bluuebunny/crossref_metadata_2025 huggingface dataset:
Unquiet on any front: Anisotropic turbulence in the solar wind
Authors: Matthaeus William H. , Bieber John W. , Zank Gary P.
Published: February 2004

Detailed models of turbulence enter into space physics in a number of ways, through descriptions of power law spectra, through estimates of heating rates, correlation scales, time scales of nonlinear interactions, and through other statistical characterizations. These turbulence properties, which are also of great interest to theorists studying plasma turbulence in the magnetohydrodynamic (MHD) approximation, are quite likely sensitively dependent upon the rotational symmetry of the turbulent fluctuations. In the past few years, advances in several areas of solar wind research suggest a change in how the community may look at the symmetries of solar wind turbulence. This should influence the standard simple turbulence models used in space physics and related areas. At issue is the gradual uncovering, through studies of several types, of the possibility that the rotational symmetry of solar wind turbulent fluctuations may be very different from that advocated traditionally. In addition, and most importantly, this suggested change of perspective on the “standard solar wind turbulence model” is seen to have quite significant and quantitative impact on diverse problems, such as cosmic ray transport, solar wind radial evolution, the coronal and solar wind heating problems, and the interpretation of particle and field data from spacecraft. These recent developments are reviewed here.
Polarity transitions and excursions of the geomagnetic field
Authors: Roberts Andrew P.
Published: February 2004

The nature of geomagnetic field behavior during polarity transitions is one of the most hotly debated issues in modern geophysics. Dynamo action in the earth's fluid outer core is known to be responsible for generating the earth's main magnetic field, however, the mechanism for polarity transition is still unknown. Polarity transitions are a fundamentally important property of the geomagnetic field, but because they have not taken place in historic time, it is necessary to turn to the paleomagnetic record to understand the mechanism by which they occur.
Detection and response to volcanic/hydrothermal events on the mid‐ocean ridge
Authors: Embley Robert W. , Fox Christopher G.
Published: February 2004

The mid‐ocean ridge is by far the most continuous volcanic system on the planet, but since it lies beneath more than 2 km of seawater, a thorough study of its thermal and chemical interaction with the ocean remains very difficult Until 1990 (the end of the period covered by the last IUGG report), literally all of our understanding of the dynamics of magmatic accretion on the mid‐ocean ridge was based on inferences from (1) geochemical, geophysical, and morphologic studies of long sections of the ridge using a variety of instruments mounted on ships' hulls or towed on long cables near the seafloor, and (2) submersible‐based mapping and sampling of small sections of the ridge, particularly hydrothermally active ones. These types of studies have continued to flourish [Parmentier, 1995; Humprhis, 1995], but the past 4 years have also seen the first near‐real‐time observations of accretion events on two Pacific spreading centers and the development of technology and techniques that can monitor the occurrence and extent of such events over a selected portion of the ridge system. These monitoring capabilities allow interdisciplinary studies of seafloor hydrothermal systems so that the thermal and chemical effects of hydrothermal venting on the oceans can be assessed.
Volcanic eruptions, prediction, hazard assessment, remote sensing, and societal implications
Authors: Self Stephen , Mouginis‐Mark Peter J.
Published: February 2004

In volcanology, the period 1991–1994 was very busy, with many active volcanoes keeping pace with the higher‐than‐average frequency of eruptions (about 60–70 per year) recorded during the late 1970's to the late 1980's (Simkin, 1993). Some large and violent eruptions occurred in well populated areas but these passed without the higher death tolls caused by eruptions in the previous decade, a reflection perhaps of increased volcanic hazard awareness, improved prediction and monitoring, and better communication between volcanologists and public officials (Peterson and Tilling, 1993). The loss of human life was limited to a little over 1000, with perhaps ∼750 of these attributable to the Mount Pinatubo eruption on Luzon in the Philippines. Many were killed by post‐eruption phenomena, such as mudflows, and by disease in the displaced populations. This large eruption, which had a world‐wide atmospheric impact, dominates the picture of volcanism in the early 1990's. However, significant eruptions also occurred at Hudson, Unzen, Spurr, Redoubt, Hekla, Mayon, Galeras, Rabaul, Kliuchevskoi, Etna (the most voluminous lava outpourings this century), and many other volcanoes. Here we assess the current state of volcano monitoring and hazard awareness against a backdrop of the eruptions of the past four years, and take a look at future developments, stressing new techniques in the field of remote sensing.
Progress in planned weather modification research: 1991–1994
Authors: Czys Robert R.
Published: February 2004

This quadrennial marked progress in understanding basic cloud processes under natural and seeded conditions, development of conceptual models, and application of advanced computer cloud models and instrumentation. Conceptual models were revised so that effects on the scale of cloud particles, precipitation processes, and cloud development no longer are artificially distinguished from one another; for example hail suppression and precipitation enhancements are now viewed as possible concurrent effects from seeding. Transport and dispersion studies using tracers have begun to show the path of seeding material and have allowed documentation of physical effects. Application of two‐ and three‐dimensional computer cloud models have helped to explain some results, to guide field operations, and to suggest further work. Instrumentation such as microwave radiometers and lidars have been used to document the spatial and temporal structure of supercooled liquid water.
Global seismic tomography of the mantle
Authors: Dziewonski Adam M.
Published: February 2004

At the end of the previous decade, a general consensus has developed that it is feasible to map on the global scale some of the largest scale 3‐D features in the Earth's deep interior and that such mapping may have fundamental significance for our understanding of the geodynamic processes, such as the flow in the mantle. General reviews of the state‐of‐the‐art for that period can be found in Dziewonski and Woodhouse [1987], Woodhouse and Dziewonski [1989] and Romanowicz [1991].

In the first four years of the 1990's, significant progress has been achieved on several fronts. One of these is introduction of the new class of data: travel times measured from the long period components of digital seismograms. These data are much more accurate than, for example, those reported by the ISC, and geophysically important patterns could be detected without inversion.
Diagenesis and reservoir quality prediction
Authors: Summa Lori L.
Published: February 2004

The modern concept of ”diagenesis“ was introduced by Walther one hundred years ago to encompass the postdepositional processes that affect sediments from deposition to low‐grade metamorphism. Since Walther (1893), diagenetic studies have been concerned with an extraordinary variety of chemical and physical interactions, each of which has the potential to significantly affect the final composition and texture of a sedimentary rock. The issues to which those studies have been applied are equally varied and include: (1) improved techniques to predict the producibility of hydrocarbon reservoirs, (2) improved techniques to predict subsurface fluid pressures, (3) better constraints on the timing of fluid flow events, (4) reconstruction of global climate change, and (5) evaluation of groundwater contamination. Commercial applications of diagenetic studies have traditionally focused on the producibility of hydrocarbon reservoirs. As such, a review of this topic serves as an effective illustration of how basic research has been commercialized, and a useful focus for the following dicussion. However, it is worth noting that decreased industrial research funding, coupled with increased government funding for environmental research have recently resulted in a gradual evolution of diagenetic publications away from the producibility of hydrocarbon reservoirs toward the producibility of uncontaminated groundwater and other environmental issues. Despite the shift in emphasis, many of the basic research issues remain unchanged whether one is focused on deep hydrocarbon reservoirs or shallow aquifers.
An introduction to the Space Physics and Aeronomy reports
Authors: Siscoe George
Published: February 2004

This quadrennium's IUGG reports serve an expanded purpose. Past reports principally recorded the progress of four years of research in discipline areas, and did so comprehensively. They chronicled advances, demises, and emergent new directions. They systematically arranged and related the content of research findings, which are otherwise spread at random over hundreds of journal articles. They provided encyclopedic coverage of current research, which benefitted the seasoned professional hunting a reference, the new profession al expanding her familiarity with the field, the professional wanting a quick up date on work in a neighboring field, and the historian mapping the content and context of research viewed from the working level. They told what happened, when it happened, who did it, and how it relates to other happenings. They were written from the working level scientist to the working level scientist. And they succeeded superbly.
Review of atmospheric radiation: 1991–1994
Authors: Stephens Graeme L.
Published: February 2004

It is appropriate to think of the discipline of atmospheric radiation as one of the building block subjects of the atmospheric sciences linking the fields of chemistry, aerosol and cloud physics, thermodynamics to global climate and climate change. A convenient way to think of the research of this discipline is to consider it divided into two broad but not necessarily distinct categories—one that seeks to understand how the interactions between radiation and the atmosphere determine the distribution of radiant energy on all scales and a second that attempts to exploit such an understanding, mostly as they apply on the smaller scale, to form the basis for most of the remote sensing methods currently used to observe the atmosphere. The first line of enquiry provides the fundamental understanding of the radiative forcing of climate, for example, and significant advances in our understanding of this forcing have emerged over the last few years. Perhaps even more activity has been invested in the second area of research especially with the emerging era of the Earth Observing System (EOS) [e.g., King et al., 1992]. Remote sensing has also become a tool in climate research over the last few years with the application of satellite data in studies of fundamental climate processes.
Understanding and predicting ENSO
Authors: Battisti D. S. , Sarachik E. S.
Published: February 2004

Throughout the 1960's and 1970's, oceanographers referred to the large‐scale warming of the equatorial eastern and central Pacific as El Niño. This anomalous warming was later shown to be associated with anomalies in the upper ocean thermal structure throughout the equatorial Pacific Ocean. At about the same time, scientists realized that the Southern Oscillation was intimately related to the large‐scale changes in the tropical Pacific Ocean. In brief, the Southern Oscillation represents the variability in the Indo‐Pacific Walker circulation in the tropics, and is manifest as a displacement of the convection over the maritime continent, and is associated with large‐scale anomalies in the surface wind and sea level pressure throughout the tropical Pacific (and into the Indian Ocean) basin.
Properties of the papers on the properties of the solid Earth
Authors: Verosub Kenneth L.
Published: February 2004

The continuing Congressional assault on the Federal budget jeopardizes some, if not all, of the funding that supports the research described in the IUGG Quadrennial Report. For this reason, it is imperative that geophysicists come out of their labs and away from their computers to consider broader questions about the place of geophysical research in the national science agenda and in American society. As editor of the section of the IUGG Quadrennial Report on the properties of the solid earth, I have had to read every paper in this section at least once. Although these papers nominally represent only one‐sixth of the geophysical research done in the United States during the past four years, I believe they are a microcosm of the problems and challenges that face the entire profession. What follows is my interpretation of what these papers say about the nature of the scientific endeavor in geophysics and its health and well‐being (or lack thereof).
Submarine landslides
Authors: Hampton Monty A. , Lee Homa J. , Locat Jacques
Published: February 2004

Landslides are common on inclined areas of the seafloor, particularly in environments where weak geologic materials such as rapidly deposited, fine‐grained sediment or fractured rock are subjected to strong environmental stresses such as earthquakes, large storm waves, and high internal pore pressures. Submarine landslides can involve huge amounts of material and can move great distances: slide volumes as large as 20,000 km³ and runout distances in excess of 140 km have been reported. They occur at locations where the downslope component of stress exceeds the resisting stress, causing movement along one or several concave to planar rupture surfaces. Some recent slides that originated nearshore and retrogressed back across the shoreline were conspicuous by their direct impact on human life and activities. Most known slides, however, occurred far from land in prehistoric time and were discovered by noting distinct to subtle characteristics, such as headwall scarps and displaced sediment or rock masses, on acoustic‐reflection profiles and side‐scan sonar images. Submarine landslides can be analyzed using the same mechanics principles as are used for occurrences on land. However, some loading mechanisms are unique, for example, storm waves, and some, such as earthquakes, can have greater impact. The potential for limited‐deformation landslides to transform into sediment flows that can travel exceedingly long distances is related to the density of the slope‐forming material and the amount of shear strength that is lost when the slope fails.
Extended period frequency domain interferometry observations at stratospheric and tropospheric heights
Authors: Kilburn C. , Fukao S. , Yamamoto M.
Published: February 2004

Frequency domain interferometry (FDI) is a method for more accurately measuring the position and thickness of various refractive index structures, as compared to the measurements under normal MST radar operation. For this paper a 7‐hour data set has been collected and analyzed, forming a longer data set than previously used at stratospheric‐tropospheric heights. A technique for fixing the height measurements within each range gate to be absolute rather than relative is presented. Two types of structure are present in the data, referred to as “layers” and “blobs.” The layers have a thickness of around 50–100 m, are often aspect sensitive, last for many hours, and exhibit fine altitude variations, some oscillatory. One layer descending over the experiment appears to be positioned at the top edge of a frontal surface zone in the overall meteorological structure. The blobs are thicker regions of around 600 m, are not aspect sensitive, and are short‐lived.
Spaced antenna and interferometric velocity measurements with MF and VHF radars
Authors: Brown William O. J. , Fraser Grahame J. , Fukao Shoichiro , Yamamoto Mamoru
Published: February 2004

The spaced antenna and interferometry techniques are applied to data collected on two MF radars (at Christchurch, New Zealand, and at Scott Base, in the Antarctic) and one VHF radar (the MU radar at Shigaraki, Japan). Velocity results obtained by the two techniques are compared as functions of characteristics such as the temporal scale and anisotropy of the scatter. In general, there was good agreement between the two techniques; however, when the temporal scale is small (indicating turbulent scatter) there was less agreement. The interferometry technique did not appear to be influenced greatly by anisotropy in the scatter. The interferometry technique was found to be affected by averaging of the Doppler spectra and by the use of an extra receiver. It is suggested that less averaging of the spectra results in increased random noise components in the spectra, which in the phase spectra are interpreted as scattering from a greater range of zenith angles. It was found that the use of three receivers rather than four also lead to scattering that appeared to originate from a greater range of zenith angles. These effects lead to lower interferometric velocity estimates that are more biased towards full correlation analysis (FCA) true velocities.
Lidar studies of particles and temperatures of the atmosphere: First results from National Central University lidar
Authors: Nee J. B. , Wang G. B. , Lee P. C. , Lin S. B.
Published: February 2004

With a Rayleigh and Mie scattering lidar, installed at the Central University in Chung‐Li, Taiwan (25°N, 121°E), we studied the high clouds, aerosols, and temperatures of the atmosphere in the 15–60 km region since July, 1993. High clouds located near the tropopause were observed consistently. The clouds had stable structure and persisted for hours. One of the clouds presented had a height of 15.6 km and a thickness of 613 m. They were probably grown in the extremely cold environment of the tropical tropopause. The stratospheric aerosol layer has been found with structure which is caused by the dynamics of the tropical winds. Temperature measurements derived from Rayleigh scattering in the range 30–60 km have provided the temperature and height for the stratopause. The effect of temperature fluctuation on the chemical species is discussed.
Spatial interferometry measurements of polar mesosphere summer echoes with the EISCAT VHF radar
Authors: Alcala C. M. , Röttger J. , Kelley M. C.
Published: February 2004

Spatial domain interferometry is a useful technique for studying the dynamics of both the ionosphere and the neutral atmosphere. In the ionospheric case the scatterers are highly localized in space and can be tracked as they drift through the beam to determine the horizontal winds. However, in the atmospheric case the scatterers can fill most of the resolution volume of the radar. For the EISCAT VHF radar in Tromsø, Norway, with its single E‐W baseline, this volume scattering only allows determination of the trace velocity parallel to the baseline. With this limitation we have applied this technique at EISCAT to study the dynamics of the measosphre. On August 11, 1992, a thin sheet of strong scatterers during a polar mesospheric summer echo (PMSE) event, initially located at 83 km, was lifted upward by 300 m within a couple of minutes. The vertical velocity at this time, determined from the measured Doppler shifts, jumped from 2 m/s downward to more than 4 m/s upward. From the cross‐spectral analysis we also see a change in the direction of the zonal wind from westward to eastward during the discontinuity in the vertical velocity. The behavior of the two velocity components is qualitatively similar to the wind corner observations of Widdel and von Zahn (1990). We also consider the possibility that a solitary wave may cause this event, but conclude that there is no compelling evidence to support this explanation.
Indian MST radar 2. First scientific results in ST mode
Authors: Jain A. R. , Rao Y. Jaya , Rao P. B. , Anandan V. K. , Damle S. H. , Balamuralidhar P. , Kulakarni Anil , Viswanathan G.
Published: February 2004

Clear air radars operating in the VHF range provide excellent information on middle atmospheric structure and dynamics with fine height and time resolutions. One such radar is installed at Gadanki, a tropical station in India. Experiments were carried out using the ST mode of this newly established MST radar to study the atmospheric wind field, characteristics of atmospheric stable layers, and clear air turbulence over this tropical station. Atmospheric stable layers are observed at various heights in the troposphere and lower stratosphere. Multilayer structures are observed near the tropopause and in the lower stratosphere. The range‐time‐intensity (RTI) maps for the zenith beam show that once these structures are formed, they are seen to last for more than an hour, indicating their large horizontal extent. The model computations of radar signal‐to‐noise ratio (SNR) for zenith beam, using simultaneous radiosonde observations taken at Madras, show a gross agreement with the observed SNR. However, the model SNR profiles do not show the fine structure observed by the radar, the limitation of the model profiles being the lower height resolution of the radiosonde measurements. The refractivity turbulence structure constant C2n is determined using SNR for 20° off‐zenith beams pointed in east, west, north, and south directions. Profiles of C2n for the four oblique beams are found to agree within 10 dB, indicating that the intensity of the turbulence for the same range bin, within the volume scanned by the radar, is the same. The parameter C2n is also computed using meteorological parameters and compared with radar C2n. The observed and model C2n profiles are found to agree within 5 dB. Radar C2n profiles are found to show large diurnal and day‐to‐day variability. The results of an experiment conducted to determine the effect of transmitted pulse length on the received signal spectral width show that the wind shear effect is important for oblique beams and for longer pulse lengths, where as the beam‐broadening effect is important for both oblique and vertical beams for all pulse lengths. Various turbulence parameters are determined using the observed spectral width after correcting for these effects.
Observations of the planetary boundary layer over equatorial Indonesia with an L band clear‐air Doppler radar: Initial results
Authors: Hashiguchi Hiroyuki , Fukao Shoichiro , Tsuda Toshitaka , Yamanaka Manabu D. , Tobing Daniel L. , Sribimawati Tien , Harijono Sri Woro B. , Wiryosumarto Harsono
Published: February 2004

An L band (1357.5 MHz) boundary layer radar (BLR) has been in continuous successful operation in Serpong, Indonesia (6.4°S, 106.7°E), since November 1992. The performance of the BLR with respect to the observation height range and the wind measurement reliability has been examined on the basis of simultaneous meteorological observations. We have found that there are two types of strong echo structures appearing systematically in the equatorial planetary boundary layer with diurnal variations on clear days. The first type is the striking appearance of a strong echo layer ascending from below 300 m (in the morning) to above 3–5 km (in the afternoon), which is identified with a diurnal variation of the top of the mixing planetary boundary layer. As expected, it is higher in the Indonesian equatorial region than in midlatitudes. Another type is layered echoes appearing at 2–3 km heights from nighttime to morning, which seem to be coincident with humidity gaps.
The new Adelaide medium frequency Doppler radar
Authors: Reid I. M. , Vandepeer B. G. W. , Dillon S. C. , Fuller B. M.
Published: February 2004

The Buckland Park Aerial Array (35°S, 138°E) is situated about 40 km north of Adelaide, Australia, on a flat coastal plain. It was designed by B. Briggs with assistance from G. Elford and constructed between 1965 and 1968. The first results were published in the late 1960s (Briggs and Elford, 1968; Briggs et al., 1969). Since then some 250 papers have been published using data from the array. Some aspects of the history of the array are described by Briggs (1993). A new medium frequency (MF) Doppler radar utilizing the array has been developed, and this paper describes some of the technical details of this new facility.
Some preliminary results obtained with the new Adelaide MF Doppler radar
Authors: Vandepeer Brenton G. W. , Reid Iain M.
Published: February 2004

A portion of the large Adelaide MF/HF antenna array has been used in conjunction with a new, 25 kW solid‐state transmitter to conduct electronic beam‐steering experiments. Thirty of the array's refurbished, independently phased antennas were connected to the 10 power amplification (PA) modules in groups of three to form a steerable beam with a one‐way half‐power half width of 5°. Phase propagation errors in the receivers were determined and used to enable accurate direction‐finding and interferometric studies to be conducted. In this paper, new methods of determining the aspect sensitivity of backscatter and the three‐dimensional linear wind field in the mesosphere and lower thermosphere (60–100 km) are introduced.
Reflection from a lossy chiral slab (with and without metallic backing) in a parallel plate waveguide
Authors: Mariotte Frédéric , Engheta Nader
Published: February 2004

In this paper we analyze theoretically the problem of reflection of guided transverse electromagnetic (TEM) mode from a lossy chiral layer located transversely in a parallel plate waveguide. We consider two cases: one where the lossy chiral slab is there by itself (without metallic backing) and the front and the back of the slab are free space regions in the waveguide; and the other where the lossy slab is backed by a perfect conductor. The effects of various parameters, particularly the loss and the chirality of the layer, on the reflected guided waves are discussed and physical insights given. This problem may offer potential applications in the design of novel thin chiral shields and absorbers in waveguides and cavities and also for the study of measurement techniques to obtain material parameters of chiral composites.
The true‐height analysis of ionograms using simplified numerical procedures
Authors: Tsai L.‐C. , Berkey F. T. , Stiles G. S.
Published: February 2004

In this paper a numerical integration method termed “μ't fitting” for application to the true‐height analysis of digitally recorded ionograms is introduced. This method can be used to analyze either the O or X waves in an ionogram and includes the effect of the Earth's magnetic field. For the second order polynomial profile analysis the μ't fitting technique utilizes 38–62% fewer numerical operations than the Gaussian quadrature integration method. Applying 5‐ (12‐) term μ' t fitting to 100 data points, the method completes a true‐height analysis in 0.77 (1.43) s, using an 80486/33 computer system. Furthermore, applying this technique to the overlapping Chapman model profile adopted by Union Radio Scientifique Internationale (URSI) Working Group G.6.2 (McNamara and Titheridge, 1977) yields rms errors of 8.3 and 7.0 meters for the O and X wave components (12‐term μ't fitting), over a set of 22 selected frequencies.
The dielectric half space as a test bed for transform methods
Authors: Grzesik J. A. , Lee S. C.
Published: February 2004

The canonical, Fresnel problem, involving normal wave incidence upon a dielectric half space, is rephrased as an elementary Fredholm integral equation conveying the global viewpoint of radiative self‐consistency. This equation is of course well‐known, but we proceed here to exploit its simple features so as to demonstrate the complementary performance of several techniques that are part of the standard mathematical repertoire in electromagnetics. The techniques utilized are (1) mode matching through global self‐consistency; (2) Laplace transformation; and (3) Fourier transformation as reinforced by analyticity arguments of the Wiener‐Hopf type in the transform plane. All three methods naturally succeed in recovering the reflection/transmission solution gotten by the usual procedure of enforcing tangential electric/magnetic field continuity at the dielectric interface. Such benchmark success in so controlled a setting would seem to vindicate the individual power of these independent, popular methods.
Solution of impedance matrix localization form of moment method problems in five iterations
Authors: Canning Francis X.
Published: February 2004

The impedance matrix localization (IML) method replaces the usual full N × N moment method matrix by a sparse N × N matrix. Typically, this matrix has about 50N nonzero elements. Iterative methods require one (or a few) matrix vector product(s) at each iteration. Each product can be accomplished in 50N operations rather than N2 for the usual moment method. There is a correspondence between the clumps of large numbers in the IML matrix and terms with a ray description such as in geometrical optics and the geometrical theory of diffraction. It is known that using these methods approximate solutions are possible while taking into account only a limited number of multiple interactions. Using this analogy an approximate factored form of the IML matrix is generated by explicitly using only a limited number of direct interactions. However, all multiple interactions involving these direct interactions are (implicitly) taken into account. This effectively gives an approximate inverse which is used in an iterative approach. A reduction in the residual of orders of magnitude per iteration is achieved. The result is a more accurate solution than was possible before and which requires only a few iterations. This method is generally applicable since the factored form is based on the structure of the IML matrix and not on any specific geometry.
Ultrawideband, polarimetric radar studies of breaking waves at low grazing angles
Authors: Sletten Mark A. , Wu Jin
Published: February 2004

This paper summarizes the results of recent laboratory investigations into the ultrawideband, polarimetric scattering properties of breaking water waves. Breaking waves were produced in a wave tank through chirped wave packets (0.5–1.0 Hz) generated by a programmable wavemaker. An ultrawideband radar system was then used to measure the polarimetric properties of the breakers over the 6–12‐GHz band at a grazing angle of 10°. An analysis of the data from these experiments shows interesting dynamics in and differences between the dominant VV and HH polarizations. In particular, the RF frequency responses of the orthogonally polarized signals differ substantially, and both the magnitudes as well as the relative phases can change appreciably over relatively short time intervals. A “bench top” model of a breaker is used to support the hypothesis that this behavior is due to the presence of small, nonlinear structures near the breaker crest and a “double‐bounce” scattering mechanism associated with them.
Parameterized ionospheric model: A global ionospheric parameterization based on first principles models
Authors: Daniell R. E. , Brown L. D. , Anderson D. N , Fox M. W. , Doherty P. H. , Decker D. T. , Sojka J. J. , Schunk R. W.
Published: February 2004

We describe a parameterized ionospheric model (PIM), a global model of theoretical ionospheric climatology based on diurnally reproducible runs of four physics based numerical models of the ionosphere. The four numerical models, taken together, cover the E and F layers for all latitudes, longitudes, and local times. PIM consists of a semianalytic representation of diurnally reproducible runs of these models for low, moderate, and high levels of both solar and geomagnetic activity and for June and December solstice and March equinox conditions. PIM produces output in several user selectable formats including global or regional latitude/longitude grids (in either geographic or geomagnetic coordinates), a set of user specified points (which could lie along a satellite orbital path), or an altitude/azimuth/elevation grid for a user‐specified location. The user selectable output variables include profile parameters (ƒ0F2, hmF2, total electron content, etc.), electron density profiles, and ion composition (O+, NO+, and O2+).
Spaced antenna analysis of atmospheric radar backscatter model data
Authors: Holdsworth David A. , Reid Iain M.
Published: February 2004

A simple computer model of atmospheric radar backscatter is used to investigate and compare various spaced antenna (SA) techniques, including the full correlation analysis (FCA) and a number of imaging interferometry techniques. The results illustrate that the FCA true velocity proves to be an excellent estimate of the model input velocity for all magnitudes of model turbulent motions. On the other hand, the interferometric velocities increase as the magnitude of the turbulent motions are increased, providing a poor estimate of the model input velocity for large turbulent motion magnitudes. Maps illustrating the interferometry‐estimated scattering positions superimposed upon the actual model scatterer positions reveal the estimated positions to be inaccurate. The estimated positions are shown to approach the zenith as the magnitude of the turbulent motions increases, confirming the volume scatter derived suggestions of Briggs (1995). Furthermore, the estimated positions have a preferred azimuth angle agreeing with volume scatter derived suggestions. The effects of receiver noise upon the interferometric techniques are investigated, revealing an effect analogous to the FCA triangle size effect whereby the estimated velocity decreases with increasing noise level. The effects of the thresholds used to preclude individual Doppler frequencies from the analyses are illustrated. The results are in excellent agreement with the experimental results obtained in a number of different studies.
VHF/UHF wave attenuation in a city with regularly spaced buildings
Authors: Blaunstein N. , Levin M.
Published: February 2004

In this work a theoretical and experimental investigation analyzing VHF/UHF radio wave propagation in a suburban environment with a grid‐type street plan is presented for the purpose of personal communication services prediction. A waveguide with randomly distributed gaps (slits) between the sides of buildings is considered as a model of straight streets with two‐ and three‐story buildings. The average field intensity and path loss at the street level, taking into account the reflection from the ground, multireflection, and diffraction from the walls and building edges, are investigated in line‐of‐sight (LOS) conditions using a new three‐dimensional multislit waveguide model. This model gives good agreement with the two‐rays model and with an experimentally found law of field intensity attenuation at the street level with high and low building density up to 1–2 km from the source.
Generalized impedance boundary conditions and model of a point conductor
Authors: Ljalinov M. A.
Published: February 2004

The presence of derivatives of high order in generalized impedance boundary conditions (GIBCs) makes possible the simulation of point defects or point conductors placed on a surface. In case of the second‐order GIBC, the model of a point conductor is formulated via appropriate contact condition. For a plane boundary the problem of diffraction by a point defect is accurately solvable. A scattering diagram for an arbitrary point conductor is computed. The resulting formula depends on relative Wiener capacity, which is an integral characteristic of a two‐dimensional scatterer. The problem of diffraction by a periodic set of point conductors on a plane surface is solved in a closed form.
Traveling ionospheric disturbance diagnostics using HF signal trajectory parameter variations
Authors: Beley Vasily S. , Galushko Vladimir G. , Yampolski Yuri M.
Published: February 2004

In the model of a perfectly reflecting surface the inverse problem of restoring dynamic and statistical parameters of traveling ionospheric disturbances (TIDs) from variations of angles of arrival and Doppler frequency shift of HF radio signals on one‐hop oblique radio paths is solved. The technique for determining dispersion law, fluctuation spectrum, geometry, direction, and velocity of TID motion is described.
Modeling of radio emissions from Neptune
Authors: Menietti J. D. , Curran D. B.
Published: February 2004

We have developed a plasma model of the Neptunian magnetosphere that includes a density cavity centered on the L = 6 magnetic field line. Assuming the O8 magnetic field model, we have performed ray tracing of smooth radio emission from Neptune, and the results generally support the findings of Ladreiter et al. (1991), but differ in details of the source locations. In addition, we have examined source locations of bursty radio emission that are consistent with propagation at small wave normal angles as hypothesized for the temperature anisotropic beam instability (TABI) (Winglee et al., 1992). The source locations are adjacent (complementary) to the sources of the smooth radio emission. Using previously developed plasma and magnetic field models for Uranus, we have performed a similar study of bursty radio emissions. Again the source locations appear to be adjacent to the source regions of smooth radio emission, consistent with the TABI.
Comparative study of acceleration techniques for integrals and series in electromagnetic problems
Authors: Kinayman Noyan , Aksun M. I.
Published: February 2004

Most electromagnetic problems can be reduced to either integrating oscillatory integrals or summing up complex series. However, limits of the integrals and the series usually extend to infinity, and, in addition, they may be slowly convergent. Therefore numerically efficient techniques for evaluating the integrals or for calculating the sum of an infinite series have to be used to make the numerical solution feasible and attractive. In the literature there are a wide range of applications of such methods to various EM problems. In this paper our main aim is to critically examine the popular series transformation (acceleration) methods which are used in electromagnetic problems and to introduce a new acceleration technique for integrals involving Bessel functions and sinusoidal functions.
Scattering of a modulated pulse by a circular cylinder with longitudinal slots: Reaction in the cylinder
Authors: Hosono Hiroyuki
Published: February 2004

Transient response from a cylinder with longitudinal slots is more complicated than that from a perfect cylinder because the electromagnetic waves are reflected from various parts of the slotted cylinder: exterior surfaces, interior surfaces, and edges. We gave the numerical analysis for E‐polarized and H‐polarized cases by combining the modified point matching method (MPMM) with the fast inversion of Laplace transform method (FILT). Numerical results for the inner field are presented and discussed. The physical meaning of the transient waveform is discussed in detail. Also, the precision of the analysis is checked carefully.
Weighted imaging Doppler interferometry
Authors: Palmer R. D. , Lei K. Y. , Fukao S. , Yamamoto M. , Nakamura T.
Published: February 2004

Development of a simplified, multiple‐receiver, wind estimation scheme is presented. The new algorithm is a modification of the three‐receiver, imaging Doppler interferometry (IDI3) technique, which estimates the location of scattering centers and their corresponding radial velocities. Using the estimated location of the scattering centers, a solution for the three components of the wind vector is obtained. The modification presented is based on a weighted least squares solution of the radial velocity equation. Many IDI3‐like analyses are hampered by the use of a threshold that determines whether a scattering center is “good” or “bad.” Using the weighted least squares solution simplifies the IDI3 procedure by eliminating the need for a threshold. It should be noted that the results obtained by IDI3 are extremely sensitive to the thresholding scheme used. In addition to eliminating the need for the thresholding procedure, the new algorithm greatly reduces the measurement variance in the horizontal wind estimates. Data collected from the Middle and Upper (MU) Atmosphere radar are used to substantiate the technique.
On the minimum ground‐based observable frequency of the Jovian decametric emission imposed by the terrestrial ionosphere
Authors: Litvinenko G. V. , Rucker H. O. , Ladreiter H. P.
Published: February 2004

For experimental observation of the Jovian decametric emission, it is important to know the low‐frequency limit of the received radiation, which depends on the Jovian elevation (angular position from the local horizon) and the ionospheric electron density distribution. We develop the corresponding analysis and present results for different Jovian positions and different models of the ionospheric electron density profile. This consideration is of special interest for the periods 1993 to 1997 and also 2005 to 2009, years for low Jovian positions observed from northern hemisphere observatories where Jupiter is in the southern hemisphere in the celestial equatorial coordinate system. For several ionospheric models we determine the using range which depends on the Jovian elevations. By the use of empirical ionospheric models from Feichter and Leitinger, [1990, 1993] of the total electron content (TEC) from which an electron density maximum can be derived, we found that the solar activity highly influences the electron peak density which, in turn, acts on the low‐frequency limit of the detectable Jovian decametric emission from ground‐based observatories.
Ionospheric predictions for South American latitudes
Authors: Ezquer R. G. , Oviedo R. del V. , Jadur C. A.
Published: February 2004

Experimental values of the critical frequencies of the ionosphere (ƒ0E,ƒ0F1 and ƒ0F2) obtained at South American stations for different solar conditions and seasons are used to check the validity of the international reference ionosphere model to predict these ionospheric variables in this region. The results obtained show that, in general, for ƒ0E and ƒ0F1 there is good agreement between the predicted and experimental values when compared. The model predicts ƒ0F1 for periods when F1 was not present. The degree of accuracy among experimental and predicted ƒ0F2 values is lower than those observed for the other characteristics, and cases with strong disagreement are observed. It is shown that in some cases a large error would be produced if the predictedƒ0F2 is used as an input to a total electron content model.
Late orogenic extension of the Betic Cordillera and the Alboran Domain: A lithospheric view
Authors: Vissers R. L. M. , Platt J. P. , van der Wal D.
Published: February 2004

The Betic Cordillera of southern Spain provides a clear example of a collisional orogen that has undergone large‐scale extensional collapse while convergent motion of the bounding plates continued. Extension was accommodated by coeval shortening in thin‐skinned fold and thrust belts around the periphery of the system, and much of the region has now subsided to form a large marine basin. The thermal and deformational record of these processes is preserved in rocks from the upper mantle, crystalline crust, and sedimentary cover. Upper mantle peridotites record evidence for exhumation in several stages from asthenospheric depths to the surface. Early stages of exhumation probably occurred during Mesozoic rifting. Cooling at midlithospheric depths reflects continental convergence, and subsequent heating indicates loss of most of the underlying lithosphere and ascent of asthenosphere, whilst the final stages of exhumation in early Miocene time reflect extensional collapse. Crustal rocks in the internal zone of the Betic Cordillera were metamorphosed down to 50 km depth and are now exposed beneath major low‐angle normal detachment zones that separate them from heavily faulted low‐grade rocks above. Cooling ages of associated mylonites indicate that these detachments were active during the early to middle Miocene. Fault‐bounded intramontane basins, developed during the early to middle Miocene, contain coarse continental sediments heavily affected by normal fault systems, followed by a less deformed late Miocene marine succession. All of these phenomena can be explained by convective removal of the lithospheric root beneath a Paleogene collisional orogen, leading to large‐scale extension followed by thermal subsidence of the center of the system.
Thermo‐mechanical modeling of the Tyrrhenian Sea: Lithospheric necking and kinematics of rifting
Authors: Spadini Giacomo , Cloetingh Sierd , Bertotti Giovanni
Published: February 2004

We present the results of quantitative forward modeling of the Sardinian rifted margin of the Tyrrhenian Sea. The purpose of this study is to investigate the thermo‐mechanical structure that affects the thinning of the lithosphere across the margin. The role of lithospheric necking during basin formation, constrained by basement topography, Moho depth, and gravity anomalies, is modeled for different compensation models. Independent constraints are obtained from the analysis of the predicted thermal structure. A deep level of necking (25 km) is required to explain the observed crustal geometries and gravity anomaly signature. The model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning. Prerift lithospheric conditions, strain rate, and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the Tyrrhenian Sea. A forward model for basin stratigraphy is presented for the polyphase history of the Tyrrhenian rifting. This model provides quantitative estimates of time‐space dependent crustal thinning and rates of extension.