single chorus element.

scholarly journals Subpacket structure in strong VLF chorus rising tones: characteristics and consequences for relativistic electron acceleration

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
John C. Foster ◽  
Philip J. Erickson ◽  
Yoshiharu Omura
Keyword(s):  
Low Frequency ◽  
Phase Variation ◽  
Electron Acceleration ◽  
Continuous Phase ◽  
Equatorial Wave ◽  
Generation Region ◽  
Electron Gyrofrequency ◽  
Wave Normal ◽  
Relativistic Electron Acceleration

AbstractVan Allen Probes in situ observations are used to examine detailed subpacket structure observed in strong VLF (very low frequency) rising-tone chorus elements observed at the time of a rapid MeV electron energization in the inner magnetosphere. Analysis of the frequency gap between lower and upper chorus-band waves identifies fceEQ, the electron gyrofrequency in the equatorial wave generation region. Initial subpackets in these strong chorus rising-tone elements begin at a frequency near 1/4 fceEQ and exhibit smooth gradual frequency increase across their > 10 ms temporal duration. A second much stronger subpacket is seen at frequencies around the local value of 1/4 fce with small wave normal angle (< 10°) and steeply rising df/dt. Smooth frequency and phase variation across and between the initial subpackets support continuous phase trapping of resonant electrons and increased potential for MeV electron acceleration. The total energy gain for individual seed electrons with energies between 100 keV and 3 MeV ranges between 2 and 15%, in their nonlinear interaction with a single chorus element.

Analytical and Optimization Study of Propagation and Reduction of Wave in Granular Sand by DEM Method

2021 ◽  
Author(s):  
Amin Moslemi Petrudi ◽  
Masoud Rahmani
Keyword(s):  
Wave Propagation ◽  
Particle Density ◽  
Propagation Speed ◽  
Granular Soils ◽  
Discrete Elements ◽  
Factors Affecting ◽  
Interparticle Force ◽  
Optimization Study ◽  
Solution Methods ◽  
Wave Propagation Speed

In this research, the discrete element method has been used to analyze wave propagation and to investigate the factors affecting wave reduction in granular soils. The method of discrete elements is important because of the possibility of preparing completely similar specimens and examining the effect of changes in a certain parameter on the Behavior of the specimens. This method also provides an understanding of the changes that have occurred at the micro-scale of granular materials that are not achievable with other laboratory and numerical methods. To model the specimens, a set of disks with specific granulation has been used for two-dimensional studies. PFC 2D software has been used to perform simulations and related analyzes such as interparticle force. The DEM code in MATLAB is used to check the wave depreciation. In this research, the optimization process was performed using experimental data and the Taguchi method using the DEM method. The results of this study show that there is a direct relationship between the number of particle set contacts and the wave propagation speed. Also, material properties such as particle density are the most important parameters affecting wave velocity. The results of the method (DEM) are done with PFC 2D software and a comparison between the results of this method with the solution methods used by other researchers is shown to be a good match.

scholarly journals Interhemispheric asymmetries in the occurrence of magnetically conjugate sub-auroral polarisation streams

2005 ◽  
Vol 23 (4) ◽  
pp. 1371-1390 ◽  
Author(s):  
M. L. Parkinson ◽  
M. Pinnock ◽  
J. A. Wild ◽  
M. Lester ◽  
T. K. Yeoman ◽  
...  
Keyword(s):  
Electric Field ◽  
Auroral Oval ◽  
Particle Interactions ◽  
Magnetospheric Substorms ◽  
Polarisation Field ◽  
Energetic Ions ◽  
Inner Magnetosphere ◽  
Flux Tubes ◽  
Ion Drift ◽  
Magnetic Flux Tubes

Abstract. Earthward injections of energetic ions and electrons mark the onset of magnetospheric substorms. In the inner magnetosphere (L4), the energetic ions drift westward and the electrons eastward, thereby enhancing the equatorial ring current. Wave-particle interactions can accelerate these particles to radiation belt energies. The ions are injected slightly closer to Earth in the pre-midnight sector, leading to the formation of a radial polarisation field in the inner magnetosphere. This maps to a poleward electric field just equatorward of the auroral oval in the ionosphere. The poleward electric field is subsequently amplified by ionospheric feedback, thereby producing auroral westward flow channels (AWFCs). In terms of electric field strength, AWFCs are the strongest manifestation of substorms in the ionosphere. Because geomagnetic flux tubes are essentially equi-potentials, similar AWFC signatures should be observed simultaneously in the Northern and Southern Hemispheres. Here we present magnetically conjugate SuperDARN radar observations of AWFC activity observed in the pre-midnight sector during two substorm intervals including multiple onsets during the evening of 30 November 2002. The Northern Hemisphere observations were made with the Japanese radar located at King Salmon, Alaska (57, and the Southern Hemisphere observations with the Tasman International Geospace Environment Radar (TIGER) located at Bruny Island, Tasmania (55. LANL geosynchronous satellite observations of energetic ion and electron fluxes monitored the effects of substorms in the inner magnetosphere (L6). The radar-observed AWFC activity was coincident with activity observed at geosynchronous orbit, as well as westward current surges in the ionosphere observed using ground-based magnetometers. The location of AWFCs with respect to the auroral oval was inferred from FUV auroral images recorded on board the IMAGE spacecraft. DMSP SSIES ion drift measurements confirmed the presence of AWFCs equatorward of the auroral oval. Systematic asymmetries in the interhemispheric signatures of the AWFCs probably arose because the magnetic flux tubes were distorted at L shells passing close to the substorm dipolarisation region. Transient asymmetries were attributed to the development of nearby field-aligned potential drops and currents.

Theory of the reflexion of low-frequency radio waves obliquely incident on the ionosphere

1974 ◽  
Vol 336 (1607) ◽  
pp. 525-542 ◽  
Keyword(s):  
Low Frequency ◽  
Extraordinary Wave ◽  
Meridian Plane ◽  
Radio Waves ◽  
Quartic Equation ◽  
Obliquely Incident ◽  
Full Wave ◽  
Magnetic Meridian ◽  
Electron Gyrofrequency ◽  
Wave Normal

The properties of the two principal reflexions for radio waves obliquely incident on a horizontally stratified ionosphere in and near the magnetic meridian plane, for frequencies less than the electron gyrofrequency, are investigated using 'full wave’ numerical methods. When the wave normal of the incident wave is close to either of two directions, which are in the magnetic meridian plane, at particular angles θ b and θ e to the vertical, then for propagation from south to north (northern hemisphere), the polarizations of the two reflexions are found to take anomalous values. This behaviour is related to the properties of the Booker quartic equation. An extraordinary wave incident at an angle near θ e in the N–S direction generates some of the upgoing ‘whistler’ mode, an d this process is also investigated.

scholarly journals Dynamics of Rupture at Frictional Rough Interfaces During Sliding Initiation

2010 ◽  
Author(s):  
Mariano Di Bartolomeo ◽  
Francesco Massi ◽  
Anissa Meziane ◽  
Laurent Baillet ◽  
Antonio Culla
Keyword(s):  
Wave Propagation ◽  
Element Analysis ◽  
P Waves ◽  
Limit Value ◽  
Different Types ◽  
Deformable Bodies ◽  
Coulomb Friction Law ◽  
Contact Surfaces ◽  
The Waves ◽  
Two Bodies

The aim of this work is to present the results from a non linear finite element analysis in large transformations of the contact interface between two deformable bodies when sliding initiates and the roughness is introduced at the contact surfaces. The two-dimensional in-plane dynamic model consists of two different isotropic elastic media separated by an interface governed by Coulomb friction law, and subject to remotely applied normal and shear tractions (pre-stress phase). Once the ratio between the local values of tangential and normal stresses reaches the limit value, the sliding initiates and local ruptures are activated (nucleation phase). The propagation of the ruptures over the interface and the wave propagation inside the solids are analyzed. The interactions between the waves propagating into the two solids (P waves, shear waves, surface waves) give raise to different types of ruptures. They can be classified depending on their velocity front (sub-Rayleigh, sub-shear, super-shear) or on their interface states (pulse-like, crack-like). A sinusoidal roughness is introduced at the contact surfaces and the analysis is performed for different values of the roughness parameters. Depending on the relative dimension between the roughness wavelength and the width of the wave fronts, two different behaviour can be observed: i) a coupling between the wave propagating into the two bodies; ii) a decoupling of the wave propagation inside the two materials, characterized by an independent wave propagation. First the wave propagation is analyzed when a single rupture is originated in pre-sliding conditions; successively, the wave generation during sliding initiation is addressed.

scholarly journals Plasma Waves in the Inner Magnetosphere

2021 ◽  
pp. 85-119
Author(s):  
Hannu E. J. Koskinen ◽  
Emilia K. J. Kilpua
Keyword(s):  
Radiation Belt ◽  
Low Frequency ◽  
Plasma Waves ◽  
Mhd Waves ◽  
Particle Interactions ◽  
Inner Magnetosphere ◽  
Very Low Frequency ◽  
Link Type ◽  
Wave Modes

AbstractUnderstanding the role of plasma waves, extending from magnetohydrodynamic (MHD) waves at ultra-low-frequency (ULF) oscillations in the millihertz range to very-low-frequency (VLF) whistler-mode emissions at frequencies of a few kHz, is necessary in studies of sources and losses of radiation belt particles. In order to make this theoretically heavy part of the book accessible to a reader, who is not familiar with wave–particle interactions, we have divided the treatise into three chapters. In the present chapter we introduce the most important wave modes that are critical to the dynamics of radiation belts. The drivers of these waves are discussed in Chap. 10.1007/978-3-030-82167-8_5 and the roles of the wave modes as sources and losses of radiation belt particles are dealt with in Chap. 10.1007/978-3-030-82167-8_6.

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