摘要:

The cylindrical shell between the earth and a homogeneous or exponentially varying ionosphere model is excited by vertically or horizontally polarized line sources; these fields are related to dipole fields in a spherical shell. Because of ionospheric anisotropy, the vertically polarized source also excites TM field components with wave numbers corresponding to TE modes, and a horizontally polarized source excites TE fields corresponding to TM modes, particularly for the higher frequencies at nighttime and for propagation westward. Among thefield components tangential to the ground surface, TM fields tend to dominate with the exception of TE modes at daytime and for lower frequencies at night. TM modes dominate in the nighttime mode sum (or interference pattern) for propagation eastward, but the two lower TE modes contribute significantly if propagation is westward. Simplified computational models that neglect the radial component of the earth's static magnetic field are justified under daytime conditions. At nighttime such calculations provide extreme changes in the attenuation rates and phase velocity variations, which are opposite to the ones observed with a dipping static magnetic field. The direction dependence of the phase velocity is eliminated by decreasing the strength of the static magnetic field.

ISSN:0048-6604    

DOI:10.1029/RS004i006p00491

年代:1969

数据来源: WILEY

摘要:

In March and April 1965 the University of Illinois and the GCA Corporation launched five Nike‐Apache rockets from the aircraft carrier U.S.N.S.Croatanas a part of the NASA Mobile Launch Expedition. As theCroatanfollowed the meridian at 78° west longitude along the west coast of South America, two rockets were launched at 13° south latitude (at the geomagnetic equator), one rocket at 30°S, one at 44°S, and one at 58°S. Launch times were chosen to correspond to a solar zenith angle of 60° at each of the four different latitudes. Each of the payloads carried a radio propagation experiment and a Langmuir probe for themeasurement of electron concentration and collision frequency in the lower ionosphere. Between 70 and 90 km, the electron concentration profiles at 13° and 58°S are nearly coincident, and the profiles at 30° and at 44°S are also nearly coincident. This pattern suggests a geomagnetic anomaly in the D region of the ionosphere comparable with the geomagnetic anomaly in theFregion. From 90 to 150 km the profiles show no systematic

ISSN:0048-6604    

DOI:10.1029/RS004i006p00517

年代:1969

数据来源: WILEY

摘要:

The use of a cubic approximation to the electron density determined by means of multifrequency absorption measurements does not always yield satisfactory results. An alternate method of determining the electron density is presented. A family of proton spectra is used, and the electron density profile resulting from each spectrum is determined. It is found that each profile produces absorption which varies as ƒ−nwith the exponentncharacteristic of the particular profile. These profiles are then varied in magnitude to produce the measured absorption. The result is an electron density profile that gives a more realistic representation of theDregion during a proton event than does a cubic approximati

ISSN:0048-6604    

DOI:10.1029/RS004i006p00521

年代:1969

数据来源: WILEY

摘要:

An aircraft carrying an ionospheric sounder traversed the boundaries of extended cloud cover near Los Angeles five times on July 18, 1967. Amplitudes of ionospheric E‐layer echoes at 3 MHz were received and recorded on magnetic tape, and median values were determined in 1‐minute intervals. Although these values scattered over ±3 decibels, the average median was lower, by 2.1 decibels, when the aircraft was over cloud cover than when the aircraft was over a cloud‐free area. The results suggest that an enhancement of the flux of visible light due to the reflecting cloud cover (estimated albedo 40%) changed the D‐layer chemistry in such a way that the electron density increased, resulting in a (6±3)% increase of two‐way non‐deviati

ISSN:0048-6604    

DOI:10.1029/RS004i006p00529

年代:1969

数据来源: WILEY

摘要:

A dispersion relation is obtained for gravity waves propagating in an atmosphere with a horizontal background wind that is variable with altitude. Also, a full‐wave solution valid in a region containing a critical level is obtained for the case of a background wind varying linearly with altitud

ISSN:0048-6604    

DOI:10.1029/RS004i006p00535

年代:1969

数据来源: WILEY

摘要:

The properties of radiation from circular arc antennas are discussed by using an asymptotic expansion method. Approximate pattern calculations of these antennas have usually been made by employing related techniques, such as the method of stationary phase. However, the stationary phase method has certain limitations, and it is not as accurate as the method presented here. The asymptotic expansion gives relatively accurate results when the radius of the arc source is large with respect to the wavelength. This requirement is usually satisfied if the antenna is to have a high directivity. The asymptotic expansion converges rapidly for observation angles away from the broadside direction, so that it is easy to determine the sidelobe energy distribution. The results given here can easily be applied to circular arc arrays with either uniform or nonuniform spacings of the elements along the arc by applying the Poisson sum formula. This is true because the resulting integrals governing the radiation fields from a circular arc array are similar to the ones discussed here.

ISSN:0048-6604    

DOI:10.1029/RS004i006p00539

年代:1969

数据来源: WILEY

摘要:

The reflection coefficient of a symmetric parallel‐plate waveguide operating in the TEM mode and illuminating a lossless dielectric layer is analyzed by wedge diffraction and geometrical optics techniques. The interactions between the waveguide and the dielectric layer are treated in terms of iterative bounce waves. The reflection from the dielectric layer and the scattering from the waveguide for cylindrical wave incidence are both represented by resultant component cylindrical waves. Thus each interacting bounce wave between the guide and the dielectric layer becomes the superposition of a finite number of cylindrical wave components. The reflection coefficient of the guide is then obtained by adding the various bounce wave contributions to the guide's free‐space reflection coefficient. For the two geometries considered, the thin‐walled guide and the ground‐plane guide, calculated results are in excellent agreement with those m

ISSN:0048-6604    

DOI:10.1029/RS004i006p00545

年代:1969

数据来源: WILEY

摘要:

A quasi‐static derivation is outlined for the problem of a shell‐enclosed homogeneous solid sphere immersed in a slowly varying electromagnetic field. The secondary magnetic potential is expressed as a zonal harmonic series whose terms are proportional to a complex multipole response functionxnof ordern. The frequency dependence of the real and imaginary parts ofxnis demonstrated to have diagnostic features related to the geometry and to the electric properties of the core and the sh

ISSN:0048-6604    

DOI:10.1029/RS004i006p00557

年代:1969

数据来源: WILEY

摘要:

The operation of a spherical electrostatic probe in a weakly ionized, collision‐dominated gas, such as theDregion of the ionosphere, is examined theoretically. A plasma consisting of one type of positive ion, one type of negative ion (or electrons), and a neutral gas is assumed to surround the (stationary) probe. The equations governing the collection of positive ions by a negatively biased probe are developed from a continuum theory after Su and Lam (1963) and are solved numerically. For highly negative probes a method is found to solve the equations in their exact form. Current‐voltage characteristics for probes of moderate size in comparison with the Debye length are presented graphically. It is shown that the current to the probe varies approximately as the 0.6 power of the probe voltage, which varies slowly with the ratio of probe radius to Debye length. The current also varies approximately as the 0.75 power of the positive ion concentration forD‐region conditions. These conclusions show the importance of including space charge in the theory and agree rather well with those of Balmain's (1966) simplified analysis. A considerable improvement is obtained over the results of Su and Lam for the regime of int

ISSN:0048-6604    

DOI:10.1029/RS004i006p00561

年代:1969

数据来源: WILEY

摘要:

Graphs of phase and group refractive indices computed from the collisionless magnetoionic theory are presented. The indices are computed for both the entire range of electron concentration and the intensity of the earth's magnetic field to be encountered by operational topside ionospheric sounders in the International Satellites for Ionospheric Studies (ISIS) series (Alouette 1, Explorer 20, Alouette 2, ISIS‐A, ISIS

ISSN:0048-6604    

DOI:10.1029/RS004i006p00573-02

年代:1969

数据来源: WILEY