bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of the Earth: Oceanic crust and uppermost mantle
Authors: Orcutt John A.
Published: February 2008

The past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere. The application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere. Borehole seismic instrumentation has become more widely employed; ocean bottom seismographs, while generally decreasing in number, have become significantly more reliable and useful; and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes. The techniques available for the analysis of seismic data have become more sophisticated. Waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models, and travel time data are regularly inverted directly for structure. Trial and error modeling has become increasingly unimportant. Marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere. This has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves.
Cycles, steps and CO2: Paleoceanography in the United States from 1983–1986
Authors: Sancetta Constance
Published: February 2008

The field of paleoceanography experienced continued growth during the last three years. The First International Conference on Paleoceanography was held in Zürich, Switzerland, in July 1983, and a new journal devoted to the topic (Paleoceanography, American Geophysical Union, Washington, D. C.) began publication in spring 1986, edited by Dr. James Kennett of the University of Rhode Island. Nine legs of the R/V Glomar Challenger concentrated upon paleoceanographic topics: Legs 71–75 in the South Atlantic, Leg 81 in the North Atlantic, Leg 85 in the equatorial Pacific, Leg 86 in the northwest Pacific, and Leg 90 in the southwest Pacific. Several special symposia and conferences resulted in volumes of collected papers, dealing with topics such as climate variability [Hansen and Takahashi, 1984], the global carbon cycle [Sundquist and Broecker, 1985], catastrophes and earth history [Berggren and van Couvering, 1984], orbital insolation and periodicity [Berger et al., 1984], and coastal upwelling [Suess and Thiede, 1983]. Some very useful books have been published which summarize existing information on radiolaria [Anderson, 1983], Neogene planktonic foraminifera [Kennett and Srinivasan, 1983], calcareous nannofossils [Haq, 1983, 1984], and biostratigraphy [Bolli et al., 1983].
Advances in marine photochemistry 1983–1987
Authors: Zika Rod G.
Published: February 2008

The area of marine photochemistry has advanced dramatically during the last four years. The increase in meetings dedicated to the subject and in related publications is a clear sign of the growing interest and importance of the topic. The experimental approaches, mechanistic process description and quantitative estimation of photo‐processes have become far more sophisticated and detailed than before. A clearer recognition has emerged on the role and importance of photochemistry in affecting the biota, chemical speciation and degradation, and atmospheric sources.
A compendium of causes and effects of processes at transform faults and fracture zones
Authors: Kastens Kim A.
Published: February 2008

A flowchart has been constructed which consolidates into a single conceptual framework a large number of the phenomena and processes which have been observed or postulated at transform faults (TFs) and fracture zones (FZs). Oceanic ridge‐ridge transform faults and their aseismic extensions are emphasized. The upstream end of the flowchart contains large‐scale boundary conditions imposed by the position of a particular transform fault in space and time, for example, slip rate. The downstream end of the flowchart contains small‐scale features characteristic of individual TFs or FZs, for example, the existence of a FZ‐parallel ridge. Features of both the upstream and the downstream ends of the flowchart can be mapped, measured, or otherwise derived by direct observation. The middle of the flow chart includes processes and phenomena which are inferred to result from the upstream boundary conditions and to cause the downstream small‐scale features, for example, thermal conduction across the plate boundary. Phenomena in this “black box” in the center of the flowchart cannot be directly observed with present technology but must be inferred. The advantages of ordering knowledge into such a flowchart are that inconsistancies, gaps in understanding, self‐limiting phenomena (feedback loops), and previously unrecognized relationships stand out and that the boundary between inference and observation is clearly drawn.
Research results from Antarctic automatic weather stations
Authors: Stearns Charles R. , Wendler Gerd
Published: February 2008

Automatic weather station (AWS) units have been deployed in Antarctica since 1980 by the U.S. Antarctic Research Program. As of June 1987, 25 AWS units are operating in Antarctica in support of meteorological research. The AWS units measure air temperature, wind speed, and wind direction at a nominal height of 3 m above the surface and air pressure at the height of the electronics enclosure. Some AWS units measure relative humidity at 3 m and air temperature difference between 3 m and 0.5 m above the surface. Three to five values for each sensor are updated at 10‐min intervals and transmitted at 200‐s intervals to data collection systems on the NOAA series of polar‐orbiting satellites. The AWS units in Antarctica are sited to support research on katabatic winds, barrier winds, surface heat fluxes, and climate. Results from the katabatic wind experiment along a line upslope from the Adelie Coast show that the katabatic wind is stronger in winter than in summer and is strongest inland from the coast. The potential temperature difference from the south pole to the Adelie Coast has the largest negative value in winter, supporting the stronger katabatic winds. The katabatic flow down the glaciers of the Transantarctic Mountains to the Ross Ice Shelf requires synoptic support because the potential temperatures on the Ross Ice Shelf are lower than at higher elevations such as the south pole. Data from AWS sites on the Ross Ice Shelf along the Transantarctic Mountains generally have southerly monthly resultant wind directions along the mountains. Ross Island with its 3000‐m‐high volcanoes deflects the southerly wind flow, resulting in an easterly wind direction at McMurdo Station. AWS units equipped to measure vertical air temperature difference and relative humidity provide estimates of the latent and sensible heat flux on the Ross Ice Shelf. Generally, the sensible heat flux is negative, and the latent heat flux is small. The collection of the AWS data by a local user terminal at McMurdo Station makes possible the use of the AWS data to support air operations.
The terrestrial plasma source: A new perspective in solar‐terrestrial processes from Dynamics Explorer
Authors: Chappell Charles R.
Published: February 2008

The geospace environment has been viewed as a mixing bowl for plasmas of both solar and terrestrial origin. Our perspective on the nature of the supply mechanisms has undergone a radical evolution over the past decade, particularly during the 5 years of the Dynamics Explorer mission. During this period, the terrestrial source has increased in importance in both magnitude and character of ionospheric outflow. These outflows include the classical polar wind, the cleft ion fountain, the auroral ion fountain, and the polar cap. The Earth can be envisioned as a multifaceted fountain which ejects particles from different spatial locations spread around the globe. These particles exhibit a range of masses from 1 to 32 amu and a range of energies from 1 eV to 10 keV. The total flux of this ionospheric outflow is very large: adequate to supply the entire magnetospheric particle population. And the implications of the outflow are significant across a broad spectrum of solar‐terrestrial processes ranging from sources of magnetospheric plasmas, to influences on ionospheric density and temperature structure, to energy transfer in phenomena such as stable auroral red arcs. The Dynamics Explorer mission has made a major contribution in the characterization of the terrestrial plasma source.
Studies of ionospheric plasma and electrodynamics and their application to ionosphere‐magnetosphere coupling
Authors: Heelis R. A.
Published: February 2008

A brief description of the contributions of the Dynamics Explorer (DE) program to an understanding of ionospheric plasma dynamics is given. In addition to being used in some further study of small‐scale structure in the equatorial ionospheric number density, the DE 2 intrumentation has been extensively used to study the bulk motion of the plasma in the equatorial ionosphere. Variations in the east‐west plasma drift, at night as a function of magnetic flux tube apex height, show a decrease in magnitude with increasing height above the altitude of the peak F region concentration. The role of both E region and F region winds in producing this behavior and the differences between DE measurements taken at solar maximum and similar observations at solar minimum have been discussed. The work described here shows a general convergence of opinion about the behavior of the ionospheric convection pattern at high latitudes during periods of southward interplanetary magnetic field (IMF). Progress has been made in describing the magnetosphere‐solar wind interaction that may be involved in the production of the convection pattern. In particular, the expected magnetic field topology and the applicability of different convection drivers have been examined. The characteristics of the high‐latitude ionospheric plasma motion during periods of northward IMF have been extensively studied. Under such conditions the existence of small‐scale (1–10 km) and medium‐scale (10–200 km) structures in the electric field and plasma motion is quite evident. Its relationship to auroral forms and in particular to the theta aurora has been examined in some detail. The interpretation of larger‐scale electric field and plasma drift features in terms of closed loop convection trajectories and the applicability of different theoretical models to the data have also been discussed.
Chemistry of the rock‐forming silicates: Multiple‐chain, sheet, and framework structures
Authors: Papike J. J.
Published: February 2008

The crystal chemistry of 16 groups of multiple‐chain, sheet, and framework silicates is reviewed. Crystal structure drawings are presented to illustrate crystal chemical features necessary to interpret chemical data for each mineral group. The 16 silicate groups considered in this review are the amphibole; nonclassical, ordered pyriboles; mica; pyrophyllite‐talc; chlorite; greenalite; minnesotaite; stilpnomelane; prehnite; silica polymorphs; feldspar; nepheline‐kalsilite; leucite‐analcite; sodalite group; cancrinite group; and scapolite. Electron microprobe analyses should be augmented by independent determinations of Fe2+/Fe3+ and H2O for many of the silicate groups discussed and by determinations of CO32−, SO42−, S2−, and Li in some of the others. However, microprobe data augmented as suggested will still be ambiguous for some of the silicate groups considered here because the structures are not completely determined or are variable, with disparate domains and/or structural modulations, e.g., pyriboles, greenalite, minnesotaite, and stilpnomelane. Nevertheless, the most rigorous way to interpret silicate mineral chemical data is based on the crystal structures involved.
A review and comparative evaluation of multilevel boundary layer parameterizations for first‐order and turbulent kinetic energy closure schemes
Authors: Holt Teddy , Raman Sethu
Published: February 2008

Multilevel parameterizations of the atmospheric boundary layer using first‐order and turbulent kinetic energy (TKE) closure schemes are reviewed. Eleven schemes, chosen as representative of both first‐order and TKE closure, are then used for comparison in a one‐dimensional barotropic planetary boundary layer model. TKE closure schemes evaluated are the E‐ε schemes in which eddy viscosity Km is determined from turbulent kinetic energy and energy dissipation ε and the l model schemes in which Km is determined from TKE and mixing length l. Comparison of model simulations of mean and turbulence structure for first‐order closure and TKE closure schemes to observational data (MONEX79) is given. The two main conclusions drawn from this comparison are that (1) the mean structure of the boundary layer is fairly insensitive to the type of closure scheme, given that the scheme properly accounts for turbulent boundary layer mixing, and (2) TKE closure is preferable to first‐order closure in predicting the overall turbulence structure of the boundary layer. Among the TKE schemes compared in this paper, the modified Detering and Etling (1985) scheme is preferred.
Magnetospheric convection during quiet or moderately disturbed times
Authors: Caudal G. , Blanc M.
Published: February 2008

We review the main processes which contribute to the large‐scale plasma circulation in the environment of the Earth during quiet times or during reasonably stable magnetic conditions (when the concept of average pattern of plasma convection can make sense). Since field‐aligned currents are the way by which plasma motion perpendicular to the magnetic field is transmitted between the remote regions (solar wind, magnetosphere) and the ionosphere, we describe the processes driving plasma convection as processes generating field‐aligned currents. The electric field distribution will then result as a consequence of the coupling between the regions generating field‐aligned current and the circuit constituted by the ionospheric conducting layer. We discuss the effects of horizontal gradients of ionospheric conductivities on the resulting electric field distribution. As concerns the mechanisms which drive field‐aligned currents, the convective derivative of plasma flow vorticity, produced by the flow deceleration of the solar wind, is believed to be the main generator for region 1 currents, whereas the azimuthal pressure gradients within the region of closed field lines are believed, in the classical view, to be the main generators for region 2 currents. In turn, we recognize two kinds of sources for producing azimuthal pressure gradients in the region of closed field lines, and we illustrate them in the framework of linear theory. These are (1) the adiabatic distortion of the distribution of energetic trapped plasma from azimuthally symmetric distribution in the presence of an electric field and (2) particle losses undergone by the plasma while it is azimuthally convected.
Synchrotron‐based X ray absorption studies of cation environments in Earth materials
Authors: Brown Gordon E. , Parks George A.
Published: February 2008

Since its development in the early 1970s, synchrotron‐based X ray absorption spectroscopy (XAS) has proven to be a versatile structural probe for studying the local environments of cations in a variety of earth materials ranging from crystalline solids, silicate glasses, and high‐temperature silicate melts to aqueous sorption systems which involve metal complexes associated with (or sorbed at) mineral/water interfaces. The structural information provided by XAS includes average interatomic distances and the number and chemical identities of neighbors within 5–6 Å of a selected cation. In many cases (e.g., short‐range ordering of cations in minerals; cation environments in gels, glasses, melts, and metamict (radiation damaged) minerals; and the structure and composition of sorbed species at mineral/water interfaces), XAS provides unique structural data not duplicated by other methods. This paper presents a tutorial review of the physics underlying XAS and data analysis methods and a selective review of applications of XAS to earth materials.
Supercomputers and their use in modeling subsurface solute transport
Authors: Barry D. A.
Published: February 2008

Supercomputers offer a wide range of possibilities for advancing knowledge and solving difficult, real‐world problems. Solute transport‐related theory and applications have long been an area of specialization within hydrology. In this review, recent applications of supercomputers to solute transport problems are presented. These applications are based mostly on the assumption of a dilute solute, allowing the governing equations to be decoupled. An application of supercomputers is the simulation of solute transport in large heterogeneous spatial domains by both direct solution of the governing equations and by particle‐tracking methods. An impetus for this research has been the rapid increase in predictive dispersion models based on analytical stochastic theory. Up until now, relatively few applications have incorporated algorithms designed with a targeted supercomputer in mind, with the result that the machine's potential cannot be exploited fully. Since many numerical problems are reduced to solutions of algebraic systems when they are implemented on computers, algorithms for linear algebraic systems of equations suitable for vector and parallel machines are discussed in some detail. Data analysis, necessary both for evaluating emerging theories and for more “routine” applications like determining model parameters, is identified as another general area that is ably handled by supercomputers. In particular, supercomputers offer a way to become less dependent on parametric assumptions and constraints, substituting, instead, raw computational power. Visualization techniques and associated facilities have flourished alongside the development of supercomputer centers. These offer the possibility for real‐time viewing of solute transport processes, both real and simulated, although little has been produced thus far. It is expected that many more researchers involved with subsurface solute transport will make use of supercomputers in the future.
Multisite Observations of the VLF Transequatorial Propagation Anomaly
Authors: Lynn K. J. W.
Published: February 2008

Phase and amplitude records of 18.6‐kHz transmissions from NPG/NLK received at eight sites varying in distance from 4,360 to 13,420 km southwest of the transmitter, confirm the existence of a region within ±20° of the magnetic equator, in which VLF propagation parameters vary significantly from their midlatitude values. At all seven sites that involved transequatorial propagation paths, anomalies (including cycle slipping) were observed during the sunrise transition. The nature and temporal occurrence of these anomalies depended on the distance of the receiver from the magnetic equator. The experimentally derived dependence on magnetic latitude of the mode conversion ratio of the two least attenuated propagating modes and their apparent interference spacing are presented.
Transequatorial Reception of VLF Radio Waves From Australia
Authors: Araki Tohru , Kitayama Seishi , Kato Susumu
Published: February 2008

The phase and the field strength of VLF signals on 15.5 and 22.3 kHz from Australia have been observed in Japan, Some new features of the phase behavior during sunrise are pointed out, and the nighttime field strength relative to the daytime field strength is compared with results observed along another transequatorial path over the American continent.
Latitude Variation of the Lower Ionosphere
Authors: Mechtly E. A. , Rao M. Mukunda , Skaperdas D. O. , Smith L. G.
Published: February 2008

In March and April 1965 the University of Illinois and the GCA Corporation launched five Nike‐Apache rockets from the aircraft carrier U.S.N.S. Croatan as a part of the NASA Mobile Launch Expedition. As the Croatan followed the meridian at 78° west longitude along the west coast of South America, two rockets were launched at 13° south latitude (at the geomagnetic equator), one rocket at 30°S, one at 44°S, and one at 58°S. Launch times were chosen to correspond to a solar zenith angle of 60° at each of the four different latitudes. Each of the payloads carried a radio propagation experiment and a Langmuir probe for themeasurement of electron concentration and collision frequency in the lower ionosphere. Between 70 and 90 km, the electron concentration profiles at 13° and 58°S are nearly coincident, and the profiles at 30° and at 44°S are also nearly coincident. This pattern suggests a geomagnetic anomaly in the D region of the ionosphere comparable with the geomagnetic anomaly in the F region. From 90 to 150 km the profiles show no systematic differences.
The Equatorial Ionospheric Anomaly and the Equatorial Electrojet
Authors: MacDougall J. W.
Published: February 2008

It is shown that for the American zone the F‐region equatorial anomaly and the equatorial electrojet are highly correlated, whereas the anomaly and the Sq current system correlate poorly. A suggested explanation for the correlation is that the eastward electric field which drives the electrojet is also present in the F‐region and there causes upward plasma flow.
On Incomplete Airy Functions and Their Application to Diffraction Problems
Authors: Levey L. , Felsen L. B.
Published: February 2008

Several diffraction problems whose solutions involve incomplete Airy functions are briefly described; general and asymptotic characteristics of these functions are summarized. A uniform asymptotic representation, in which the incomplete Airy functions serve as canonical functions, is given for the class of integrals characterized by two saddle points arbitrarily positioned relative to an end point. Proceeding from an appropriate boundary‐layer expansion, the functions and their properties are applied in a detailed analysis of the fields near the point of confluence of the caustic of a converging wave and the shadow boundary resulting from the presence of an opaque obstacle.
Turbulence and Waves in a Stratified Atmosphere
Authors: Stewart R. W.
Published: February 2008

To distinguish rigorously between wave motion and turbulence in a stratified fluid seems impossible, although useful approximations seem feasible. The task is made more difficult by the fact that properties of turbulence are very little like those described in most theories of turbulence, even when the Reynolds number is quite high.
Waves and Turbulence in Stably Stratified Fluids
Authors: Bretherton F. P.
Published: February 2008

Following a review of recent advances in the general theory of wave motions, we suggest that Boltzmann's equation may be used to describe the propagation and interaction of packets of internal gravity waves in a stably stratified shear flow. The relationship of this picture of weakly interacting random waves to patches of clear air turbulence is examined.
Billow Mechanics
Authors: Scorer R. S.
Published: February 2008

Billows are the most common form of dynamic instability in the free air where the air is stably stratified. They occur mainly in layers where the static stability is much larger than average and therefore where there are already large gradients of temperature and humidity. They are produced predominantly by the tilting of these very stable layers in the wavy airflow produced by hills. The billows form a cat's‐eye pattern of motion that becomes statically unstable in the closed circulations. Consequently, the gradients inside are destroyed by the buoyancy‐induced mixing, and large gradients are produced at the boundary of the circulations. The original stable layer is thus replaced by two stable layers at a distance apart of the order of 5 times the depth of the original layer. During the overturning, large gradients of temperature are produced at the wavy boundary, which is itself corrugated by the internal mixing motions.
Remote Probing of the Moon by Infrared and Microwave Emissions and by Radar
Authors: Hagfors T.
Published: February 2008

The results of the remote probing of the moon by means of infrared and microwave emissions and by radar are reviewed. Also, we discuss how the various observational results can help to explain physical parameters of the lunar surface, such as thermal and electrical conductivities, dielectric constant, density, particle sizes in the lunar regolith, depth of the surface layer, roughness of the surface, variation of these parameters from point to point on the surface, and amount of heat generated in the lunar interior.
Radar Maps of the Moon at 70‐cm Wavelength and Their Interpretation
Authors: Thompson T. W. , Pollack J. B. , Campbell M. J. , O'Leary B. T.
Published: February 2008

Polarized and depolarized radar maps of the moon have been obtained at the Arecibo Ionospheric Observatory at a wavelength of 70 cm. These maps show strong positive anomalies, many of which are associated with young craters. These anomalies and the average diffuse component of radar echoes are attributed to the scattering behavior of surface and subsurface rocks. We have been able to approximately match the observed spatial and wavelength variation of the diffuse component, as well as the absolute value of its cross section, with theoretical calculations that use a Mie scattering description of the single scattering behavior of the rocks, and to employ the Surveyor spacecraft's determination of the size distribution of surface rocks. Furthermore, we have found that surface rocks appear capable of accounting for temperature anomalies (IR hot spots) which are associated with these craters.
Atmospheres of Mars and Venus: A Review of Mariner 4 and 5 and Venera 4 Experiments
Authors: Eshleman Von R.
Published: February 2008

Spacecraft measurements have revealed a hot, dense, CO2 atmosphere on Venus and a cold, thin, CO2 atmosphere on Mars. The surface pressure on Mars varies markedly with topographic elevation and probably with latitude and season. The lowest regions of the atmosphere of Venus have yet to be probed. Several thin micro wave‐absorbing cloud decks, perhaps consisting of water droplets or compounds of mercury, exist in the atmosphere of Venus. It may be possible to explain the ionospheres of Mars and Venus in terms of the photochemistry of CO2 and lighter trace elements plus the effects of the impinging solar wind.
The Mariner 1969 Occultation Measurements of the Upper Atmosphere of Mars
Authors: Fjeldbo Gunnar , Kliore Arvydas , Seidel Boris
Published: February 2008

Data from the Mariner 1969 radio occultation measurements are utilized to derive altitude profiles for the refractivity, the free electron number density, and the plasma temperature above the occultation points. Initial results indicate that the ionosphere was denser and warmer in 1969 than during the quiet solar conditions prevailing at the time of the Mariner 4 encounter with Mars in 1965. The dayside ionosphere consists of two layers with peak densities of the order of 7×104 and 1.7×105 electrons/cm3 at 110‐ and 135‐km altitude, respectively. Assuming that CO2+ is the principal ion in the main layer yields a topside plasma temperature of 400°—500°K. A marked change in the scale height near 250 km may reflect the transition to a lighter ion such as CO+ No clear signature of nighttime ionosphere was observed.
Dynamics of the Interaction of the Solar Wind With a Planetary Atmosphere
Authors: Cloutier Paul A.
Published: February 2008

Dynamics of the interaction of a magnetized supersonic plasma flow (solar wind) with a planetary ionosphere are examined. The flow behavior across a bow magnetohydrodynamic shock and in the post‐shock region, where the flow interacts with the planetary ionosphere, is analyzed. It is argued that the pressure balance between the solar wind and the post‐shock plasma is provided mainly by static gas pressure rather than by a large magnetic field ‘build‐up.’
Unacceptable Height Correlation Coefficients and the Quasi‐Specular Component in Rough Surface Scattering
Authors: Barrick D. E.
Published: February 2008

The purpose of this note is to put to rest once and for all the use of an erroneous result derived from the linear (or exponential) height correlation coefficient in the physical optics formulation of rough surface scatter. The form of the correlation coefficient near the origin must be quadratic so that the physical optics integral can be evaluated asymptotically. Hence, the theoretical shape of the quasi‐specular component for backscatter is not due to the nature of the correlation coefficient but to the form and behavior of the probability density function for the surface slopes evaluated for tilts near their mean values, the horizontal.
Interpretation of D‐Region Electron Densities
Authors: Sechrist C. F.
Published: February 2008

D‐region electron densities measured by rockets during the November 12, 1966, solar eclipse are shown to imply an effective recombination coefficient at an altitude of about 80 km of the order of 10−5 cm3 sec−1. The D‐region electron densities between 65 and 83 km are computed for full‐sun conditions assuming this value of recombination coefficient, the [37+] profile of Narcisi and Bailey [1965], and the NO profiles of Barth [1966], Pearce [1969], and Hesstvedt and Jansson [1969]. Electron densities between 60 and 65 km are estimated on the basis of the above‐mentioned NO profiles and the negative‐ion model of LeLevler and Branscomb [1968]. Also, electron densities between 80 and 90 km are computed by assuming an effective electron‐ion recombination coefficient for NO+ and O2+ of 10−6 cm3 sec−1. There is a reasonable agreement between the computed electron densities and those measured by rockets launched from Wallops Island near 60° solar zenith angle. These results suggest that variability of D‐region electron densities may be caused by changes in H2O vapor concentration induced by atmospheric circulation or eddy transport effects.
Ionospheric Storms at Midlatitudes
Authors: Mendillo M. , Papagiannis M. D. , Klobuchar J. A.
Published: February 2008

The total electron content of the ionosphere often responds in a dramatic way to increases in geomagnetic activity. By monitoring the VHF signals from the geostationary satellite ATS 3, it has been possible to study in detail the very pronounced increases in total content often found during the afternoon hours on the day of the commencement of a magnetic storm. Comparisons with magnetic field data show that the enhancements in electron content coincide with increases in the total magnetic field. This simultaneity suggests that, when the magnetosphere is compressed during the initial phase of a storm, the ionization stored in the magnetic tubes of force may be dumped into the topside of the F region. Such a depletion of the protonosphere is in agreement with whistler measurements, which indicate that a contraction of the plasmasphere occurs during periods of increased magnetic activity.
Measures of Beam Concentration for Scalar Radiation
Authors: Susman Leon , Kahn Walter K.
Published: February 2008

It is well known that, for radiating structures supporting scalar spherical modes of indexn≤N, the maximum obtainable directivity is limited to (N+1)2; the pattern functions for the corresponding arrangement of excitation coefficients are found in closed form. Alternate measures of beam concentration are formulated and optimum pattern functions are computed in closed form. These alternate measures, which are here called beam spread, depend on the entire radiation pattern (weighted by an appropriately chosen weight factor) and are reciprocal to the measures of directivity proposed by Synge (1966). The radiation patterns corresponding to optimizing the classical directivity and beam spread, with respect to a weight function (1 ‐ cos θ), are compared, and it is found that optimizing beam spread yields superior side‐lobe structure at the expense of a slight loss in directivity. The extension of these techniques to other weight functions is also explored.
An Analytical‐Numerical Approach to Analysis of Ionospheric Wave Propagation
Authors: Raemer Harold R. , Verma Yash Pal
Published: February 2008

The work discussed in the present paper was undertaken in response to difficulties experienced with numerical integration approaches. The technique involves the modeling of the medium as a set of horizontal strata in which the ambient gas parameters are ‘nearly’ constant, i.e., slowly varying. A perturbation theory allows us to take into account the slow vertical variation in a purely analytical way that is based on a knowledge of the system‐equation solutions for a homogeneous medium. The computer is used to find eigenvalues of the system matrix and to provide the numerical coefficients for the solution matrix, which is expressed analytically as a function ofz, the vertical distance coordinate. Illustrative numerical results are presented that show eigenvalues (corresponding to modes of propagation) and certain elements of the solution matrix for a typical ionospheric parameter regime.
Eigenvalues of Spheroidal Wave Functions and Their Branch Points for Complex Values of Propagation Constants
Authors: Oguchi Tomohiro
Published: February 2008

Eigenvalues of spheroidal wave functions are calculated as functions of complex propagation constants; they are displayed on a complex plane to form ‘eigenvalue charts.’ These charts show that the eigenvalues have many branch points in the complex planes of their arguments. The values of the branch points and the corresponding eigenvalues are then calculated exactly; a range of several points is shown in a table. These values are the universal constants; they are very important, because they are the basis for determining a complete set of spheroidal wave functions, they give the circle of convergence of the power‐series expansions of the eigenvalues, and they also aid in the discovery of domains in which the eigenvalues are obtained by either prolate or oblate asymptotic expansions.
HF Radar and Auroral Absorption
Authors: Agy Vaughn
Published: February 2008

A description is given of a method, based on riometer observations, for the calculation of auroral absorption of HF radio waves propagating over high‐latitude paths. Emphasis is on HF radar, but the method is appropriate for use in predicting circuit performance of high‐latitude HF communications. The assumptions made and the approximations used are stated explicitly so that, when better information becomes available, explicit corrections can be made. The calculations have been programmed for digital computer and the output for a given set of conditions consists of a map on which are shown contours of median auroral absorption of radio waves returned (by ground backscatter) to the radar site. For the present, only the points on the earth that are reached by one‐hop E‐layer and/or F‐layer propagation are considered.
Changes of Lower Ionosphere Electron Densities with Solar Zenith Angle
Authors: Mechtly E. A. , Smith L. G.
Published: February 2008

The University of Illinois and the GCA Corporation launched a series of four Nike Apache rockets from Wallops Island, Virginia, on July 24, 1968, for the study of changes of lower ionosphere electron densities with solar zenith angle on the same day. An improved method of data analysis is outlined. Profiles of electron density for each of the four rockets are presented and compared with two profiles from years of quiet sun, 1964 and 1965. Evidence is found for an initial increase of free electrons followed by a decrease and then an increase in electron number density as the solar zenith angle changes from 94° to 18°. This pattern suggests a sequence of processes; i.e., electron detachment, recombination, and photo‐ionization.
Study of Magnetospheric Field Oriented Irregularities—the Mode Theory of Bell‐Shaped Ducts
Authors: Scarabucci R. R. , Smith R. L.
Published: February 2008

The propagation of whistler energy in slight enhancements or depressions of ionization aligned with the geomagnetic field has been studied earlier in the two limiting cases of a discontinuous boundary or very slowly varying density gradients. These two approaches have yielded different results, particularly for the trapping of energy in enhancements of ionization. Therefore a study of the reflection and transmission for the full range of gradients is desirable. In this paper, full‐wave methods are applied to bell shaped ducts of arbitrary scale size. The results indicate criteria for applicability of the two simplifying limiting cases. This phase of the study is further extended by examination of a coupling theory. For a variety of magnetospheric conditions the cross‐coupling terms between characteristically different waves are negligible; this leads to almost perfect reflection and substantiates the use of the simpler phase‐integral techniques. By using the phase integral techniques, we have derived a fairly complete description of possible modes excited in bell shaped ducts. For each mode a theoretical whistler spectrogram is obtained. Extensions of the theory to apply to nonuniform magnetic fields may lead to predictions of a hyper‐fine whistler structure.
Tidal Winds at Ionospheric Heights
Authors: Richmond A. D.
Published: February 2008

Tidal winds excited by thermal or gravitational forces propagate into ionospheric altitudes and generate currents by dynamo action. The vertical and horizontal structure of these winds is altered by various dissipative forces which gain importance at these altitudes. In this paper, the dissipative effects of the Lorentz force, molecular viscosity, and molecular heat conductivity are considered in terms of a perturbation treatment. Both the rotation and the sphericity of the earth are explicitly taken into account. For propagating tidal modes, the dissipative effects are found to reduce and reverse the amplitude growth with height predicted by dissipationless tidal theory. Quantitative differences are obtained between the behavior of tides on a rotating earth and of internal gravity waves of comparable frequencies and vertical wavelengths on a non‐rotating earth.
On the Construction and Use of a Simple Ionospheric Model
Authors: Nisbet J. S.
Published: February 2008

The parameters controlling the development of a simple model of the E and F regions of the ionosphere are discussed. Uses of such models in scientific investigations and engineering applications are given. A computer model is described that will provide estimates of the electron and ion densities in middle latitudes as a function of latitude, longitude, altitude, season, time, and solar activity. Statistical parameters for midlatitude blanketing sporadic E are presented. An analytic expression is used for the CIRA 1965 neutral atmospheric models. The F1 region is treated using a photoequilibrium model with three ionic constituents and 62 ionizing radiation groups. The F2 layer uses theoretical models arranged to fit boundary conditions of NmF2, HmF2 and the electron density at 1000 km. Values of NmF2 are obtained by using the CCIR atlas of ionospheric characteristics. The midlatitude sporadic E layer is treated by presenting three parameters of the layer: the probability of observing sporadic E with a blanketing frequency greater than 0.5 MHz, the average peak electron density when sporadic E is observed, and the standard deviation (assuming log normal distributions for the peak electron density). The restrictions on the model and the availability of data on suitable boundary conditions are discussed. Suggestions for further development of models of the ionosphere are given.
A Study of the Geomagnetic Disturbance Field Asymmetry
Authors: Crooker Nancy Uss , Siscoe George L.
Published: February 2008

Hourly averages of the H component of the low‐latitude geomagnetic disturbance field are Fourier analyzed to obtain the amplitude G and local‐time phase ϕ of the first diurnal harmonic for the one and one‐half years of the IGY. The amplitude G is found to correlate roughly with the AE index and, in particular, to exhibit the same storm‐time behavior. For major storms, G can exceed 100γ and, in the example shown, exceeds 80γ for an interval of six hours. The phase ϕ tends to be located near 1800 LT, and this characteristic is nearly independent of AE. A comparison of the observed phase and that associated with the usual bay return current suggests a two‐component model of the disturbance field asymmetry, with one component at a non‐bay orientation. The non‐bay component is discussed in terms of possible ionospheric and magnetospheric currents. The second possibility seems to require currents located on the plasmapause to sustain the large forces involved in the asymmetry.
Theory of HF and VHF Propagation Across the Rough Sea, 2, Application to HF and VHF Propagation Above the Sea
Authors: Barrick Donald E.
Published: February 2008

This paper deals with an estimation of the effect of sea state on HF and VHF ground‐wave propagation loss across the ocean. For this estimation, an expression is employed that was derived in part 1; it gives the effective surface impedance in terms of the spatial height spectrum of the surface. Two empirical models are employed for the height spectrum of the ocean, the directional Neumann‐Pierson model and the isotropic Phillips wind‐wave model. These effective surface impedances accounting for sea state are then inserted into a standard ESSA computer program giving the basic transmission loss above a spherical earth. The dependence on sea state is plotted in curves which show the excess loss in decibels over a smooth sea. The propagation loss to points at various heights above the sea is also calculated. Normal sea state variations are seen to be negligible below about 2 MHz but produce a maximum excess loss at about 10 to 15 MHz.
Intertropical F2 Ionization During June and July 1966
Authors: Vila Paul
Published: February 2008

Detailed diurnal variations of F2 layer ionization in true heights have been obtained over the Tamanrasset meridian (5°S to 30°N) for 20 almost consecutive days in June and July 1966. Our improved time and latitude resolution in charting the evolution of the maximum ionization parameters, ƒ0F2 and hMF2, through the entire intertropical range made it possible for us to follow the movements of the two areas of greatest density known as ionization ‘crests’; their diurnal displacement on either side of the magnetic equator was found to differ from theoretical simulations, even those which take neutral wind into account. The asymmetry of their pattern in latitude and local time varies from one day to another much more than expected. The ‘summer’ side northern crest changes most; the maximum latitude extension of this crest varies in a complex manner with ap magnetic activity indices. Fast evolution phases, during early crest formation, and the deviation of the ionization structure from its expected ‘arch’ magnetic symmetry suggest a new type of low‐latitude transitory process.
Rocket Observations of Sporadic‐E Layers
Authors: Smith L. G. , Mechtly E. A.
Published: February 2008

The characteristics of midlatitude sporadic‐E layers are observed using rocket payloads incorporating a probe and a propagation experiment.Layers below 120 km show evidence of preferred altitudes. The slopes of layers are within 1° of horizontal. The horizontal dimensions are deduced to be several hundred kilometers. Individual profiles of daytime layers show a range of shapes ranging from triangular to rectangular. The plasma frequency derived from the peak electron density in the layer is found to agree with the blanketing frequency given by the local ionosphere sounder.
Excitation of Parametric Instabilities by Radio Waves in the Ionosphere
Authors: Fejer J. A. , Leer Egil
Published: February 2008

The excitation of parametric instabilities by radio waves in a magnetoplasma is discussed. A uniform medium is assumed and linear approximations are used. Excitation by a pump wave of ordinary polarization is hardly affected by the magnetic field. Low or zero frequency ion waves and high frequency Langmuir waves are excited simultaneously. For an extraordinary pump wave, the excited high frequency electrostatic waves are in the Bernstein mode. The threshold is slightly higher and excitation can occur only within certain ‘allowed’ frequency bands. A new type of parametric instability in which the excited waves are electromagnetic in nature and which is more strongly affected by the inhomogeneous nature of the medium is discussed qualitatively.
Radio Occultation Measurements of The Mars Atmosphere with Mariners 6 and 7
Authors: Hogan Joseph S. , Stewart Richard W. , Rasool S. I.
Published: February 2008

An analysis of the Mariner 6 and 7 occultation data has been completed. Final profiles of temperature, pressure, and electron density have been obtained for the Mariner 6 and 7 entry and exit cases, and results are presented for both the lower atmosphere and the ionosphere. The results of a detailed analysis of the systematic and formal errors introduced at each stage of the data reduction process are also included.

At all four occultation points, the lapse rate of temperature was subadiabatic up to altitudes in excess of 20 km. A pronounced temperature inversion was present above the surface at the Mariner 6 exit point. All four profiles exhibit a sharp, superadiabatic drop in temperature at high altitudes, with temperatures falling below the frost point of CO2. These results give a strong indication of frozen CO2in the middle atmosphere of Mars.

The analysis for the upper atmosphere indicates peak electron populations of 1.59±0.2×105cm−3near 137 km and 1.73±0.2×103cm−3near 138 km, at the Mariner 6 and 7 entry points, respectively. The plasma scale heights above these maxima were 43±6 and 47±4 km, corresponding to average topside temperatures of 388±54 and 424±35°K, for Mariner 6 and 7 entries, respectively.
Plasma Transport in the Equatorial F Region
Authors: McClure J. P. , Peterson V. L.
Published: February 2008

From simultaneous observations of vertical drift velocity and electron concentration near the dip equator, the photoionization and chemical loss rates for the electrons are deduced. At 300 km, q = 200 to 400 ion‐pairs cm−3 sec−1, and β = 2 to 4 × 10−4 sec−1. The horizontal plasma transport term of the continuity equation is derived and compared with the corresponding vertical transport term. These terms dominate the electron concentration profiles above 500 km.
Stable Solutions of Ionospheric Fields in the Propagation of ELF and VLF Waves
Authors: Galejs Janis
Published: February 2008

Stable solutions of the ionospheric fields are derived by a modified matrix multiplication technique for a vertical geomagnetic field and large values of the local refractive index. In an alternate method one ignores the coupling between propagating and attenuated magnetoionic modes at large altitudes in the presence of a dipping geomagnetic field. These two methods are used to integrate fields above the F region and to compute propagation parameters of ELF and VLF waves.

The propagation parameters of ELF fields are dependent on the altitude of the F region and on the geomagnetic field and may exhibit irregular frequency variations. In the VLF range the propagation parameters of terrestrial waves are adequately specified without including the effects of an F region. Application of the reciprocity theorem for a magnetoionic medium shows that an effective excitation of the terrestrial guide requires satellite sources of excessive dipole moments.