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Author: Wenyao Gu
Publisher:
ISBN:
Category : Physics
Languages : en
Pages : 0
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Book Description
Signals from ground-based very low frequency (VLF) transmitters can leak through the ionosphere and propagate in the inner magnetosphere as whistler-mode waves. They interact with energetic electrons from the Earth’s radiation belts, and precipitate them into the ionosphere. The effect of wave-particle interactions is affected by signal propagations, which depend on the spatial variation of the cold plasma population (as the propagation medium). Therefore, a further understanding of transmitter signal propagation and cold plasma medium is essential for investigating wave-particle interactions. First, a case study is performed on Russian Alpha transmitter signals observed by the Van Allen Probes. The signals are in ducted propagation, experience multiple reflections, and excite triggered emissions. The ducted propagation is justified by a ray-tracing technique, and the nonlinear cyclotron resonance theory is tested by the observed triggered emissions. Second, we perform a statistical study on the distribution of the two propagation modes, ducted and nonducted, by the use of observed Russian Alpha transmitter signals. The statistics show the dominance of nonducted signals in the plasmasphere in terms of both occurrence and power. The proportion of ducted signals is enhanced at higher L-shells and during active geomagnetic conditions. Finally, we statistically analyze the spatial and temporal distributions of inner-magnetospheric cold plasma density irregularities, which are responsible for ducted propagation. The density irregularities deep inside the plasmasphere are dominant in the night and dusk sectors and show no significant variation with geomagnetic conditions. In contrast, the density irregularities in and near the plasmasphere boundary layer occur at post-midnight during quiet times and expand throughout the night sector during active times.
Author: Wenyao Gu
Publisher:
ISBN:
Category : Physics
Languages : en
Pages : 0
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Book Description
Signals from ground-based very low frequency (VLF) transmitters can leak through the ionosphere and propagate in the inner magnetosphere as whistler-mode waves. They interact with energetic electrons from the Earth’s radiation belts, and precipitate them into the ionosphere. The effect of wave-particle interactions is affected by signal propagations, which depend on the spatial variation of the cold plasma population (as the propagation medium). Therefore, a further understanding of transmitter signal propagation and cold plasma medium is essential for investigating wave-particle interactions. First, a case study is performed on Russian Alpha transmitter signals observed by the Van Allen Probes. The signals are in ducted propagation, experience multiple reflections, and excite triggered emissions. The ducted propagation is justified by a ray-tracing technique, and the nonlinear cyclotron resonance theory is tested by the observed triggered emissions. Second, we perform a statistical study on the distribution of the two propagation modes, ducted and nonducted, by the use of observed Russian Alpha transmitter signals. The statistics show the dominance of nonducted signals in the plasmasphere in terms of both occurrence and power. The proportion of ducted signals is enhanced at higher L-shells and during active geomagnetic conditions. Finally, we statistically analyze the spatial and temporal distributions of inner-magnetospheric cold plasma density irregularities, which are responsible for ducted propagation. The density irregularities deep inside the plasmasphere are dominant in the night and dusk sectors and show no significant variation with geomagnetic conditions. In contrast, the density irregularities in and near the plasmasphere boundary layer occur at post-midnight during quiet times and expand throughout the night sector during active times.
Author: Kevin Graf
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The effects of ground-based very low frequency (VLF) transmitters on the ionosphere and magnetosphere are investigated. VLF transmitters, used primarily for Naval communications with submarines, are also capable of heating the ionosphere and inducing the precipitation of energetic electrons from the Earth's radiation belts. Controlled modulation experiments are performed with the 21.4 kHz, 424 kW VLF transmitter NPM in Lualualei, Hawaii, and physical effects of the NPM transmissions are studied with sub-ionospherically propagating VLF probe signals. Observed perturbations to the probe signal are not consistent with expectations from transmitter-induced electron precipitation nor to off-path scattering from a concentrated heating region near the transmitter but rather appear to be the result of scattering from extended lateral heating of the ionosphere by the NPM transmitter. A large-scale computational modeling framework confirms theoretically that this form of ionospheric heating can account for the observed probe signal modulations, establishing that the lateral extent of ionospheric heating due to VLF transmitters is several thousand kilometers, significantly greater than previously recognized. The trans-ionospheric propagation of VLF waves is also investigated as updated attenuation estimates are provided for multiple scenarios.
Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category : Magnetosphere
Languages : en
Pages : 128
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Book Description
Magnetospheric growth of coherent VLF signals transmitted from Siple Station, Antarctica is inhibited by whistler mode echoes of earlier transmitter signals. This new phenomenon, called echo-induced suppression, is observed at least a third of the time that transmissions from Siple Station are detected at the receiving station in Roberval, Quebec, Canada. Suppression levels as high as 20 dB are observed. Though the echo is usually much weaker than the direct signal the level of suppression is directly related to the amplitude of the echo. The echoes reduce triggering of emissions as well as the growth of the signal. Echo-induced suppression is not explained by linear wave-wave interference. The echoes are thought to restrict growth by reducing the coherence of the total input signal. According to quasi-linear theory, wave growth is regulated by changes in the particle pitch angle distribution that results from wave-particle interaction. These new results suggest that coherent waves tend to limit their own growth, even when modification of the particle pitch angle distribution is unimportant. Other phenomena such as whistler-induced suppression of signal growth are thought to be related to echo-induced suppression. Wave-induced growth suppression provides an indirect verification of the existence of discrete ducts for the propagation of VLF signals in the magnetosphere.
Author: Robert A. Helliwell
Publisher: Courier Corporation
ISBN: 0486151212
Category : Technology & Engineering
Languages : en
Pages : 370
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Book Description
The investigation of whistlers and related phenomena is a key element in studies of very-low-frequency propagation, satellite communication, the outer ionosphere, and solar-terrestrial relationships. This comprehensive text presents a history of the study of the phenomena and includes all the elements necessary for the calculation of the characteristics of whistlers and whistler-mode signals. An introduction and brief history are followed by a summary of the theory of whistlers and a detailed explanation of the calculation of their characteristics. Succeeding chapters offer a complete atlas of a variety of whistlers, including those observed in satellites and those generated by nuclear explosions; the results of satellite observation of whistler-mode propagation; the method of reducing whistler data and obtaining electron density information; a full atlas of the various kinds of emissions; and an outline and comparison of the theories of generation of emissions.
Author: O. G Villard (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 20
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Book Description
This report summarizes theoretical and experimental work sponsored by the Defense Advanced Projects Agency at Stanford University through the Office of Naval Research Contract No. N00014-75-C-1095. The primary purpose of this work, which was conducted during the interval 1 January 1975 through 28 February 1977, was to investigate the possibility of obtaining a relatively inexpensive method for the controlled artificial generation of ultra-low-frequency (ULF; frequencies less than 5 Hz) geomagnetic pulsations. Because of the great penetration of these signals in sea water, the controlled artificial source could conceivably be used as a transmitter to communicate with deeply submerged receivers at a low data rate. A second purpose of the work was to investigate the feasibility of using airborne loop antennas for air/undersea communication at ULF. The following are the major conclusions of this work; (1) The controlled artificial generation of ULF geomagnetic pulsations by the 'peninsula method, ' i.e., by the passage of a ULF-modulated electric current around a relatively nonconducting peninsula in the sea or in a large saline lake, is feasible and that further experiments, in particular, a fullscale ULF wave generation experiment, appear desirable. (2) The controlled artificial generation of ULF geomagnetic pulsations by the 'VLF method, ' i.e., by the injection of ULF-modulated VLF signals into the magnetosphere from a large ground-based VLF transmitter, appears possible, but further theoretical and experimental studies are required to clarify the generation mechanism.
Author: K. G. Budden
Publisher: Cambridge University Press
ISBN: 9780521369527
Category : Science
Languages : en
Pages : 694
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Book Description
This book is concerned with the ionosphere and the magnetosphere, and the theory of their effect on radio waves. It includes accounts of some mathematical topics now widely used in this study, particularly W. K. B. approximations, Airy integral functions and integration by steepest descents. The subject is divided into ray theory and full wave theory. Ray theory is useful for high frequencies when the ionosphere is treated as a horizonally stratified medium. The discussion of the magnetosphere, whose structure is more complicated, includes an account of whistlers and ion cyclotron whistlers. The book has been planned both for final year undergraduates and as a reference book for research. It is suitable as a course book on radio propagation for students of physics or electrical engineering or mathematics. Some of the topics are presented from an elementary viewpoint so as to help undergraduates new to the subject. The later parts are more advanced. Because the subject is so large and has seen many important recent advances, some topics have had to be treated briefly, but there is a full bibliography with about 600 references.
Author: A. R. W. Hughes
Publisher: Alpha Science Int'l Ltd.
ISBN: 9788173194856
Category : Science
Languages : en
Pages : 390
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Book Description
Contributed articles presented at the Workshop.
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309373085
Category : Science
Languages : en
Pages : 254
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Book Description
Active remote sensing is the principal tool used to study and to predict short- and long-term changes in the environment of Earth - the atmosphere, the oceans and the land surfaces - as well as the near space environment of Earth. All of these measurements are essential to understanding terrestrial weather, climate change, space weather hazards, and threats from asteroids. Active remote sensing measurements are of inestimable benefit to society, as we pursue the development of a technological civilization that is economically viable, and seek to maintain the quality of our life. A Strategy for Active Remote Sensing Amid Increased Demand for Spectrum describes the threats, both current and future, to the effective use of the electromagnetic spectrum required for active remote sensing. This report offers specific recommendations for protecting and making effective use of the spectrum required for active remote sensing.
Author: Henning F. Harmuth
Publisher: Springer Science & Business Media
ISBN: 9780306463167
Category : Science
Languages : en
Pages : 296
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Book Description
Most texts on electromagnetic theory follow the classical approach of steady state solutions of Maxwell's equations. In Interstellar Propagation of Electromagnetic Signals, the authors, H. Harmuth and K. Lukin, point out the deficiencies in Maxwell's theory and present an exciting new way of obtaining transient or signals solutions. This book can be used by researchers, graduate students and scientists in the areas of physics, astrophysics, astronomy and electromagnetic theory or electromagnetics.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 436
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Book Description
