VLF and ELF Propagation During Sudden Ionospheric Disturbances - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook VLF and ELF Propagation During Sudden Ionospheric Disturbances write by E. C. Field. This book was released on 1969. VLF and ELF Propagation During Sudden Ionospheric Disturbances available in PDF, EPUB and Kindle. The study presents the results of a theoretical analysis of the propagation of electromagnetic waves in the very-low-frequency (VLF) and extremely-low-frequency (ELF) ranges in the earth-ionosphere cavity during solar flares. The calculations, which are based upon nominal models of ambient conditions and solar-flare x-ray fluxes and spectra, result in mode-attenuation coefficients which are in good general agreement with observations. The propagation is enhanced relative to ambient conditions at ELF and upper VLF frequencies but is degraded in the lower VLF range. This general behavior is quite insensitive to the details of the assumed x-ray spectrum, the main requirement being a sufficient concentration of x-ray energy in the 1 - 8 A wavelength band. This class of spectrum tends to cause a moderate lowering of the D-region accompanied by an increase in the height gradient of conductivity in the reflection region; this in turn causes the observed phenomena at ELF and VLF during sudden ionospheric disturbances. (Author).
Sudden Ionospheric Disturbances and the Propagation of Very-low-frequency Radio Waves
Sudden Ionospheric Disturbances and the Propagation of Very-low-frequency Radio Waves - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Sudden Ionospheric Disturbances and the Propagation of Very-low-frequency Radio Waves write by Edward T. Pierce. This book was released on 1963. Sudden Ionospheric Disturbances and the Propagation of Very-low-frequency Radio Waves available in PDF, EPUB and Kindle. The changes in VLF radio noise accompanying a solar flare and its associated sudden ionospheric disturbance (SID) are surveyed. The onset time of the effects is about 10 minutes, but may be less than 2 minutes for perhaps 5 percent of the incidents. The alteration in propagation conditions implies an increase in noise on frequencies exceeding 20 kc and a decrease below 10 kc. If a local thunderstorm develops, the time phasing is very similar to that of an SID incident, but noise at all frequencies is enhanced. A detailed examination of the formative processes of the lower ionosphere is made. Values of the rate coefficients for attachement, detachment (photo, collisional, and associative), electron-ion recombination, and ion-ion recombination, are deduced for heights from 40 to 100 km. The balance equations for the lower ionosphere are solved for the cases of equilibrium conditions and of the departure from equilibrium associated with the approach of night. Two specific examples indicate that contours of electron density, and therefore of ionospheric conductivity, are far from parallel to the surface of the earth. It follows that the attenuation coefficient for VLF propagation by day can differ according to the solar zenith angle by as much as 20% from the mean daytime value. (Author).
A model for propagation of ELF and VLF waves below naturally perturbed ionospheres
A model for propagation of ELF and VLF waves below naturally perturbed ionospheres - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook A model for propagation of ELF and VLF waves below naturally perturbed ionospheres write by J. Galejs. This book was released on 1967. A model for propagation of ELF and VLF waves below naturally perturbed ionospheres available in PDF, EPUB and Kindle. A terrestrial propagation model is studied where the earth to ionosphere waveguide system is cylindrically stratified, the dip angle of the static magnetic field is assumed to be arbitrary and the waves propagate in East to West or West to East directions at a constant magnetic latitude. The profiles of ionospheric electronic density chosen for the numerical computations are representative of sudden ionospheric disturbances (SID), solar flares, auroral absorption or polar cap absorption (PCA) events. The resulting phase velocity and attenuation rates of ELF and VLF signals are compared with those computed under representative quiet daytime conditions. PCA events (which give the most dramatic effects) cause a lowering of the effective ionosphere; the resulting propagation is nearly isotropic and the phase velocities are decreased at ELF and increased at VLF. The attenuation rates are increased at ELF and also in the lower part of the VLF band. The propagation parameters are affected to a lesser degree by the other events: ionospheric density perturbations at heights below 60 km have more readily discernable effects at ELF, while the changes of the ionospheric density gradient at larger heights are observable at VLF. However, these differences are not uniquely distinguishable from propagation characteristics obtainable under quiet daytime conditions. (Author).
ELF Propagation Under Disturbed Conditions, Comparison of Theory with Available Data
ELF Propagation Under Disturbed Conditions, Comparison of Theory with Available Data - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook ELF Propagation Under Disturbed Conditions, Comparison of Theory with Available Data write by E. C. Field. This book was released on 1978. ELF Propagation Under Disturbed Conditions, Comparison of Theory with Available Data available in PDF, EPUB and Kindle. An extensive literature survey has identified a number of low-frequency noise measurements relevant to the effects of ionospheric disturbances on ELF propagation. These measurements pertain to the behavior of earth-ionosphere cavity resonances and ELF/VLF noise intensity at the time of: (1) the Starfish high-altitude nuclear detonation, (2) more than thirty solar flares, and (3) two polar-cap-absorption events (PCAs). Until controlled-source ELF experiments are carried out under disturbed conditions, these collateral data provide the only means by which codes that predict ELF propagation in nuclear environments can be compared with experiment. A full-wave propagation code similar to predictive codes developed under DNA auspices is used to compute ELF propagation anomalies due to Starfish, PCA events, and a large number of model x-ray flares. The results of these calculations are compared--to the extent possible--to the available data. Despite the inadequacies of the data, we are able to verify key theoretical predictions. Good agreement is demonstrated between code predictions and ELF/VLF noise intensity during solar flares. Both experiment and theory consistently show that the vast majority of flares cause the intensity to increase at frequencies between 30Hz and 1 kHz, decrease between 5 kHz and 10 kHz, and increase between 10 kHz and 30 kHz. This agreement, which occurs over three frequency decades, strongly implies the correctness of the predictive codes.
Propagation of ELF and VLF Waves Near the Earth
Propagation of ELF and VLF Waves Near the Earth - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Propagation of ELF and VLF Waves Near the Earth write by I︠A︡kov Lʹvovich Alʹpert. This book was released on 1970. Propagation of ELF and VLF Waves Near the Earth available in PDF, EPUB and Kindle.
