摘要:

The extended WKB method is employed to obtain a solution of the differential equation governing the dependence of field strength on height. The excess permittivity is represented as an exponential function of height. The method yields asymptotic solutions which become less accurate as the frequency decreases. It is found that the first‐order solution can be used down to 300 kHz. For lower frequencies, the more complicated second‐order solution is necessary, which can then be used down to 10 kHz. The results are compared with those based on an airless earth and an equivalent earth of 4/3 times the true rad

ISSN:0048-6604    

DOI:10.1029/RS006i007p00681

年代:1971

数据来源: WILEY

摘要:

Detailed diurnal variations ofF2layer ionization in true heights have been obtained over the Tamanrasset meridian (5°S to 30°N) for 20 almost consecutive days in June and July 1966. Our improved time and latitude resolution in charting the evolution of the maximum ionization parameters, ƒ0F2andhMF2, through the entire intertropical range made it possible for us to follow the movements of the two areas of greatest density known as ionization ‘crests’; their diurnal displacement on either side of the magnetic equator was found to differ from theoretical simulations, even those which take neutral wind into account. The asymmetry of their pattern in latitude and local time varies from one day to another much more than expected. The ‘summer’ side northern crest changes most; the maximum latitude extension of this crest varies in a complex manner withapmagnetic activity indices. Fast evolution phases, during early crest formation, and the deviation of the ionization structure from its expected ‘arch’ magnetic symmetry suggest a new type of low‐latitude tr

ISSN:0048-6604    

DOI:10.1029/RS006i007p00689

年代:1971

数据来源: WILEY

摘要:

In recent years, measurements by rocket, balloon, and satellite of cosmic X rays have suggested the possibility of observing ionospheric effects from celestial X‐ray sources such as Scorpius XR‐1, using low and very low frequency radio transmissions. The behavior of the nighttimeDregion under ionization by the X‐ray spectrum of the Scorpius source is estimated for several stellar zenith angles. Although Scorpius XR‐1 is the strongest source in the southern hemisphere, the integrated flux of all the other X‐ray sources is comparable to that of Scorpius XR‐1 and appears to modify the effect of Scorpius XR‐1 alone on VLF data recorded in the southern hemisphere. Observations of the VLF transmission NBA (18 kHz, Balboa, Panama) made at Tucuman, Argentina, during 1963–1964 show a sidereal time variation in the diurnal amplitude change that follows the variation in the per cent illumination of the propagation path by Scorpius XR‐1 during the nighttime hours. Even though the diurnal amplitude change can be shown to have a sidereal time variation, the diurnal phase change at Tucuman, Argentina, does not vary much throughout the year and yet remains consistently lower than that observed over a path of the same length from NBA to Boulder, Colorado, in the northern hemisphere. Therefore, it is suggested that the integrated effect of all the X‐ray sources illuminating the southern hemisphere is to enhance the ionization in the southern hemisphere nighttimeD‐region, thus, producing the smaller diurnal phase change observed at Tucuman compared with that observed on a Boulder recording of the NBA signal over a propagation path of the same length in th

ISSN:0048-6604    

DOI:10.1029/RS006i007p00699

年代:1971

数据来源: WILEY

摘要:

A laboratory model of a section of the earth‐ionosphere has been designed and constructed to provide a means for systematically investigating the effect of ionospheric perturbations on long range VLF paths. This model provides a capability for the investigation of a wide variety of different disturbed ionospheric conditions. For any given configuration, all the pertinent parameters are clearly defined and repeatable. This is in contradistinction to naturally occurring events, for which many parameters that are important for a clear interpretation are either unknown or, at best, poorly known. The design rationale and the construction methods are presented in this paper with initial experimental data obtained from the model for uniform propagation paths. It is shown that these data are in good agreement with theoretical data obtained for the modeled conditions. Data are also presented for propagation paths through a nuclear type ionospheric perturbation. These data exhibit both amplitude loss and phase advance caused by the perturbatio

ISSN:0048-6604    

DOI:10.1029/RS006i007p00709

年代:1971

数据来源: WILEY

摘要:

The geometrical optics convergence coefficient has been determined up to now only when the transmitter and the receiver are both situated on the ground or when the transmitter is at the base of the ionosphere and the receiver is on the ground. This paper presents formulas for the convergence coefficient regardless of the positions of the transmitter and the receiver in the earth‐ionosphere waveguide. There are four different possible paths of the ray. The convergence coefficients are calculated for each of them, and numerical results are give

ISSN:0048-6604    

DOI:10.1029/RS006i007p00717

年代:1971

数据来源: WILEY

摘要:

The laterally inhomogeneous anisotropic ionosphere is represented by a changing ionospheric surface impedance. The fields across such discontinuities can be estimated by computing the propagation characteristics on the various segments as in a homogeneous environment and by applying the resulting propagation parameters to the appropriate segments of the path. For fields observed across a day‐to‐night boundary, the resulting error is of the order of one percent. The effects of more localized ionospheric perturbations depend on their azimuthal and transverse extent. In the lower ELF range, areas with transverse dimensions of one to two thousand kilometers affect the propagation path across the perturbation to about the same extent as a propagation path tangential to the periphery of the perturbed reg

ISSN:0048-6604    

DOI:10.1029/RS006i007p00727

年代:1971

数据来源: WILEY

摘要:

The scattering of electromagnetic waves from a turbulent plasma has been examined experimentally at 31 GHz. The 31‐GHz cross section data agree well with a scattering model proposed earlier and with 9.4‐GHz data measured earlier. Measurements were made to determine the dependence of the cross section on bistatic angle and electron density. Comprehensive diagnostic measurements were made on the plasma so that the radar measurements could be compared to the scattering model. A synthetic‐aperture, or coherent processing, experiment was also performed to relate the instantaneous scattered field in a small volume (specified by the resolution obtainable by coherent processing techniques) to the instantaneous distribution of electrons in the same volume. The measurements confirm the validity of first‐order Born theory when applied to instantaneous rather than time‐averaged q

ISSN:0048-6604    

DOI:10.1029/RS006i007p00737

年代:1971

数据来源: WILEY