bluuebunny/crossref_metadata_2025 huggingface dataset:
Incoherent scatter contributions to studies of the dynamics of the lower thermosphere
Authors: Evans John V.
Published: February 2008

This paper reviews what has recently been learned by means of the incoherent scatter radar technique concerning the dynamics of the lower thermosphere (100–150 km). In this region, thermal tides generated in situ and propagating upward from below appear to be the principal source of motions at low and middle latitudes. The winds that they establish can drive ions across magnetic field lines, thereby establishing electric currents and polarization electric fields (which in turn modify the motions of the ions). Efforts to understand this region have traditionally been made through calculations of the tidal amplitudes, from studies of magnetometer records, and from vertical wind profiles observed via chemical releases from rockets. The direct measurements of the temperatures, winds, and electric fields made possible by means of incoherent scatter radar probing have confirmed some early ideas and also have revealed considerably more complexity than had been anticipated. Presently available evidence indicates that the interval 100– 125 km is dominated by upward propagating solar semidiurnal tidal modes (e.g., (2, 4) and (2, 5)) generated in the mesosphere where background winds couple energy out of the (2, 2) mode, which is the mode most strongly excited in the stratosphere‐mesosphere. These higher‐order modes appear to be damped above 120 km by viscous dissipation. In the region 125–150 km the (1, −2) trapped diurnal mode generated by direct absorption of solar EUV seems to be the predominant one at midlatitudes, although some of the energy remaining in the semidiurnal (2, 2) mode appears to leak up to these heights. Nearer the equator it appears that the (2, 2) tide dominates the region below 200–300 km, particularly in summer. These tides create winds that appear capable of explaining a variety of related phenomena including the Sq (solar quiet) dynamo current system, the generation of sporadic E layers and layers intermediate between the E and F layers, and the drift of ions in directions normal to the magnetic field at F region heights (i.e., electric field induced drifts) seen within the plasmasphere during the day.
Applicability of array algebra
Authors: Snay Richard A.
Published: February 2008

Matrix equations, as occur in the techniques of least squares estimation and prediction, transform into equivalent array equations when the data are gridded. The mathematical model and the weight matrix associated with the data must also conform to certain requirements for this transformation. In comparison to the matrix equations the array equations result in significant savings in the number of computations and in the required storage.
The North Atlantic general circulation west of 50°W determined by inverse methods
Authors: Wunsch Carl
Published: February 2008

We review linear inverse theory in the context of its application to determining the general circulation of the ocean. Inverse methods are intimately related to least squares and rank deficient regression problems. Results are dependent upon the model assumed; in this paper all models are linear, geostrophic, and mass conserving, and they differ only in the initial reference pressure for the dynamic computations. We show how to compute the resolution of both the observations and the solutions, the degree of data independence, and the solution variance. To handle the underdetermined nature of the problem, we impose a conventional requirement of maximum simplicity relative to the initial model. More generally, the methodology provides a powerful technique for handling imperfect and noisy chemical and dynamical tracers and for assimilating a great variety of different information into dynamically consistent circulation schemes. In the latter part of the paper the methods are applied to the western North Atlantic west of the 50°W meridian. An attempt to use a full data set failed owing to the nonsynoptic nature of the observations. Two initial models were then applied to a reduced data set defined by seven boxes in which conservation of total mass and of four additional layers was required. Model I, which initially has a reference level at the bottom, leads to a large Gulf Stream transport (124 Sv) with an active recirculation zone to the south. Model II begins with a reference level at 2000 dbar and leads to a weaker Gulf Stream with recirculation zones on both sides. The southern recirculation breaks up into smaller scales. Both models yield a strong large‐scale gyre to the south of the Mediterranean salt tongue. The residual error is 2–3 Sv rms in both models, but it appears that systematic errors due to the seasonal variability probably exceed this value.
Dynamo magnetic field generation
Authors: Levy E. H.
Published: February 2008

The character of Earth's magnetic field, its internal source and its general shape, have been known since the time of Gilbert, some 400 years ago. The origin of the field has been the subject of speculation since that time; but it is hardly more than twenty years since our understanding of the generation mechanism began to fall together.

From our modern perspective we can see that the phenomenon of natural magnetic field generation is common to bodies in the universe. Three of the nine planets in the solar system—Mercury, Earth, and Jupiter—are known with confidence to possess magnetic fields of internal origin. In addition we know of the sun's contemporaneously generated magnetic field. The Galaxy apparently contains a large scale magnetic field. Magnetic fields are common in stars and have intensities which cover a wide range. Some white dwarf stars and some neutron stars apparently possess magnetic fields with intensities far beyond those attained in the laboratory. While this is not an appropriate place to review all of these, it is worth keeping in mind that the subject addresses more bodies than just Earth and even the planets. Today it is reasonable to take the point of view—even if only as a working hypothesis—that many and perhaps all of these magnetic fields have their origins in active or previously active hydromagnetic dynamos.
Seismic source theory
Authors: Johnson Lane R.
Published: February 2008

It is remarkable that seismology has progressed as far as it has while the knowledge in one vital area, that of the seismic source, has remained in a rather primitive state. However, if the recent research effort in the United States is any indication, this situation may be changing, because several promising lines of attack upon the problems of the seismic source have been generated during the past four years.

For the sake of this review, studies of the seismic source will be divided into two basic groups, the theoretical studies which are directed primarily at formulating models of the earthquake process, and the observational studies which are directed primarily at obtaining the data necessary to either check the theoretical studies or investigate the consequences of interpreting earthquakes in terms of a specific model.
Low latitude airglow
Authors: Meier R. R.
Published: February 2008

During the past few years, the study of airglow emissions from tropical latitudes has led to progress in several areas of aeronomic research. The understanding of radiative processes involving recombining atomic and molecular oxygen ions has progressed to the point that F‐region dynamics can be inferred from simultaneous observations of selected lines. Weak emissions related to precipitating particles, minor species, and the South Atlantic Anomaly have been studied with sensitive instrumentation. New techniques using high resolution interferometers and imaging devices have been employed to study phenomena previously unobserved.
Cosmic ray intensity over long time scales
Authors: Forman M. A. , Schaeffer O. A.
Published: February 2008

In this report we review recent work on variations of cosmic ray intensity on time scales longer than, or which may have occurred before, the modern era of direct observations of cosmic rays. The possibility of discovering such variations comes mainly from the fact that cosmic‐ray nuclei above a modest energy make nuclear interactions leading to characteristic “cosmogenic” nuclear debris in targets like meteorites, lunar rocks, and planetary atmospheres, which are exposed to them. High Z cosmic rays also make etchable tracks in glassy and crystalline targets. Cosmogenic nuclei which happen to be chemically or isotopically distinct from the targets are detected as radioactive (half lives less than) about 109 years) or stable nuclides, especially rare gases, in meteorites, lunar and terrestrial materials.
Stable isotope geochemistry
Authors: O'Neil James R.
Published: February 2008

There has been an explosion of stable isotope data in the literature over the past few years. Establishment of routine analytical techniques and advances in mass spectrometry have made entrance into this field far less formidable than in former years. Today there are about 150 laboratories throughout the world where research in stable isotope geochemistry is conducted. In August, 1976 a conference devoted entirely to stable isotope investigations was held at the New Zealand Institute of Nuclear Sciences in Lower Hutt, New Zealand.
Quasi‐static earthquake mechanics
Authors: Stuart William D.
Published: February 2008

Viewed as a boundary value problem of continuum mechanics, the subject of earthquake mechanics reduces to the study of (1) constitutive properties (stress‐deformation laws) and geometry of fault zones and surroundings, and (2) remotely applied boundary conditions. In the purely quasi‐static formulations described here, a precise criterion for instability leading to dynamic rupture is also needed. The present consensus supports the concept of an earthquake cycle in which the somewhat arbitrarily chosen successive stages are (1) slow increase of stress due to remote loading, (2) the onset, propagation, and cessation of earthquake rupture, and (3) post‐seismic adjustment. Although no single rigorous model yet exists for the complete cycle because of simplifying constitutive assumptions, there are detailed models for each stage.
Air‐sea interaction and dynamics of the surface mixed layer
Authors: Garwood R. W.
Published: February 2008

Since the last U.S. Report on ocean‐atmosphere interactions by Wyrtki [1975], there has been significant progress in air‐sea interaction research in general. The title of this report reflects the particular interest in the dynamics of the upper‐ocean turbulent boundary layer or mixed layer. More recently, larger‐scale experiments have investigated the upper‐ocean and lower‐atmosphere interactive processes on a variety of space and time scales. The most notable cooperative ventures that have involved U.S. scientists in the past four years are the Air Mass Transformation Experiment [AMTEX, 1975], the continuing Joint Air‐Sea Interaction (JASIN) experiment [Pollard, 1975, 1978], the North Pacific Experiment (NORPAX), the Mixed Layer Experiment (MILE, 1977) and MONEX, the Monsoon Experiment ([Garp, 1976]; [Singh, 1978]).
Equatorial oceanography
Authors: O'Brien James J.
Published: February 2008

The equatorial ocean has always captured the attention of oceanographers. Almost all medium‐to‐large scale oceanic motions are dominated by the effect of the earth's rotation, the Coriolis acceleration. At the equator, this apparent acceleration vanishes and very special physics apply. The most striking phenomena is upwelling that occurs in a narrow latitude band a few degrees wide along the equator due to the prevailing easterlies (westward winds).
The Global Atmospheric Research Program
Authors: Perry John S. , O'Neill Thomas H. R.
Published: February 2008

Four years ago, our report on the Global Atmospheric Research Program (Perry, 1975) was written while an observational armada assembled for the GARP Atlantic Tropical Experiment (GATE). Now, the data resulting from that massive effort have been archived and serve as raw material for a still‐growing body of research on the tropical atmosphere. Again we write on the eve of a still more audacious adventure: The Global Weather Experiment, as we now term the First GARP Global Experiment (FGGE). Designed to advance our ability to predict weather and our understanding of climate, this massive international undertaking will similarly nourish research throughout the world in the global problems of weather and climate.
Polar meteorology and climatology 1975–78
Authors: Radok Uwe
Published: February 2008

Polar meteorology and climatology took giant steps forward with the IGY which for the first time revealed the full extent and complexity of the cryosphere. Since then the advance of polar knowledge has been much slower but has continued, thanks above all to the industrial development of the Arctic. Another important factor has been the ever increasing sophistication of satellite techniques and computer modeling; in fact their contributions to polar meteorology so far have hardly progressed beyond their infancy. At the same time, a new thrust has developed with chemical and optical studies of the polar atmosphere and the palaeoclimatic interpretation of deposited polar precipitation.
Geomagnetic depth sounding by induction arrow representation: A review
Authors: Gregori G. P. , Lanzerotti L. J.
Published: February 2008

Considerable important research in upper atmosphere geophysics is carried out through the use of arrays of ground‐based magnetometers. In order to better delineate the ionospheric and magnetospheric currents and waves as measured by these arrays, it is important to understand the conductivity of the earth's structure under the individual stations. Geomagnetic depth sounding studies are used to deduce the earth's conductivity profiles. In most studies, ‘induction arrows,’ or ‘induction vectors,’ are plotted on maps for graphical representations of lateral inhomogeneities in underground conductivity structures. Different methodologies and different arrow conventions have been used by a number of authors for deriving these vectors, often without relating their techniques to other work in the field. We review herein the various methodologies (except transfer functions) and present a unifying picture to the representations that should prove useful to researchers in both space physics and solid earth physics.
Unusual animal behavior before earthquakes: A review of possible sensory mechanisms
Authors: Buskirk Ruth E. , Frohlich Cliff , Latham Gary V.
Published: February 2008

To determine whether reports of unusual animal behavior before earthquakes are plausible, we have compared these reports with recent laboratory studies of animal sensory thresholds. Our major conclusion is that some animals are much more capable than humans of perceiving certain kinds of geophysical stimuli which may precede earthquakes. These geophysical stimuli are seismic or acoustic waves at low frequency (below 50 Hz), electric field changes, and olfactory stimuli. For example, recent studies suggest that some birds and fish are more sensitive than humans to sounds with frequencies below 40 Hz, and many animals are exceptionally good at perceiving low‐frequency vibrations through their skin. Certain fish are sensitive to electric field changes as small as 10−5 V/m, and some laboratory mammals also respond to significantly weaker fields than humans. For these electric and acoustic stimuli the reported levels of geophysical precursors are within the reported perceptible range of some animals which show unusual behavior prior to earthquakes. In addition, stimuli caused by the release of gases from small cracks may well be perceived by some animals before earthquakes. Recent research has confirmed the remarkable olfactory sensitivity of some animal species, but no quantitative comparisons with geochemical precursors can be made yet. We find no evidence that magnetic field precursors or precursory high‐frequency (above 10 kHz) sounds are the cause of unusual animal behavior before earthquakes. Although some animals are highly sensitive to these stimuli, observed magnetic precursors tend to be of low amplitude amid relatively high noise levels, and high‐frequency sound is severely attenuated within a short distance from the earthquake hypocenter. Knowledge of animal sensory capabilities may suggest an instrumental strategy for detecting earthquake precursors. We recommend further geophysical research in seismic areas to measure (1) seismic waves in the frequency range 10–50 Hz, (2) earthquake‐related electric field changes and air ionization, and (3) coseismic or preseismic release of trapped gases other than radon. Further biological research can refine our understanding of (1) responses to sounds and vibrations with frequencies below 50 Hz, (2) the effects of electrical and electrostatic changes on animal behavior, (3) behavioral responses to odors, and (4) sensory capabilities of common domestic animals like horses, dogs, and chickens, which are seldom studied but commonly mentioned in the preearthquake reports.
Duality of the magnetic flux tube and electric current descriptions of magnetospheric plasma and energy flow
Authors: Atkinson G.
Published: February 2008

The duality between electric current and magnetic flux tubes is outlined for the magnetosphere. Magnetic flux tubes are regarded as fluid elements subject to various stresses. Current closure then becomes the dual of stress balance, and Poynting vector energy flow a dual of J · E dissipation. The stresses acting on a flux tube are magnetic stresses, which correspond to currents at a distance, and plasma stresses, which correspond to local currents. The duality between current and stress is traced for ionospheric ion drag forces, solar wind stresses at the magnetopause, inertial effects, and the effects of energetic plasma on flux tubes. The stress balance and dual current systems are outlined for idealized magnetospheres of increasing complexity. For a simple magnetosphere with no convective flow, the balanced stresses are solar wind pressure and neutral sheet plasma pressure. The corresponding current systems are the Chapman‐Ferraro magnetopause currents and the magnetotail current system. The introduction of convective flow introduces further stresses: ionospheric ion drag, Alfvén layer shielding, and an imbalance in day‐night magnetic stresses due to transport of flux tubes to the nightside by the solar wind. These stresses balance, and hence the corresponding additional currents (the ionospheric Pedersen current and the electrojets, the partial ring current, and two other current systems from the magnetopause and tail) must form a closed current system and do so by the region I and II field‐aligned currents of Iijima and Potemra. The energy flow in the above models is described in terms of both Poynting vectors and the above current systems. Temporal variations examined are (1) an increase in dayside merging and/or nightside reconnection, (2) an increase in the energy density of plasma in the plasma sheet, (3) an increase in ionospheric conductivity, and (4) an increase in solar wind pressure. Each of the first three requires an increase in all the currents and stresses associated with convective flow. The symptoms of variation 3 are very similar to many of those observed during magnetospheric substorms, and it is concluded that ionospheric conductivity enhancement is important in substorms, since it represents a major change in the forces affecting the flow and, in the dual picture, of the currents associated with the flow. Finally, the effect of aurora‐associated magnetic‐field‐aligned electric fields are considered, and the variation in the flows when the east‐west component of electric field parallel to the arc is included. Quite different plasma transport may result even though the north‐south meridian cross sections are the same.
Auroral kilometric radiation: A theoretical review
Authors: Grabbe Crockett L.
Published: February 2008

A number of theories have been proposed in recent years to explain auroral kilometric radiation. These include an anisotropic velocity distribution instability, mode conversion of electron cyclotron waves to ordinary mode radiation, soliton radiation, beam‐driven instability of electromagnetic waves via low‐frequency turbulence, a loss cone instability, beating of coherent electrostatic waves, and beam amplification of electromagnetic waves via coherent density fluctuations. These will all be reviewed, and comparisons of prediction made with observations. Emphasis will be placed on the three recent proposals.
A review of snow acoustics
Authors: Sommerfeld R. A.
Published: February 2008

Snow acoustics can be divided into two major areas. One is the attempt to understand the acoustic properties of snow and to relate them to other material properties. In this area the major advance has been the recent understanding that snow must be treated as a porous medium and that the ice framework, the pore air, and their interaction all play important roles in acoustic propagation. It appears that a more realistic model of the ice framework must be used before the full range of snow's acoustic properties can be modeled adequately. The second area is acoustic emissions. High‐frequency acoustic emissions have aided in the development of a texture‐oriented constitutive relationship. Low‐frequency acoustic emissions have been shown to have the potential for predicting avalanches, at least under some conditions.
The sign convention for quadrature Parkinson arrows in geomagnetic induction studies
Authors: Lilley F. E. M. , Arora B. R.
Published: February 2008

Time series analysis, which is basic to modern geophysical data processing, involves a choice between working with a time dependence of e+iωt or e−iωt. In published work the choice made is sometimes not explicitly stated, leaving ambiguity in the interpretation of complex quantities with quadrature parts. Parkinson arrows are used in geomagnetic induction studies to summarize anomalous vertical magnetic fluctuations at different observing stations and to indicate regions of high electrical conductivity. Such arrows are now regularly computed as real and quadrature pairs. The general convention is often adopted of ‘reversing’ a calculated real arrow so that it will point toward a conductivity increase, but for quadrature arrows the practice between various published papers has generally not been so consistent. The present paper demonstrates that consistent practice for reversing or not reversing quadrature Parkinson arrows is possible when the initial convention for time dependence is taken into account. A reversal practice is determined for interpretation in terms of a simple channeling model. A related matter is the definition of phase. Phase values are also generally ambiguous unless the time dependence used (e−iωt or e+iωt is stated.
Current status of IMS plasma wave research
Authors: Anderson Roger R.
Published: February 2008

Much progress has been made in plasma wave research as a result of the International Magnetospheric Study (IMS) in all areas from ground‐based studies to multiple‐satellite observations. Studies in all the areas have contributed to better understandings of the propagation and generation of magnetospheric plasma waves and the impact the waves have on other magnetospheric phenomena. Plasma wave measurements have been used as both local and remote sensing determinations of plasma parameters. The role of plasma waves at the various magnetospheric boundaries has been extensively studied using the IMS sources. Plasma wave observations during the IMS have tested many existing theories and led to the foundation of many new theories. Several suggestions for future directions of plasma wave research are offered.
Random fluctuations, persistence, and quasi‐persistence in geophysical and cosmical periodicities: A sequel
Authors: Forbush S. E. , Duggal S. P. , Pomerantz M. A. , Tsao C. H.
Published: February 2008

The method of Chree analysis (superposed epochs) has been used in many disciplines, including geophysics, astrophysics, and solar‐terrestrial relationships. However, procedures to test the statistical significance of the results obtained thereby have not been available heretofore. Claims for statistical reality of average variations (from Chree analyses or otherwise) are unacceptable without testing the assumption that deviations from the average variation are random and sequentially independent. In many phenomena this assumption is not valid. One objective of this paper is to expand established methods for the analysis of variance in order to provide a statistical procedure for testing the Chree analysis result from data with nonrandom deviations from average. In addition, the statistical method developed by Bartels (1935) to determine the quasi‐persistency of deviations from average signals in the form of sine waves is also applied to the Chree analysis problem. The two alternative procedures for evaluating the significance of Chree analysis results (or variations otherwise obtained) are then compared to determine the circumstances under which one of them may be preferable.
Middle atmosphere dynamics
Authors: Hartmann Dennis L.
Published: February 2008

This review attempts to summarize briefly the efforts of scientists in the United States to understand the large‐scale dynamics and climatology of the middle atmosphere, which have appeared in the reviewed literature between January 1979 and September 1982. Some significant contributions have no doubt been overlooked; and for this I must ask the pardon of both the reader and the omitted author.

The body of the review is divided into six sections and followed by a final section suggesting a few of the areas where progress may be expected in the future. The six major subject headings are: (1) New phenomena; (2) Large‐scale waves and instabilities; (3) Equatorial wave, mean‐flow interaction–long‐period oscillations; (4) Extratropical wave, mean‐flow interaction–Sudden warmings; (5) Climatology and general circulation of the middle atmosphere; and (6) Transport of trace chemicals. The division into sections is of course rather arbitrary. Some papers fit well in more than one section, and others do not fit neatly into any of the subheadings chosen.
Overview of cosmic ray studies and associated topics (1979‐1982)
Authors: Shea M. A.
Published: February 2008

The reviews of cosmic ray studies (1979–1982) cover a broad area reflecting the present scope of this discipline. Cosmic ray physics long ago transcended the narrow restricted specialties of composition, flux and modulation. In fact the cosmic ray energy regime appears to be anything above “thermal” (a remark attributed to Professor Bruno Rossi). At the present time the relationship of cosmic ray studies to solar‐terrestrial physics encompasses an extremely wide range of interrelated and associated astrophysical phenomena from the sun, to the interplanetary medium and throughout the domain of the heliosphere.
Solar cycle and long term changes in the solar wind
Authors: Feynman J.
Published: February 2008

During the last four years substantial progress has been made in the study of variations of the solar wind on time scales of decades to hundreds of years. Solar cycle changes in 3 dimensions have been described and the cyclic evolution of solar sources studied. Work on longer term changes has made a good start. Data sets and methods of scientific analysis are being developed. Estimates have been made of pre‐space‐age solar wind properties. The existance of the eleven year cycle for the last 1,500 years was studied. The non‐random nature of variations over many solar cycles was confirmed but there is still controversy concerning the periodic nature of the 80–100 year variation. There is evidence that variations of the Maunder and Sporer types may be periodic.
The magnetosphere of Saturn
Authors: Schardt A. W.
Published: February 2008

The Pioneer 11, Voyagers 1 and 2 encounters with Saturn provided a wealth of information about its complex magnetosphere. The magnetic dipole moment of Saturn is rotationally aligned and only one‐fifth of that expected from pre‐encounter modeling. The bow shock stand‐off distance is about 22 RS and varies with solar wind pressure proportional to p−1/6. The satellites Titan, Dione, and Tethys are probably the primary sources of magnetospheric plasma. For <10 keV thermal plasma, β is less than one in most of the magnetosphere, but contributions from ∼20 keV plasma may increase this value significantly. Outside of ∼4 RS, energetic particles are energized by diffusing inward while conserving their first and second adiabatic invariants. Particles are lost by satellite sweep‐out, absorption by the E ring and probably also by plasma interactions, which produce a slot region between 4 and 9 RS. The inner magnetosphere is characterized by a cold plasma population (<10 eV/charge), which probably consists primarily of 0+ and has a scale height from the Equator of only 0.2 RS. Intense penetrating radiation exists in the inner magnetosphere from 4 RS to 2.265 RS, which coincides with the outer edge of the A ring. The energetic protons ⩾50 MeV have approximately the spectrum expected from a cosmic ray albedo neutron decay source. A proton component below 0.5 MeV was also found, as well as an electron flux with energies primarily above 1.5 MeV. Submicron charged dust gains constitute a new type of magnetospheric particle and their properties may explain the evolution of the B ring spokes and other B ring features.
New tools for magnetospheric research
Authors: Greenwald R. A.
Published: February 2008

This report examines some of the new techniques that are being used to increase our understanding of the Earth's magnetosphere and the manner in which it couples to the high latitude ionosphere. Particular attention is devoted to experiments in which one attempts to modify the environment in the magnetosphere and high latitude ionosphere, and to the increased usage of incoherent and coherent scatter radars for high latitude studies of magnetosphere‐ionosphere coupling. We also note the trend toward developing constellations of satellites and ground‐based instrumentation in order to obtain a better understanding of the global nature of magnetosphere‐ionosphere coupling and the increased use of large computer‐based suites of geophysical data.
Introduction to the Report on Geodesy
Authors: Chovitz Bernard H.
Published: February 2008

The growing interaction of geodesy with its kindred disciplines, oceanography and tectonophysics, may have been the most significant trend in geodetic activity during this past quadrennium. Geodetic observing systems are now capable of measuring so much more precisely (to the centimeter level) and over such a broader extent (like the oceans), that their results add materially to knowledge of crustal and mantle structure, of ocean bottom relief, and of oceanic circulation. Especially important is the application of precise, repetitive geodetic measurements to the detection and analysis of time‐varying effects. Examples are the utilization of altimeter data to yield ocean boundary current changes, and of radio interferometry and laser ranging to systematically monitor polar motion, Earth rotation, and crustal movements.
Induction of currents in long submarine cables by natural phenomena
Authors: Meloni A. , Lanzerotti L. J. , Gregori G. P.
Published: February 2008

The influence of induced currents on long submarine cables has been observed for nearly a century. The currents originate from time variations in the magnetic field of external origin (magnetospheric, atmospheric tides) and earth and ocean tides. Steady earth currents of internal origin have also been proposed as a possible source. The induced currents will depend upon the length, depth, and geomagnetic location of the cables. Present understanding of the phenomena is reviewed. Also discussed are potential scientific problems which might be addressed with data from such long cables and possible limitations on the information obtained. Such problems include studies of (1) the deep conductivity structure of the earth, (2) telluric currents flowing in mid‐oceanic ridges, (3) the spatial extent of external source fields, and (4) a possible role of electromagnetic eddy currents in fluctuations of the earth's spin rate.
Interpretation methods for magnetometer arrays
Authors: Gough D. I. , Ingham M. R.
Published: February 2008

In recent years, interpretation methods for magnetometer array studies have developed sufficiently to justify a review. Such studies investigate structure in the earth to depths of about 600 km using induction by various external current systems, which are briefly described. The use of magnetograms and Fourier transform anomaly maps for identification and location of induced currents is discussed. Characteristics of various types of anomalies are considered. This is followed by a discussion of the separation of time‐varying fields into external and internal parts by the use of surface integration. A section on transfer function analysis includes single‐station transfer functions and complete solutions of the induction matrix with various methods of estimation of the normal field. We next discuss representations of transfer functions by means of induction arrows, hypothetical event analysis, and Z/H pseudosections. Some conditions for stability of transfer functions are defined. Methods of one‐dimensional modeling and inversion are followed by a discussion of four methods of numerical modeling of two‐dimensional structures. Current channeling is considered briefly, and the paper ends with a short section on numerical and analogue modeling methods for three‐dimensional conductive structures.
Advances in short term climate prediction
Authors: Barnett T. P. , Somerville R. C. J.
Published: February 2008

Dynamical and several empirical and statistical approaches to short term climate prediction are surveyed. General circulation models have displayed considerable potential for this application. Physical/synoptic and purely statistical methods have been intensively developed and tested in recent years. Important problems have been recognized in areas such as predictability, forecast verification and evaluation, and combining complementary approaches to prediction.
Models of crustal deformation
Authors: Rundle John B.
Published: February 2008

This review is principally concerned with theoretical models of crustal deformation developed during this quadrennium. Observational data, as well as topics in lithospheric flexure and isostasy, are covered in companion reviews in this volume. Progress has been made toward constructing both new inelastic, and inhomogeneous elastic, models of earthquake‐induced crustal deformation. Most of the inelastic models involve dislocations or Green's functions in an elastic or anelastic lithosphere which overlies a Maxwell viscoelastic asthenosphere.
Azimuth, energy, Q, and temperature: Variations on P wave amplitudes in the United States
Authors: Butler Rhett
Published: February 2008

Mean relative P wave (1 s) amplitude characteristics are determined for standardized seismic stations in the United States. Data are compiled from three azimuths: to the north, explosions in Russia; to the northwest, earthquakes along the Asian‐Pacific arc; and to the south‐southeast, earthquakes in South America. Characteristic receiver amplitudes are found to be azimuthally dependent. High‐amplitude areas occur in the central United States, and lowest amplitudes occur along the Rocky Mountain front range and the Rio Grande rift zone. Amplification effects of low‐velocity sediments are significant in the central United States. Azimuthal amplitude variations in the eastern United States are consistent with an anomalous attenuating or defocusing body in the lower mantle beneath Colombia, South America. Nonazimuthal amplitude studies are tied to the azimuthal data set to increase station amplitude coverage. The regional and local stability of amplitudes is analyzed. Amplitudes are stable with an average variation of a factor of about 1.3 around the regional mean. For seismic stations situated on hard bedrock, the squared amplitude variations are related to energy variations in the P wave fronts. Acknowledging the likely importance of elastic focusing/defocusing and scattering effects at individual stations, variations of anelastic attenuation are derived that are consistent with the observed energy‐amplitude variations. Assuming that the variations of anelastic attenuation occur in the upper 400 km of the earth, high‐amplitude stations may be unattenuated, low‐amplitude stations are consistent with Q ∼ 110, and a mean amplitude implies Q ∼ 220–240. The range of variation of Q is mapped into temperature variations, assuming a thermally activated Q mechanism and an olivine activation energy for the upper mantle. The apparent Q variations are consistent with temperature variations of 135°–287°C between high‐ and low‐amplitude seismic station sites. Geophysical and physiographic correlations with the P wave amplitude variations are discussed. Accounting for the motion of the North American plate, low P wave amplitudes along the Rocky Mountain front may be related to the uplift of the Colorado Plateau. Low amplitudes extending from northern Texas to New England lie along the approximate boundary of the continental craton.
Acoustic properties of sediments: An update
Authors: Hampton Loyd
Published: February 2008

This paper will summarize our knowledge of the propagation of sound in marine sediments. This knowledge is important to a wide range of acoustic problems, extending from the high‐frequency applications of detection of objects buried in the bottom sediment to the very low frequency application characterizing the propagation of acoustic energy over hundreds of kilometers. In these applications the ocean bottom becomes an important part of the acoustic waveguide. The desirable goal of a complete theoretical understanding of propagation has not been achieved. However, recent measurements of acoustic attenuation in the frequency range of a few hundred hertz are almost an order of magnitude smaller than have previously been measured, and these results may now permit progress in a more complete characterization of the acoustic properties of sediments. (The research performed on this topic by the author under the guidance of R. Reid was published in 1967 (“Acoustic Properties of Sediments,” J. Acoust. Soc. Am., 42, 882–890, 1967). This paper will briefly review aspects of that work and trace the progress in this area of research since that publication.)
Thermochemical properties of silicate glasses and liquids: A review
Authors: Richet Pascal , Bottinga Yan
Published: February 2008

A prerequisite for thermodynamic modeling of silicate melts is a knowledge of basic thermodynamic data for glasses and liquids. The recent advances in the measurement and rationalization of these data are thus reviewed in this paper, with particular emphasis on the influence of the thermal history of glasses on their various thermochemical properties. Above room temperature the heat capacities of glasses (Cpg) do not depend sensitively on thermal history. They are almost additive functions of the chemical composition, which can now be empirically calculated to within about 1%. In contrast, the heat capacities of liquids (Cpl) do not generally vary linearly with composition, especially for aluminosilicates. But more experimental data would be useful to improve the accuracy of the models proposed for calculating the heat capacity of molten rocks. The available enthalpies of fusion (ΔHf), which depend measurably on the thermal history of the glasses used in solution calorimetry measurements, are summarized for silicates of geochemical or theoretical interest, and new values have been derived for some additional compositions. The usefulness of these data for calculating the entropies of liquids is pointed out, in particular for calculating the entropies and configurational entropies of the liquids. Finally, available enthalpies of mixing of glasses and liquids are also summarized. A few examples are used to illustrate the major influence of the thermal history of glasses on their mixing properties, and it is suggested that the ternary excess enthalpies of mixing observed in simple systems could be a spurious consequence of neglecting this influence.
Modeling contaminant transport in the subsurface: An interdisciplinary challenge
Authors: Abriola Linda M.
Published: February 2008

Recent work on the modeling of contaminant transport in saturated groundwater systems is presented. Emphasis is placed on the conceptualization and quantification of chemical and physical processes relating to transport. Geochemical, sorption, and biological transformation models are included as well as models describing transport in fractured media, dispersion and immiscible phase flow. Developments in the numerical modeling of the transport equation are also discussed briefly.
Atmospheric columnar vortices
Authors: Snow John T.
Published: February 2008

The family of atmospheric columnar vortices includes tornadoes, waterspouts, firewhirls, dust devils and a variety of other whirlwinds. Each member of the family is characterized by the presence of a relatively tall, concentrated vortical core. Descriptions of such swirling flows are inherently complex, reflecting the presence of a multiplicity of length and velocity scales. In many cases, the flow is both three‐dimensional and unsteady.
Thermospheric ion and neutral composition and chemistry
Authors: Breig E. L.
Published: February 2008

A summary is presented of research contributions by U. S. scientists during the years, 1983–1986, toward an increased understanding of the properties and behavior of the earth's thermosphere and F‐region ionosphere. As part of the more‐extensive aeronomy report to IUGG, this review addresses specifically the composition and relevant chemical and thermal processes that influence this region of the atmosphere. The discussion focuses on the separate neutral and ion species, and on the temperatures of the electrons, ions, and neutral gas. Related aspects of the solar radiation and photoelectrons are also included. Direct observational results and analyses are emphasized, along with references to pertinent findings from basic laboratory and theoretical studies.
The bowshock and magnetopause
Authors: Elphic R. C.
Published: February 2008

The explosive growth of magnetopause and bowshock research reported by Russell and Greenstadt [1983] has continued unabated through the 1983 to 1986 quadrennium. Shock research has gone far beyond the tentative exploratory work seen in the last two quadrennia: a sizable volume of collisionless shock parameter space has been explored both in careful data analysis and in theory and sophisticated simulations. Research on the magnetopause has progressed somewhat more slowly than shock research, but new results and exciting ideas concerning reconnection and energy transfer through the magnetopause have not been lacking in the past four years. Much of this shock and magnetopause research has been due, directly or indirectly, to knowledge gained from the multi‐spacecraft ISEE mission. Exciting results from AMPTE and the recent comet missions have opened whole new areas of shock research.
The time‐varying geomagnetic field
Authors: Voorhies Coerte V.
Published: February 2008

The scope of this review is limited to papers on the large scale geomagnetic field of deep internal origin and its secular variation published by U.S. authors and their colleagues during the 1983–1986 quadrennial. The many fine papers on this broad topic by authors outside the U.S. are regretfully excluded; fortunately, most of them are cited by the U.S. authors listed in the reference section of this review. LaBreque and Mayhew [this issue] review papers treating the smaller scale fields usually attributed to visco‐inductively and remanently magnetized crustal geologic structures. Review articles dealing with external fields are surveyed by M. Schulz in the Magnetosphere section of this U.S. National Report. Booker and Chave [this issue] review papers concerning the use of more rapidly fluctuating externally induced internal fields to probe the electrical properties of the crust and upper mantle. Lund and Olson [this issue] review papers concerning paleo‐secular variation and core geodynamo theory.
Rock‐forming minerals: Crystal chemistry, spectroscopy, disorder, high pressure, and synchrotron radiation
Authors: Prewitt Charles T.
Published: February 2008

The complexion of research efforts on rock‐ forming minerals has changed substantially in the past four years because of an increasing interest in the physical and chemical properties of minerals and how understanding of these proper‐ ties can contribute to the solution of important geological problems. This is illustrated by activities of the American Geophysical Union Committee on Mineral Physics where geophysicists, geochemists, mineralogists, crystallographers, and petrologists have begun to have regular meetings an scientific sessions designed to promote collaboration and cooperation. The general term that is being applied to all of this is “mineral physics,” not an entirely accurate term, but one that seems to cover most bases and to satisfy most participants. The Mineral Physics Committee was formed at the Philadelphia AGU meeting in 1983 and has continually expanded its role since that time, including holding a workshop and writing a report on the subject [Bassett, 1986]. For example, sessions on the mineral physics theme occupied all five days of the 1986 Fall AGU Meeting in San Francisco. Because of the interest in the subject, this review on rock forming minerals is written with emphasis on current developments in mineral physics that are of primary interest to mineralogists, petrologists, and geochemists. Other aspects of mineral physics, such as elasticity of minerals, is beyond the scope of this review.
Ocean chemical fluxes 1983–1986
Authors: Brewer Peter G. , Glover David M.
Published: February 2008

This review covers U.S. contributions in marine chemistry 1983–1986 in the areas of nutrient chemistry, carbon cycle, trace elements, oxygen cycling, radioisotopes (natural and artificial), particles and primary productivity. In most cases a simple review of important trends in this very large and diverse literature set is all that can be considered. The literature explosion in these areas results in more than 350 references.
Temperature anisotropies in the terrestrial ionosphere and plasmasphere
Authors: Demars H. G. , Schunk R. W.
Published: February 2008

The available theoretical and experimental evidence for ion and electron temperature anisotropies in the terrestrial ionosphere‐plasmasphere system is reviewed. The review is concerned only with temperature anisotropies in the thermal (less than 1 eV) populations and does not cover energized auroral populations, such as ion beams, conics, and bowl distributions. Currently, the bulk of the work dealing with temperature anisotropies has been theoretical. Various models have been used to predict ion and electron temperature anisotropies, including kinetic, semikinetic, hydromagnetic and generalized transport models. Temperature anisotropies have been predicted in the polar wind, along plasmapause field lines, during the refilling of the outer plasmasphere after depletion by a magnetic storm, and at F region altitudes in regions of rapid plasma convection. The experimental evidence for temperature anisotropies, on the other hand, is limited. Some of the observations support the theoretical predictions, while other observations indicate the presence of temperature anisotropies in regions where the models predict isotropic temperature distributions. More extensive observations are needed in order to elucidate the underlying processes controlling the thermal structure in the ionosphere‐plasmasphere system.