摘要:

Anomalous refractive profiles and inversion layer structures at the Western Test Range, Vandenberg, California, were measured using airborne sensors. When the marine inversion layer was traced inland, the refractive gradient was observed to undergo upward warping, waving, dilation, lensing, and splitting. Refraction corrections computed using airborne‐measured, full cross sections along the radar line of sight were at times more than twice as large as those corrections resulting from single‐point radiosonde or aircraft spiral inputs, which must assume a spherically stratified atmosphere. Ray‐tracing techniques could reliably predict the location of actually observed radio holes (areas where radar loss‐of‐lock occurs) only when inputs from full, three‐dimensional, airborne cross section

ISSN:0048-6604    

DOI:10.1029/RS010i005p00491

年代:1975

数据来源: WILEY

摘要:

That theF2layer is bifurcated into two sublayers and that this structure travels poleward has been revealed by previous computations published by the author. Examination of vertical sounding data shows that such a travelling bifurcation occurs mainly near noon in the seasons other than June solstitial months during years of high solar activity. It is found that the formation of bifurcation is principally due to the combined effect of the upward drift, which changes from increasing to decreasing at 1000 LT, and the slow diffusion. The effects of other parameters on the bifurcation and ionospheric characteristics and the cause of the bifurcation which occurs at sunrise are also studied. The continuity equation of electron density is then solved with appropriate values of ionospheric parameters suggested from the above study. The computedf0F2at the equator during daytime is a very good reproduction of the observed one, and does not show any bifurcation as usually observed. The causes of agreement or disagreement between the computed and the observed values of critical frequency and height of layer peak are discussed.

ISSN:0048-6604    

DOI:10.1029/RS010i005p00507

年代:1975

数据来源: WILEY

摘要:

The impedance of a short electric dipole antenna has been measured from rockets in the ionosphere. The EIDI I experiment was launched in conditions where the plasma was expected to be nearly isotropic (operating frequencies 4.48 and 6.09 MHz,f0F2⋍ 9 MHz,fH⋍ 1 MHz). It was designed to detect and measure or to eliminate most of the unwanted effects which complicated the data reduction of previous experiments: outgassing, telemetry radiation, etc. The number of parameters measured simultaneously on board (impedances with variable bias and RF excitation level, resonance frequencies,Te, dc current drawn by the antennas, vehicle potential) and from the ground or an overhead satellite was large enough to provide numerous cross checks and to determine the sheath dimensions.The impedance is very weakly spin‐modulated over most of the flight; the collision frequency is very low (v/ω ⋍ 10−5) unlike some of the previous experiments where collision losses were dominant. The measured values of the impedance are given as a function ofX=f2p/f2where the other parameters

ISSN:0048-6604    

DOI:10.1029/RS010i005p00517

年代:1975

数据来源: WILEY

摘要:

The interpretation of the experiment EIDI I, described in a companion paper, is undertaken. A relatively complete calculation of the impedance is done including the effect of the temperature of the plasma by using the Vlasov equation and hydrodynamic equations, the structure of the sheath using a simple model of it, the collision frequency computed for an equilibrium plasma, and an estimation of various other small effects (wake, ionospheric gradient, motion of ions, …). The result so obtained is in very good agreement with the experiment for the most part but a strong discrepancy appears in the resistance whenX>1. This indicates that the main features of the theory are correct except that a loss mechanism is missing; some hypothetical ones are discusse

ISSN:0048-6604    

DOI:10.1029/RS010i005p00529

年代:1975

数据来源: WILEY

摘要:

Previously a mode conversion model was presented which allowed for both the vertical inhomogeneity and anisotropy of the ionosphere. Horizontal inhomogeneity along the direction of propagation was modeled by a slab approximation. The required height gain functions were determined by full‐wave solutions and their associated integrals evaluated numerically. In this paper results of a modified mode conversion model are compared with those of the original. In the modified model, height gain functions are discarded above some heighthin the guide and are approximated below heighthby Airy functions. Merits of the modified version are that a full‐wave program for height gains is not required, and that the associated integrals may be performed analytically. An obvious disadvantage is the free parameterh. The modified mode conversion model can be implemented with about the same ease as a WKB method and has one distinct advantage over the latter, namely, that mode numbering in any given slab is immaterial. Results of both mode conversion models are compared at several frequencies in the VLF band with experimental sunrise results obtained with a multifrequency oblique sounder system located on the island of Hawaii. In particular, comparisons are made with vertical field measurements in southern California. Approximate agreement is found. Discrepancies between modelling results and data are generally larger than the differences between the two mode conversion mod

ISSN:0048-6604    

DOI:10.1029/RS010i005p00537

年代:1975

数据来源: WILEY

摘要:

A “worst case” of scintillation activity is presented by the analysis of data of a period of severe magnetic activity, August 3–10, 1972. The effect of the dense ionospheric irregularities produced by these storms on scintillation at high latitudes is viewed as a function of local time and the invariant latitude of the propagation path, as well as magnetic activity. Storm period data taken at high, middle, and equatorial latitudes are analyzed and compared with the seasonal means. In the high‐latitude irregularity region, dramatic increases of scintillation index at 254 MHz were noted. Cumulative amplitude probability distribution functions are given for the high‐latitude data with the aim of giving to systems designers signal statistical data for “worst case” conditions. Middle‐latitude stations show little reaction to the magnetic activity. At equatorial latitudes during July and August, the longitude of the observatory determines the reaction. Accra (Ghana) data show a slight decrease in scintillations during the August storms. At Huancayo (Peru) scintillations increase in the post

ISSN:0048-6604    

DOI:10.1029/RS010i005p00547

年代:1975

数据来源: WILEY

摘要:

The field of a gaussian beam is examined in detail. It is shown that the usual formula for the field does not satisfy the wave equation within the Rayleigh distance except in the limit of large waist diameter. For small waist sizes the departure from the results of the usual formula can be substantial within a distance of about 1.3 wavelengths from the source. An exact formula is found for the on‐axis radiation. In order to make this study, certain features such as the obliquity factor, which is commonly ignored, have to be considered in detail. This leads to the need for a physical characterization of the source, which is not capable of a unique specification. The choice is probably not critical—the usual formulas for the transformation of gaussian beams do not need to refer to it at all—and the one used here pertains closely to the condition of radiation from the dielectric‐air interface of a solid stat

ISSN:0048-6604    

DOI:10.1029/RS010i005p00555

年代:1975

数据来源: WILEY

摘要:

A low frequency solution to the diffraction problem of anE‐polarized plane wave incident on a dielectric‐loaded slit in a perfectly conducting plane is obtained. The dielectric loading consists of a circular cylinder just filling the slit and concentric with the slit center. The method used is a significant improvement over the traditional pseudo‐power‐series method of solution. Thus, when the dielectric is absent, our values differ by less than 2.1% from the exact Mathieu function solution atka= 2.4,abeing the half width of the slit. The gap between the high and low frequency solutions has therefore been bridged. When a dielectric is present, the limitka= 2.4 will be multiplied by 1/∈1/21. It is found that the transmission usually increases with the dielectric constant. Some curves are given to illustrate th

ISSN:0048-6604    

DOI:10.1029/RS010i005p00565

年代:1975

数据来源: WILEY

摘要:

The important points governing the design of a multiple‐pulse measurement of the incoherent scatter autocorrelation function in theEregion are discussed. Since the requirements for good signal‐to‐noise ratio and good resolution are contradictory, compromises must be made. These considerations dictated the choice of two multiple‐pulse schemes which are now being used at the National Astronomy and Ionosphere Center in Arecibo, Puerto Rico. These schemes, one involving five pulses and one involving seven, are described and a few typical examples of the results obtained are presented. The data show that it is now practical during the day, or at night in reasonably strong sporadic‐Elayers, to make accurate measurements of the complex autocorrelation function in theEregion with an altitude resolution of the order of 1 to 3 km in a time of less than 10 min. The number of heights which can be studied simultaneously is limited only by computer capabilities. In the measurements reported here ten altitudes wer

ISSN:0048-6604    

DOI:10.1029/RS010i005p00573

年代:1975

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/RS010i005p00581

年代:1975

数据来源: WILEY