bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrodynamics and plasma processes in the ionosphere
Authors: Heelis R. A.
Published: February 2008

This quadrennium has seen great advances in our understanding of both small and large scale plasma processes and electrodynamics at low and high latitudes in the ionosphere. At low latitudes our advances include an assessment of the roles of the E‐ and F‐region neutral winds in providing the large scale electric field in the region as well as the influence of electric fields of magnetospheric origin on the motion and distribution of plasma. The factors affecting the creation and evolution of plasma structure with many different scale sizes has also been extensively studied. At high latitudes a more complete understanding of the effects of the interplanetary environment on the large scale motion of ionospheric plasma has been obtained. These studies have used a variety of ground based and in‐situ techniques to derive the instantaneous global convection pattern. The self consistency of electric fields, field‐aligned currents and ionospheric conductivity has been well established. The examination of many mechanisms for producing the myriad of plasma structures at high latitudes has also been undertaken. While all these studies have considerably advanced our understanding of the complex ionospheric environment, they have also served to formulate the future research efforts that will be required to adequately advance the field.
Magnetospheric electric fields and currents
Authors: Mauk B. H. , Zanetti L. J.
Published: February 2008

With special, but not exclusive, emphasis on contributions made by scientists within the United States, we review scientific progress made in understanding the character and operation of macroscopic, earth magnetospheric electric fields and electric currents within the time frame 1983 to 1986, inclusive. Our review of this extremely broad area is strongly constrained by overlap with related reports in this issue. The related reports cover the aurora, ionospheric electrodynamic phenomena, the magnetopause, the magnetotail, the ring current, and magnetic field models. Our emphasis will be on the interior regions of the magnetosphere and on the boundary region results that emphasize connection to the interior regions.
U.S. National Report to the International Union of Geodesy and Geophysics: U.S. progress in auroral research: 1983–1986
Authors: Gorney D. J.
Published: February 2008

Progress in auroral research during the period 1983–1986 has been immense, benefiting from both an excellent heritage of theoretical work and extensive archived data sets, as well as a currently‐active system of ground and satellite‐based observing platforms and healthy interactions among theoretical groups. Scientific journals in this field have maintained the maturity, efficiency and quality needed to assure rapid and accurate dissemination of new results at an ever‐increasing pace. This review paper highlights progress by U.S. authors during 1983–1986 in the broad area of auroral research. Atmospheric emissions and their use as a tool for remote‐sensing the dynamics, energetics and effects of auroral activity is a subject which is emphasized here because of the vast progress made in this area on both observational and theoretical fronts. The evolution of primary auroral electrons, the acceleration of auroral ions, small‐scale electric fields, auroral kilometric radiation, auroral empirical models and activity indices are also reviewed. An extensive bibliography is supplied, including, for completeness, a number of relevant publications not necessarily cited in the text.
Coincident seismic reflection/refraction studies of the continental lithosphere: A global review
Authors: Mooney Walter D. , Brocher Thomas M.
Published: February 2008

Nearly 50 coincident seismic reflection/refraction studies to depths of at least the Moho provide an improved understanding of the continental lithosphere. Some conclusions include the following: (1) A transparent upper crust, a common observation on vertical reflection profiles, cannot generally be correlated with velocity gradients or low‐velocity zones. Rather, a commonly transparent upper crust may be explained by short‐wavelength, steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source‐generated noise. (2) The reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity (6.6–7.3 km/s) and to consist of laminated high‐ and low‐velocity layers with typical thicknesses of 100–200 m. (3) Landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high‐ and low‐velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin. (4) The crust‐mantle boundary may differ sufficiently when imaged with vertical incidence and wide‐angle data to justify the retention, for the present, of the concept of separate reflection and refraction Mohos. While there is good evidence that these features are coincident within measurement uncertainties in most regions, recently recorded data from the Basin and Range admit the possibility for noncoincidence in that area. (5) Upper mantle reflections which cannot be migrated into the lower crust remain rare, despite isolated unequivocal examples. Thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust. The wide‐angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come. (6) There appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments; these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes. (7) No truly three‐dimensional coincident experiment (i.e., including three‐dimensional migration) has been conducted, but some three‐dimensional data have been collected using both methods. Measurements of attenuation, Poisson's ratio, and anisotropy within the crust using coincident data sets remain frontiers.
A Lagrangian analysis of turbulent diffusion
Authors: Bennett Andrew F.
Published: February 2008

This is an analysis of diffusion of a scalar field by molecular transport and isotropic turbulence. Existing results are surveyed, and some new results are advanced. The discussion is supported with oceanographic and atmospheric observations of dispersion and diffusion. The existing results were originally obtained using a variety of mathematical techniques. However, all results are derived here using an approximate solution of the Lagrangian form of the advection‐diffusion equation. The approximation is equivalent to neglecting the spatial dependence of the transformation factors in the Lagrangian representation of the molecular flux divergence. Examinations of the diffusive subranges show the approximation to justified: infinitesimal line stretching is either controlled by relatively large scale shears (viscous‐diffusive subrange at large Prandtl number) or else is negligible during the diffusion process (inertia‐diffusive subrange at small Prandtl number). Estimation of scalar mean fields, total variances, and wave number spectra requires, in general, joint statistics of infinitesimal line stretching and either single particle displacement or particle pair separation. Normality is assumed for displacement statistics; separation statistics are determined from the Richardson‐Kraichnan equation. A simple derivation of that equation is presented here. Joint stretching‐separation statistics are modeled by a uniform shear flow, with time‐dependent amplitudes described by the Wiener process (white noise). With the possible exception of this random process, the only mathematics required here is elementary calculus, so details have been kept to a minimum. In the diffusion problems considered here, the turbulence is isotropic. However, both the approximate solution of the advection‐diffusion equation and the equations for joint displacements are equally valid for inhomogeneous turbulence.
Recent advances in fine particle magnetism: Implications for paleomagnetism
Authors: Smith Guy M. , Halgedahl Susan L.
Published: February 2008

It is becoming increasingly obvious in paleomagnetism that the older practice of using large numbers of samples to improve statistical measures of accuracy is often not adequate to reveal the signal of greatest geological importance. “Blanket” demagnetization treatments are now largely outdated, except for the most ideally behaved samples (a rapidly vanishing phenomenon in many locales). Variations in characteristic remanent directions between neighboring (and supposedly contemporaneous) but lithogically distinct rock units can no longer be simply treated as “noise”. We now recognize that such differences may actually reflect rock magnetic effects rather than such factors as the short‐term behavior of the geomagnetic field or local variations in structure. Multiple overprints, often the result of moderate reheating and/or chemical alteration, can result in an uncertain relationship between the timing of emplacement and the acquisition of remanence. In the past, rocks which presented such problems could often be avoided in favor of more straightforward units. Much of that geological “cream” has been skimmed, however. Further progress in many areas, particularly the determination of the APW path and reversal stratigraphy in the Paleozoic, will require a better understanding of magnetization processes in order to resolve the above‐mentioned problems and produce accurate and reliable results.
Underground nuclear explosions: Verifying limits on underground testing, yield estimates, and public policy
Authors: Sykes Lynn R.
Published: February 2008

The period 1982 to 1986 has seen greatly increased activity in a number of problems related to the verification of nuclear test ban treaties. The greater activity results from a combination of scientific advances, major decisions by the United States Government about the negotiation of test ban treaties, the Soviet moratorium on testing, and much greater interest by the U.S. Congress in nuclear testing, test bans and other aspects of arms control. This review seeks to cover a range of activity that extends from scientific research to governmental decisions and public policy. A major aim has also been to provide a detailed bibliography on what is a wide range of topics. It is still not complete for what is a huge so‐called “gray literature” of reports to various government agencies. The discussion that follows only covers a selected number of these publications and reports.
Determination of the intensity of the Earth's magnetic field during archaeological times: Reliability of the Thellier Technique
Authors: Aitken M. J. , Allsop A. L. , Bussell G. D. , Winter M. B.
Published: February 2008

After indicating the basis of the technique, its use with a cryogenic SQUID magnetometer is outlined, particular emphasis being given to the need for stringent reliability criteria. Comparison of results for some samples is made with results obtained using the Shaw alternating‐field technique, and the agreement is satisfactory. Determinations made on 14 samples fired during the last 150 years give results which on average are in close agreement (within 2%) with observatory‐based values, the standard deviation of a sample from the predicted value being ±6%.
Imaging results from Dynamics Explorer 1
Authors: Frank L. A. , Craven J. D.
Published: February 2008

We provide an overview of several of the most significant results from the global imaging instrumentation on board the Earth‐orbiting spacecraft Dynamics Explorer 1. These topics include (1) the evolution of the auroral oval during substorms, (2) fluctuations of polar cap area encircled by the auroral oval during a magnetic substorm, (3) the mapping of poleward arcs of the auroral oval into the plasma sheet boundary layer, (4) the theta aurora, (5) atmospheric holes, (6) the geocorona, and (7) the rates of water loss from comet Halley.
Thermosphere dynamics: Contributions from the first 5 years of the Dynamics Explorer Program
Authors: Killeen T. L. , Roble R. G.
Published: February 2008

Instrumentation flown on the Dynamics Explorer 2 (DE 2) spacecraft enabled the dynamics of both the neutral and the ionized components of the Earth's upper atmosphere to be monitored over the lifetime of the spacecraft, from August 1981 to February 1983. The direct measurements of global thermospheric vector neutral winds and ion drifts were supplemented by observations of neutral and ionic constituent abundances and temperatures, precipitating particle fluxes and pitch angle distributions, electric and magnetic fields, and global‐scale auroral luminosity distributions. Analysis of this unique and comprehensive global data base has led to advances in our understanding of the manner in which the Earth's thermosphere responds dynamically to the insertion of energy and momentum. We review the scientific progress achieved over the past 5 years through the efforts of members of the Dynamics Explorer science team and the other interested scientists who have used the DE data base to investigate the dynamical response of the thermosphere.
Magma genesis, plate tectonics, and chemical differentiation of the Earth
Authors: Wyllie Peter J.
Published: February 2008

Magma genesis, migration, and eruption have played prominent roles in the chemical differentiation of the Earth. Plate tectonics has provided the framework of tectonic environments for different suites of igneous rocks and the dynamic mechanisms for moving masses of rock into melting regions. Petrology is rooted in geophysics. Petrological and geophysical processes are calibrated by the phase equilibria of the materials. The geochemistry of basalts and mantle xenoliths demonstrates that the mantle is heterogeneous. The geochemical reservoirs are related to mantle convection, with interpretation of a mantle layered or stratified or peppered with blobs. Seismic tomography is beginning to reveal the density distribution of the mantle in three dimensions, and together with fluid mechanical models and interpretation of the geoid, closer limits are being placed on mantle convection. Petrological cross sections constructed for various tectonic environments by transferring phase boundaries for source rocks onto assumed thermal structures provide physical frameworks for consideration of magmatic and metasomatic events, with examples being given for basalts, andesites, and granites at ocean‐continent convergent plate boundaries, basalts and nephelinites from a thermal plume beneath Hawaii, kimberlites in cratons, nephelinites from continental rifts, and anorogenic granites. The fluid dynamics of rock‐melt‐vapor systems exerts strong control on igneous processes and chemical differentiation. Unravelling the processes during subduction remains one of the major problems for understanding mantle heterogeneities and the evolution of continents.
The early environment and its evolution on Mars: Implication for life
Authors: McKay Christopher P. , Stoker Carol R.
Published: February 2008

There is considerable evidence that the early climate of Mars was very different from the inhospitable conditions there today. This early climate was characterized by liquid water on the surface and a dense atmosphere composed predominantly of CO2. The duration of these warm initial conditions on the surface of Mars is uncertain, but theoretical models suggest that they could have persisted for hundreds of millions up to a billion years. From studies of the Earth's earliest biosphere we know that by 3.5 Gyr ago, life had originated on Earth and reached a fair degree of biological sophistication. Surface activity and erosion on Earth make it difficult to trace the history of life before the 3.5‐Gyr time frame. If Mars did maintain a clement environment for longer than it took for life to originate on Earth, then the question of the origin of life on Mars follows naturally. The fossil evidence of early life on Earth provides clues as to what form fossils on Mars might take. Of particular interest are stromatolites, macroscopic layered structures that result from the anchoring of sediments by microorganisms living in the photic zone. Since over two thirds of the Martian surface is more than 3.5 Gyr old, the possibility exists that Mars may hold the best record of the events that led to the origin of life, even though there may be no life there today.
Volcanic hazards and their mitigation: Progress and problems
Authors: Tilling Robert I.
Published: February 2008

At the beginning of the twentieth century, volcanology began to emerge as a modern science as a result of increased interest in eruptive phenomena following some of the worst volcanic disasters in recorded history: Krakatau (Indonesia) in 1883 and Mont Pelée (Martinique), Soufrière (St. Vincent), and Santa María (Guatemala) in 1902. Volcanology is again experiencing a period of heightened public awareness and scientific growth in the 1980s, the worst period since 1902 in terms of volcanic disasters and crises. A review of hazards mitigation approaches and techniques indicates that significant advances have been made in hazards assessment, volcano monitoring, and eruption forecasting. For example, the remarkable accuracy of the predictions of dome‐building events at Mount St. Helens since June 1980 is unprecedented. Yet a predictive capability for more voluminous and explosive eruptions still has not been achieved. Studies of magma‐induced seismicity and ground deformation continue to provide the most systematic and reliable data for early detection of precursors to eruptions and shallow intrusions. In addition, some other geophysical monitoring techniques and geochemical methods have been refined and are being more widely applied and tested. Comparison of the four major volcanic disasters of the 1980s (Mount St. Helens, U.S.A. (1980), El Chichón, Mexico (1982); Galunggung, Indonesia (1982); and Nevado del Ruíz, Colombia (1985) illustrates the importance of predisaster geoscience studies, volcanic hazards assessments, volcano monitoring, contingency planning, and effective communications between scientists and authorities. The death toll (>22,000) from the Ruíz catastrophe probably could have been greatly reduced; the reasons for the tragically ineffective implementation of evacuation measures are still unclear and puzzling in view of the fact that sufficient warnings were given. The most pressing problem in the mitigation of volcanic and associated hazards on a global scale is that most of the world's dangerous volcanoes are in densely populated countries that lack the economic and scientific resources or the political will to adequately study and monitor them. This problem afflicts both developed and developing countries, but it is especially acute for the latter. The greatest advances in volcanic hazards mitigation in the near future are most likely to be achieved by wider application of existing technology to poorly understood and studied volcanoes, rather than by refinements or new discoveries in technology alone.
Nowcasting of precipitation systems
Authors: Browning K. A. , Collier C. G.
Published: February 2008

Digital remotely sensed observations of the atmosphere, particularly from radars and satellites, have become increasingly available over the last 15 years. Together with developments in computer technology this has stimulated the design and operation of a variety of systems to exploit these data in weather forecasting. Growing awareness of the importance of detailed site specific weather information and forecasts from zero to a few hours ahead has led to the emergence of a particular kind of forecasting called nowcasting which depends on the exceptionally detailed knowledge of the current pattern of weather that remote sensing can provide. This type of weather forecasting is reviewed, with emphasis on the measurement and extrapolation up to about 2 hours ahead of fields of various weather parameters, especially rainfall. Trends in the design of nowcasting systems are discussed, and potential benefits summarized.
Similarity and scale in catchment storm response
Authors: Wood Eric F. , Sivapalan Murugesu , Beven Keith
Published: February 2008

Until recently, very little progress had been made in understanding the relationship between small‐scale variability of topography, soil, and rainfalls and the storm response seen at the catchment scale. The work reviewed here represents the first attempt at a systematic theoretical framework for such understanding in the context of surface runoff generation by different processes. The parameterization of hydrological processes over a range of scales is examined, and the concept of the “representative elementary area” (REA) is introduced. The REA is a fundamental scale for catchment modeling at which continuum assumptions can be applied for the spatially variable controls and parameters, and spatial patterns no longer have to be considered explicitly. The investigation of scale leads into the concept of hydrologic similarity in which the effects of the environmental controls on runoff generation and flood frequency response be investigated independently of catchment scale. The paper reviews the authors' initial results and hopefully will motivate others to also investigate the issues of hydrologic scale and similarity.
The lithosphere of the Earth as a nonlinear system with implications for earthquake prediction
Authors: Keilis‐Borok V. I.
Published: February 2008

The lithosphere of the Earth can be viewed as a hierarchy of volumes, from tectonic plates to grains of rock. Their relative movement against the forces of friction and cohesion is realized to a large extent through earthquakes. The movement is controlled by a wide variety of independent processes, concentrated in the thin boundary zones between the volumes. A boundary zone has a similar hierarchical structure, consisting of volumes, separated by boundary zones, etc. Altogether, these processes transform the lithosphere into a large nonlinear system, featuring instability and deterministic chaos. From this background some integral grossly averaged empirical regularities emerge, indicating a wide range of similarity, collective behavior, and the possibility of intermediate‐term earthquake prediction.
An Explanation of VLF Diurnal Phase Change Observations
Authors: Kaiser A. B.
Published: February 2008

The observed diurnal phase changes of VLF radio waves show large deviations from the theoretical first‐mode phase change. The main features of the deviations are explained by the presence of a second mode that is larger than the first mode at night but that is small during transitions and during daytime. The data indicate that for frequencies above 16 kHz, nighttime second‐mode dominance extends out to several megameters from the transmitter, in agreement with theoretical predictions.
Formulas for Ray Paths in Ionized Layers with Application to Oblique Ionograms and Duct Modes
Authors: Woyk (Chvojková) E.
Published: February 2008

Analytical formulas including those for group and phase paths for radio rays in quasiparabolic (ionospheric) layers with spherical symmetry are presented in a convenient table. Their most important singularities are summarized in another table. By means of these formulas a transmission‐slider technique is presented for the determination of the shapes of oblique ionograms. The phenomenon of low‐angle cutoff is explained as well as the phenomenon of the trapping of waves. For a trapped wave it is shown that the group path between successive reflections is independent of the direction of the ray. The properties of rays in spherical layers are summarized, and some simple cases with nonspherical layers are discussed. In particular, a method is given for ray tracing in a wedge.
Dispersion Relations for a Compressible Isotropic Turbulent Plasma
Authors: Collin R. E.
Published: February 2008

An analysis of the propagation of the mean or average plane wave in a compressible isotropic turbulent plasma is presented. It is shown that the average wave separates into a longitudinal and a transverse mode, and their dispersion relations are derived. The analysis is based on the first‐order smoothing theory in the form developed by Keller and assuming a Gaussian correlation function. It is found that mode coupling is a strong effect in the short correlation length region but becomes negligible for long correlation lengths. Useful approximations to the dispersion relations are also given for the short, intermediate, and long correlation length regions as well as numerical results for the perturbed propagation constant of the average transverse wave. The application of the theory to a random dielectric medium is pointed out and a quantitative evaluation of the importance of the depolarization term, i.e. the grad div term, in the vector Helmholtz equation is made.
Lower Ionosphere Electron Densities Measured During the Solar Eclipse of November 12, 1966
Authors: Mechtly E. A. , Seino K. , Smith L. G.
Published: February 2008

The University of Illinois and the GCA Corporation, supported by NASA, launched four Nike‐Apache rockets from Cassino, Brazil, during the solar eclipse of November 12, 1966. The measurement of D‐region ionization loss rates was the principal aeronomic objective of the four rockets. Each rocket carried a 3385‐kHz radio propagation experiment and a Langmuir probe. The probe data were calibrated by the radio data to give electron number densities. At the mesopause (82 km) the electron densities were 800, 400, 300, and 100 cm‐3 at full sun (2 hours after totality), at 2.5% visibility of the solar disk, at second contact and at third contact, respectively. The full‐sun measurement of electron density at 65 km was 100 cm−3. By the time of second contact, the electron density diminished to less than 10 cm−3 at 70 km and below. At the time of third contact, the electron density was less than 10 cm−3 at 75 km and below. No significant differences were visible between the electron densities observed at second and third contact and at 2.5% visibility for altitudes between 95 and 100 km. A well‐defined sporadic‐E layer was observed at 104 km.
Incoherent Scatter Correlation Function Measurements
Authors: Farley D. T.
Published: February 2008

Single‐pulse and double‐pulse methods for measuring the cross‐correlation (two polarizations transmitted and received) or auto‐correlation (one polarization only) function of the scattered signal are described. The statistical errors associated with various forms of multi‐bit (no quantization errors in the sampling process), one‐bit, and hybrid estimators of the correlation function are calculated and compared, both for large and small signal‐to‐noise ratios. Roughly speaking, when the signal correlation is small, the hybrid estimators require π/2 and the one‐bit π2/4 times as many independent samples as the multi‐bit estimators to achieve the same statistical accuracy, but this disadvantage is often more than compensated for by an increase in the effective sampling rate. When the correlation is 0.5 or more, there may be a substantial difference between estimators of the same class (multi‐bit, for example). Systematic distortions of the correlation function and limitations on resolution associated with the finite receiver bandwidth and transmitted pulse length are calculated. The effect of a refractive index slightly less than unity is mentioned.
Horizontally Oriented Antennas in the Presence of an Anisotropic Ground
Authors: Galejs Janis
Published: February 2008

The ground surface exhibits a varying conductivity for different horizontal directions. It is excited by vertically or horizontally polarized waves. The ground produces a coupling between TM and TE field components. The net horizontal fields are modified by the anisotropy, except for the horizontal magnetic fields of the TM modes, which remain the same as under isotropic conditions; the horizontal electric fields are decreased near the directions of higher ground conductivity. The resulting pattern distortions of a horizontal wire antenna are explained by using simple closed‐form expressions.
Note on the Observation of Small‐Scale Atmospheric Turbulence by Doppler Radar Techniques
Authors: Lhermitte Roger M.
Published: February 2008

The paper discusses the applicability of microwave pulse Doppler radar techniques to the observation of small‐scale turbulent air motion. Emphasis is placed on a quantitative analysis method that utilizes the variance of the Doppler radar observed spectrum of velocity of man‐made radar targets used as tracers for the turbulent air motion.
The Spectral Gap
Authors: Bretherton F. P. , Bull G. , Lindzen R. S. , Pao Yih‐Ho , Reiter E. R. , Wilhelmsson H.
Published: February 2008

The primary problem we discussed is how to distinguish by means of spectral analysis the different types of dynamics believed to be dominant on different scales in the atmosphere; in particular, synoptic scales (dominated by rotation), mesoscale (waves or buoyancy), and microscale (‘turbulence’). The group rapidly concluded that they did not know how to do this, even in principle, and this report describes their observations on the subject.

For this purpose, spectra should be plotted (Figure 1) such that the area under a given portion of the graph is directly proportional to the contribution to the mean‐square fluctuation. All spectra are based on an average over an ensemble of realizations of the relevant field: 1. by combining records taken on separate occasions, or 2. by subdividing a continuous record into separate parts, or 3. by taking a Fourier series for a single record and smoothing the result, (which is ultimately equivalent to no. 2 above).
Fossil Turbulence
Authors: Woods J. D. , Högström V. , Misme P. , Ottersten H. , Phillips O. M.
Published: February 2008

Fossil turbulence is the name given to the three‐dimensional microstructure of temperature, humidity, or some other scalar property that is advected by the mean flow. (The first use of the expression seems to be attributable to Woods, but the physical phenomenon that it represents has been recognized for some time by fluid dynamicists.) The fossil turbulence was produced by a turbulent field that has since decayed; its scalar fluctuations occur at an intensity and on a scale that cannot be accounted for by the existing velocity field.

The relevance to this colloquium of fossil turbulence in the atmosphere is that it may produce appreciable radar backscattering, provided that it contains significant three‐dimensional refractive‐index structure on a scale equal to half the radar wavelength (typically 5–50 cm). Similarly, fossil turbulence may be of importance in radio forward‐scattering, although the relevant scale sizes here are larger (typically 3 meters or more) and depend on radio wavelength and scattering angle. Fossil turbulence, if it exists in the atmosphere, will also affect line‐of‐sight radio propagation and the propagation of optical and acoustical waves, its effects depending on the propagation geometry and the frequency of the propagating waves.
Very Long Baseline Interferometry with Large Effective Bandwidth for Phase‐Delay Measurements
Authors: Rogers Alan E. E.
Published: February 2008

The degree of delay‐measurement precision that is achievable by very long baseline interferometry depends on the effective bandwidth of the recorded signals. Methods of extending the effective recorded bandwidth for a fixed tape‐recorder bandwidth are examined in theory. Two major schemes (simultaneous recording of many widely separated frequency channels and recording sequentially different frequency channels) are examined in detail. Other techniques which involve rapid sampling and temporary ‘buffering’ of data bits are discussed. Methods of processing the data to achieve the maximum‐likelihood estimates of phase delay, fringe phase, and fringe rate are derived. Factors that determine the optimum choice of frequency channels are discussed by using a delay ‘resolution or ambiguity’ function. This function is analogous to the beam‐pattern function of a one‐dimensional antenna array. Theoretical signal‐to‐noise ratios for the delay and fringe phase measurements are derived by using a simple vector representation of the signal and noise.
Scattering by Two Cylinders
Authors: Olaofe G. O.
Published: February 2008

The boundary‐value problem of multiple scattering by two equal, parallel, but non‐overlapping, circular cylinders is considered. Solutions are derived in the form of infinite sums for the scattering intensities and cross sections, but numerical results are presented only for the extinction and back‐scattering cross sections, both of which are treated as functions of the separation distance between the two cylinders. Endfire and broadside illumination are distinguished from each other.
Perturbation Analysis for Reflection From Two‐Dimensional Periodic Sea Waves
Authors: Wait James R.
Published: February 2008

Reflection of a vertically polarized electromagnetic plane wave from a periodic rough surface is considered. The surface is characterized locally by a boundary impedance. By using a perturbation analysis, we obtained expressions for the spectral components of the reflected waves. It is shown that the results at grazing incidence lead to an effective surface impedance that is consistent with an earlier analysis by Rice (1950) for a perfectly conducting sinusoidal surface.
Charged Particles in Bianisotropic Media
Authors: Kong J. A.
Published: February 2008

Both electric and magnetic fields are shown to be present for charged particles at rest in bianisotropic media. A bianisotropic medium can be realized by a moving medium, a Tellegen medium, or a magnetoelectric medium. The coexistence of both fields may lead to radiation of energy for certain kinds of constitutive parameters that specify the properties of the medium. Electromagnetic field solutions of a charged particle in a Tellegen medium and a uniformly moving uniaxial medium are calculated. Physical implications of the various results are discussed.
ADA: An Instrument for Measuring Attenuation Due to Rain Over Slant Paths
Authors: Zawadzki I. I. , Rogers R. R.
Published: February 2008

ADA is an instrument the principle of which is based on empirical relations among rainfall rate, reflectivity, and attenuation. It is used in connection with a weather radar which provides a display of the attenuation due to rain at 10 GHz over the radar line of sight. With ADA a large amount of data applicable to the assessment and design of satellite communication systems can be accumulated in a relatively short period of time. It is estimated that the ADA‐measured attenuations, expressed in decibels, are accurate to within a factor of two.
An Investigation of the Ionospheric D Region at Sunrise: 1, Time Variations of Ozone, Metastable Molecular Oxygen, and Atomic Oxygen
Authors: Turco R. P. , Sechrist C. F.
Published: February 2008

As a step in determining the behavior of the D‐region ionization at sunrise, the development of atomic oxygen and ozone over sunrise has been investigated taking into account the absorption of solar ultraviolet radiation by the time‐varying, nonuniform ozone distribution over the mesosphere at sunrise. The dissociation rates of ozone and molecular oxygen are calculated and used to determine the time variations in the O and O3 densities at sunrise for a model considering only the oxygen allotropes. Transport processes were neglected in the sunrise calculations because chemical time constants are shorter than those for transport. However, the assumed initial presunrise atomic oxygen and ozone distributions, based on an average of theoretical and experimental results, do include the effects of transport. It was found that at altitudes from 60 to 80 km there is a delay in the ozone sunrise, and thus a delay in the development of the atomic oxygen density. [O]/[O3] was computed during sunrise, and a similar delay in its sunrise increase was observed. The production of metastable oxygen O2(1Δg,) by the photodissociation of ozone in the Hartley band at sunrise was also investigated. A simplified chemical scheme for O2(1Δ) is presented, from which a closed‐form solution for the O2(1Δ) densities over sunrise was obtained. O2(1Δ) may be important in the ion chemistry at sunrise, and can contribute to the early appearance of electrons in the D‐region.
Chatanika, Alaska, Auroral‐Zone Incoherent‐Scatter Facility
Authors: Leadabrand R. L. , Baron M. J. , Petriceks J. , Bates H. F.
Published: February 2008

This paper announces the operational status of an auroral‐zone incoherent‐scatter radar. The Stanford Research Institute 1290‐MHz incoherent‐scatter radar, which was moved to Chatanika, Alaska (L = 5.7), an auroral‐zone location near Fairbanks, is now producing interesting new results. The siting of the radar is such that D‐, E‐, and F‐region incoherentscatter measurements can be made without ground‐clutter interference. Although coherent auroral‐clutter echoes can at times be seen at relatively low elevation angles in the north, auroral echoes are sufficiently weak at 1290 MHz in the sidelobes of the antenna that they are not detectable during normal incoherent‐scatter measurements. The capabilities of the radar system are outlined, and samples are presented of the type of incoherent‐scatter results being obtained.
Plasma Turbulence: Theories and Experiments
Authors: Gentle K. W.
Published: February 2008

Although there is still only an incomplete understanding of plasma turbulence, knowledge has increased rapidly during the past few years. For weak turbulence, theory and experiment agree on the nature and strength of the interactions that occur. For strong turbulence, there is no general theory, but for some cases we have experimentally confirmed phenomenological laws which enable one to make quantitative estimates of the turbulent effects.
The Instability of Inhomogeneous Plasma Streams
Authors: Zhelyazkov I. , Rukhadze A. A.
Published: February 2008

The instability of plane‐parallel plasma streams with a nonuniform velocity profile, both in the absence and in the presence of a longitudinal magnetic field, has been investigated. The results for plasma streams are compared with those of ideal conductive liquid flows. Although for instability in a plane‐parallel ideal‐liquid flow the theorem of Rayleigh [1880] is valid, it is not so for plasma streams.
Some Results of a Mode‐Conversion Program for VLF
Authors: Pappert Richard A. , Snyder Floyd P.
Published: February 2008

A mode‐conversion program has been developed which allows for the vertical inhomogeneity of the ionosphere as well as its anisotropy. As an illustration of the potential use of the program for diagnostic studies at VLF, the sunrise amplitude study of Walker [1965] is numerically modelled with allowance for four modes. Exponential profiles of varying reference height and scale height are used to simulate the terminator. Of the models studied, best agreement is obtained with a terminator thickness of 1000 km. Despite the multimode nature of the models, Crombie's [1964] model is found to be valid for the path studied. This is because of weak conversion from the third and fourth nighttime modes to the first daytime mode.
Two‐beam observations of ionospheric irregularity structure and velocity at Arecibo
Authors: Brice N. M. , Conrad J. C. , LaLonde L. M. , Steinfeld A. H.
Published: February 2008

A new technique has been developed for measuring irregularity structure and velocity in the ionospheric E and F regions. The Arecibo incoherent‐scatter radar was modified to measure electron‐density profiles simultaneously with two beams: one fixed beam pointed at the zenith, and a second beam could be varied over 360° in azimuth and from 2 to 20° in zenith angle. Fluctuations in ionization density were observed to drift from one beam to the other so that information was obtained about both the horizontal velocity and the structure of these disturbances. Velocities of 100 to 200 m sec−1 and horizontal scale sizes of 50 to 100 km were deduced for the E region and roughly 400 m sec−1 and 500 km for the F region. A plot of velocity versus altitude shows a spiral structure with a vertical wavelength of 20 to 30 km in the E region.
Theory of incoherent‐scatter measurements using compressed pulses
Authors: Gray R. W. , Farley D. T.
Published: February 2008

The use of compressed pulses, in particular binary phase‐coded pulses, in incoherent‐scatter observations is investigated quantitatively. Since pulse compression requires coherent integration, the compression will be degraded by the time variations in the scattering medium. The degradation is small and easily corrected for as long as the total duration of the pulse (before compression) is less than Tx, the time delay at which the autocorrelation function of the scattering process first becomes negative. For longer pulses the distortions become more serious. With compressed pulses it is a relatively simple matter to achieve a range resolution of less than 1 km in incoherent‐scatter measurements.
Statistics for ionospherically diffracted VHF/UHF signals
Authors: Rino C. L. , Fremouw E. J.
Published: February 2008

In this paper a general characterization of the statistics for an ionospherically diffracted, monochromatic plane wave is presented. The main results are restricted to weak scatter, although two possible extensions that accommodate large phase perturbations and multiple scatter are discussed. A detailed discussion of the first‐order statistics of amplitude is given. The general Gaussian distribution is discussed together with its Nakagami‐distribution approximation and the log‐normal distribution. By using a segment of ATS‐3 satellite data recorded at Lima, Peru, we show equally good fits to Gaussian and log‐normal distributions at least for the limited dynamic range available. The Nakagami distribution provides only a poor approximation. A transverse scale size of 600 m is inferred, which we believe is representative of the nearly linear dependence of the measured field's correlation distance on the Fresnel‐zone radius.
Further studies of backscattering from a finite cone
Authors: Senoir Thomas B. A. , Uslenghi Piergiorgio L. E.
Published: February 2008

Certain errors in the second‐order contributions to the scattered field derived in an earlier study are pointed out, and the corrected formulas are presented. The results are compared with experimental data, and an explanation is suggested for the remaining small discrepancies.
Instabilities in charge sheets and current sheets and their possible occurrence in the aurora
Authors: Webster Harold F. , Hallinan Thomas J.
Published: February 2008

An experimental demonstration has been given of the initiation of a vortex‐forming instability in sheets of charge by perturbations in the shape of the sheet. The net motion of charge along the sheet wherever the sheet is bent is shown to be related to displacement of the potential minimum in the sheet. These results suggest the existence of an instability in current sheets which also produces vortex forms. There is evidence that both of these instabilities result in the formation of vortexes in the aurora.
Commission 7. Radio electronics
Authors: Collins R. J.
Published: February 2008

This session was held jointly with session 1.1.

This session was held jointly with session 6.1.

This session was held jointly with session 1.3.

Four papers were delivered. Three of these were reviews of various aspects of microwave semi‐conductor‐device research, and the fourth was on some specific aspects of work in Poland.
Irregularity motions in the polar ionosphere
Authors: Basler Roy P. , Scott Thomas D. , DuPuy Robert L.
Published: February 2008

The frequency spectrum of a CW HF radio signal transmitted from an aircraft and propagated over a 1‐hop path inside the polar cap was recorded for about 50 nighttime hr during August 1967. Two different general types of disturbance were observed in these records: (a) a diffuse spectral broadening which was always present to some extent, even under quiet conditions, but which on some occasions was increased by as much as a factor of 2; and (b) discrete frequency anomalies, which were recorded at a rate of about two per hour, and which generally appeared above the carrier frequency (about 9 MHz) and decreased in frequency with a median slope of —2.2 Hz min−1. These discrete anomalies can be interpreted most satisfactorily in terms of Doppler‐shifted reflections from moving ionospheric irregularities. On the basis of this interpretation, the observations are taken to show that irregularity velocities are often in the range from 0.5 to 1.0 km sec−1, with a preferred direction of motion roughly toward the quadrant from geographic E to S and centered on geomagnetic E. However, the measurements were relatively insensitive to geomagnetic N‐S movements and to low velocities.
Estimation of tropospheric refractive bending from atmospheric emission measurements
Authors: Gallop Marshall A. , Telford Larry E.
Published: February 2008

Refraction effects cause radio waves travelling through the atmosphere to be bent. Without knowledge of the atmospheric parameters along the ray path, the degree of bending cannot be calculated deterministically. Since atmospheric emission at microwave wavelengths is dependent on temperature, pressure, and relative humidity, radiometric data contain information about these parameters. This study will make use of a Monte Carlo simulation of the atmosphere to demonstrate that atmospheric emission measurements can be used with surface refractivity to increase greatly the accuracy with which refractive bending can be estimated.
Ray‐tracing synthesis of HF radar signatures from Gaussian plasma clouds
Authors: Rao P. B. , Allen E. M. , Thome G. D.
Published: February 2008

HF radar signatures have been synthesized from a time‐dependent Gaussian ion cloud using a three‐dimensional ray‐tracing progam that can take into account both electron collisions and the earth's magnetic field. The ion cloud model is based on the theory of ambipolar diffusion and the model parameters are based upon the observations made during a barium cloud test conducted at White Sands, New Mexico. Ray‐tracing results have been generated for both ordinary (O) and extraordinary(X) modes as well as for the “no‐field” case. The results, presented in the form of a time‐history of the Doppler shift and the scattering cross section, are found to be quite similar for all three cases. Relative to the O mode, the X‐mode variations lag in time and obtain a maximum cross section which is greater only by about 2 db. The variations for the no‐field case fall in between that of the O and X, but closer to the O mode. The results show that the cloud is extremely defocussing with an estimated defocussing factor (relative to free space) for the X mode increasing from 7.6 × 103 to 1.85 × 107 over the interval 5 to 190 sec of cloud's life. The ray‐tracing signatures are compared to those synthesized by means of a hard expanding ellipsoid method with a view to evaluating the importance of underlying ionization. The effects are found to be such as to introduce a significant time lag in Doppler history and to cause a cross section reduction by a factor that builds up with time from 5 db to more than 30 db. A comparison drawn between the observed and the ray‐tracing signatures leads to the conclusion that good agreement between the two can be expected only when the clouds experience either slow or no deformation and striation but not otherwise.