bluuebunny/crossref_metadata_2025 huggingface dataset:
The statistics of extremes, with application to El Niño
Authors: Ponte Rui M.
Published: February 2008

The possibility of El Niño being a result of the random superposition of stochastically forced equatorial Kelvin waves is investigated, with the help of the theory of statistics of extremes, which provides us with the tools to evaluate the threshold crossing statistics of the sea level (SL) and sea surface temperature (SST) anomaly fields. Knowledge of the probability density function and the power spectrum of a random process allows one to compute the threshold crossing statistics of the process (e.g;, the mean rate of crossings of some level, the mean time or distance between successive crossings, or the mean time or distance it stays above some level after each crossing). A linear, stratified, equatorial β plane Kelvin wave ocean model is forced by stochastic zonal winds. The zonal velocity field is used to advect mean zonal temperature gradients to produce SST anomalies. Solutions are obtained in terms of the zonal wave number‐frequency spectra of SL and SST. These spectra are used to compute the threshold crossing statistics of the respective fields. The results are sensitive to some of the assumptions (e.g., spectral shape of forcing and values of spectral cutoffs). The time and space scales for the SL and SST excursions above 2 standard deviations are found to be small, when compared with observed El Niño scales. The stochastic assumption is reinterpreted as a possible triggering mechanism, rather than as a full explanation, for El Niño occurrences. Better knowledge of the wind stress forcing spectrum (zonal wave number and frequency) is needed in order to test the plausibility of the stochastic argument in a more conclusive way.
History of satellite missions and measurements of the Earth Radiation Budget (1957–1984)
Authors: House Frederick B. , Gruber Arnold , Hunt Garry E. , Mecherikunnel Ann T.
Published: February 2008

We review here the history of satellite missions and their measurements of the earth radiation budget from the beginning of the space age until the present time. The survey emphasizes the early struggle to develop instrument systems to monitor reflected shortwave and emitted long‐wave exitances from the earth and the problems associated with the interpretation of these observations from space. In some instances, valuable data sets were developed from satellite measurements whose instruments were not specifically designed for earth radiation budget observations. The effort of understanding the earth radiation budget has been the work of many people from different countries of the world, an effort of proud accomplishment.
Overview of the physical oceanography report
Authors: Knox Robert A.
Published: February 2008

I sincerely hope that no reader of the Physical Oceanography Report will substitute a perusal of this overview for a reading of the papers themselves. To do so would be to mistake the firefly for the fire. It is difficult enough (impossible, really) to convey a wholly accurate and complete picture of 1982–86 progress in U.S. physical oceanography by means of a small collection of review papers, substantial though they are. A short overview can only hope to mention some key themes and results, offering a limited appetizer for the subsequent feast.
Equatorial dynamics
Authors: Eriksen Charles C. , Katz Eli Joel
Published: February 2008

Substantial progress has been made in equatorial ocean dynamics during the period 1983–1986 largely as a result of several multiinstitution programs. These programs have been built around strong observational components and provide greatly improved descriptions of equatorial phenomena. They have stimulated numerical and analytical modelling efforts, which have generated results for comparison with observations. In this report we restrict discussion to dynamical aspects of equatorial ocean circulation, both steady and time‐dependent.
Polar wander and paleomagnetic reference pole controversies
Authors: Kent D. V. , May S. R.
Published: February 2008

The purpose of this paper is to review the progress made over the past four years in studies of Phanerozoic and Precambrian polar wander, with an emphasis on the contributions made by U.S. scientists. We perceive a general theme embracing the notion that the accuracy of cratonic “reference poles” and therefore of apparent polar wander (APW) paths is not as good as was generally believed four years ago. A renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts, namely the western Cordillera and Appalachians of North America, the Andes of South America, and elsewhere which seek to document the existence or non‐existence of displacements of suspect terranes (i.e., rotation and/or translation) with respect to their presently associated cratons. (Some of the results of this research are reviewed in this volume by Hillhouse and McWilliams). An important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the Paleozoic and Mesozoic APW paths for North America, is that the reliability of concordance/discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study, but also on the precision and accuracy of the appropriate cratonic reference pole.
Seismology in the United States, 1983–1986
Authors: Hanks Thomas C.
Published: February 2008

Any seismologist trying even to carry, let alone read, the EOS abstract volumes for recent AGU Meetings knows full well of the substantial growth in seismological research during this reporting period, the four years of 1983 through 1986. Indeed, the number of Seismology Section abstracts has grown from 188 (Fall, 1982) to about 320 (Fall, 1986), to be more or less precise. At a time when research monies seem to be no better than stable (and declining in real terms) and when job opportunities for seismologists seem to have never been worse, at least in the professional lifetimes of most of us, something must be amiss, but certainly this is not the great vitality and diversity in seismological research during the past four years.

The current reporting period saw the consortium approach brought to full flower in several fields of seismology, and these include CALCRUST, a consortium of California universities to investigate the crustal structure of the southwestern United States with seismic reflection data; DOSECC (Deep Observation and Sampling of the Earth's Continental Crust), a consortium to drill and make measurements within scientifically dedicated deep holes to sample active processes that make and remake the continents; EDGE, a consortium of university, government, and private industry scientists intent on exploring the oceanic/continental transitions along U.S. continental margins, using seismic and potential field methods; and IRIS (Incorporated Research Institutions for Seismology), whose prospectus includes a major upgrading of the global seismic network, an advanced portable array of 1000 seismic units for a host of active and passive experiments, and a data management center to store and utilize the vast quantities of data forthcoming from the first two activities. Each of these fledglings can trace their basic nature and motivation, if not their specific scientific agendas, to COCORP (Consortium for Continental Reflection Profiling), now a teenager, whose activities were summarized by Phinney and Odom[1983] for the last reporting period and by W. D. Mooney for the current one.
Seismotectonics
Authors: Hill David P.
Published: February 2008

Research on seismicity and its relation to current tectonic processes by U.S. scientists and institutions advanced over the last four years on a wide front both topically and geographically. Common to much of this research is a growing recognition that preexisting structures and heterogeneous fault geometry strongly influence broad seismicity patterns [e.g., Wesnousky et al., 1983; Wheeler and Bollinger, 1984] as well as the faulting style and rupture pattern of individual earthquakes [e.g., Sibson, 1986; Jones et al., 1984]. Recognition of the latter, in particular, has enhanced the physical meaning of the widely‐used concepts “asperity,” “barrier,” “seismic gap,” and “characteristic earthquake” [Beck and Ruff, 1984; Mendoza and Dewey, 1984; Sanders and Kanamori, 1984; Sykes and Seeber, 1985; also see Schwartz, this issue]. One topic that stands out in particular because of the increased attention given it over the last four years is volcanic seismicity. The eruptions of Mount St. Helens in 1980, El Chichon in 1982, Nevada del Ruiz in 1985, and the unrest in Long Valley caldera beginning in 1980 renewed interest in the long‐standing question regarding the nature and significance of volcanic b‐type (low‐frequency) earthquakes, harmonic (volcanic) tremor, and the relation of earthquakes to magmatic processes in general.
Tectonophysics 1983–1986: An overview
Authors: Chapman David S.
Published: February 2008

Exciting developments in concepts, technology, and analyses have marked the last four years of research in tectonophysics. This introduction to the Tectonophysics section of the 1983–1986 IUGG Quadrennial Report serves as a sketch of some of these developments. My observations are drawn from, and are largely restricted to, the ten review articles that follow; selected or comprehensive reading of the reviews is recommended for the specialist.

Most of the topics have been reviewed in previous IUGG reports, although not always in each one. For example rheology of the lithosphere, lithospheric stress and deformation, and mantle convection have all been reviewed in the previous two reports (1979, 1983) whereas plate motions have not been reviewed in this series since 1979 and the thermal state of the lithosphere since 1975. Other reviews substitute for subjects covered previously; the review on accretionary prisms, for example, substitutes for continental passive margins reviewed last time. Two areas of renewed or growing importance in tectonophysics are represented by the reviews on mineral and melt physics and on the role of pore fluids in tectonic processes.
Continental tectonics: Selected topics
Authors: Bruhn Ronald L.
Published: February 2008

Cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the Mesozoic and Cenozoic. Terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution. Deep crustal thrust systems, with large lateral transport and vertical stacking of slices of crystalline basement were documented in the Cordillera and Appalachians. New geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic, rather than gravitational stresses. Lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts, resulting in extension within the upper part of the lithosphere coeval with shortening at depth.
Marine chemistry and paleoceanography in the United States—1983–1986
Authors: Schink David R.
Published: February 2008

This report represents a continuing evolution in the editorial format. Eight years ago the Marine Chemistry report consisted of a single article. Four years ago the Marine Organic section was separated from the rest. In this report the subject has been divided into nine articles. As a consequence we find some duplication, some inconsistencies and some gaps, but these are balanced by a more diverse perspective and perhaps broader coverage. Readers should note that the article by Thomas Church reviews only the first three years of the quadriennium due to the demands of his field program and other practical constraints. In the article on Paleoceanography, Constance Sancetta has properly confined the review to articles related to oceanic processes, and thus omitted the very active discussion related to the global Cretaceous‐Tertiary boundary.
Tracers and modeling
Authors: Sarmiento J. L.
Published: February 2008

The major tracer activity of the last four years was the completion in 1983 of a survey of the North and Tropical Atlantic begun in 1981 as part of the Transient Tracers in the Ocean (TTO) project (Brewer, et al., 1985). An early set of papers (Brewer et al., 1983, and Swift, 1984) discussed evidence from these observations for the freshening of the North Atlantic due to cessation of overflow across the Iceland‐Scotland ridge in the period between Geosecs and TTO. Broecker et al. (1985a) examined observations further south within the deep Northeastern Atlantic and showed that there was no change of nutrient contents in this region during the same time span, consistent with their conclusion that there is no ventilation of this region from the north. Kawase and Sarmiento (1985 and 1986) used the TTO data to produce a series of nutrient and salinity maps and property‐property plots on density surfaces in the thermocline and middepth waters. Of particular interest in these studies is the evidence from silica‐salinity observations of strong cross‐isopycnal mixing and advection in the equatorial region.
Deep Sea Drilling Project geothermal measurements: A review
Authors: Hyndman R. D. , Langseth M. G. , Von Herzen R. P.
Published: February 2008

In this article the geothermal measurements made from the scientific drilling ship Glomar Challenger are evaluated, edited, and reviewed. For a number of sites the heat flow values given in the Initial Reports of the Deep Sea Drilling Project have been revised; less than half of the boreholes in which thermal measurements were attempted gave reliable data. By the end of the Deep Sea Drilling Project (DSDP) in 1983, reliable borehole heat flow measurements had been obtained at some 80 sites in all of the world oceans except the Arctic. The reliable values are considered to represent the deeper heat flux to within 20%; for a few the accuracy is within 5%. Most temperature measurements have been obtained using probes penetrating the undisturbed sediments at the bottom of the hole at subbottom depths of between 75 m and 250 m, although some data have been obtained at depths less than 30 and over 1000 m. Temperatures have been obtained a significant distance into the crust in eight holes. The main general conclusions are as follows: (1) There are no large or systematic differences between borehole heat flow values and oceanographic probe values obtained nearby. Such a test of shallow‐penetration oceanographic probe measurements was one of the first objectives of the DSDP heat flow program. (2) There are very few clear, smooth changes of borehole heat flow with depth in areas with thick sedimentary sections that are indicative of either long‐term bottom water temperature changes (tens to thousands of years) or large heat production in the sediments. Vertical migration of sediment interstitial pore water is suggested by nonlinear temperature‐depth profiles at a few sites, particularly where the sediment is relatively thin and the temperature gradient is high. (3) Temperatures in the crustal parts of deep‐sea drill holes exhibit a wide range of behavior, generally indicating hydrothermal circulation in the upper crust. At five sites, seawater is inferred to be moving down the holes into the crust, indicating low formation pressures and very high permeability in the upper crust. In two deep holes, however, such flow is limited to above several hundred meters into the crust, and heat fluxes close to theoretical cooling lithosphere values for the age of the crust (6 and 7 Ma) are found at greater depth. These sites suggest that hydrothermal circulation may be concentrated at shallow depths in the crust. Summary tables are presented of the heat flow data considered to be reliable after review and revision, and an appendix provides detailed comments on all the measurements for which data are available. Geothermal measurements are continuing on the new Ocean Drilling Program ship JOIDES Resolution.
A review of finite difference methods for seismo‐acoustics problems at the seafloor
Authors: Stephen Ralph A.
Published: February 2008

Understanding seismic wave propagation in realistic seafloor environments is essential for many problems in marine seismology. Finite difference methods are becoming increasingly popular in solving propagation problems as the limitations of other techniques which apply only at high frequency or for flat‐lying media become fully appreciated. The seafloor problem, a high contrast in Poisson's ratio at a rough sharp interface, is particularly challenging, and many published formulations fail to solve it accurately. The purpose of this paper is to summarize the published finite difference formulations for the elastic wave equation and to outline their applicability to seafloor problems.
Physics of the quiet magnetosphere
Authors: Stern David P.
Published: February 2008

Global properties of the Earth's magnetosphere are mainly studied in one of two ways : by focusing on specific events, e.g., substorms, or by analyzing average behavior. This collection of reviews deals with the second aspect.

All four articles began as invited reviews at the International Association of Geomagnetism and Aeronomy symposium on the quiet magnetosphere, held in Vancouver, Canada, August 17, 1987, as part of the nineteenth International Union of Geodesy and Geophysics General Assembly. One invited speaker, Igor I. Alexeev, was unable to attend, and one talk, by G.‐H. Voigt, was transferred to the symposium from the general contributions session.
El Niño, past and present
Authors: Enfield David B.
Published: February 2008

El Niño events—anomalous warmings of the tropical Pacific with associated climatic and economic impacts around the globe—have occurred at several‐year intervals since before written records began with the logs of Francisco Pizarro in 1525. In this review, the history of El Niño research is traced from its beginnings through the key innovations of Bjerknes and Wyrtki to the unusual 1982–1983 event. Recent research is then reviewed, with detailed discussions of two important processes: instability growth and vacillation between climate states. Throughout the paper there are adjunct discussions of extraregional teleconnections, ecological impacts, and research on El Niño in the ancient record. The final section discusses the present paradigm for vacillations between El Niño and non‐El Niño states and speculates on the possibly chaotic nature of El Niño. El Niño and its atmospheric counterpart, the Southern Oscillation, appear to occur as an internal cycle of positive and negative feedbacks within the coupled ocean‐atmosphere climate system of the tropical Pacific, although hypotheses based on external forcing also exist. All events are preceded by westerly wind anomalies on the equator near the date line. Baroclinic equatorial Kelvin waves are generated, propagating eastward toward South America where they depress the thermocline and raise sea level, while the deep, upper ocean reservoir of warm water in the western Pacific is depleted. Sea surface temperature (SST) anomalies in the cool eastern Pacific occur primarily because the normal source of cold water is depressed below the reach of mixing and upwelling processes. In the central equatorial Pacific, eastward advection by anomalous zonal flows is the principal mechanism. Nonlinear heat transfer to the lower atmosphere creates a positive ocean‐atmosphere feedback resulting in the unstable growth of anomalies along the equator. Much of the present research aims at determining how the ocean‐atmosphere system vacillates between the El Niño and non‐El Niño states. Coupled models suggest that a longer time scale, negative‐feedback process produces the transitions: at the apex of an El Niño development an anomalous atmospheric convection above the areas of maximum SST produces areas of reduced upper layer thickness in the off‐equatorial ocean, which slowly propagate westward to the western boundary as Rossby waves and back to the central equatorial Pacific as upwelling Kelvin waves, reestablishing the normal cooling process. A similar negative feedback of opposite sign completes the second half of an oscillation, returning again to the El Niño state. However, the notion that El Niño‐Southern Oscillation variability results only from an internal feedback process is still highly contentious, and a number of external forcing mechanisms have been proposed.
Spectral analysis of time series generated by nonlinear processes
Authors: MacDonald Gordon J.
Published: February 2008

The theory of nonlinear dynamics can assist in the selection of appropriate models to guide the analysis of observational time series. Weak and moderate nonlinearities lead to periodic or quasi‐periodic functions having discrete spectral lines. These functions are best analyzed by using the classical periodogram for equally spaced data and Lomb's extension of the periodogram for unequally spaced data. Strong nonlinearities can lead to aperiodic functions that have the continuous spectra characteristic of chaos. Power spectral analysis alone cannot be used to distinguish stochastic input to the time series from contributions to the continuum caused by deterministic nonlinearities. The evaluation of higher‐order spectra (bispectra, etc.) provides one means of distinguishing between those parts of the continuum due to hidden determinism and those due to stochastic input. This paper outlines a procedure for the analysis of mixed spectra modeled by a nonlinear system. First, an acceptable false alarm rate for misidentifying noise as a spectral peak is set. A normalized periodogram is then evaluated, and the highest peak is tested against the limit set by the false alarm criteria. The phase and amplitude of the maximum peak are estimated by least squares, provided the peak is judged to be significant. These parameters, together with the periodogram‐determined frequency, are used for a point‐by‐point subtraction of the sinusoid from the record. The prewhitening procedure is continued until all significant peaks are removed, leaving the estimated continuum part of the spectrum. In order to illustrate the procedure and general concepts, three examples are analyzed. A calculated time series showing the long‐term variation of Earth's obliquity demonstrates the difficulty of analyzing a quasi‐periodic function when the length of the record is insufficient to separate nearby lines in the spectrum. Quasi‐periodic behavior is shown by the sunspot record, which has 15 significant peaks at the 0.05 level; 12 of the peaks are simple combination tones of the other three. Analysis of unequally spaced observations is illustrated by the Vostok ice record of CO2 variation. The detected peaks of CO2 variation include the 100,000‐, 40,000‐, and 20,000‐year peaks detected in oxygen isotope records.
Tropospheric chemical composition: Overview of experimental methods in measurement
Authors: Ayers G. P. , Gillett R. W.
Published: February 2008

It is now universally acknowledged that the composition of the atmosphere has changed with time over the millenia and will continue to change as a result of human activities. The linking of changes in atmospheric composition with changes in global climate and the possibility that climate change may be induced over the next few decades as a result of humankind's affects upon atmospheric composition have been the most recent impetus for an increased interest worldwide in atmospheric chemistry. Public concerns about urban smog, the Antarctic ozone hole, other secular changes in global ozone levels, acidic deposition, and now climate change have combined to stimulate a plethora of measurement programs aimed at providing the data base on atmospheric composition and chemical processes without which theoretical models cannot be properly tested. This review aims to give some insight into methods used by experimentalists to measure various aspects of tropospheric chemical composition. The field of atmospheric chemistry is far too large to review in a single article, so selected topics have been chosen which serve to illustrate a range of the common measurement methods used and the difficulties involved in quantitatively determining trace species at levels which can be below 1 part in 1012 in the gas, aqueous, and aerosol phases.
Stokes Phenomenon
Authors: Millington G.
Published: February 2008

The Stokes phenomenon is studied with respect to an equation of Bessel type, and it is shown that the Stokes lines are associated with the cut in the complex plane required to make the complex exponential integral single‐valued. The Stokes constant is derived by considering the continuity conditions at all points along a single Stokes line. Numerical examples are given for the calculation of Hankel functions and the roots of the Airy integrals and their derivatives. Applications to phase‐integral theory and possible extensions to other equations are indicated.
Insulated Cylindrical Antenna Immersed in a Compressible Plasma
Authors: Galejs Janis
Published: February 2008

A cylindrical antenna is embedded in a dielectric cylinder, which is surrounded by a compressible isotropic electron plasma. The antenna impedance is formulated variationally by considering the effects of surface waves supported by the antenna structure. The surface waves alter the antenna current distribution for frequencies near the plasma frequency, but their amplitude is decreased as the thickness of the antenna insulation increases. The antenna solution is verified by examining the electric surface fields excited by the approximated antenna current distributions, and the results are compared with other numerical solutions.
VLF Wave Propagation Along a Mixed Path in the Curved Earth‐Ionosphere Waveguide
Authors: Chang David C.
Published: February 2008

An investigation of VLF radio‐wave propagation across a land‐sea boundary has been completed. The influence of the homogeneous ionosphere and the curvature of the earth, as well as the ground discontinuity, are considered. The problem of finding the field strength due to a horizontal line source is first formulated as a Wiener‐Hopf type problem via the concept of equivalent surface impedance and is subsequently solved in the Fourier‐transform plane. This solution has direct correspondence with that for dipole excitation and is expressed analytically in terms of the reflection and transmission coefficients of modes in the two sections of the earth‐ionosphere waveguide.
A Note on Transition Fading Statistics at VLF
Authors: Schneider A. , Carlston P. K.
Published: February 2008

A preliminary analysis suggests that the VLF signal strength minima (in decibels) observed during transition fading can be described by the First Asymptotic Distribution of the statistical theory of extreme values. In addition, the distribution of outage time relative to a fixed threshold level during transition fading seems to follow the Third Asymptotic Distribution.
Polarization of Obliquely Reflected Waves From an Isotropic Plane‐Stratified Plasma
Authors: Heading John
Published: February 2008

A recently devised realistic model of an inhomogeneous isotropic plane‐stratified plasma is examined analytically when electromagnetic waves of both magnetic and electric type are incident upon the layer from below. Properties of the reflected wave are investigated so as to express the characteristics of the polarization ellipse of the reflected wave in terms of the characteristics of the polarization ellipse of the incident wave.
Electromagnetic Induction in a Conducting Sphere with a Concentric Shell
Authors: Wait James R. , Spies Kenneth P.
Published: February 2008

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 function xn of order n. The frequency dependence of the real and imaginary parts of xn is demonstrated to have diagnostic features related to the geometry and to the electric properties of the core and the shell.
Phase and Group Refractive Indices From the Collisionless Magnetoionic Theory
Authors: Colin L. , Chan K. L. , Lee J. G. K.
Published: February 2008

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‐B).
Commission 1: Progress in Radio Measurement Methods and Standards
Authors: Beatty R. W. , Baird R. C. , Barnes J. A. , Beatty R. W. , Birnbaum G. , Birnbaum M. , Bussey H. E. , Chapin E. W. , Engen G. F. , Mumford W. W. , Nahman N. S. , Schafer G. E. , Selby M. C. , Weinschel B. O.
Published: February 2008

On Friday, October 13, 1967, the General Conference of Weights and Measures adopted the atomic definition of the unit of time, the second. The development of atomic frequency standards is still most heavily weighted toward cesium beam devices, with considerable work also on hydrogen masers [Vessot et al., 1966; McCoubrey, 1967]. Probably because of budget problems, there has been little work on thallium beams. There has been significant interest in optical frequency standards with a notable development of a methane‐stabilized laser by John Hall [Barger and Hall, 1969].
Approximate Boundary Conditions in the Electrodynamics of Stratified Tensor Media
Authors: Kuzmin N. A.
Published: February 2008

Approximate boundary conditions in the first and second approximations are obtained for stratified tensor media. The approximate conditions make possible the solution of electrodynamic problems without examination of the fields inside the anisotropic layers. The layer thickness in all cases is assumed to be small compared with the wavelength in any layer. The accuracy of the approximate boundary conditions is estimated for one particular example. It is shown that boundary value problems involving ferrite layers near the waveguide walls reduce to solutions of eigenvalue problems with definite boundary conditions along the periphery.
Dependence of Nondeviative Ionospheric Absorption on Solar Zenith Angle and Frequency
Authors: Rai R. K.
Published: February 2008

Results are presented of theoretical investigations of the nature of nondeviative radio‐wave absorption at vertical incidence, in an isothermal ionospheric region where collisional frequency is comparable to the exploring frequency and where the recombination coefficient is not constant but is a function of height. It has been shown that in such cases the variation of nondeviative absorption with solar zenith angle and frequency may be represented by the expression:L ∝ {(cosX)π/(ω±∣ωL∣)C+n}where symbols have their usual meaning. The values of n and C are such that (2 — C) ≥ n ≥ 0 and 3/2 ≥ C ≥ 1/2.
An Investigation of the Total Electron Content in the Equatorial Anomaly of East Africa
Authors: Hunter A. N. , Hibberd F. , Mulokwa W.
Published: February 2008

Measurements of total electron content by Faraday fading have been made at three frequencies on BE‐B at Nairobi from October 10, 1954, to the present day; two passes a day are recorded. Similar measurements on one frequency only have been made at Dar es Salaam and Addis Ababa. A computer program has been written which is specially suitable for low‐latitude stations and computes the M values and total electron content as a function of latitude. Errors arise from reduction of the records to locate the transverse point and from approximations in the theory. However, more serious errors are due to insufficient knowledge of the effective height and inclination of the ionosphere. Comparisons of the electron content computed at Nairobi with computations made by Koster and Golton show differences in detail but agreement in general form. Many more records remain to be reduced, to which may be added results for the BE‐C, but the results so far are very variable. On many occasions when an equatorial anomaly in total content is expected to show in total content, it does not appear. The expected pattern for the development of the equatorial anomaly is most apparent during the equinoxes.
Turbulent Fluctuations of Humidity and Their Measurement
Authors: Coantic M. , Leducq D.
Published: February 2008

The turbulent transfer of water vapor in the lowest atmospheric layers is the principal mechanism of energy exchange between air and sea and plays an important part in problems of electromagnetic‐wave propagation. Since experimental study of this transfer requires the measurement of humidity fluctuations, their characteristics have to be estimated to delineate suitable measuring devices. This estimate is obtained from the following information: (a) Equations governing the mean distributions, turbulent fluxes, and levels of fluctuations of humidity. These expressions bring out the analogy existing between humidity and temperature and enable the identification of various mechanisms of generation, transfer, and dissipation inside the surface layer of a stratified atmosphere. (b) Experimental results for the mean profile, the transfer rate, and the turbulence level of water vapor in typical cases. (c) Predictions of the spectral distribution and of time and space scales of the turbulence of humidity. Once the estimate is made, it is then possible to define specifications for devices measuring humidity fluctuations for use in either the field or the laboratory. Various methods of measurement can be considered; i.e., psychrometry, measurement of dew‐point, use of the hot wire, absorption of Lyman–α or infrared radiation, measurement of refractive index, or use of the ionic probe. Although small time‐constant psychrometers offer some interest, electromagnetic techniques appear most promising.
Atmospheric Structure Deduced from Forward‐Scatter Wave Propagation Experiments
Authors: Gjessing Dag T.
Published: February 2008

This review is concerned with the relative potentials of various experimental radio techniques from the point of view of determining the atmospheric fine‐scale structure. After having derived a unified set of simple approximate expressions for the ‘measured quantity’ in terms of parameters describing the refractive‐index time‐space structure, some of the more important sources of error are discussed. Finally, on the basis of numerous experimental results, the form of the refractive‐index spectrum is deduced by using the previously derived theoretical expressions.
Propagation of Oblique E Waves in a Warm Plane Stratified Plasma
Authors: Tang Ting‐wei
Published: February 2008

In this paper, the propagation of an oblique E‐mode electromagnetic wave in a plane stratified collision‐free plasma is investigated. A singularity associated with the electric field near the plasma resonance is shown to disappear when the effect of the finite temperature of the plasma is taken into account. By allowing for a weak spatial dispersion, a fourth‐order warm‐plasma field equation is obtained, and a connection formula based on an analytical continuation of integral solutions is deduced. The connection formula is then applied to the problem of mode coupling between electromagnetic E waves and electrostatic plasma waves.
Comparison of the Chemical Composition of Lunar Surface Material Determined by Radioastronomical Observations With the Results of Chemical Analysis Obtained by Surveyor
Authors: Troitskii V. S. , Bondar' L. N. , Zelinskaya M. R. , Strezhneva K. M.
Published: February 2008

It is of great interest to compare the results of the chemical analysis of the lunar surface material made by ‘Surveyor’ with that based on the data of the radio astronomical investigations of the electromagnetic properties of the lunar material. The method of determining the chemical composition by the equipment brought onto the moon by Surveyor 7 has been described by Turkevich et al. [1968].

From ground‐based optical observations of the moon, attempts to estimate the chemical composition of the lunar surface material have been made, for example, by comparing the polarization properties with those observed for terrestrial rocks. Yet, optical methods are not very effective, as their results depend chiefly on the geometrical properties of the surface (i.e. the roughness). Radar measurements provide the reflection coefficient and some limited data on the nature of the lunar material. They allow, for example, one to distinguish between a metallic and a dielectric reflector.
Heat Transfer in The Atmosphere of Venus—Summary*
Authors: Avduevsky V. S. , Marov M. Ya. , Noykina A. I. , Polezhaev V. I. , Zavelevich F. S.
Published: February 2008

A study of the thermal conditions in the lower atmosphere of Venus has been made based on the measurements obtained by the space probes Venera 4, Venera 5, and Venera 6 [Avduevsky et al., 1969a, b; Pravda, 1969]. Following the results reported earlier [Avduevsky et al., 1968], we constructed models of the radiative and convective heat transfer. Calculations of the outgoing radiative fluxes were made for selected bands at wave numbers ranging from 500 to 7700 cm‐1; to allow for the angular distribution of the radiation field, different assumptions for the percentage of water vapor and the optical properties of the clouds were adopted. This plane‐stratified model depends on the assumption that the atmosphere is transparent to the short‐wave end of the solar radiation spectrum.
Radar Measurements of the Surface Topography and Roughness of Mars
Authors: Rogers A. E. E. , Ash M. E. , Counselman C. C. , Shapiro I. I. , Pettengill G. H.
Published: February 2008

During the period surrounding the 1969 opposition, the planet Mars was observed with the Haystack radar to determine the topography in a belt near the equator. Elevation values obtained for the same surface location on Mars on different days of observation agree, for high signal‐to‐noise ratio cases, to within about 100 meters. Preliminary results show that the variation of surface height with longitude between latitudes 3°N and 12°N is similar to that measured for latitudes near 22°N during the 1967 opposition. The most notable difference is found near 215° longitude, where at 22°N there is a highland at Elysium, although at 5°N a lowland is found. Optically dark regions often have a high radar cross section. However, the topography shows no significant correlation with either the visual or the radar brightness.
Topography and surface Features of Mars—Summary*
Authors: Binder Alan B.
Published: February 2008

Radar ranging data taken along the +21.5° parallel of Mars have shown conclusively that elevation differences of up to 11 km occur on the planet. The highest areas observed are desert regions; the maria lie in low areas or on slopes. The canals identified in the radar data all occur in broad and frequently deep valleys which are related to a planet‐wide lineament system. It was found that the topographic contours based on the radar data readily fit the visual surface features even in the areas where the features are very complex.
On the Possibility of Determining the Nature of the Surface Material of Mars From its Radio Emission
Authors: Troitskii V. S.
Published: February 2008

As is known, the study of the moon's thermal radiation provides a rather complete picture of the thermal behavior of its surface and also information on some of its other physical properties [e.g. Troitskii 1967]. The phase variation of the thermal radiation provides most of the information for such an analysis, and the method may also be applied to investigate the surfaces of Venus [Troitskii, 1964] and Mercury [Vetukhnovskaya et al., 1968]. For Mars, however, we cannot observe from the earth sufficiently large phase variations. In practice, it is only really possible to observe the more or less completely illuminated side of Mars.
Lunar Occultation Observations of Jupiter at 74 cm and 128 cm
Authors: Gulkis Samuel
Published: February 2008

An immersion occultation of Jupiter by the moon on October 19, 1968, UT was recorded at wavelengths of 128 cm (234 MHz) and 74 cm (405 MHz) with the 140‐foot radio telescope of the National Radio Astronomy Observatory at Green Bank, West Virginia. One dimensional brightness distributions are derived from the occultation curves. They show a small asymmetry in the structure of the belts. The results have been combined with observations made at shorter wavelengths to show that there is a significant increase in the angular size of the emission at the longer wavelengths and that the relativistic electron energy spectrum must have a narrow range of energies close to the planet (∼1.5 RJ). The importance of the variation of the magnetic field strength on the radiation emitted from an ensemble of electrons trapped in a dipole field is discussed.
Long‐Term Variations of the Decimeter Radiation of Jupiter
Authors: Gerard Eric
Published: February 2008

The total flux density of Jupiter was measured from December 1967 to August 1968 and was found to vary. There is good evidence for a positive correlation with solar activity as measured by the 10.7‐cm flux; the most probable phase lag lies between 3 and 9 days.
Amplitude Variations of 15‐GHz Radio Waves Transmitted Through Clear Air And Through Rain
Authors: Straiton A. W. , Bailey C. R. , Vogel W.
Published: February 2008

This paper describes point‐to‐point and radar return attenuation measurements through the atmosphere at a frequency of 15.3 GHz. Clear air fluctuations along a 20‐km path were <1.5 db except in unusual situations, such as during a frontal passage or for a strong ground moisture layer occurring just before sunrise. Observations of a general rain showed an attenuation rain rate ratio of 0.1 db/km/mm/hr. Radar observations of a more intense shower showed a relatively small attenuation because of the limited extent of the rain cell.
Effect of Oblate Raindrops on Attenuation at 30.9 GHz
Authors: Semplak R. A.
Published: February 2008

An experiment that measures the difference in attenuation of horizontally and vertically polarized fields propagating along a 1.89‐km path at 30.9 GHz is discussed. For a rain‐induced fade of 18.5 db/km, differences between attenuations in horizontal and vertical polarizations as large as 3 db/km have been observed. There is good agreement when these microwave measurements are compared with calculations based on raindrop shapes that were measured visually by an independent investigator. From the data, we conclude that there are significant differences between attenuations in these polarizations for rain‐induced fades and that we should think in terms of an effective rain rate for vertical polarization that is less than that measured by rain gages.
Propagation and Group Velocity in a Warm Magnetoplasma
Authors: Aubry M. P. , Bitoun J. , Graff Ph.
Published: February 2008

The full adiabatic theory is used to describe wave propagation in a warm magnetoplasma for frequencies around the plasma frequency and the upper hybrid resonance frequency. By comparison with the microscopic theory for directions perpendicular and parallel to the static magnetic field, we can well define the range of validity of the full adiabatic theory, which can then be used for computation of the group velocity. The variation of this group velocity as a function of frequency for several directions of propagation is shown for models corresponding to the ionosphere and the far magnetosphere. Three factors deserve attention: (1) the upper hybrid resonance and its neighborhood can be rigorously studied for far magnetospheric conditions by using the full adiabatic theory; (2) the computed modes present a mixed electrostatic‐electromagnetic character; (3) The minima in group velocities for pseudoresonance frequencies progressively fill up as the temperature increases.
A Note on the Applicability of the Booker Theorem to Magnetoactive Plasmas
Authors: von Roos Oldwig
Published: February 2008

In this note it is shown that a recently found theorem [Booker et al., 1968] relating the reflexion coefficients for electromagnetic scattering from a variety of stratified media to each other in a simple way is inapplicable in cases where a static magnetic field is present. Calculations of VLF propagation in the lower ionosphere can therefore not be simplified by a utilization of the above‐mentioned theorem.
Asymmetric Phase Error in Circular Apertures
Authors: Duncan J. W.
Published: February 2008

The diffraction pattern of a circular aperture is determined under the condition that the aperture phase function is ξ(r) cos ф′, where (r, ф′) are polar coordinates in the aperture and function ξ(r) defines the radial variation of phase. The asymmetric phase error causes beam squint and distortion of the radiation pattern. The diffraction pattern is calculated by computer methods assuming ξ(r) = βr2 and ξ(r) = βr3, where β = 0, π/4, and π/2 rad. The edge taper of the aperture field is specified as 0 db, ‐12 db, and ‐20 db. An integral formula is derived for calculating um, the position of the pattern maximum. The analysis is used to determine the beam squint of a satellite‐mounted reflector antenna that undergoes asymmetric distortion in the space environment.
Studies of VLF Radiation Patteras of a Dipole Immersed in a Slightly Lossy Magnetoplasma
Authors: GiaRusso D. P. , Bergeson J. E.
Published: February 2008

Power patterns are presented for VLF radiation (500 Hz to 30 kHz) from arbitrarily oriented, point magnetic and electric dipole sources in a two‐component, slightly lossy magnetoplasma. The patterns show that energy tends to be transported primarily along the magnetic axis of a confinement cone for higher VLF frequencies but that the inclusion of ion motion destroys the confinement cone for extremely low frequencies.
VLF Field Strength Variations From an Airborne Trailing‐Wire Antenna
Authors: Kelly Francis J.
Published: February 2008

The periodic variations in field strength and phase received from an inclined, elevated VLF transmitting antenna as the antenna is moved in a circular path (orbit) are calculated. This is a simplified model of a trailing‐wire transmitting antenna carried by an orbiting aircraft. The earth‐ionosphere waveguide propagation model with an isotropic homogeneous ionosphere is used. For an inclined orbiting antenna, the magnitude and sense (whether increasing or decreasing at a given time) of the variations are found to depend on the range of the receiver from the transmitter. For an antenna whose inclination angle oscillates with its orbital position, the orbit‐produced variations are both range‐dependent and bearing‐dependent. Either one or two relative maximum values of field strength occur per orbit. Additional complications introduced by an anisotropic ionosphere are also considered.
Dipole Antenna Radiation in a Compressible, Anisotropic Electron Plasma Overlying an Imperfectly Conducting Half‐Space—Lunar Applications: 2. Integration and Results
Authors: Phillips R. J. , Ward S. H.
Published: February 2008

The Fourier‐Bessel integrals of part 1 (in this issue) are evaluated by the saddle‐point method. By utilizing the arguments of ray optics, an algorithm is devised to find the saddle points by a numerical search procedure on dispersion surfaces. Reflection coefficients show a strong oscillatory structure as a function of frequency in the vicinity of the plasma frequency. This phenomenon is caused by rapid changes in ray convergence and by constructive‐destructive interference of reflected modes. Branch‐cut contributions yield lateral waves traveling along the dielectric boundary. The dominant lateral wave species is the modified extraordinary (MEX) mode launched by an acoustic‐acoustic reflection. Other lateral waves are less important, and for these species, the position of the observer can go from the propagating zone to the shadow zone as the frequency is increased upward from the plasma frequency.