bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of algorithms for understanding the temporal and spatial variability of the Earth's Radiation Balance
Authors: Brooks David R. , Harrison Edwin F. , Minnis Patrick , Suttles John T. , Kandel Robert S.
Published: February 2008

A brief description is given of how temporal and spatial variability in the earth's radiative behavior influences the goals of satellite radiation monitoring systems and how some previous systems have addressed the existing problems. Then, results of some simulations of radiation budget monitoring missions are presented. These studies led to the design of the Earth Radiation Budget Experiment (ERBE). A description is given of the temporal and spatial averaging algorithms developed for the ERBE data analysis. These algorithms are intended primarily to produce monthly averages of the net radiant exitance on regional, zonal, and global scales and to provide insight into the regional diurnal variability of radiative parameters such as albedo and long‐wave radiant exitance. The algorithms are applied to scanner and nonscanner data for up to three satellites. Modeling of daily shortwave albedo and radiant exitance with satellite sampling that is insufficient to fully account for changing meteorology is discussed in detail. Studies performed during the ERBE mission and software design are reviewed. These studies provide quantitative estimates of the effects of temporally sparse and biased sampling on inferred diurnal and regional radiative parameters. Other topics covered include long‐wave diurnal modeling, extraction of a regional monthly net clear‐sky radiation budget, the statistical significance of observed diurnal variability, quality control of the analysis, and proposals for validating the results of ERBE time and space averaging.
Analysis methods for kinematic data from local earthquakes
Authors: Thurber Clifford H.
Published: February 2008

A review of the techniques underlying the basic analysis of local and regional earthquakes is presented, describing modern methods for earthquake location, velocity inversion, and fault plane solution. These three topics require a method for ray tracing, determining the seismic ray path connecting the earthquake source to the observing station. A basic introduction to common ray tracing techniques is presented. Earthquake location based on Geiger's method remains the most common in use. Our understanding of this fundamental problem has been enhanced by a variety of studies, and by progress in geophysical inverse theory, but difficulties with the method remain. Alternatives to Geiger's method are reviewed to emphasize the continuing need for study of earthquake location techniques. The more complex problem of simultaneous inversion is receiving increasing attention. Algorithms have been developed to deal with a wide range of velocity structures, including layered, continuous one‐dimensional, and three‐dimensional models. Modern techniques for manipulating and transforming large matrix equations have been critical to the success of simultaneous inversion. Finally, methods for determining fault plane solutions are reviewed, such as first motion, amplitude ratio, and polarization, and techniques are discussed for inferring stress orientation from sets of focal mechanisms.
Intermediate and deep seismicity and lateral structure of subducted lithosphere in the Circum‐Pacific Region
Authors: Burbach G. VanNess , Frohlich Cliff
Published: February 2008

In this paper we present a region‐by‐region review of the Wadati‐Benioff zone structure of most of the world's seismically active subduction zones, focusing primarily on the intermediate and deep seismicity. Lateral changes in Wadati‐Benioff zone structure are common in every major subduction zone. In this study we use these changes to define possible boundaries between portions or “segments” of lithosphere with differing subduction geometries. Although earthquake data seldom have the resolution to show conclusively whether these boundaries separate independent blocks of lithosphere, the available data indicate that the active process at most of these segment boundaries is ductile deformation of the subducting plate, rather than tearing. We found the strongest evidence for the existence of tears where tears are geometrically necessary, such as where a transform boundary terminates a trench, as at the New Hebrides, Tonga, and South Sandwich Trenches. Weak evidence suggesting other tears does exist in some regions, such as Taiwan, the Japan/Izu‐Bonin corner, and the Philippines. The causes of these changes in structure are, in most cases, unclear. Only about 34% of the possible segment boundaries coincide with subducting bathymetric features. Some boundaries occur where there is apparent lateral strain caused by anomalous trench geometry. We have designed a simple modeling procedure which incorporates published plate motion and the observed geometry of trenches and Wadati‐Benioff zones to estimate the lateral strain in subduction zones throughout the circum‐Pacific region. Although no observed subduction zone has a perfectly strain‐free geometry, there is a broad range of geometries for which the lateral strain is small. Indeed, the observed geometry of most subduction zones involve relatively little lateral strain. Comparison with centroid moment tensor focal mechanisms indicates that in zones where the modeling predicted little lateral strain, the mechanisms of intermediate and deep earthquakes show no effects of lateral stress, and downdip stresses are clearly dominant. In regions such as the Mariana Arc, where the model predicts very large lateral extension, lateral tension is very evident in the focal mechanisms. In regions such as the Hokkaido corner, where the modeling predicts large compressional strains, the plate appears to buckle, and bending stresses parallel to the trench are evident. In general this study finds that subducted lithosphere is remarkably cohesive and rigid, and only rarely deforms by breaking or stretching.
Minor constituents in the upper stratosphere and mesosphere
Authors: Rusch David W. , Clancy R. Todd
Published: February 2008

This brief review of advances in our understanding of the physical processes important in the upper stratosphere and mesosphere is intended to highlight specific issues and to focus on areas in which further research is needed.
The magnetospheres of Jupiter, Saturn, and Uranus
Authors: Connerney J. E. P.
Published: February 2008

This report focuses on recent (1983–1986) developments in the study of the magnetospheres of the outer planets, Jupiter, Saturn, and Uranus. I have attempted to review only that work published during the 1983–1986 quadrennium, and I have largely restricted the review to work done in the United States. The reference list reflects these selection criteria. A more complete topical review and earlier references can be found in the previous quadrennial reports on the magnetospheres of Jupiter (Birmingham, 1983) and Saturn (Schardt, 1983).
Heliospheric shocks (excluding planetary bow shocks)
Authors: Mihalov J. D.
Published: February 2008

Even though it took place less than halfway through the last four year period, the AGU Chapman Conference in Napa Valley, California, during February, 1984, highlighted in many ways current U. S. contributions to the study of heliospheric shocks. Considerable recent progress in the theoretical understanding of these discontinuities has been summarized in the collections of the review papers from the Conference, so that those excellent papers have been an important source for the preparation of this Report.

In addition, detailed analyses of ISEE‐3 interplanetary shock observations, and reports on additional data from the outer heliosphere, particularly major disturbances during 1982, have been published since the last Quadrennial Report, and are summarized hereafter. The Pioneer and Voyager spacecraft in the outer heliosphere also have traveled closer to the heliospheric boundary, and further inferences of the boundary location have been made, although it has not yet been directly detected. In addition, details are not yet available concerning the type of shock transition with which it may be associated. More general characteristics of shocks in the outer heliosphere, and out of the solar equatorial plane to ∼25 deg latitude or more, are available from the Pioneer and Voyager data. Also, collection and analyses of data from the inner heliosphere have been extended. Finally, new analyses and observations of coronal shocks have been done, and theoretical studies of this phenomenon have been advanced.
Control surveys
Authors: Wade Elizabeth B. , Zilkoski David B.
Published: February 2008

North American Datum (NAD 83) Readjustment Project. The new adjustment of the North American Datum of 1983 was completed in July 1986. A simultaneous mathematical adjustment of 250,000 stations was performed to eliminate distortions in the horizontal part of the National Geodetic Reference System (NGRS). The datum uses the Geodetic Reference System of 1980 (GRS 80) ellipsoid. The datum reference uses Doppler point positions for the definition of the earth's center of mass and Very Long Baseline Interferometry (VLBI) observations for the definition of scale and orientation. The parameters to be applied to Doppler X, Y, Z coordinates in the NWL 9D coordinate system to transform into the NAD 83 are: −0.811I″ rotation, −0.6 ppm scale, and + 4.5 meters Z offset. Datum transformation procedures are being developed to allow users to convert from NAD 27 to the NAD 83.
Satellite positioning
Authors: Schutz Bob E.
Published: February 2008

Satellite positioning has progressed significantly in the period from 1983 to 1986. Greater reliance has been placed on the technique in surveying applications as well as other areas of geodesy and geodynamics. Based on the results and experiences gained, it appears that Satellite Laser Ranging, Lunar Laser Ranging, TRANSIT positioning and the Global Positioning System will be used in a complementary manner. As currently applied, laser techniques have established absolute positioning and reference systems in a global sense or over large ares, whereas GPS has been used to densify the measurements in local areas, e.g., in the vicinity of a laser ranging or very long baseline interferometry site. A reduction in TRANSIT activity was observed during the reporting period as greater emphasis was placed on GPS. Applications of other techniques to satellite positioning have been developed also, especially directed toward determination of geodetic and geophysical quantities or in support of particular missions, such as oceanographic satellites.
Anisotropy of magnetic susceptibility: Sedimentological, igneous, and structural‐tectonic applications
Authors: MacDonald William D. , Ellwood Brooks B.
Published: February 2008

As was noted by Graham [1954], anisotropy of magnetic susceptibility (AMS) data has many applications to the study of geological processes. This type of anisotropy expresses directional variation in the magnetization induced in a rock, most notably in its iron oxides and especially in its magnetite and hematite. The AMS is commonly expressed by an ellipsoid, of which the principal axes are K1, K2, and K3, from greatest to least. This ellipsoid is generally interpreted in terms of the distribution and shape of grains of magnetic minerals in a rock although the ellipsoid determined depends also on magnetocrystalline anisotropy and on factors of instrumental technique [Ellwood et al., in press, 1987], The challenge for the geoscientist in analyzing AMS data is first to identify the origin of the AMS geometry, then second to relate that geometry to the natural processes which produced the inferred or measured distribution of magnetic materials.
Infrared measurements of column abundances of several trace gases in the Antarctic atmosphere
Authors: Murcray F. J. , Murcray F. H. , Murcray D. G.
Published: February 2008

Atmospheric emission measurements were made in 1978 from an LC 130 aircraft from Point Mugu, California to McMurdo Station, Antarctica, and from McMurdo over the Antarctic continent on several different flights. These included a number of flights over the south pole. In December 1980, infrared solar spectra were obtained from the ground at South Pole Station. Infrared solar spectra were also obtained from South Pole during late November and early December 1986. These latter measurements were extended to cover additional spectral regions to obtain column densities of a number of additional constituents. The results obtained from these measurement series are reviewed and where measurements were made during both periods, compared. Spectral absorption or emission features due to HNO3, NO, NO2, HCl, H216O, H218O, HDO, CH4, and N2O were used to obtain data on the total column abundances for these compounds.
Models for midcontinent tectonism: An Update
Authors: Hinze William J. , Braile Lawrence W. , Keller G. Randy , Lidiak Edward G.
Published: February 2008

During the past decade, significant progress has been made in defining the nature of midcontinent tectonism as a result of an improved geophysical/geologic data base which permits an integration of seismicity data, crustal structures, and current stress directions. Critically placed microseismic networks have shown that many earthquakes with common focal mechanisms occur in specific spatial patterns. The direction of the maximum horizontal compressive stress is generally directed east‐northeast, which supports an origin associated with ridge‐push forces related to movement of the North American plate. Crustal structures have been mapped locally by seismic studies and regionally by extensive gravity and magnetic anomaly data. These data have been used to relate current seismicity and associated tectonism to one of two models. Increasing evidence from across the midcontinent supports reactivation of preexisting zones of crustal weakness appropriately oriented with respect to the prevailing stress field, the ‘zone of weakness model’, as the dominant control on contemporary tectonism and the ‘local basement inhomogeneity model’ as a mechanism for minor, low‐energy release earthquake activity.
Quasi‐static magnetospheric MHD processes and the “ground state” of the magnetosphere
Authors: Voigt G.‐H. , Wolf R. A.
Published: February 2008

From the viewpoint of magnetic equilibrium and convection theories, we discuss whether there exists a theoretically well‐defined ground state of the Earth's magnetosphere. As a basis for this discussion, we review the quasi‐static MHD theory and show in a two‐dimensional (2‐D) model that the convecting magnetosphere can (mathematically) reach a steady state. The steady state configuration has fairly stretched magnetotail field lines and is, therefore, likely to be unstable to the tearing mode instability which ultimately leads to substorm onset in magnetotail regions with stretched field lines. We present an interpretation of the substorm phenomenon in terms of sequences of quasi‐static MHD equilibrium states and argue that, under the influence of convection, magnetic substorms occur periodically in Earth's magnetosphere, thus being an integral part of the entire convection cycle. After explosively releasing plasma and magnetic field energies in a substorm, the magnetosphere starts the convection process again from a low‐energy state. In addition to “smooth” tail field configurations, there exist oscillatory equilibrium tail structures with lower potential energy.

We discuss the concept of the ground state of the magnetosphere within the context of 2‐D quasi‐static MHD models for the near‐Earth magnetosphere. However, we are unable to find a definition of a single magnetospheric ground state that is conceptually simple and computationally feasible. The term “ground state” denotes the lowest energy state of a system, which for a magnetosphere in quasi‐static force equilibrium is the empty vacuum magnetic field configuration with zero thermal plasma pressure. The real magnetosphere never approaches that state. Therefore we propose the term “average magnetosphere” for defining a baseline configuration that corresponds to average solar wind conditions. Earth's magnetosphere is convectively driven and powered by the solar wind. Thus all potential energy states W = ∫ [P/(γ − 1) + B²/2µ0] dV that belong to a particular convection time sequence between substorm events are transient in time. Therefore the newly defined “average magnetosphere” has a potential energy 〈W − Wvacuum〉 representing the time average of equilibrium states over the substorm cycle. Thus a “quiet” magnetosphere would have a net potential energy lower than the average, whereas an “active” magnetosphere would have a higher energy. It is an unresolved theoretical problem, however, to determine the lowest and highest possible energy states for the magnetosphere that are compatible with the thermodynamic condition of quasi‐static convection.

Three‐dimensional (3‐D) magnetospheric equilibria have not been computed yet, but we describe our experience with Stern's stretch transformations and a magnetofrictional method for calculating 3‐D magnetospheric MHD equilibria.
The recent climate record: What it can and cannot tell us
Authors: Karl Thomas R. , Tarpley J. Dan , Quayle Robert G. , Diaz Henry F. , Robinson David A. , Bradley Raymond S.
Published: February 2008

While a great deal of climate data have been gathered over the past hundred years, there remains a number of problems limiting our ability to fully utilize these data in reconstructing the climate of the past century. This is particularly true for research demanding high precision and/or detailed local or regional‐scale climate analyses. In this review we consider our ability to quantify climate change with respect to near‐surface air temperature (measured 1.25–2 m above ground), sea surface temperature, precipitation, snow cover, sea ice, and vegetation measured from space and the Earth's surface. Among the data issues we discuss are calibration, observing practices, urbanization, station changes, data representativeness, data access, and areal coverage. The diversity of measurements over the past century and the new monitoring system being introduced via space‐based and surface‐based platforms offer an unparalleled opportunity for global monitoring; but to quantify climate change, we must tackle such issues as changing retrieval algorithms, relatively short periods of record, satellite Earth location precision, incompatibility with previous conventional historical observations, calibration, and potentially overwhelming data volumes. A new specialty within the climate field is beginning to emerge to address these problems. Despite the litany of problems the instrumented climate record can tell us a great deal about the spatial distribution and secular trends in temperature and precipitation over many areas of the world. In the future a blend of many data types and observing systems will be necessary to better quantify climate change. These large data sets will have to be made accessible to scientists in such a way that allows them an opportunity to check the veracity of their hypotheses and predictions regarding climate change.
The measurement of wavelength in space plasmas
Authors: LaBelle J. , Kintner P. M.
Published: February 2008

A plasma wave can be described by its frequency and wave vector, while a nonlinear plasma structure such as a solitary wave can be described by its temporal signature and scale size. Time series or frequency measurements are relatively easy to perform from spacecraft, but wavelength or scale size measurements are difficult. Nevertheless, direct measurements of wavelength have contributed to understanding plasma waves and fluctuations; for example, such measurements have established the widespread existence of spatial irregularities in the magnetosphere, determined the characteristics of waves upstream of the Earth's bow shock, and allowed the size and motion of double‐layer‐like structures along auroral field lines to be inferred. In this paper we review progress in making measurements of wavelength and scale sizes. The different techniques for inferring wavelength are described, and then a series of case studies is considered to demonstrate applications.
Incoherent Scatter Power Measurements; a Comparison of Various Techniques
Authors: Farley D. T.
Published: February 2008

The straightforward way to determine the mean scattered power is to square‐law detect the incoming signal and average the results. This is also the optimum technique from a statistical point of view. Various other detection schemes are only slightly inferior, however, and may be substantially more convenient when the entire signal processing problem is considered. This paper examines the pros and cons of a number of these possibilities.
A Parametric Study of VLF Modes Below Anisotropic Ionospheres
Authors: Snyder Floyd P. , Pappert Richard A.
Published: February 2008

Weakly attenuated components of the VLF mode spectrum associated with propagation below highly anisotropic ionospheres are presented as a function of frequency and azimuth. In particular, results for the phase velocity, attenuation, polarization mixing ratio, and excitation factor for vertical dipole excitation are presented in the frequency range of 10–30 kHz for midlatitude paths, whereas azimuthal dependencies are presented for a frequency of 19.8 kHz and dip angles of 0° and 60°. The ionospheres are described by exponential electron density and collision frequency profiles, and the primary region of wave‐plasma interaction falls in the highly anisotropic region of the ionosphere. It is shown that polarization mixing is much more pronounced for a westerly propagation path than for an easterly path at midlatitudes, and, as a result, principally TE modes can be expected to influence the mode sum for frequencies at least as low as 20 kHz for propagation to the west. On the other hand, as has been shown previously, contribution to the mode sum by principally TE modes for propagation to the east becomes significant only near 30 kHz.

Azimuthal anomalies include drastic polarization changes in going from easterly to westerly paths. For example, in the case of transverse propagation at the magnetic equator, it is shown that modes that are pure TM for propagation to the east may be pure TE for propagation to the west. Tantamount to this is the statement that modes that have dominant excitation for propagation to the east may have vanishing excitation for propagation to the west. Azimuthal dependencies are shown to be very often characterized by rapid variation of the mode constants in the neighborhood of north‐south or south‐north propagation. These variations manifest themselves in marked differences of the mode sum for azimuthal changes at least as small as 10°. Unfortunately, the azimuthal dependencies of the mode constants do not appear to lend themselves to any simple analytical approximations.
Radio Loss of Lateral Waves in Forest Environments
Authors: Dence D. , Tamir T.
Published: February 2008

The radio loss between two small dipoles located in a forest is examined in the frequency range of 2–200 MHz by characterizing the forest in terms of a dissipative slab backed by an imperfectly conducting ground. A careful derivation of the total radio loss L shows that it consists of four distinct constituents: (1) a basic loss L0 associated with the forest‐air interface, (2) a separation loss L8 due to the vegetation above the antenna, (3) a wave‐interference loss Li due to field reflections at the ground plane, and (4) an antenna input resistance loss Lr produced by the ground proximity. The functional variation of these losses is consistent with previously obtained results that viewed the field in terms of a lateral wave, which now affords a simple physical interpretation for each of the separate factors enumerated above. By choosing parameters describing typical forests, we show that the variation of the four constituents leads to a total loss whose behavior agrees with available experimental data and with previous theoretical considerations pertinent to high antennas. In contrast to these, the present investigation predicts, for low antennas, that vertical polarization is preferable to the horizontal one and that communication conditions may be further improved if the operating frequency is increased rather than decreased. The antenna height gain effect is also examined in detail, and it is shown to be strongly affected by the ground proximity in a manner that had not been recognized hitherto.
The Generalized Thin‐Film Optical Method in Electromagnetic Wave Propagation
Authors: Altman C. , Cory H.
Published: February 2008

The simple thin‐film optical method is generalized to take into account intermode coupling and oblique incidence in a plane stratified magnetoionic medium. In analogy with the simple thin‐film optical method, all partial reflections within a thin, elementary layer are given as a geometric series of matrix products, which are summed to yield the over‐all transfer coefficient matrices of the elementary layer in terms of the characteristic waves of the medium (off‐diagonal elements representing the over‐all intermode coupling coefficients). The analysis is extended by an iterative procedure, layer by layer, starting high in the ionosphere and terminating at the ionospheric base to yield the over‐all transmission and reflection coefficient matrices of the medium. The ‘reverse iteration,’ starting low and extending upward, yields transfer coefficient matrices of intermediate ionospheric slabs but at the price of a more complex iteration procedure. The method is free of the tendency to numerical swamping and in the case of normal incidence simplifies considerably. Applications to LF and hydromagnetic wave propagation in the lower ionosphere are given.
Plane‐Wave Dispersion in Gyrotropic Media
Authors: Johnston Tudor Wyatt
Published: February 2008

The biquadratic plane‐wave dispersion relation (Appleton‐Hartree type) for anisotropic dielectrics or anisotropic magnetic materials is extended to include the case of a medium that has both dielectric and magnetic properties. The quartic equation (generalized Booker quartic) for the refractive‐index vector component normal to a given fixed component is also developed for the same medium and is discussed, together with the connection with the subsidiary biquadratic equation used in anisotropic waveguide analysis.
Equatorial E8 and Daytime Blanketing E8 Drifts at Ibadan
Authors: Oyinloye J. O.
Published: February 2008

The daytime measurements of the velocities and other fading characteristics of equatorial Es and blanketing Es irregularities in the frequency range 4–6 MHz are presented for Ibadan. The modes of signal returns by the two groups of Es are discussed. The experimental results suggest that the equatorial Es irregularities observed in the 4‐6 MHz frequency range at Ibadan are of a similar nature to those observed at 50 MHz at Huancayo during a weak electrojet. A tentative inference from the equatorial Es results is that the magnitudes of equatorial Es velocities may be independent of the relative strength of electrojet intensity.
Radiation from Sources in a Moving, Conducting Medium
Authors: Kalafus Rudolph M
Published: February 2008

A relativistic formulation for the fields of sources in a uniformly moving, isotropic, dispersionless, conducting medium is developed in terms of Green's functions. Solutions are found in closed form for the cases of stationary charge sources and harmonic current sources. Cerenkov phenomena are observed and discussed. The work differs from former treatments in that a self‐consistent scheme is given which accounts for relaxation effects involving conduction charges. The results apply for all values of conductivity.
The Spectrum of Temperature
Authors: Panofsky Hans A.
Published: February 2008

Temperature spectra at South Dartmouth, Massachusetts, U. S. A., between 16‐ and 91‐meter elevation are shown to be consistent with Monin‐Obukhov scaling. The high‐frequency portions of the spectra vary as k−5/3 (where k is the wave number), in accordance with the Kolmogorov hypothesis. The universal constant in this law, determined by two partially independent methods, results in about 0.7 for the one‐dimensional temperature spectrum, if k is measured in radians per unit length. Although not very accurate in itself, this result is in good agreement with laboratory estimates.
Neutral Winds and the Behavior of the Ionospheric F2 Region
Authors: Cho H. R. , Yeh K. C.
Published: February 2008

The continuity equation of ionization and the equation of motion of the neutral atmosphere are solved simultaneously in the ionospheric F2 region for different seasons in different epochs of solar activity. The model atmosphere used is that given by L. G. Jacchia (1965). Epstein functions are used to simulate the electron and ion temperature profiles. An ionization production function in a Jacchia model atmosphere is derived and used. The computed wind velocity and f0F2 behavior are presented and compared with other theoretical results as well as the existing experimental data. The meridional wind is found to agree reasonably well with the incoherent scatter data. It is found that the declination effect resulting from neutral winds can be used to explain certain experimental observations in a semi‐quantitative manner.
Vertical and Horizontal VLF Fields Excited by Dipoles of Arbitrary Orientation and Elevation
Authors: Pappert R. A , Bickel J. E.
Published: February 2008

Vertical and horizontal electric field mode sums are calculated for vertical, horizontal, and inclined point dipole radiators beneath a nighttime ionosphere for propagation to the east and to the west. The results indicate that in most circumstances the largest signal levels are obtained by recording the vertical electric field produced by a vertical antenna; however, there are circumstances in which horizontal dipoles for transmitting and/or receiving can be used to advantage.
The Trend of Ionospheric Absorption During Shortwave Fade‐Outs Related to the Trend of Enhancement of Solar X‐ray Flux
Authors: Schwentek H. , Hartmann G. , Kreplin R. W.
Published: February 2008

During the period July 1967 to July 1968 about 60 shortwave fade‐outs, both weak and strong, were observed at Lindau through simultaneous use of several shortwave paths particularly established for absorption measurements. The frequencies used were 2.50, 2.614, 2.775, and 6.09 MHz; the distance between transmitter and receiver was about 300 km. Moreover, a riometer was used with a corner reflector antenna directed at the polestar (27.6 MHz). For the quoted shortwave fade‐outs the Naval Research Laboratory made available stored data of solar X‐ray flux in minute intervals; the data were obtained from satellites OGO 4 and Solrad 9 in the wavelength ranges 0.5–3, 1–8, 8–20, and 44–60 Å. The analysis of the various effects shows that there is a very good correlation between the enhancements of solar X‐ray flux and the enhancements of ionospheric absorption. The beginning and maximum of the shortwave fade‐outs are delayed by 0.5 to 4 minutes in relation to the beginning and maximum of the bursts, with the longer delay corresponding to the shorter wavelength. The end of the effects cannot be determined so definitely; the time differences between bursts and shortwave fade‐outs vary between ±7 minutes. Usually, the trend and detail of the shortwave fade‐outs very nearly follow the trend of the burst; thus, bursts may be considered equivalent to shortwave fade‐outs. For a number of very clear weaker effects the additional absorption ΔL has been found to be proportional to the additional flux ΔXE. For a very strong effect after a saturation ΔL increases again. The relative maximums of absorption ΔL/L during shortwave fade‐outs are proportional to the relative enhancement of flux ΔXE/XE.
Corotating Regions in the Solar Wind, Evident in Number Density Measured by a Radio‐Propagation Technique
Authors: Croft Thomas A.
Published: February 2008

Coherent phase‐modulated signals at 50 and 423 MHz are transmitted from Stanford University to specially equipped spacecraft orbiting the sun. Differential group delay and phase advance are measured; each of these parameters is approximately proportional to the average electron number density along the signal path. The experimental method enables us to discriminate between temporal and spatial variations of the solar wind by virtue of inherent spatial averaging. During the past 4.5 years, 10,000 hours of these data have been obtained from Pioneers 6, 7, 8, and 9 and Mariner 5. At times, measurements have been taken for two periods each day, by the use of first one spacecraft ahead of earth and then one behind. With such a technique, corotating flow patterns are clearly visible. Hourly samples are presented of the best data that were obtained by Pioneers 8 and 9 during the two‐year period ending in February 1970. The density patterns reveal corotating regions in each of which a recognizable character is maintained during several rotations but for less than a year. This result is in contrast to results of other observers, who have seen corotating features lasting up to 1.5 years. The short duration observed here may be due to noisiness in these data or it may be typical of the active sun, whereas a longer duration is typical of quiet times. The observed density patterns are not consistent with the concept of steady corotating flows because large transients occur too fast and because identifiable features recur with nearly (but not exactly) the same period on successive rotations of the sun. These patterns could be a result of the corotation of thin steady streams that fluctuate both north‐south and east‐west by distances well in excess of the cross‐sectional extent of the streams. It is also possible (and more likely) that the data indicate some corotating regions in which the solar wind is featureless and of low density and other regions characterized by high density and the prevalence of outward traveling plasma disturbances.
Calculation of an Equivalent Current System in the Polar E Region
Authors: Czechowsky P.
Published: February 2008

In order to interpret VHF aurora backscatter communications, it is necessary to get some information about the extent, the movement, and the strength of the polar electrojet. In this paper a method is given to calculate an equivalent current system in the polar E region by determining the unknown parameters (height, direction, width of the current, etcetera) from the measured disturbance vectors of the earth's magnetic field, ΔH, ΔD, and ΔZ. With a model of a simple current‐density distribution it is possible to solve the Biot‐Savart formula. The consideration of positive, negative, and induced currents leads to a system of nonlinear equations of eight unknown parameters in this special instance. With an iterative method given by Newton and Raphson this system of equations can be solved if approximate values of the solution are known. These approximate values are given by physical conditions or can be obtained by model calculation. In this paper, results are shown for a current system calculated with values of ΔH, ΔD, and ΔZ from the magnetograms of Leirvogur, Lerwick, Eskdalemuir, and Hartland during a period of about five hours on March 23–24, 1969.
Interactions Between the Ionosphere and the Magnetosphere for Sq and L Variations
Authors: Matsushita S.
Published: February 2008

After a short discussion of the dynamo theory for producing electric current systems for Sq and L variations, results of mapping these dynamo‐region electrostatic fields into the magnetosphere are briefly presented. The mapped electrostatic fields, together with the earth's main magnetic field, produce drift motions of magnetospheric plasma particles. Using the same but reversed mapping procedure, magnetospheric electrostatic field effects on the dynamo region are discussed. Highly localized geomagnetic variations during relatively quiet periods can be explained by this effect. Also a possibility of producing Sq‐type electric currents in the dynamo region by the magnetospheric electrostatic fields caused by motions in the plasmasphere is examined. This magnetospheric effect on Sq may be greater than other effects due to magnetospheric electric currents (such as magnetopause, tail, and quiet‐ring currents). It is concluded that future direct measurements of electrostatic fields (or electrostatic drifts) may determine which of the two mechanisms (dynamo action or plasmaspheric motions) is the major cause of the production of the ionospheric Sqcurrent system, although the dynamo action seems to be the main cause of L variation.
Tropospheric Effect on Electromagnetically Measured Range: Prediction from Surface Weather Data
Authors: Hopfield H. S.
Published: February 2008

Knowledge of the height integral of atmospheric refractivity (n — 1), where n is the refractive index, is essential for prediction of atmospheric range effect at any elevation angle. Observed values of the height integral for the lower, nonionized atmosphere can be obtained from weather balloon ascent data. Year‐long collections of data from widely separated locations were used to relate this integral to surface data. Although (n — 1) at any point in a dry atmosphere depends on both pressure and temperature (the ratio P/T), the height integral of the observed dry part of (n — 1) is a linear function of surface pressure only, not of temperature. This is theoretically correct since P/T is equivalent to density, and the integral of density with height yields surface pressure. By application of this finding, the equivalent height for a (theoretically justified) quartic (n — 1) model (dry part) should be found to vary directly as surface temperature; the value obtained (least‐squares fit to observed data) is 40.1 km for surface T = 0°C with a height expansion coefficient of 0.149 km per surface degree C. This would reduce the equivalent height to zero near 0° Kelvin. This theoretical model matches observed height integrals with an rms error of a few millimeters out of 2.3 meters (far less than 1%). Agreement between stations is excellent. A study of the more variable but much smaller wet part is in progress. The wet part is significant at radio but not at optical frequencies.
Image Theory for an Arbitrary Quasi‐Static Field in the Presence of a Conducting Half Space
Authors: Weaver J. T.
Published: February 2008

The approximate image theory for quasi‐static fields in the presence of a conducting half space is treated in full generality by considering an arbitrary periodic source. The general theory is developed in terms of a magnetic Hertz vector aligned perpendicular to the plane surface of the conductor. It is shown that its solution above the conductor can be expressed as the combined Hertz potentials of the source and its image located at a certain complex depth, plus terms that become negligibly small for points somewhat farther than a skin depth from the ordinary mirror image of the source. Image approximations for the individual electric and magnetic field components are derived. The magnetic field is expressed entirely in terms of the magnetic field of the source and its complex image, but the electric field, unless it is everywhere parallel to the surface of the conductor, depends in addition on the mirror image of the source. The general theory is illustrated by its application to the particular examples of magnetic dipole and infinite line current sources.
VLF Observations of Nighttime D‐Region Ionization Enhancement by the Scorpius XR‐1 X‐ray Source
Authors: Chilton C. J. , Crary J. H.
Published: February 2008

In recent years, measurements by rocket, balloon, and satellite of cosmic X rays have suggested the possibility of observing ionospheric effects from celestial X‐ray sources such as Scorpius XR‐1, using low and very low frequency radio transmissions. The behavior of the nighttime D region under ionization by the X‐ray spectrum of the Scorpius source is estimated for several stellar zenith angles. Although Scorpius XR‐1 is the strongest source in the southern hemisphere, the integrated flux of all the other X‐ray sources is comparable to that of Scorpius XR‐1 and appears to modify the effect of Scorpius XR‐1 alone on VLF data recorded in the southern hemisphere. Observations of the VLF transmission NBA (18 kHz, Balboa, Panama) made at Tucuman, Argentina, during 1963–1964 show a sidereal time variation in the diurnal amplitude change that follows the variation in the per cent illumination of the propagation path by Scorpius XR‐1 during the nighttime hours. Even though the diurnal amplitude change can be shown to have a sidereal time variation, the diurnal phase change at Tucuman, Argentina, does not vary much throughout the year and yet remains consistently lower than that observed over a path of the same length from NBA to Boulder, Colorado, in the northern hemisphere. Therefore, it is suggested that the integrated effect of all the X‐ray sources illuminating the southern hemisphere is to enhance the ionization in the southern hemisphere nighttime D‐region, thus, producing the smaller diurnal phase change observed at Tucuman compared with that observed on a Boulder recording of the NBA signal over a propagation path of the same length in the northern hemisphere.
Synchrotron Radiation From Auroral Electrons
Authors: Wang C. S. , Lee Y. H. , Kim J. S.
Published: February 2008

The expression for the total power radiated by an electron moving in a helical path was derived from Schwinger's general equation for synchrotron radiation. The equation derived was used to predict the synchrotron radiation from incoming auroral electrons at three different stations, one in the auroral zone and the other two at midlatitudes. The results of the calculations for the station in the auroral zone agree with the data observed by Parthasarathy and Berkey at College, Alaska. The synchrotron radiation from the incoming auroral electrons indeed offers an explanation for the observations of auroral noise observed at College, Alaska.
New Dynamic Aspects of Intertropical F2 Ionization
Authors: Vila Paul
Published: February 2008

Diurnal changes in F2 ionization distribution as measured during June and July 1966 over the Tamanrasset meridian reveal two types of asymmetric phenomena distorting the crest‐and‐trough system (formerly known as the equatorial F2 ionization anomaly). The first type corresponds to a general time variation of the latitude asymmetry. Our observations yield four independent parameters of this asymmetry; for 80% of the time, the variation can be attributed to ion drag due to a time‐varying meridian air wind. Magnetic activity is correlated with the amplitude of this wind, and the low‐altitude thermospheric circulation is discussed. Day‐to‐day fluctuations of the diurnal evolution pattern suggest a possible long‐term control of the equatorial electric field by the general dynamo current system. A second type of asymmetry shows more intense, local, and short‐lived phases superimposed on the fountain and neutral wind fluctuations. It has the character of a transitory forced‐diffusion process. We believe that the factor responsible is electron temperature gradients produced by conjugate photoelectron heating.
Photoelectron Fluxes Measured at Millstone Hill
Authors: Cicerone R. J. , Bowhill S. A.
Published: February 2008

Measurements of the intensities of plasma lines in the radar incoherent‐scatter spectrum are reported. The measurements were performed with the UHF radar at Millstone Hill, Massachusetts, on February 9, 1969. Theory of the plasma lines is reviewed, and problems of data interpretation are discussed. The plasma‐line intensities are interpreted in terms of photoelectron upward and downward flux components at 560 km. The net upward flux there is found to be 3.6 × 108 cm−2 sec−1. From the measured fluxes and a simplified picture of photoelectron transport, the escape flux and the arriving conjugate‐point flux are found. In addition, the opacity of the protonospheric field tube connecting Millstone Hill and its conjugate point is estimated as 0.85 for photoelectrons.
Scattering in Velocity‐Dependent Systems
Authors: Censor Dan
Published: February 2008

Scattering of electromagnetic waves by arbitrary objects moving in free space is discussed. The objects move at constant velocities. The formalism is relativistically exact and applies to arbitrary distances from the scatterer. The results are recast in terms of the dominant (far‐field) frequency; this is useful for low velocities and near‐field frequencies. Numerical results are given for scattering by two‐dimensional moving monopoles and dipoles.
Arrays With Electrically Long Elements
Authors: King Ronald W. P. , Sandler Sheldon S.
Published: February 2008

A new method is described for determining the properties of arrays of parallel elements that are at least a wavelength long. This is a first step in a study of the behavior of arrays when the elements are driven by pulsed instead of steady‐state voltages. The new solution for the distributions of current in and driving‐point admittances of the coupled elements makes use of a method of successive approximations in which the boundary condition on the tangential electric field is satisfied separately for the induced and the driven current. The procedure begins with the known solution for an isolated, electrically long antenna and modifies this to take account of the mutual interaction. Graphs of the currents in electrically long two‐ and three‐element arrays are shown, and driving‐point admittances are given.
Theory of Wave Propagation Along a Thin Wire Parallel to An Interface
Authors: Wait James R.
Published: February 2008

A solution is given for the boundary value problem of a wave propagating along a thin wire parallel to the interface between two homogeneous half‐spaces. A general modal equation is derived for the propagation constant of the transmission current on the wire. It is shown how this result reduces to earlier known solutions obtained under more restrictive conditions.
On the Boundary Conditions in Theoretical Model Calculations of the Distributions of Minor Neutral Constituents in the Upper Atmosphere
Authors: Shimazaki Tatsuo
Published: February 2008

The upper and lower boundary conditions are important in theoretically modeling the height distributions of minor neutral constituent concentrations in the upper atmosphere by solving continuity equations. This paper discusses the effects of such boundary conditions on their concentrations. It is shown that the upper boundary condition of no diffusive flux at 150 km does not affect seriously the minor constituent density distributions except for H and HO2 above ∼120 km, where the escape flux of H reduces their concentratibns substantially. It is also shown that our previous model calculations have used the condition of constant flux with height at the lower boundary. It is suggested that reliable measurements of minor constituents in the upper stratosphere may be useful in improving the lower boundary condition for the mesosphere models and in simplyfying the modeling procedures.
Attenuation of Waves in Plasmas
Authors: Suchy Kurt
Published: February 2008

Among the variety of problems arising from attenuating influences on the propagation of waves, three will be reviewed: (a) determination of the correct gas‐kinetic description of collisions between the plasma particles and their relation to the conductivity tensor and the dispersion equation, (b) the generalization of the basic laws of geometric optics for moderate collisional absorption, and (c) the calculation of wave‐mode attenuation arising from linear‐mode coupling in a full‐wave theory for a cold, stratified, magnetized absorbing plasma.