bluuebunny/crossref_metadata_2025 huggingface dataset:
Oceanic fine and microstructure
Authors: Gregg M. C.
Published: February 2008

During the past quadrennium there has been a large increase in the effort directed toward the smallest scales of variability in the ocean. The importance of this undertaking in relation to the basic physics of the sea was discussed in the previous quadrennial report by C. S. Cox and in general discussions by Charnock [1972] and Gregg [1973]. The work has included instrumentation, the development of complete data acquisition systems as well as individual sensors; observation, the display of high‐quality data to millimeter scales as well as more quantitative information on spectral levels and dissipation rates; analytical models, principally the development of a framework for discussing and comparing observations of temporal and spatial variability; and laboratory experiments, which have shown continued insights into double diffusivity phenomena and shear instabilities.

In discussing particular developments in each of these categories there must be mention of work done on internal waves; however, for a complete discussion of this area the reader is referred to the companion review in this series by M. G. Briscoe.
On the general ocean circulation
Authors: Sturges W.
Published: February 2008

In this article I will attempt to review some features of the general ocean circulation as they have come into print over the past 4 years. While preparing for this article I became more keenly aware of the truth of the expression ‘one man's signal is another man's noise.’ There is a clear trend in oceanic studies, not restricted to the past 4 years, to recognize the enormous variability found in the ocean. An important part of this variability, associated with the so‐called mesoscale eddies, is discussed in this review series by Robinson. But the ‘general ocean circulation,’ as I understand it, is the signal—sometimes strong, but often weak—that emerges from the background. As an example of a case where the signal‐to‐noise ratio is really bad, I have estimated [Sturges, 1974b] that it would take about 50 years of current meter data to allow a calculation of mean flow to within ±20% in the deep water just beyond a western boundary current. Schmitz et al. [1975] have found that by averaging current meter records over a few degrees of latitude, the signal begins to emerge with a few years of data. These results are consistent with the finding [e.g., Thompson, 1971] that for deep currents the rise in spectral power density toward lower frequencies levels off at periods of about 3 months. The primary reason for the problem we have with the signal‐to‐noise ratio is, quite obviously, that we do not have observational series that are long enough, or else that we do not understand the physics of the processes very well, or both.
U.S. contribution to Southern Ocean dynamics
Authors: Baker D. James
Published: February 2008

United States activity in general circulation problems in the Southern Ocean has recently been increasing rapidly. The data base collected through the Eltanin program through 1972, the promise of increased meteorological coverage by FGGE in 1978, and the development of long‐term current meter technology have led to the establishment of the U.S. component of the International Southern Ocean Studies, an International Decade of Ocean Exploration program sponsored by the National Science Foundation (1973). This program io designed to study the structure and long‐term variations in the current systems of the Southern Ocean; the first year‐long array of current meters was placed in the Drake Passage in January 1975. First studies on the problem of winter formation of antarctic bottom water (AABW) under ISOS began in September 1974; these will continue in order to determine the feasibility of monitoring such production (see below for further field studies on AABW).
Numerical weather prediction
Authors: Leith C. E.
Published: February 2008

Various numerical models are in use for prediction of the large‐scale motions of the atmosphere for operational or research purposes, and all seem to have comparable skill for several days, as shown by Druyan [1974] in a comparison of the Goddard Institute for Space Studies (GISS) [Somerville et al., 1974] model forecasts with those at the National Meteorological Center (NMC) [Shuman and Hovermale, 1968], the Fleet Numerical Weather Central (FNWC) [Kesel and Winninghoff, 1972], and the Geophysical Fluid Dynamics Laboratory (GFDL) [Miyakoda et al., 1972]. There have also been many models developed for treating limited areas with higher resolution, as described in a paper by Chen and Miyakoda [1974], in which many references to such models may be found.

The principal topics of this review, however, will be the recent research on the question of the theoretical predictability of the large‐scale motions of the atmosphere, on the design of a global observing and data assimilation system, and on the development of statistical‐dynamical forecasting models. These all relate to the first objective of the Global Atmospheric Research Program (Garp), namely, increasing the accuracy of forecasting over periods of 1 day to several weeks.
Meteorological satellite accomplishments
Authors: Allison L. J. , Arking A. , Bandeen W. R. , Shenk W. E. , Wexler R.
Published: February 2008

The year 1975 marks the fifteenth anniversary of the U.S. meteorological satellite program, which began on April 1, 1960, when the Tiros 1 experimental satellite was launched. Television pictures taken by the spinning Tiros 1, in a near‐earth, non–sun‐synchronous orbit, were often oblique and poorly illuminated. Nevertheless, they showed the organization of weather systems with a clarity never before seen and revealed phenomena that previously were unknown. Within a few days of the launch of Tiros 1 the new data were being used operationally to improve weather services [National Environment Satellite Service (NESS), 1971]. At the same time extensive research was carried out to increase our knowledge of the atmosphere and to develop techniques to utilize the new type of data.
Petrology of lunar soils
Authors: Heiken Grant
Published: February 2008

The moon is covered with a thin layer of unconsolidated debris called the lunar regolith. A typical sample of this regolith could be characterized as a gray, poorly sorted pebble‐ or cobble‐bearing silty sand having a bulk density of about 1.5 g/cm³. It consists of lithic and mineral fragments mostly from the local underlying bedrock and glass formed as melt by meteorite impacts. Most investigators conclude that regolith samples are formed primarily by impact‐cratering processes, although some may contain a minor pyroclastic component. The lunar regolith sampled by man commonly is stratified, the layers being interpreted as ejecta from primary or secondary impact craters. Physical and chemical indices of exposure at or near the lunar surface indicate that these layers, some sampled at depths of several meters, were once at the lunar surface. Each layer, which has distinct physical, petrographic, and chemical characteristics controlled by source areas for soil particles and the time of exposure to meteorite bombardment at the lunar surface, is here referred to as a lunar soil. The upper few millimeters of each soil layer, when exposed to the lunar environment, is subjected to intensive bombardment and reworking by micrometeorite impacts. These impacts break up soil particles (comminution) and melt a portion of the impacted soil. The melt, mixed with soil particles, forms irregular clusters called agglutinates. Micrometeorite bombardment of the surface soil layer continues until the layer is buried by fresh ejecta or is destroyed by a larger impact.
Precipitation of particles at low and middle latitudes
Authors: Paulikas G. A.
Published: February 2008

The phenomenology and aeronomic effects of charged particle precipitation at middle and low latitudes are reviewed. This paper includes discussions of the behavior of quasi‐trapped electrons observed at middle and low latitudes, discussions of the precipitation of protons from the ring current into the low‐latitude atmosphere, and a summary of the effects of the South Atlantic magnetic anomaly on charged particles trapped at low altitudes. A brief summary and review of controversial observations of charged particle fluxes at low altitudes is also included.
Aeronomic effects of the South Atlantic Anomaly
Authors: Gledhill J. A.
Published: February 2008

Experimental and theoretical values for precipitated electron and proton fluxes in the area of the South Atlantic geomagnetic anomaly are reviewed. Observations of airglow which have been reported in the literature suggest that there is no enhancement in the Brazilian region, though there may be some in the southeastern part of the Atlantic area. There is evidence from various types of observations that the electron density in the ionosphere is greater over the South Atlantic than at comparable places elsewhere, especially during magnetic disturbances, and similarly the ion density shows enhanced values. Electron and neutral temperatures may also be higher than normal in the anomalous region. Observations are required in all these fields, coordinated with particle flux measurements from rockets and satellites in the area, to confirm the reality of the effects and their relationship to particle precipitation.
Magnetospheric electric fields and their variation with geomagnetic activity
Authors: Kivelson Margaret Galland
Published: February 2008

Diverse and independent measurements of the variation of particle convection boundaries with geomagnetic activity are used to obtain relations between the magnitude of a large scale electric field and the Kp index. The relations are compared with measured fields and with models and are found to be consistent with diverse observations and probably more reliable than results previously obtained.
The current status of speculations on the composition of the core of the Earth
Authors: Brett Robin
Published: February 2008

The earth's core, at a pressure of between 1.3 and 3.7 Mbar and a temperature between 3000° and 5000°C, consists primarily of Fe‐Ni in the inner core and molten Fe alloyed with from 8 to 20% of a light element, most likely S or Si, giving an average atomic number for the elements in the outer core of about 23. If the core accreted before the mantle, then the apparent disequilibrium of some elements with respect to core and mantle is explained, but it is difficult to explain the presence of appreciable quantities of a light element that are required in the core. Alternatively, the core formed by melting, coalescence, and subsequent collapse of metallic particles in a protoearth that was relatively homogeneous initially. Such collapse would raise the temperature of the earth as much as 2300°K. Silicon must be present in the core if (Fe + Mg)/Si> 1 in the mantle and if that ratio for the bulk earth lies within the limits set by the sun and chondrites. If Si is present, the apparent chemical disequilibrium between metallic Si in the core and Fe2+and Fe3+in the mantle must be explained. Arguments for S in the core based on the abundance of S in rocks of crustal and mantle origin appear to have little foundation; however, there are strong geochemical and cosmochemical arguments justifying the presence of S in the core if the earth accreted at relatively low temperatures. The intriguing speculation that the bulk of the earth's potassium is present in the outer core, thus providing energy for core and mantle, remains to be tested by more partitioning experiments. A number of explanations exist to explain the apparent disequilibrium of some elements between core and mantle; however, none is satisfactory. The core formed soon after the earth accreted; in fact, the age generally taken as the age of the earth probably represents the time of core formation.
Trace element geochemistry: Applications to the igneous petrogenesis of terrestrial rocks
Authors: Frey F. A.
Published: February 2008

Trace element geochemistry, like the entire field of geochemistry, has applications in many earth science problems. In a brief contribution, it is not possible to report on recent advances in all aspects of trace element geochemistry; thus, I focus on applications in determining the origin and evolution of terrestrial igneous rocks. Important advances in trace element geochemistry arising from lunar and meteorite studies are reviewed in the sections on meteorites and planetology. This report primarily reviews progress from 1975 through 1978, but a few important 1973–1974 papers are included as are significant foreign contributions.
Positioning by satellites
Authors: Brown Duane C.
Published: February 2008

During the previous reporting period (1971–1974) accuracies of geodetic positioning by satellites had been pushed from the level of 5 meters rms or so characteristic of the NGS Worldwide Geodetic Satellite Triangulation to the level of 1 meter rms characteristic of routine satellite Doppler positioning based on use of precise ephemerides. To be sure, within this period the threshold of 1 meter was being broached by various NASA laser ranging experiments and by various experiments with Very Long Baseline Inferferometry (VLBI). These, however, were in the category of special exploratory endeavors involving only a relatively few stations occupied for extended periods and could hardly be regarded as routine.

During the current reporting period (1975–1978) accuracies have been pushed in several disciplines toward the 10 cm level, and the stage is being set for advancement toward the 1 cm level. This has been a period of extraordinary progress with particular impetus being provided by the challenge of precise monitoring of crustal movements over extensive regions of high seismic activity. More mundane, but of greater immediate impact has been the spectacular increase in the application of satellite Doppler positioning throughout the world. From the standpoint of economic significance this certainly qualifies as the most important single development in positioning by satellites during the current period. Accordingly, Doppler technology is accorded special prominence in this review. This is not to slight the impressive advances made in laser tracking and VLBI technology. However, these topics are addressed at some length in other sections of this issue and thus need not be pursued as deeply here. A similar remark applies to the Global Positioning System which is still in an early developmental stage and can therefore presently be addressed more from the standpoint of theoretical potential than from practical experience.
Boundary layer physics and turbulence—Theoretical aspects
Authors: Paegle Jan
Published: February 2008

Theoretical descriptions of the atmospheric boundary layer have not changed substantially during the past four years. The Monin‐Obukhov theory remains the most complete description of the surface layer. Rather idealized models of the deeper convective boundary layer are also reasonably accurate. The stable boundary layer is still poorly understood, and the controversy persists in several attempts to relate boundary layer motions to deeper tropospheric flow.
Carbon dioxide and climate
Authors: Marland Gregg , Rotty Ralph M.
Published: February 2008

During the years 1975–1978 concern over the increase of CO2 in the atmosphere expanded from the laboratory into the public policy arena. This was a period during which a profusion of international symposia, technical papers, and public‐policy‐oriented discussions drew wide attention to the potential dangers of unchecked growth of atmospheric CO2 and man's alterations of the global carbon cycle. At the same time, the interdisciplinary interactions focused attention on the gaps in understanding, the uncertainties in the models, the inadequacies of the data, and the difficulties inherent in forecasting. Recognizing the social, political, and economic implications should fossil fuel burning be implicated as a cause of major [unfavorable] changes in climate, the scientists involved have called for increased understanding through stimulated scientific inquiry, and for flexibility in public policy options.
Cloud physics: A review for 1975–1978 IUGG Quadrennial Report
Authors: Cotton William R.
Published: February 2008

Major advances in cloud physics for the period 1975 to 1978 are reviewed. The topics include the physics of nucleation, precipitation physics, electrical charging processes, dynamics of convective clouds, physics and dynamics of layer clouds, and clouds in extratropical cyclones.

2.0 Warm‐cloud Nucleation and Cloud Condensation Nuclei

The experiments of Katz and Kocmond (1973) cast considerable doubt upon the ability of heterogeneous nucleation (condensation) theory as described by Fletcher (1962) to predict the relationship between the size and critical supersaturation of aerosols. The former concluded that salt particles, nucleating water at a given supersaturation, produced droplets whose radii were two to three times larger than the radii predicted by theory. More recent experiments, however, by Twomey (1977), using atmospheric aerosol, and Gerber, et al. (1977), using both NaCl and (NH4)2 SO4 aerosol, provide rather convincing evidence that the relationship between size and critical supersaturation predicted by theory is consistent with their experimental results.
Observations of large‐scale traveling Rossby waves
Authors: Madden Roland A.
Published: February 2008

Considerable evidence for the existence of large‐scale (zonal wave numbers 1, 2, and 3) traveling Rossby waves, or waves of the second class, has been published. Analyses indicate that these observed waves disperse according to theory, the largest longitudinal and latitudinal scales moving fastest toward the west. Zonal wave numbers 1 and 2 in the geopotential or pressure fields nearly always propagate westward, wave number 3 propagates both eastward and westward, and wave number 4 nearly always propagates eastward. For zonal wave number 1 the largest latitudinal scale disturbances move around the earth in about 5 days. Smaller latitudinal scales range in period from 1 to 3 weeks. The most often reported period is near 16 days. For zonal wave number 2, most frequent periods reported are near 4 and 15 days. Vertical structures of the traveling large‐scale waves that have been studied so far resemble those of external waves with very small phase change with height and some indication of an amplitude increase with height. These large‐scale traveling waves may be important in furthering our understanding of time variations in the general circulation and in efforts to improve the skill of numerical weather prediction models.
The geomagnetic coast effect
Authors: Parkinson W. D. , Jones F. W.
Published: February 2008

Near most coastlines the vertical component of the geomagnetic variation field is abnormally large and correlates positively with the inland horizontal component. This phenomenon is known as the geomagnetic coast effect. The few coastal locations at which it is absent are tectonically anomalous. The ratio of vertical to horizontal components decreases inland at a rate which depends on the geological nature of the continent. The effect varies only slightly with period, reaching a broad maximum between periods of 30 and 90 min. A number of models have been investigated by either calculation or analogue modeling, but the complete problem dealing with finitely conducting irregular oceans overlying a less conducting lithosphere has not yet been solved. Eddy currents flowing entirely in the seawater would be induced only by the vertical component of the magnetic field. Observations, combined with analogue model experiments, suggest that induction by horizontal components is also important. This requires flow of current in the lithosphere beneath the oceans.
Intrinsic luminosities of the Jovian planets
Authors: Hubbard W. B.
Published: February 2008

We review available data and theories on the size and nature of interior power sources in the Jovian planets. Broad band infrared measurements indicate that Jupiter and Saturn have interior heat fluxes about 150 and 50 times larger, respectively, than the terrestrial value. While Neptune has a modest heat flux (∼5 times terrestrial), it is clearly detected by earth‐based measurements. Only Uranus seems to lack a detectable interior heat flow. Various models, ranging from simple cooling to gravitational layering to radioactivity, are discussed. Current evidence seems to favor a cooling model in which the escape of heat is regulated by the atmosphere. This model seems capable of explaining phenomena such as the uniformity of effective temperature over Jupiter's surface and the different emission rates of Uranus and Neptune. In such a model the heat radiated from the atmosphere may derive from depletion of a thermal reservoir in the interior, or it may derive from separation of chemical elements during formation of a core. Calculations indicate that in the earlier stages of cooling, Jupiter and Saturn may have more homogeneous abundances of hydrogen and helium and radiate energy derived from simple cooling. At a subsequent phase (which may be later than the present time), hydrogen and helium will separate and supply gravitational energy. Either model is consistent with a hot, high‐luminosity origin for the Jovian planets.
Transport coefficients of low‐energy cosmic rays in interplanetary space
Authors: Palmer I. D.
Published: February 2008

The propagation of energetic particles along and across the interplanetary magnetic field is governed by the large‐scale field geometry and by scattering in small‐scale turbulent fields. Values of the scattering mean free path parallel to the field, λ∥(R), are reviewed in prompt solar bursts and nonimpulsive (corotating) events. Analysis of intensity and anisotropy profiles in combination is a powerful tool for elucidating λ∥(R). A consensus is found: at 1 AU, λ∥ = 0.08–0.3 AU over a wide range of rigidity, R = 5 × 10−4 to 5 GV. Efforts to explain the discrepancy between empirical values of λ∥ and scattering theory are discussed. Quantitative measures of λ∥ in rare scatter‐free events, where λ∥ ≳ 1 AU, are discussed because they can provide important details of the scattering process and the magnetic power spectra. Cross‐field diffusion due to random walk of field lines is revisited. Recent values deduced from magnetic power spectra in interplanetary space, magnetic diffusion at the sun, Jovian electron propagation, and cosmic ray events are evaluated. Again, a consensus is sought, and a reasonable mean is K⊥r/β = 1021 cm² s−1. Previous arguments against a significant K⊥r are reassessed, including the problem of the persistence of intensity fluctuations in cosmic ray events. Combining the consensus for K⊥r/β with that for λ∥ gives K⊥r/K∥ < 0.1 at 1 AU, and thus neglect of K⊥r in the modeling of solar cosmic ray events appears justified (although account needs to be taken of coronal propagation). The outlook for the future includes better empirical values of λ∥ down to Ep ∼ 10 keV and Ee ∼ 1 keV, comparison with scattering theories at these energies, and comparison between empirical and theoretical λ∥ in other regions such as the magnetosheath and upstream solar wind.
Control surveys
Authors: Gergen John G. , Whalen Charles T.
Published: February 2008

North American Datum (NAD) Readjustment Project. The NAD readjustment project of the National Geodetic Survey (NGS) consists of three major tasks: the validation of all field projects, the validation of individual blocks, and the solution of the equations associated with each observation. Associated tasks include: researching mathematical models, defining detailed procedures, and developing required software. The validation of 4,890 field projects involved the keying of 2.5 million direction observations, the reprocessing of 60,000 electronic distance measurements, and the separate least‐squares adjustment of each field project.

Block validation consists of the systematic analysis of observational data within more than 800 blocks. This task began in July 1982, and is expected to continue for 2 years. The partitioning of the U.S. horizontal network into blocks, and the systematic reduction of the equations by the Helmert blocking method, represents the last task of the project. Block validation testing began in the fall of 1982.
Radio interferometry
Authors: Carter William E.
Published: February 2008

In the previous Quadrennial Report, Clark [1979c] concluded that, after slightly more than one decade of development and refinement, the technique of Very Long Baseline Interferometry (VLBI) had “come of age.” However, by the close of 1978, only the most tentative first steps had been taken by the geodetic community toward the deployment and operation of VLBI geodetic surveying systems. There was not a single dedicated geodetic VLBI observatory in the world. Even at major astronomical observatories, geodetic VLBI observing sessions were elaborate productions involving the very scientists and engineers who designed and built the instrumentation operating the data acquisition systems.
The benthic boundary layer and sediment transport
Authors: Nowell Arthur R. M.
Published: February 2008

The major problems facing scientists studying marine boundary layer fluid mechanics in 1979 concerned the specific mechanismic operating in the regions of the top and the bottom of the boundary layer. At the top, the mechanisms of fluid escapement from the boundary layer and mixing into the ocean interior could only be postulated. Approximations of diffusivity across the top of the layer were being debated, the values of which were more articles of faith than physically validated estimates (cf. Armi, 1979; Garrett, 1979). At the bottom, the intermittent generation of stress (cf. Gordon, 1975; Heathershaw and Simpson, 1979) was held responsible for the wide variability observed in the drag coefficient, and the thickness of the viscous sub‐layer was claimed to be greater than that traditionally found from laboratory studies (Caldwell and Chriss, 1979).
The computation of body wave synthetic seismograms in laterally homogeneous media
Authors: Chapman C. H. , Orcutt J. A.
Published: February 2008

Synthetic seismograms, computed for realistic, horizontally stratified media, are now routinely used as an aid to seismic interpretation. This paper reviews the theoretical background to these methods and presents comparisons of the two popular algorithms, reflectivity and WKBJ seismograms, for a variety of earth models. The transformed wave equations are developed from the equations for a spherical, gravitating medium in a symmetric form suitable for body wave calculations. Four methods of solving these equations in general, inhomogeneous layers are described: the WKBJ and Langer asymptotic expansions and the WKBJ and Langer iterative solutions. Together with the earth‐flattening transformation and the ray expansion, transformed solutions for body waves can then be obtained for realistic layered media. Four methods of inverting the frequency and wave number transformations are also described: the real and complex spectral and slowness methods. Although realistic seismic models are normally sufficiently complicated that numerical calculations are essential, before proceeding with numerical comparisons we have included a review of the canonical signals included in body wave seismograms. These analytic results for direct rays, partial and total reflections, turning rays on forward and reversed branches, head waves, interface waves, Airy caustics, and Fresnel and interface shadows are useful to anticipate and understand numerical problems and results. Finally, a comparison of Green's functions for crustal, mantle, and whole earth models, calculated using the WKBJ and reflectivity algorithms, is included.
SNC meteorites: Clues to Martian petrologic evolution?
Authors: McSween Harry Y.
Published: February 2008

The shergottites, nakhlites, and Chassigny (SNC meteorites) are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body. The mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks, although their ratios of Fe/(Fe + Mg) and certain incompatible elements and their oxygen isotopic compositions are distinctive. All have crystallization ages of 1.3 b.y. or younger and formed from magmas produced by partial melting of previously fractionated source regions. Isotope systematics suggest that the SNC parent body had a complex and protracted thermal history spanning most of geologic time. Some meteorites have been severely shock metamorphosed, and all were ejected from their parent body at relatively recent times, possibly in several impact events. Late crystallization ages, complex petrogenesis, and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet. Trapped gases in shergottite shock melts have compositions similar to the composition measured in the Martian atmosphere. Ejection of Martian meteorites may have been accomplished by acceleration of near‐surface spalls or other mechanisms not fully understood. If SNC meteorites are of Martian origin, they provide important information on planetary composition and evolution. The bulk composition and redox state of the Martian mantle, as constrained by shergottite phase equilibria, must be more earthlike than most current models. Planetary thermal models should benefit from data on the abundances of radioactive heat sources, the melting behavior of the mantle, and the timing of planetary differentiation. Calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides, and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years. Concentrations of volatile elements indicate that the SNC parent body was not volatile depleted, and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing. By providing comparisons for spectral reflectance data and Viking soil analyses, these meteorites may also constrain surface mineralogy and weathering mechanisms.
A history of presatellite investigations of the Earth's Radiation Budget
Authors: Hunt Garry E. , Kandel Robert , Mecherikunnel Ann T.
Published: February 2008

Studies of the earth's radiation budget now form a major part of climate research using measurements made from earth‐orbiting and geostationary satellites. However, there has been considerable interest in this topic well before the development of space observing systems. In this paper we provide the historical perspective to radiation of budget studies and describe the early studies from the beginning of this century until the 1960s.
Centered and eccentric geomagnetic dipoles and their poles, 1600–1985
Authors: Fraser‐Smith A. C.
Published: February 2008

Using a unified approach, expressions are derived for the various pole positions and other dipole parameters for the centered and eccentric dipole models of the earth's magnetic field. The pole positions and other parameters are then calculated using the 1945–1985 International Geomagnetic Reference Field Gauss coefficients and coefficients from models of the earth's field for earlier epochs. Comparison is made between (1) the recent pole positions and those pertaining since 1600 and (2) the various theoretical pole positions and the observed dip pole positions.
The application of inverse theory to seamount magnetism
Authors: Parker Robert L. , Shure Loren , Hildebrand John A.
Published: February 2008

The traditional least squares method for modeling seamount magnetism is often unsatisfactory because the models fail to reproduce the observations accurately. We describe an alternative approach permitting a more complex internal structure, guaranteed to generate an external field in close agreement with the observed anomaly. Potential field inverse problems like this one are fundamentally incapable of a unique solution, and some criterion is mandatory for picking a plausible representative from the infinite‐dimensional space of models all satisfying the data. Most of the candidates are unacceptable geologically because they contain huge magnetic intensities or rapid variations of magnetization on fine scales. To avoid such undesirable attributes, we construct the simplest type of model: the one closest to a uniform solution as measured by the norm in a specially chosen Hilbert space of magnetization functions found by a procedure called seminorm minimization. Because our solution is the most nearly uniform one we can say with certainty that any other magnetization satisfying the data must be at least as complex as ours. The theory accounts for the complicated shape of seamounts, representing the body by a covering of triangular facets. We show that the special choice of Hilbert space allows the necessary volume integrals to be reduced to surface integrals over the seamount surface, and we present numerical techniques for their evaluation. Exact agreement with the magnetic data cannot be expected because of the error of approximating the shape and because the measured fields contain noise of crustal, ionospheric, and magnetospheric origin. We examine the potential size of the various error terms and find that those caused by approximation of the shape are generally much smaller than the rest. The mean magnetization is a vector that can in principle be discovered from exact knowledge of the external field of the seamount; this vector is of primary importance for paleomagnetic work. We study the question of how large the uncertainty in the mean vector may be, based on actual noise, as opposed to exact, data; the uncertainty can be limited only by further assumptions about the internal magnetization. We choose to bound the rms intensity. In an application to a young seamount in the Louisville Ridge chain we find that remarkably little nonuniformity is required to obtain excellent agreement with the observed anomaly while the uniform magnetization gives a poor fit. The paleopole position of ordinary least squares solution lies over 30° away from the geographic north, but the pole derived from our seminorm minimizing model is very near the north pole as it should be. A calculation of the sensitivity of the mean magnetization vector to the location of the magnetic observations shows that the data on the perimeter of the survey were given the greatest weight and suggests that enlargement of the survey area might further improve the reliability of the results.
Progress in unsaturated flow and transport modeling
Authors: van Genuchten Martinus Th. , Jury William A.
Published: February 2008

This paper reviews recent progress in modeling water flow and solute transport in the unsaturated (vadose) zone. Much progress has been attained in the analytical and numerical description of vadose zone transfer processes. A variety of deterministic models are currently available for describing and predicting these processes. The most popular ones continue to be the classical Richards equation for unsaturated flow and the Fickian‐based convection‐dispersion equation for solute transport. While deterministic solutions of these equations remain useful tools in research and management, their practical utility for predicting actual field water and solute concentration is increasingly being questioned. Problems caused by preferential flow through soil macropores and by spatial and temporal variability in soil hydraulic properties have caused some disillusionment with the classical models. A number of alternative deterministic and stochastic formulations have been proposed to specifically deal with preferential flow and/or spatial variability. Those models have greatly increased our understanding of field scale transport processes, and have in some cases led to better practical tools for management purposes.
Field studies in groundwater hydrology—A new era
Authors: Anderson Mary P.
Published: February 2008

Recent field studies aimed at obtaining a three‐dimensional understanding of groundwater systems are described. Studies of plumes of contaminated groundwater as well as studies focusing on aquifer recharge, the interaction of groundwater with surface waters, and the siting of a geologic repository for high‐level radioactive waste are included in the discussion.
Energetics and dynamics of the Earth’s thermosphere
Authors: Killeen T. L.
Published: February 2008

The Earth's thermosphere, i.e., the region above the mesopause (∼80–90 km) where the neutral gas temperature increases towards an asymptotic value determined by the variable sources of solar heating, has remained the subject of extensive experimental and theoretical study during the last few years. Since the time of the previous IUGG quadrennial report, results from several comprehensive experimental undertakings have been reported and the theoretical and semi‐empirical models of the region have matured considerably. Previous reviews in this series by Dickinson (1975), Mayr and Harris (1979), and Roble (1983a) have charted the progress made in our understanding of the thermosphere up to 1982. Other valuable review articles have appeared over the years that have concentrated on various aspects of thermospheric research including composition and variability [Carignan, 1975; Hedin, 1979; Prölss, 1980; Prölss and Roemer, 1985, 1987], incoherent scatter radar observations [Evans, 1975], tides and tidal forcing [Evans, 1978; Forbes and Garrett, 1979; Lindzen, 1979; Forbes, 1984], gravity waves [Hunsucker, 1982; Fritts 1984], ionospheric processes and electrodynamics [Richmond, 1983, 1986], thermospheric photochemistry [Torr, 1985; Torr and Torr, 1982; Roble, 1986a], atmospheric emissions [Bates, 1982, 1983; Vallance Jones et al, 1985] and thermospheric winds and temperatures [e.g., Straus, 1978; Rishbeth, 1979, 1982; Meriwether, 1983; Killeen, 1985; Rees, 1985; Mayr et al, 1985; Roble, 1983b,1986b].
Quadrennial review of the magnetotail
Authors: Huang C. Y.
Published: February 2008

There has been a great deal of interest in the magnetotail during the past quadrennial period. This has been in part due to the passage of ISEE 3 through the distant magnetotail. The investigation of the region from 60 to 220 RE from the earth has contributed much to our understanding of tail structure and dynamical response to geomagnetic activity. As always the question of substorms and the nature of energy transfer is a focus for many publications.
Numerical simulations of magnetospheric plasmas review and Quadrennial Report to the IUGG
Authors: Palmadesso Peter J. , Ganguli Supriya B. , Fedder Joel A. , Lyon John G.
Published: February 2008

This article provides a broad survey of U. S. progress during the quadrennium 1983–1986 in the category ‘numerical simulations of magnetospheric plasmas’. There has been a substantial increase of activity in this area during this period. Simulations have been instrumental in providing valuable insights into large scale dynamic phenomena, nonlinear effects, and complex kinetic phenomena in a wide variety of subject areas, including shocks and double layers, ionosphere‐magnetosphere coupling phenomena, and important microphysical processes such as broadband electrostatic noise. The methodology of computer simulation has also been advanced during this quadrennium. Vlasov algorithms have been improved; hybrid codes in 2 and 3D have been developed and applied to magnetospheric problems; and complex problems have with increasing frequency been subjected to a multipronged attack in which several types of simulation models, each designed to accurately model phenomena within a particular range of temporal or spatial scales, are employed synergistically.
Morphology of geomagnetic reversals
Authors: Bogue Scott W. , Hoffman Kenneth A.
Published: February 2008

Geophysicists from the United States have been very active in the international effort to understand the nature of the geomagnetic field during polarity reversals. The traditional justification of this research, that knowledge of transitional field behavior may eventually help constrain theoretical geomagnetic dynamo models, remains compelling. But in addition, the paleomagnetic observation and modeling of transitional field behavior has developed a life of its own. Two recent discoveries, that many organisms navigate using the geomagnetic field (e.g., Blakemore and Frankel [1981]) and that the magnetic field of Uranus may be in the midst of a polarity change [Ness et al., 1986], have even begun to stimulate public interest in geomagnetic reversals. Both authors of this report have been pleasantly surprised at the interest expressed by non‐scientists when conversations have somehow drifted onto the topics of our research.
Crustal geologic studies with Magsat and surface magnetic data
Authors: Mayhew Michael A. , LaBrecque John L.
Published: February 2008

In this review we discuss the contributions during the last quadrennium which involved both Magsat and aeromagnetic data, including new techniques for interpreting this data, specific regional investigations, and laboratory studies intended to understand the connection between magnetic anomalies and the magnetic mineralogy of their sources.

In recent years it has become commonplace to present the data obtained from magnetic surveys in the form of digital images. Techniques for applying special filters appropriate for potential fields and the image enhancement tricks developed by the remote sensing community have come in to widespread use, and were very much in vogue among U.S. investigators during this quadrennium. A key paper by Cordell and Grauch (1985) described a procedure for extracting full information from an aeromagnetic survey for the purpose of mapping basement units under variable‐thickness sedimentary cover; it combines a Taylor series approximation with standard FFT computations (Hildenbrand, 1983). A topographically draped survey is continued to a level surface just above the highest topography using the Taylor series technique, downward continued to the mean basement level via FFT and applying a low‐pass filter, then draped over the basement surface. Aliasing problems exist, but are minor. Magnetization boundaries are then delineated by the horizontal gradient of the pseudogravity distribution. Using sparse well data for constraint, it was possible to make a basement magnetization map for the San Juan Basin, New Mexico, in a detail which would not have been possible with the original data as flown. Blakely and Simpson (1986) developed an automated procedure for delineating magnetization (or density) boundaries for machine application of the Cordell‐Grauch method; this is simply an efficient way of finding the loci of maxima in the horizontal gradient for a grid of data.
Oceanic ridge crest processes
Authors: Rona Peter A.
Published: February 2008

Oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth, atmospheric and biologic sciences. This deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere, hydrosphere, atmosphere and biosphere, and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data. These techniques include crustal drilling with borehole logging (Deep Sea Drilling Project reports), high‐resolution bathymetry (Sea Beam, etc.), side‐scan sonar (SeaMARC I and II, GLORIA, etc.), imagery with video and photography, multichannel seismics, determination of water column properties (CTD with rosette sampler, etc.), and submersible applications.
Advances in the chemistry of rivers, estuaries, microcosms, and salt marshes—1983–1986
Authors: Church Thomas M.
Published: February 2008

There have been dramatic advances in our knowledge of chemical processes in coastal waters during the past several years. Much of this work in the U.S. has focused on estuaries using larger seasonal data sets, advanced analytical techniques, and process oriented studies. The processes of interest include the scavenging of riverine substances in estuaries, the recycling of nutrient components, diagenetic exchange with anoxic sediments, and tidal flushing of land derived material and pollutants to the sea. As estuarine systems interact with the geo‐ and biosphere in a complex way, empirical data sets have been supplemented by experimental approaches including mixing experiments and controlled microcosms. Since most river‐estuarine systems experience tidal flushing, fringing intertidal salt marshes/mangroves appear to be important buffers for chemical storage, recycling, and exchange.

Principle rivers of the world provide an important means for the transport of terrestrial constituents to the ocean. However, estuaries constitute an important transition zone which can provide a buffer for the extraction and recycling of those elements which eventually reach the sea. There have been important advances over the past several years by U.S. investigators showing how inorganic and organic constituents of rivers are involved either in direct (riverine) or indirect (estuarine) transport to coastal waters. These more recent studies provide both a quantitative basis and process orientation for delineating estuarine transport. This report will summarize progress in the United States since 1982 in studies of rivers, estuaries, microcosms and salt marshes.
The lack of reproducibility in experimentally determined intensities of the Earth's magnetic field
Authors: Walton D.
Published: February 2008

Present techniques for obtaining palaeomagnetic intensities can fail to detect mineral alteration occurring during heating in the laboratory. It is very likely that this alteration is responsible for much of the poor reproducibility of ancient intensities of the geomagnetic field. A technique is described which can detect it, with a significant improvement in both the reproducibility and accuracy of the results.
Comment on “The lack of reproducibility in experimentally determined intensities of the Earth's magnetic field” by D. Walton
Authors: Aitken M. J. , Allsop A. L. , Bussell G. D. , Winter M. B.
Published: February 2008

After indicating the basis of the technique, its use with a cryogenic SQUID magnetometer is outlined, particular emphasis being given to the need for stringent reliability criteria. Comparison of results for some samples is made with results obtained using the Shaw alternating‐field technique, and the agreement is satisfactory. Determinations made on 14 samples fired during the last 150 years give results which on average are in close agreement (within 2%) with observatory‐based values, the standard deviation of a sample from the predicted value being ±6%.
The mystery of the Antarctic Ozone “Hole”
Authors: Solomon Susan
Published: February 2008

Total ozone levels over Antarctica have declined by about 50% over the past decade, principally during the spring seasons. This unprecedented and unanticipated change in the total ozone column has precipitated a great deal of research into the dynamics and chemistry of the Antarctic, and their contributions to the observed behavior of ozone there. Observations of the total ozone column and its vertical profile over Antarctica are reviewed. Theoretical models to explain the mysterious change in ozone abundances are described, along with observations of Antarctic temperatures. Both chemical and dynamical processes occurring in Antarctic spring may be related to polar stratospheric clouds. The radiative and chemical properties of these clouds are summarized. Available observations of other chemical species besides ozone (e.g., nitrogen dioxide, chlorine monoxide) are also discussed. The current status of the evidence supporting various theories of the behavior of ozone in the Antarctic is summarized.