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Dissertation

Analysing transient effects in the ionosphere using narrowband VLF data.

01 Jan 2009-
TL;DR: In this article, a multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals.
Abstract: Very Low Frequency (VLF) radio waves propagate within the Earth-ionosphere waveguide with very little attenuation. Modifications of the waveguide geometry affect the propagation conditions, and hence, the amplitude and phase of VLF signals. Changes in the ionosphere, such as the presence of the D-region during the day, or the precipitation of energetic particles, are the main causes of this modification. Using narrowband receivers monitoring remote VLF transmitters, the amplitude and phase of these signals are recorded. A multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals. Data was then analysed for effects from extragalactic gamma ray bursts, terrestrial gamma ray flashes and solar flares. Only X-rays from solar flares were shown to have an appreciable affect on ionospheric propagation.
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Journal ArticleDOI
TL;DR: In this paper, the authors studied the time-averaged gamma-ray burst spectra accumulated by the spectroscopy detectors of the Burst and Transient Source Experiment (BTSE).
Abstract: We studied the time-averaged gamma-ray burst spectra accumulated by the spectroscopy detectors of the Burst and Transient Source Experiment. The spectra are described well at low energy by a power-law continuum with an exponential cutoff and by a steeper power law at high energy. However, the spectral parameters vary from burst to burst with no universal values. The break in the spectrum ranges from below 100 keV to more than 1 MeV, but peaks below 200 keV with only a small fraction of the spectra breaking above 400 keV; it is therefore unlikely that a majority of the burst spectra are shaped directly by pair processes, unless bursts originate from a broad redshift range. The correlations among burst parameters do not fulfill the predictions of the cosmological models of burst origin. No correlations with burst morphology or the spatial distribution were found. We demonstrate the importance of using a complete spectral description even if a partial description (e.g., a model without a high-energy tail) is statistically satisfactory.

2,288 citations


"Analysing transient effects in the ..." refers background or methods in this paper

  • ...The spectrum is well-fit by the Band et al. (1993) model, with parameters determined by Golenetskii et al. (2008) α = −0....

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  • ...The spectrum is well-fit by the Band et al. (1993) model, with parameters determined by Golenetskii et al. (2008) α = −0.822(−0.012,+0.014) β = −3.87(−1.09,+0.44) Ep = 651(−14,+13) keV....

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  • ...The spectrum is well-fit by the Band et al. (1993) model, with parameters determined by Golenetskii et al....

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  • ...Band et al. (1993) developed a phenomenological model that accurately fits a large range of observed GRB spectra....

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Book
01 Feb 1996
TL;DR: In this article, the authors provide the theoretical basis for a variety of applications of electromagnetic (radio) waves to communications, navigation, and remote sensing, and this book is based on fundamental research in electromagnetic wave propagation that James R. Wait performed in the Central Radio Propagation Laboratory (CRPL) of NBS from 1956 to 1962.
Abstract: This book [1] was written at an important point in the development of applications of electromagnetic (radio) waves to communications, navigation, and remote sensing. Such applications require accurate propagation predictions for a variety of path conditions, and this book provides the theoretical basis for such predictions. The book is based on fundamental research in electromagnetic wave propagation that James R. Wait performed in the Central Radio Propagation Laboratory (CRPL) of NBS from 1956 to 1962. The mathematical theory in the book is very general, and the “stratified media” models are applicable to the earth crust, the troposphere, and the ionosphere. The frequencies of the communication, navigation, and remote sensing applications treated in this book range all the way from extremely low frequencies (ELF) to microwaves. The mathematical theory of electromagnetic wave propagation is based on Maxwell’s equations [2], formulated by James Clerk Maxwell in the 1860s. Experimental propagation studies in free space [3] and over the earth [4] also go back over 100 years. Research in radio science, standards, and measurements began in NBS in the early 1900s, and the long history of radio in NBS has been thoroughly covered by Snyder and Bragaw [5]. CRPL was moved to Boulder in 1954, and Wait joined the organization in 1955. The mathematics of electromagnetic wave propagation in stratified (layered) media is very complicated, and progress in propagation theory in the early 1900s was fairly slow. Wait’s book [1] included the most useful theory (much of which he developed) and practical applications that were available in 1962. A hallmark

1,394 citations


"Analysing transient effects in the ..." refers background in this paper

  • ...2 shows the experimentally determined attenuation as a function of frequency consolidated from a number of sources (Wait, 1962)....

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  • ...There are many ways to calculate the propagation conditions, most based on numerical or approximate analytical solutions of waveguide mode propagation (Budden, 1957; Wait, 1962)....

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  • ...Figure 1.2 shows the experimentally determined attenuation as a function of frequency consolidated from a number of sources (Wait, 1962)....

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Book
11 Dec 1995
TL;DR: An Introduction to Modern Astrophysics as mentioned in this paper is a comprehensive, well-organized and engaging text covering every major area of modern astrophysics, from the solar system and stellar astronomy to galactic and extragalactic astrophysics and cosmology.
Abstract: An Introduction to Modern Astrophysics is a comprehensive, well-organized and engaging text covering every major area of modern astrophysics, from the solar system and stellar astronomy to galactic and extragalactic astrophysics, and cosmology. Designed to provide students with a working knowledge of modern astrophysics, this textbook is suitable for astronomy and physics majors who have had a first-year introductory physics course with calculus. Featuring a brief summary of the main scientific discoveries that have led to our current understanding of the universe; worked examples to facilitate the understanding of the concepts presented in the book; end-of-chapter problems to practice the skills acquired; and computational exercises to numerically model astronomical systems, the second edition of An Introduction to Modern Astrophysics is the go-to textbook for learning the core astrophysics curriculum as well as the many advances in the field.

601 citations


"Analysing transient effects in the ..." refers background in this paper

  • ...Occurring in regions of high magnetic intensity, such as sunspot groups, solar flares are caused by the sudden release of magnetic energy (Carroll and Ostlie, 1996)....

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Journal ArticleDOI
TL;DR: In this article, Monte Carlo simulations of the runaway breakdown of air are used to calculate the spectra of terrestrial gamma-ray flashes (TGFs), which are then compared with RHESSI and CGRO/BATSE observations.
Abstract: Author(s): Dwyer, JR; Smith, DM | Abstract: Monte Carlo simulations of the runaway breakdown of air are used to calculate the spectra of terrestrial gamma-ray flashes (TGFs), which are then compared with RHESSI and CGRO/BATSE observations. It is found that the recent RHESSI spectrum is not consistent with a source altitude above 24 km but can be well fit by a source in the range of 15-21 km, depending upon the electric field geometry of the source. Because 15 km is not unusual for the tops of thunderstorms, especially at low latitudes, and is lower than typical minimum sprite altitudes, the RHESSI data imply that thunderstorms and not sprites may be the source of these TGFs. On the other hand, the soft energy spectrum seen in some BATSE TGFs is inconsistent with such large atmospheric depths, indicating that there may exist two distinct sources of TGFs, with altitudes below 21 km and above 30 km. Copyright 2005 by the American Geophysical Union.

272 citations

Journal ArticleDOI
TL;DR: A review of developments in ELF and VLF radio-wave propagation research over the last 50 years of the Journal of Atmospheric and Solar-Terrestrial Physics can be found in this paper.

251 citations


"Analysing transient effects in the ..." refers background in this paper

  • ...Barr et al. (2000) give a useful overview of this research....

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