bluuebunny/crossref_metadata_2025 huggingface dataset:
Thunderstorms as possible micrometeorological sink for stratospheric water
Authors: Johnston Harold S. , Solomon Susan
Published: April 2008

The dryness of the stratosphere has been explained, in general terms, as water condensation from the rising branch of the Hadley cell at the tropical tropopause (Brewer, 1949), but Ellsaesser (1974) suggested that the mean tropical tropopause is not cold enough to account for the observed water vapor mixing ratios. During intense thunderstorms that in part penetrate the tropopause, investigators have observed (1) an increase in local stratospheric water vapor and (2) the temporary presence of air parcels substantially colder than and higher than the tropopause. These cold parcels are calculated to have extremely low water vapor mixing ratios, and their occurrence in the stratosphere suggests a mechanism whereby the effective condensation temperature could be systematically colder than the tropopause. Ice crystals from the cloud, evaporating in the warmer stratosphere, presumably cause the observed increase in water vapor, but mixing of cold desiccated air parcels with lower stratospheric air would tend to decrease its water content. Thus there are opposing factors concerning the role of severe cumulonimbus storms on stratospheric water, and it may require detailed, microphysical analysis to see which effect is larger.
The radiation field wave forms produced by intracloud lightning discharge processes
Authors: Weidman Charles D. , Krider E. Philip
Published: April 2008

The large‐amplitude radiation field pulses produced by intracloud lightning discharge processes have been recorded with submicrosecond time resolution. The wave forms are distinctly different from those produced by return strokes in cloud‐to‐ground lightning, yet they are surprisingly alike within a discharge and in different discharges. The shapes tend to be bipolar, with two or three narrow, fast‐rising pulses superimposed on the initial half cycle. Pulses with a positive initial polarity are usually produced in the several tens of milliseconds prior to the first return stroke in a cloud‐to‐ground discharge. Positive pulses tend to occur at regular intervals and have a mean full width of about 40±13 μs. Negative pulses are usually produced during isolated cloud discharges at more random intervals and have shapes similar to the positive pulses but with more variability. The implications of the field shapes and polarities for the physics of intracloud discharge processes are discussed.
Infinite cloud model of electrification by the precipitation mechanism in the presence of high rates of ion generation
Authors: Spangler J. D. , Rosenkilde C. E.
Published: April 2008

We have extended a simple, infinite cloud, precipitation mechanism model of thundercloud electrification to include effects due to the presence of radioactive aerosol particles resulting from fresh debris from a nuclear explosion. These effects involve ion generation, current due to motions of ions and charged aerosol particles, and collection of ions and aerosol particles by hydrometeors and cloud droplets. Our conclusion is that an ion pair generation rate G ≳ 1012 m−3 s−1 will prevent significant electric field growth.
Numerical modeling of the glaciers‐ocean‐atmosphere global system
Authors: Sergin V. Ya.
Published: April 2008

In order to carry out a study of the origins and thermodynamic mechanisms of the large‐scale climate oscillations and glaciations of the earth which have occurred over the last few hundred thousand years, a simplified thermodynamic model of the glaciers‐ocean‐atmosphere global system is constructed. The dynamics of the system are analyzed by computer, and the perturbations due to deviations of the earth's orbit and to tectonic forces are examined. The characteristic regimes of the system are auto‐oscillations, which exist with realistic numerical values of all parameters. Auto‐oscillations occur in the northern hemisphere owing to nonlinear interactions between two large inertial components which are determined by the heat capacity of the ocean and mass accumulation in continental ice sheets. The southern hemisphere represents an aperiodic system where oscillations are induced and occur on account of energy and mass transfer across the equator. The periods of calculated auto‐oscillations vary from 20,000 to 80,000 years. The length of climatic waves generated in the presence of external disturbances exceeds the auto‐oscillation period of the model. These results are in good agreement with paleoclimatic reconstruction data. The calculated variations in the mean temperature of both hemispheres, the temperature differences between the equator and pole, the sizes of marine and continental ice covers, the ocean level, and other values are of the same order of magnitude as those of empirical data. The transition from a relatively warm epoch (when continental ice sheets are absent) to conditions characteristic of the Pleistocene is modeled. The calculated curves show how weak temperature fluctuations are succeeded by large‐scale oscillations. Thus the simulation results not only provide an answer to the question concerning the cause of oscillations in the earth's climate and glaciation during cold epochs, but they also explain the absence of oscillations during warm epochs: in the absence of the second inertial link (continental ice) the system is essentially aperiodic.
A revised estimate for the radiocarbon age of North Atlantic deep water
Authors: Broecker Wallace S.
Published: April 2008

The extent to which the admixture of water of Antarctic origin influences the 14C/C ratio in North Atlantic deep water (NADW) has been heretofore underestimated. When this correction is properly made, a ventilation time for the deep western Atlantic is reduced to only about 100 years. The production rate of the northern component of NADW entering the western basin must be of the order of 30 Sv. If this northern component water is assumed to be the major supplier of new 14C to the deep sea, the carbon isotope ventilation time of the world deep ocean must be of the order of 900 years. However, since the new deep waters formed around the perimeter of the Antarctic are thought to enter the deep sea at a rate of about 20 Sv, the water ventilation time for the deep sea is of the order of 550 years.
Heat transfer through the thermal skin of a cooling pond with waves
Authors: Wesely Marvin L.
Published: April 2008

The temperature drop measured across the cool skin of a cooling pond is examined for 64 10‐min data collection periods taken with wind speeds of 3–8.5 m s−1 (effectively at a height of 10 m) and surface temperatures of 18°–37.5°C. The total heat transfer through the skin is found with the use of bulk aerodynamic estimates of the latent and sensible heat flux densities and empirical expressions for the long‐wave radiation exchange at the surface. Although it is questionable to describe the characteristics of a surface with waves by use of formulae derived partially on the assumption that a rigid boundary exists at the air‐water interface, the parameterizations that result seem on the average to perform quite well. For example, values of the numerical proportionality coefficient λ [Saunders, 1967], which relates the total heat transfer to the temperature drop, increase slightly from 6 to 7 as water temperature increases; these values are near those reported previously. No variation of λ with wind speed is detected. If λ is replaced by a numerical coefficient that also takes into account the difference of the thicknesses of the thermal and viscous sublayers, the new coefficient Λ ≈λPr1/3, where Pr is the Prandtl number, does not vary significantly with temperature of the surface skin.
Sulfur, potassium, and phosphorus associations in aerosols from South American tropical rain forests
Authors: Lawson Douglas R. , Winchester John W.
Published: April 2008

Aerosol samples from South American tropical rain forests near Manaus, Brazil, and Zongo, Bolivia, before and during rainfall periods, collected by using cascade impactors and time sequence filter samplers (‘streakers’) contained elements that may be classified into two distinct groups in the coarse particle size range (>1‐μm aerodynamic diameter). One group, whose atmospheric concentrations are suppressed during rainfall episodes, consists of the elements Al, Si, Ca, and Fe, which may be soil derived. The other group, consisting of the elements S, K, and P, shows little, if any, reduction in concentration caused by rainfall. The fact that the latter group is associated with the forest as a potential source and has elemental ratios corresponding to those found in biological materials is evidence of a biogenic source for S, K, and P in coarse aerosol particles over tropical rain forests sufficient to account for the observed concentrations of ∼50 ng S/m3, ∼100 ng K/m3, and ∼50 ng P/m3. These data suggest that organic matter released to the atmosphere contains not only nonmetals but potassium and perhaps additional metals.
Bubble populations and spectra in coastal waters: A photographic approach
Authors: Johnson B. D. , Cooke R. C.
Published: April 2008

A photographic analysis of bubbles generated in coastal seas by breaking waves and general turbulence has allowed the number and spectrum of sizes of bubbles greater than 17 μm in radius to be counted and observed. A distribution of numbers and sizes is presented for bubbles at 1.5‐m depth arising from wave activity driven by winds of from 8 to 10 m s−1; under these conditions the number of bubbles was 2.7×104 m−3. In winds of 11–13 m s−1 the numbers of bubbles determined from photographs were 4.8×105 m−3 0.7‐m depth, 1.6×105 m−3 at 1.8‐m depth, and 1.6×104 m−3 at 4‐m depth. The data acquired by this technique enable us and others to calculate the rate of the invasion of atmospheric gas into and out of the sea and to investigate the production of nonliving organic particulate matter by the processes of adsorption and bubble dissolution. The numbers of bubbles that do not dissolve completely but rise to the sea surface and burst are also calculable and are fundamental to quantifying the production of marine aerosols. A comparison of this technique with classical acoustic methods is now imperative.
Application of the parametrical surface wave prediction Model to rapidly varying wind fields during JONSWAP 1973
Authors: Günther H. , Rosenthal W. , Richter K.
Published: April 2008

The capability of a parametrical surface wave model to predict the sea state on a small array for highly variable wind fields is shown for three examples. The model treats the wind sea, for which the nonlinear interaction is most effective, in a parametrical sense. The swell is propagated along characteristics, and the source function for the swell is assumed to be zero. The model output is compared with wave measurements from the JONSWAP 73 experiment.
230Th, 231Pa, and open system dating of fossil corals and shells
Authors: Szabo Barney J.
Published: April 2008

Conventional uranium series and S‐R open system methods of age determination were applied to the dating of unrecrystallized fossil corals and molluscan shells. Two of the six corals have remained closed systems with respect to uranium and daughter isotopes 230Th and 231Pa; the other four coral samples were dated by the S‐R model. Analyses of coexistent mollusk shells revealed complex migrational patterns of uranium, thorium, and protactinium in these samples. Three of the six shells yielded acceptable conventional U series or S‐R model ages.
Meteorological aspects of the drift of ice from the Weddell Sea toward the mid‐latitude westerlies
Authors: Schwerdtfeger W.
Published: April 2008

Persistent, moderate to strong southerly surface winds, so‐called barrier winds, develop along the east side of the Antarctic Peninsula when the prevailing easterlies over the central and southern Weddell Sea carry cold, stable air masses toward the 1200‐ to 2000‐m‐high mountain barrier. Because of the lack of observations from the Weddell Sea itself, wind data for the topographically similar Ross Ice Shelf area are used to estimate the probable lateral extent of barrier winds. Frequency and duration of different types of winds at the key station Matienzo (65°S, 60°W) indicate the importance of the barrier effect for the drift of large ice masses northward and northeastward to the relatively low latitude of 63°S. Such a guided discharge of ice into the belt of the subpolar and mid‐latitude westerlies, not to be found in other sectors of the Antarctic, has a profound effect on the temperature conditions over the southern South Atlantic. Evidence for each of these statements is presented.
Size distribution, chemical composition, and optical properties of urban and desert aerosols in Israel
Authors: Levin Z. , Lindberg J. D.
Published: April 2008

Measurements of aerosol size distributions, chemical composition, and optical properties were carried out at two locations in Israel. Tel Aviv was chosen as an urban region, and Mitzpe Ramon as a desert region. The measurements indicate that the size spectra between 0.15 and 12 μm can be approximated by a power law type of distribution. The spectra in Tel Aviv show higher concentrations and greater slopes than those from the desert. Diurnal variations between day and night are observed in the size distribution of the summertime measurements in Tel Aviv. These are believed to be related to the increase in aerosol size due to absorption of water vapor during high relative humidity periods. The chemical composition in Tel Aviv was found to depend strongly on the meteorological conditions. During westerly flow, which is the prevailing wind direction in Tel Aviv, the aerosols contain large amounts of NaCl particles, which are not usually found in the desert. During Sharav conditions (dry conditions and easterly flow) the aerosols in Tel Aviv are, as is expected, very similar to those found in the desert. The optical measurements also suggest strong differences between Tel Aviv and the desert. Filter samples of atmospheric particulate matter from Tel Aviv always appeared darker than those from the desert site. Measurements of imaginary refractive index in the 0.3‐ to 1.7‐μm spectral region are presented. These measurements are consistently higher by a factor of 2–4 in Tel Aviv as compared to simultaneous samples from the desert site. Seasonal variations also have been observed, and their possible causes are discussed. The size distribution, composition, and imaginary refractive index observations are interpreted in terms of aerosol origins and prevailing local and synoptic scale meteorological conditions.
A case of transport and deposition of Saharan dust over the Italian Peninsula and southern Europe
Authors: Prodi Franco , Fea Giorgio
Published: April 2008

A severe case of Saharan dust transport and deposition with rain over Italy and southern Europe has been investigated by combining all available data including meteorological information, analyses of air sampling filters and sampled dust with rain, and satellite information on cloud cover. This typical straight transport case is characterized by a trough oriented south‐north, a cold front on the mobilization area, and a warm advection from the south. Meteorological analysis included relative topography, maps of pseudo‐potential temperatures, and barotopographies of ϑp = 45°C. The conditions of dust mobilization have been investigated and strong updrafts and thermals, with and without concomitant convective clouds, proved to be responsible for it. The size distribution of particles in rainfall residue has shown two modes, with diameters around 0.2 and 1 μm. X ray diffractometric analysis and SEM pictures have shown that the two modes are also different in composition, the smaller particles being composed of clay platelets and the larger of quartz grains. The mass concentration of the dust layer has been evaluated in 154 μg/m3. Wet removal through in‐cloud scavenging processes was the effective mechanism of deposition of the dust, as muddy rain has been observed at the ground long before the dust was observed in air sampling filters at mountain stations.
Sea surface temperature near a bay inlet zone
Authors: Powell Mark D. , SethuRaman S.
Published: April 2008

Results of an investigation of the radiometric sea surface temperature distribution near Shinnecock Inlet off Long Island are presented. The data were gathered by 10 individual aircraft flights during the summer of 1975. Inflow into or outflow from the inlet could be easily identified with sea surface temperature measurements.
Some aspects of the oceanography of the Gulf of Mexico using satellite and in situ data
Authors: Vukovich Fred M. , Crissman Bobby W. , Bushnell Mark , King William J.
Published: April 2008

Satellite infrared data and in situ data were combined to study synoptic‐scale and mesoscale fronts in the Gulf of Mexico in the period 1973–1977. Deep northward penetrations of the Loop Current were noted in the winter, and a major warm gyre developed in the winter, 1974. Other major warm gyres were seen to develop in the early spring (1974 and 1977). In all cases, a very large meander developed off the southern part of the west Florida shelf prior to the development of the major warm gyre. Smaller meanders were seen to move along the Loop Current boundary at an average speed of 28 km/day and with an average wavelength of 210 km.
Modulation characteristics of sea surface waves
Authors: Ramamonjiarisoa A. , Mollo‐Christensen E.
Published: April 2008

Observations of ocean surface waves under steady wind conditions show that they do not obey the linear dispersion relation, thus confirming that previously reported results of laboratory experiments also apply to the ocean. It is also shown that mechanically generated surface waves of near‐breaking amplitude follow a similar dispersion relation. Observations of coherency of wave signals between two points are also reported, showing the coherency to be higher than in a wave field consisting of independently propagating Fourier components. It is also demonstrated that the observed spectra, coherencies, and dispersions can be described in terms of modulated Stokes‐like carrier waves propagating with an angular spread and a lag between amplitude and phase modulations. This is solely proposed as a method of description of observations since there is no present theory for the dynamics of a process where crests are lost due to crest pairing. This violates a crucial premise of modulation theories.
Optical and particulate properties at oceanic fronts
Authors: Zaneveld J. Ronald V. , Pak Hasong J.
Published: April 2008

Distributional patterns of optical and particulate properties at oceanic fronts follow general patterns. These patterns are examined by means of three examples: the front associated with the Columbia River plume in winter, the upwelling front off the Oregon coast during the summer, and the front in the eastern equatorial Pacific. It is shown that the optical and particulate matter distributions at oceanic fronts are the result of three major processes: (1) advection of inorganic matter into the frontal zone, (2) advection of biological materials into the front, and (3) generation of particulate matter by biological processes in the front itself.
Differential radar scattering properties of model hail and mixed‐phase hydrometeors
Authors: Aydin K. , Seliga T. A. , Bringi V. N.
Published: April 2008

The differential reflectivity (ZDR) radar signal contains information on the shape and alignment of ice phase hydrometeors. Under certain circumstances, then, this signal and reflectivity factor can be used to identify the presence of hail particles. Such interpretations require knowledge about the scattering properties of various types and shapes of hydrometeors, including ice, water‐coated ice, and graupel. These hydrometeors are examined for their differential scattering properties obtained from computations using the transition (T) matrix method of Waterman and an extension of this theory to two‐layered bodies. Differential radar cross sections together with circular depolarization ratios are presented, and several instances of possible hail detection by radar using ZDR signatures are illustrated.
A generalized analysis of dual‐polarization radar measurements of rain
Authors: Stapor D. P. , Pratt T.
Published: April 2008

In the study of meteorological phenomena by radar, it has been shown that dual‐polarization radar measurements can yield useful data about precipitation structures within the radar beam. The techniques available for dual‐polarized radar measurement are differential reflectivity (ZDR), linear depolarization ratio (LDR), and circular depolarization ratio (CDR). This paper presents a theoretical analysis of backscattering from a volume filled with raindrops using Rayleigh scattering theory. A generalized radar equation is given in matrix form, and the dependence of backscatter measurements in terms of a rainstorm model including raindrop shape, size, and canting angle is examined. Calculated results which show the dependence of ZDR on beam elevation angle and polarization angle are presented. Some results for LDR and CDR are presented, showing how these quantities depend on raindrop parameters.
Dual‐wavelength processing: Some effects of mismatched antenna beam patterns
Authors: Rinehart Ronald E. , Tuttle John D.
Published: April 2008

Dual‐wavelength radar studies aimed at the detection of hail generally assume that the two radars used are sampling identically the same volume in space. In this paper we examine the effects of mismatched antenna beam patterns, both the main lobes and the side lobes, on dual‐wavelength hail detection. Mismatched beam patterns produce erroneous hail signals which can be quite misleading. The NCAR CP‐2/M33 dual‐wavelength radar produced erroneous negative hail signals as large as − 20 dB in some parts of storms, while the new CP‐2 dual‐wavelength radar produces erroneous positive hail signals as large as + 9 dB. We discuss how well matched the antenna beam patterns must be to produce acceptably low erroneous hail signals. We also discuss the serious implications of these findings on earlier dual‐wavelength studies.
Simultaneous measurements of rain by airborne distrometer and dual‐polarization radar
Authors: Cherry Stephen M. , Goddard John W. F. , Ouldridge Martin
Published: April 2008

An experiment is described where rain at heights well above ground level was observed simultaneously by an airborne distrometer and a dual‐polarization radar. The parameters of the distribution of drop sizes and the rainfall rate were computed from both sets of observations assuming the distribution to have a negative exponential form. The parameters derived from the two sources of data are compared, and differences discussed.
Application of dual linearly polarized radar data to prediction of microwave path attenuation at 10–30 GHz
Authors: Leitao M. J. , Watson P. A.
Published: April 2008

This paper describes a methodology for analysis of dual linearly polarized radar data for the prediction of path attenuation at 10–30 GHz from long term point rainfall data. Detailed knowledge of the physical structure of precipitation in conjunction with scattering theory is used to provide attenuation predictions.
The scattering of an H‐polarized plane wave from an axially slotted infinite cylinder: A dual series approach
Authors: Johnson William A. , Ziolkowski Richard W.
Published: April 2008

The azimuthal current induced by an H‐polarized plane wave with an arbitrary angle of incidence on an infinite cylinder with an infinite axial slot is considered. A system of dual series equations is derived from the modal expansions of the tangential field components by enforcing the electromagnetic boundary conditions. This dual series system is then solved for the modal coefficients with techniques borrowed from the Riemann‐Hilbert problem of complex variable theory. The resulting infinite system of linear equations for the modal coefficients can be handled in an efficient manner. A comparison of the generalized dual series solution with a purely numerical method of moments solution based upon vector and scalar potentials is made. In contrast to this method of moments solution, it explicitly contains the behavior of the solution near the aperture rim and can generate the current values in a shadow region for small to large ratios of cylinder radius to wavelength without additional special considerations.
Normalized relationship among errors and sidelobe levels
Authors: Hsiao James K.
Published: April 2008

This paper examines the effect of errors on the peak sidelobe level of a phased array. The sidelobe level distribution of the radiation pattern for both linear and planar arrays is seen to be Rician. A set of constant probability curves is presented which relates the allowable phase and amplitude errors with the allowable sidelobe level deterioration. Examples are presented to demonstrate how these curves can be used to design a low sidelobe array with a better tolerance of error. These curves, or extensions of them, provide a useful tool for the engineer designing an array antenna. For a planar array with correlated errors the total variance σ is the root‐sum‐square of the error in each element σμ (including both correlated and uncorrelated errors) and the contribution of correlated error in a subarray σc. Both σμ and σc are functions of the errors and the illuminations, but σc is also a function of the pattern of the subarray in which the errors are correlated.
Radiation from pulsed electron beams in space plasmas
Authors: Harker K. J. , Banks P. M.
Published: April 2008

A theoretical study has been made of the electromagnetic radiation arising from pulsed electron beams. The study assumes an electron beam which has a well‐organized spatial structure determined by a fixed trajectory in a magnetic field and on/off pulsing governed by the electron source. From this model the electromagnetic radiation is determined by adding coherently the radiation from each individual electron in the helical stream. The radiation per unit frequency interval is determined, as well as the radiation per unit solid angle, as a function of both propagation and ray angles, electron beam pulse width and separation, total number of pulses, and beam current. As expected for a coherent process, it is found that the radiated power varies at the square of the beam current. The relatively high efficiency of the beam in producing electromagnetic radiation is illustrated by consideration, among others, of a 1‐keV, 100‐mA beam used in recent experiments on the space shuttle. For these parameters the total radiated power per steradian is calculated at selected angles to be greater than 1% of the total beam power carried as electron kinetic energy. These results provide a useful theoretical basis for planning future electron beam experiments in space plasmas.
A simulation study of the loss cone driven cyclotron maser applied to auroral kilometric radiation
Authors: Wagner J. S. , Lee L. C. , Wu C. S. , Tajima T.
Published: April 2008

We study the linear growth and nonlinear saturation of electromagnetic radiation amplified by a hot (5–20 keV) population of electrons possessing a loss cone velocity distribution in the presence of a cold (20–500 eV) electron population. A relativistic electromagnetic simulation code is used to study the emission process. Three cases are presented in detail to illustrate the generation process of auroral kilometric radiation. The first case, which has an electron plasma frequency ωpe = 0.2ωce (electron cyclotron frequency) and possesses a double loss cone distribution, exhibits a strong narrow peak of the fast extraordinary mode (X mode) radiation just above the X mode cutoff frequency. The second case with ωpe = 0.2ωce and a single loss cone distribution shows a preferred direction of propagation for the amplified radiation. The third case with ωpe = 0.5ωce shows a peak in the ordinary mode (O mode) radiation. In all cases, the radiation saturates by turbulent scattering of resonant particles into the loss cone.
The Io decametric emission cone
Authors: Green James Lauer
Published: April 2008

The Planetary Radio Astronomy (PRA) Experiment on board Voyager 1 and 2 observed intense Jovian decametric (or DAM) radiation from Jupiter for several months before and after encounter with the giant planet. As measured by the PRA experiment the DAM emissions from 2 to 40 MHz have a characteristic “arclike” shape in frequency versus time spectrograms. Much work has already been done relating observations of DAM emission with the position of the satellite Io. The PRA data are reorganized in this study in order to account for the relative positions of Io and Jupiter and to aid in determining the causes of the DAM arclike structure. Nearly 2 months of the PRA data were transformed into a coordinate system for which Io and Jupiter remain fixed and the spacecraft data are sorted into bins of spacecraft system III (65°) longitude. A 1/RJ2 normalization factor is applied to all the sorted data to take into account the radial distance dependence of this emission. The results of this analysis technique indicate that the Io‐dependent DAM emissions, as seen by both Voyager 1 and 2, are generated in hollow cones at all frequencies over the fixed Io longitudes studied (from 200° to 260°). Comparing the characteristics of the DAM emission at the edges of the emission cones (in two ranges of spacecraft longitude), distinct differences can be found. In addition, the edges of the emission cones are, in many cases, broad in longitude (30° or more). Three‐dimensional raytracing calculations within a model Jovian magnetosphere are used in an effort to explain the shapes of the DAM emission cones. Using a general emission mechanism which ultimately generates radiation in the R‐X mode above the R=0 cutoff, qualitative agreement with the observations can be made which indicates that the observed arc structure is largely a propagation effect. The greatest bending of the DAM model rays occurs on one edge of the emission cones and is almost entirely due, at frequencies below 25 MHz, to the large region of enhanced (above dipole) magnetic field believed to exist around 155°. Enhanced plasma densities found in the Jovian ionosphere may produce an additional propagation effect at frequencies greater than 25 MHz.
Determination of a vector potential
Authors: Senior Thomas B. A. , Ksienski David A.
Published: April 2008

A vector potential is determined for a static field attributable to sources induced on a perfectly conducting surface B. With the electrostatic problem it is shown that for closed and open surfaces existing methods for the construction of the potential are inconvenient and inadequate respectively, and alternative solutions are developed in both cases.
Radiative transfer theory for active remote sensing of a layer of nonspherical particles
Authors: Tsang L. , Kong J. A. , Shin R. T.
Published: April 2008

The radiative transfer theory is applied to calculate the scattering by a layer of randomly positioned and oriented nonspherical particles. The scattering amplitude functions of each individual particle are calculated with Waterman's T matrix method, which utilizes vector spherical wave functions for expansion of incident, scattered, and surface fields. The orientation of the particles is described by a probability density function of the Eulerian angles of rotation. A rotation matrix is used to relate the T matrix of the principal frame to that of the natural frame of the particle. The extinction matrix and phase matrix of the radiative transfer equations are expressed in terms of the T matrix elements. The extinction matrix for nonspherical particles is generally nondiagonal. There are only two attenuation rates in a specified direction of propagation. The radiative transfer equations are solved by an iterative method to first order in albedo. Numerical results are illustrated as functions of incidence angle and frequency with applications to active remote sensing.
The HF‐induced plasma line below threshold
Authors: Fejer J. A. , Sulzer M.
Published: April 2008

Observations at Arecibo of the HF‐induced plasma line for low powers of the HF modifying transmitter are described and interpreted. The observed spectra were centered on the radar frequency minus the HF modifying frequency and had the same shape and width as the ion line of incoherent backscatter. The importance of the standing‐wave nature of the HF pump wave for such observationsis stressed.
Day‐to‐day changes in ionospheric electron content at low latitudes
Authors: Dabas R. S. , Bhuyan P. K. , Tyagi T. R. , Bhardwaj R. K. , Lal J. B.
Published: April 2008

The day‐to‐day variability in ionospheric electron content (IEC) is studied using the diurnal IEC maximum data obtained from multistations located in the latitude range between 15.0°N and 30.0°N in the Indian zone during solar minimum. Depending on the location of the observing station, the changes in IECmax values, of about ±20 to 40%, are found to occur in the form of single day abnormality, alternate day abnormality, and long‐term periodic fluctuations. The magnitude of fluctuations is found to be maximum at a station which is near the crest of the equatorial anomaly belt. The long‐term periodic variations, other than annual and semiannual variations, are different for different locations and seasons and show a periodicity of about 45 days in winter in the equatorial anomaly region only and about 27 days in summer at all the stations. The changes are not always correlated with solar or magnetic activity changes. It is observed that short‐as well as long‐term variations in IECmax at stations within and near the crest of the equatorial anomaly belt are controlled mainly by the electrojet strength variation.
High‐resolution frequency determination of discrete signal components
Authors: Walton E. K.
Published: April 2008

An algorithm is presented which combines the advantages of the Gaussian window with the computational efficiency of the fast Fourier transform and which permits the determination of the frequency of discrete signal components with high accuracy.
Ionospheric heater beam scanning: A new technique for ELF studies of the auroral ionosphere
Authors: Rietveld M. T. , Barr R. , Kopka H. , Nielsen E. , Stubbe P. , Dowden R. L.
Published: April 2008

ELF/VLF wave generation by modulation of the auroral electrojet has previously been performed near Tromsø, Norway, with an HF heating beam pointed in a fixed (zenith) direction. By varying the phases of the HF waves transmitted from adjacent rows of antennas in the transmitting antenna array, the beam direction can now be scanned in the north‐south plane at frequencies from zero to approximately 5 kHz. In one type of beam scanning the amplitude of the heating beam is ELF modulated while the beam direction is simultaneously swept slowly, in sawtooth fashion, about the zenith. Variations in the ELF field strength, measured on the ground as the source is swept in this manner, are shown to be associated with spatial variations of the auroral ionosphere in the north‐south direction. We compare these spatial variations with those observed by STARE.
ELF and VLF radiation from the “polar electrojet antenna”
Authors: Barr R. , Stubbe P.
Published: April 2008

First, an approximate evaluation is made of the ELF/VLF dipole moment of the polar electrojet antenna established by ionospheric heating via the use of powerful HF waves amplitude modulated with frequencies in the ELF/VLF range. Then, the theory of reciprocity is used to determine the magnitude of the ELF/VLF waveguide excitation produced by such a dipole immersed in the ionosphere. Propagation under a series of ionospheres ranging from quiet auroral nightime to disturbed auroral daytime is considered.
Aspects of modern nonlinear dynamics: Soliton and chaos phenomena
Authors: Christiansen Peter L.
Published: April 2008

A brief description of the two most important phenomena in modern nonlinear dynamics—solitons and chaos—is presented. The competition between order and disorder in nonlinear systems can only be studied through computer experiments.
Quasi‐particle method for propagation in inhomogeneous media
Authors: Marcuvitz N.
Published: April 2008

In the conventional geometric‐optic approximation to wave propagation excited by a source of finite extent, each source point emits rays that transport wave energy along well‐defined trajectories, but with transport properties exhibiting singularities in caustic regions where the cross section of ray bundles vanishes. In the first‐order quasi‐particle approximation the extended source is viewed as a phase space distribution of point quasi‐particles whose space‐time dependent kinetic properties such as density, average velocity, etc., provide nonsingular measures of the space‐time transport of amplitude, wave number, frequency, etc., of the wave train modulation even in caustic regions. The range of ap‐ plicability of the quasi‐particle method is examined in terms of relative space‐time scales characteristic of the excitation and medium.
The mode‐matching method with a generalized singular‐smoothing procedure for analyzing the edge‐type scattering problem with several edge points
Authors: Okuno Y. , Matsuda T.
Published: April 2008

A numerical technique is presented for solving a two‐dimensional edge‐type scattering problem where the scatterer has several edge points. The technique is based on the mode‐matching method with a singular‐smoothing procedure. Analytical foundations of the technique, including convergence theorem, are described, and a computer‐aided numerical algorithm is developed. To show the validity of the technique, plane wave diffraction by a trapezoid grating is analyzed. Numerical data on the speed of convergence show the effectiveness of the technique.
The application of the conjugate gradient method for the solution of operator equations arising in electromagnetic scattering from wire antennas
Authors: Sarkar Tapan K.
Published: April 2008

In this paper the method of conjugate gradient is presented for the solution of operator equations arising in electromagnetics. The particular problem to which the conjugate gradient method has been applied is the electromagnetic scattering from arbitrary oriented wire antennas. With this iterative technique, it is possible to solve electromagnetic problems involving electrically large structures without storing any matrices as is conventionally done in the method of moments. The basic difference between the proposed method and the matrix methods (Rayleigh‐Ritz, Galerkin's, method of moments) for the same expansion functions is that for the iterative technique we are solving a least squares problem. Hence, as the order of the approximation is increased, the proposed technique guarantees a monotonic convergence for the residuals AI‐Y, whereas matrix methods, in general, do not yield monotonic convergence. The conjugate gradient method converges for any initial guess; however, a good one may significantly lower the computation time. Also, explicit error formulas are given for the rate of convergence. Numerical results are presented for electromagnetic scattering from arbitrary oriented thin‐wire antennas.
New integral equations for scattering by penetrable objects, II
Authors: Kleinman R. E. , Roach G. F.
Published: April 2008

The problem of scattering of time‐harmonic incoming waves by homogeneous penetrable objects of arbitrary shape (cylinders of arbitrary cross section in two dimensions) may be recast as a pair of boundary integral equations to determine two unknown densities from which the field quantities may be obtained. The kernels of the integral equations usually involve the free space Green's functions for the Helmholtz equation with wave numbers appropriate to both the exterior and interior regions. Recent work on scattering by impenetrable objects has shown that considerable advantage is gained by modifying the free space Green's function with the addition of a linear combination of radiating cylindrical or spherical waves (multipoles) whose coefficients are chosen in some optimal manner. In the present paper, this method is extended to the penetrable case. Here the fundamental solution in the exterior is again modified by the addition of outgoing waves while the interior Green's function is modified by the addition of standing waves. The coefficients of the added terms are determined to minimize the norm of the boundary integral operator.
Electromagnetic fields of corrugated conical horns with elliptical cross section described by Lamé functions
Authors: Worm S. C. J.
Published: April 2008

The corrugated conical horn with elliptical cross section is investigated. Use is made of the analytical solutions of the Lamé differential equations. In the investigations we use the anisotropic surface impedance model. The problem of wave propagation in an anisotropic elliptical cone is formulated as an eigenvalue problem. This problem is solved, and plots are given of the separation constant as a function of the opening angle of the cone with the aspect ratio of the elliptical cross section as a parameter. The radiation of an anisotropic elliptical horn excited by a hybrid mode is determined using the spheroconal wave expansion method. Satisfactory agreement between computations and measurements is obtained. It is found that with this type of horn it is theoretically possible to perfectly generate circularly polarized radiation patterns of elliptical cross section.
Accurate theory for a new leaky‐wave antenna for millimeter waves using nonradiative dielectric waveguide
Authors: Sanchez A. , Oliner A. A.
Published: April 2008

An almost rigorous analysis is presented for a new leaky‐wave antenna of simple configuration. The new structure is based on a recent nonradiative modification of H guide and is suitable for millimeter wavelengths. The analysis employs a transverse equivalent network that yields a dispersion relation in closed form. Numerical values are presented for the phase and leakage constants and for a typical example of antenna performance.
The effective cross‐section method for dielectric waveguides in or on a substrate
Authors: Kuester Edward F.
Published: April 2008

It has previously been shown that the propagation constants of step‐index dielectric waveguides of arbitrary cross section and small index contrast can be computed accurately by using a related metallic waveguide of a certain “effective cross‐section.” In this paper we extend the method to treat waveguides whose cladding is inhomogeneous and whose refractive index is not necessarily close to that of the core (guiding) region. The results are applied to dielectric waveguides embedded into or embossed upon a dense substrate region. The expressions obtained are, again, quite simple and require knowledge only of the TM‐mode eigenvalues of a similarly shaped metallic waveguide.
Wave propagation along a conductor in a low‐conductivity seam
Authors: Delogne Paul
Published: April 2008

The mode equation for wave propagation along a thin conductor wire located in a low‐conductivity seam embedded between two more conducting half spaces is reduced to a transmission line formulation. The latter is particularly adequate for iterative solution. Numerical results are shown and discussed. Extension to leaky feeders and application to remote sensing of seam discontinuities are proposed.
A geometrical theory of diffraction for a half plane residing on the interface between dissimilar media: Transverse magnetic polarized case
Authors: Coblin R. Dawson , Pearson L. Wilson
Published: April 2008

An asymptotic ray analysis of the diffraction of an electromagnetic plane wave by a perfectly conducting half plane that resides on the interface separating half spaces filled with dissimilar media is developed for the case where the plane of incidence is perpendicular to the edge. The diffraction problem is formulated as an integral equation whose unknown is the tangential component of electric field residing on the uncovered half of the interface plane. This integral equation is solved by using the Wiener‐Hopf technique. Asymptotic analysis of the resulting diffracted fields is carried out in the angular spectral plane and ray interpretations are assigned to the asymptotic terms. In addition to geometrical optics and edge‐diffracted field components, which arise in the Sommerfeld diffraction problem, a lateral wave field is found to contribute to the total (asymptotically evaluated) field. The possibility for a Zenneck wave to be present arises also when the media exhibit magnetic contrast, although this possibility is not explored in the present paper.
Radiation from the junction of two open waveguide sections
Authors: de Ruiter H. M.
Published: April 2008

A general theory is developed for the reflection, transmission, and radiation of electromagnetic fields at the junction of two open waveguides. It employs the integral equation formulation for the field in the junction plane, in which point‐source solutions in the two joining waveguides occur as kernel functions. The integral equations are solved by using the axial spectral representations of the kernel functions, together with the Fourier integral expansion with respect to the transverse coordinates. Numerical results are presented for a terminating slab waveguide, operating in the TE0 surface wave mode and radiating into free space.
High‐power electromagnetic wave propagation in a partially filled plasma waveguide
Authors: Vegas A. , Calderón M. A. G. , García J. L.
Published: April 2008

In this paper an exhaustive study of interaction of high‐frequency (ƒ = 2450 MHz) electromagnetic wave with a longitudinally magnetized guide plasma column, in a partially filled plasma waveguide, is carried out. The behavior of the plasma, confined to a linear machine with a uniform magnetic field
, depending on the work pressure, the static magnetic field applied, the wave polarization, and the incident power level, is experimentally studied. The paper presents conclusive evidence of anomalous absorption of an intense right‐hand circularly polarized wave at high magnetic fields. The study was carried out with a continuous Argon plasma.
Linear array arrangement for microwave tomography
Authors: Peronnet G. , Bolomey J. Ch. , Jofre L.
Published: April 2008

Recent developments both in measurement techniques and reconstruction algorithms have shown the possibility of quasi‐real time microwave tomography. These technical developments always require more sophisticated experimental arrangements in order to reduce the microwave circuits complexity, decrease the measurement time, and improve the resolution. This paper deals with the use of crossed linear arrays convenient for tomography by transmission. Numerical simulations and initial experimental results show the relative advantages of such arrangements as compared to the more classical two‐dimensional arrays.
A cross‐correlation receiver for radio astronomy employing quadrature channel generation by computed Hilbert transform
Authors: Lo W. F. , Dewdney P. E. , Landecker T. L. , Routledge D. , Vaneldik J. F.
Published: April 2008

A real‐time digital signal processor for an earth rotation synthesis radio telescope is described. The processor accepts 4 MHz baseband signals, quantizes them to three levels, and performs delay equalization, cross correlation, and phase rotation. The inphase cross correlation of the input signals is calculated for 16 values of delay spaced by 62.5 ns. The quadrature correlator output is produced from the inphase output by numerical computation by using a band‐limited form of the Hilbert transform. The values of inphase and quadrature visibility at the exact value of delay are derived by interpolation. Errors arising in this signal processing method are investigated and shown to be small in the adopted design. A high‐speed, 16‐bit microcomputer is employed to allow many of the required operations to be performed in software. The processor produces four complex interferometer outputs simultaneously and is capable of producing ten such outputs. Interferometer visibility records of the radio source 3C66 are presented.