摘要:

Cross‐polarization distortion (XPD) due to nonspherical raindrops may be a serious problem for 18.5‐ and 30‐GHz microwave radio communications, but no measured data have yet been published. This paper presents a simple approach for estimating XPD due to rain from the effects of differential attenuation on canted spheroidal raindrops. Values of average raindrop canting angle, θA, are predicted from R. A. Semplak's measurements of differential attenuation taken over a one‐year period, published in 1970. Independent observations of canting angle from two rainstorms, published in 1971 by M. J. Saunders, agree with the predicted values and also indicate values for the senses (positive versus negative) of raindrop canting angles. Estimated values of XPD due to rain are graphically presented for various frequencies, rain rates, and typical path lengths. The paper concludes that the operational limits placed on communications by XPD due to rain are comparable to the limits due to rain attenuation o

ISSN:0048-6604    

DOI:10.1029/RS006i010p00833

年代:1971

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/RS006i010p00841

年代:1971

数据来源: WILEY

摘要:

The vertical flux of O+in theFregion has been obtained from incoherent scatter radar measurements at Millstone Hill. The paper reports an investigation of the altitude variation of the flux during two 24‐hour periods in March taken a year apart. We find that except for a brief period around sunrise the flux is always directed downwards at altitudes below 500 km and its magnitude seems governed simply by the competing processes of production, loss, and diffusion. On the quiet day above 535 km the flux is directed upward in the afternoon when the electron density is not changing with time. This upward flux reached a peak value of ∼108ions cm−2sec−1near 700 km altitude and then decreased at higher altitudes. This decrease is attributed to charge exchange with hydrogen. During the night on this day there is evidence for a downward flux of 3 × 107O+ions cm−2sec−1from the protonosphere. Additional H+ions may be diffusing through the 1000‐km level and contributing to the maintenance of the nighttimeFlayer, but they would not be detected in our observations. On the disturbed day there is no evidence of a flux of ionization into the protonosphere except at sunrise. We suggest that this change is brought about by a large reduction in the abundance of neutral hydrogen, resulting from increased escape either via the polar wind or from the heating of the atmosphere in the vicinity of the auroral zones. Thus, it is suggested that the abundance of neutral hydrogen at the base of the exosphere is reduced at high latitudes during m

ISSN:0048-6604    

DOI:10.1029/RS006i010p00843

年代:1971

数据来源: WILEY

摘要:

Measurements of the vertical flux of O+in theFregion have been made by the incoherent scatter technique at Millstone Hill. In part 2 of this paper, evidence was presented for the existence of fluxes of ≥ 108cm−2sec−1into the protonosphere during the day. In this paper we employ the altitude variation of the O+flux to infer the magnitude of the proton flux in the charge‐transition region. Based on continuity considerations and the theory of minor ion diffusion in the topside of theFlayer, we have attempted to determine the abundance of H+in the altitude interval where it is a minor ion. The results indicate that the abundance of neutral hydrogen near 600 km must exceed about 105cm−3. However, the absence of detectable amounts of H+in the signal spectra taken near 1000 km indicates that the transition altitude must be above 1000 km and in turn the neutral‐hydrogen abundance cannot exceed this estimate by more than a

ISSN:0048-6604    

DOI:10.1029/RS006i010p00855

年代:1971

数据来源: WILEY

摘要:

A description of the latitudinal, diurnal, seasonal, and solar‐cycle variations ofF‐layer‐produced scintillations, based on a comprehensive review of the literature, is given. Three distinct latitudinal regimes are discussed in regard to scintillation behavior and the quantitative utility of observations reported in the literature. A semiquantitative empirical model is suggested to describe the strength of scintillation‐producing irregularities ofF‐layer electron density. Recent work suggests that more quantitative modeling might now be fruitful, but gaps in fully quantitative data exist. The prime needs are for observations at very high latitudes and for calibration of scintillation indices used at very low

ISSN:0048-6604    

DOI:10.1029/RS006i010p00863

年代:1971

数据来源: WILEY

摘要:

A VLF propagation and aD‐region aeronomy model have been used to predict the effect of two solar eclipses on VLF propagation to Aztec, Arizona. Transmissions at 12.2 kHz from Hawaii were monitored during the eclipse on September 11, 1969; and transmissions at 12.0 kHz from Trinidad, at 24 kHz from transmitter NBA, at 12.5 kHz from Forestport, New York, and at 17.8 kHz from transmitter NAA were monitored during the eclipse on March 7, 1970. The VLF phase predictions were found to agree with measurements except for the two nearly coincident northerly paths from Forestport and NA

ISSN:0048-6604    

DOI:10.1029/RS006i010p00871

年代:1971

数据来源: WILEY

摘要:

At HF or higher frequencies, in computing the polarization conditions along a radio ray traveling in the ionosphere, it is often sufficient to express the results in terms of the Faraday rotation of the plane of polarization, obtained as an integral (along the path) of the phase difference between the ordinary and extraordinary components. The computation simplifies when the quasilongitudinal (QL) approximation of magneto‐ionic theory can be applied. The QL approximation is invalid at any point where the ray becomes transverse to the geomagnetic field, and in some regions around that point. In 1963 George A. Dulk showed that neglect of this effect may lead to major errors. In considering an oblique path with sky‐wave reflection, it is easy to be misled into thinking that a transverse condition is unlikely except on east‐west paths, particularly in equatorial regions. On the contrary, transverse conditions are likely to occur under a wide range of conditions at all latitudes and for all propagation directions. This presentation describes conditions of ray geometry and magnetic latitude, which result in transversality at some point along the path. The method for defining the conditions is shown to be applicable even when the ray is permitted to follow a twisted path in three dimensions, and the geomagnetic field is defined under very general assumptions. The basic results are also directly applicable to problems concerned with the reflection of HF signals by field‐aligned ion

ISSN:0048-6604    

DOI:10.1029/RS006i010p00879

年代:1971

数据来源: WILEY

摘要:

A multiple midlatitude 6300‐Å auroral arc occurred during the recovery phase of a geomagnetic storm on March 8/9, 1970. Variations of the arcs were characterized by a southward shift in position and by a diminution in intensity with time before midnight. During the recovery phase of the storm, well‐defined magnetic baylike disturbances occurred. The vairations in both position and brightness of the concurrent arc were strongly correlated with changes in theHandDcomponents of these geomagnetic field deviations. An equivalent current system is determined from these baylike disturbance fields observed at twenty‐six magnetic observatories for periods when the correlation was strongest. The current system found is similar to that of theDP1 field, with a superimposedDP2 field. The changes in these fields that are associated with the bayklie disturbances are presented to account for the transient variations observed in the intensity and position of the midlatitude auror

ISSN:0048-6604    

DOI:10.1029/RS006i010p00887

年代:1971

数据来源: WILEY

摘要:

In this paper, the backscattered electric field is derived when a plane electromagnetic wave is incident upon a perfectly conducting sphere coated with a radially inhomogeneous dielectric. The Mie series is obtained and then subjected to an asymptotic analysis that is valid for very short wave‐lengths. In particular, the first two terms for the reflected portion of the electric field are derived and the formulation for the creeping wave contribution is presented. Also, a numerical computation of the monostatic cross section is performed for various thicknesses of the coating by considering the reflected portion of the backscattered electric field. It is shown that this particular type of inhomogeneous sheath reduces considerably the monostatic cross section of the perfectly conducting sphere as its thickness increase

ISSN:0048-6604    

DOI:10.1029/RS006i010p00893

年代:1971

数据来源: WILEY

摘要:

In scattering processes involving moving objects an exchange of electromagnetic and mechanical power takes place. The problem is considered for arbitrary objects in one, two, and three dimensions. It is shown that the energy balance depends on the scattering amplitude, evaluated at the frequency of excitation, on this frequency itself, and on the velocity in question. Three cases are considered: objects moving in free space, objects moving together with the surrounding medium, and objects moving through a medium, at rest with respect to the observer. An interesting result is the fact that objects moving in the direction of the incident wave cause a loss of electromagnetic energy smaller than the gain occurring when the objects move in the opposite direction. This is a first‐order effect in the velocit

ISSN:0048-6604    

DOI:10.1029/RS006i010p00903

年代:1971

数据来源: WILEY