bluuebunny/crossref_metadata_2025 huggingface dataset:
Saltation and Martian sandstorms
Authors: Maegley Wendel J.
Published: February 2008

A brief topical review of current knowledge available for predicting the characteristics of sandstorms is presented. Particular emphasis is placed on extrapolations to Mars where saltation of loose surface material appears to be a necessary condition for initiation of observed dust storms. Considerable data are now available to predict threshold winds under earth's environmental conditions, but techniques for predicting the quantity of material transported and the height and velocity to which it travels are still crude. Extrapolation of current knowledge to Mars is probably sufficient only for estimating purposes and landing craft design. The upcoming Viking landing mission on Mars will, it is hoped, shed additional light on the problem.
Mare basalt petrogenesis—A review of experimental studies
Authors: Kesson S. E. , Lindsley D. H.
Published: February 2008

Melting experiments on mare basalts are complicated by technical problems. The quality of the experimental results can be evaluated from the following criteria: (1) attainment of equilibrium (except in rate studies), (2) acceptable monitoring and control of pressure and temperature, (3) acceptable control of oxygen fugacity, and (4) preservation of constant bulk composition of the sample; i.e., reaction of the sample with its container must be controlled within narrow limits. Melting experiments in vacuum and in controlled gas atmospheres confirm petrologic and geochemical observations that most of the chemical variety among the (olivine normative) low‐Ti basalts is due to fractionation of olivine plus or minus minor spinel. The chemical variety among the high‐Ti basalts is likewise controlled by near‐surface fractionation processes, but the low‐K and high‐K groups cannot be interrelated in such a manner. Crystallization experiments have also shown that porphyritic textures can sometimes be produced by a single‐stage cooling history. High‐pressure studies indicate that the low‐Ti suite originated by partial melting of an olivine‐pyroxenite mantle at depths ranging from 200 to 350 km (to 500 km including green glass). It is generally agreed that a spectrum of low‐Ti parental magmas could be produced over this depth interval, the most olivine normative liquids originating at greatest depths. Experimental results suggest that the high‐Ti suite (and orange glass) formed by partial melting of an intrinsically Ti rich olivine‐pyroxenite mantle at depths similar to those at which the low‐Ti suite is produced. Alternatively, the high‐Ti basalts can be interpreted as hybrid liquids whose petrogenesis involves the assimilation of subcrustal Ti‐rich material by parental magmas of low‐Ti type and origin. The Ti‐rich zone is believed to have formed during an early differentiation event. Isotopic data indicate a prior differentiation history for mare basalt source regions.
Rare gas fractionation patterns in terrestrial samples and the Earth‐atmosphere evolution model
Authors: Ozima Minoru , Alexander E. Calvin
Published: February 2008

Rare gas abundances in various terrestrial materials can be classified into three distinct fractionation patterns: type 1 shows a progressive enrichment in the heavier gases (shales, natural gases, holocrystalline submarine basalts, seawater and groundwater), type 2 shows a large enrichment of Ne and a slight apparent enrichment of Xe (glassy margins of submarine basalts, a subaerial basalt, an olivine xenolith from Hawaii), and type 3 shows large enrichments of Ne, Kr, and Xe relative to Ar (thucolite and a shale sample). The type 1 pattern is formed by the low‐temperature adsorption of rare gases usually via the rare gases dissolved in seawater. The type 2 pattern is interpreted as a combination of high‐temperature diffusion, solubility, and bulk melting in the mantle. The type 3 pattern probably represents a hybrid pattern. These patterns are consistent with an earth‐atmosphere evolution model which assumes (1) that the present rare gas abundances in the atmosphere closely approximate the rare gas inventory of the whole earth except for xenon and (2) that the average rare gas abundance pattern in the solid earth is roughly similar to that in the atmosphere except for Xe.
The elastic properties of composite materials
Authors: Watt J. Peter , Davies Geoffrey F. , O'Connell Richard J.
Published: February 2008

The determination of the elastic properties of composite materials (multiphase aggregates, polycrystals, and porous or cracked solids) from the elastic properties of the components may be approached in several ways. The problem may be treated statistically, via scattering theory, through variational principles, or by the assumption of specific geometries for the material under consideration. Each of these methods is reviewed in turn. The widely used Voigt‐Reuss‐Hill average can be a poor approximation for both two‐phase composites and polycrystals, and its replacement by the two Hashin‐Shtrikman bounds is recommended. For pore‐containing or crack‐containing media, specific geometry models must be considered if useful results are to be obtained. If aggregate theory is used to estimate the moduli of individual components of a composite whose bulk properties are known, the shear moduli of the component phases must be matched (within a factor of 2 or 3) for the method to be useful. Results for nonlinear composites (which allow calculation of the pressure variation of aggregate moduli) have been obtained for only a few special cases.
Implications of Pacific Island and seamount ages for the origin of volcanic chains
Authors: Jarrard Richard D. , Clague David A.
Published: February 2008

Available age data from the Hawaiian, Marquesas, Kodiak‐Bowie, Society, Caroline, and Guadalupe chains, all WNW trending Pacific chains, follow patterns of generally increasing ages to the WNW. The inferred rates of volcanic propagation for these chains are not significantly different and apparently offer strong support for the hypothesis that volcanic chains are formed by ‘hot spots’ which do not move with respect to each other. However, age data from the Austral‐Cook chain follow no simple pattern: ages are both younger and older than would be expected from the ‘fixed hot spot’ hypothesis. Eocene and Cretaceous ages from along the Hawaiian ridge are inconsistent with the otherwise systematic age progression along this chain. The limited age data from the older NNW trending chains show little evidence of age progression. The best dated of these older chains, the Line chain, could have formed synchronously along most of its length.
Heliocentric distance dependence of the interplanetary magnetic field
Authors: Behannon Kenneth W.
Published: February 2008

Recent and ongoing planetary missions have provided and are continuing to provide extensive observations of the variations of the interplanetary magnetic field (IMF) both in time and with heliocentric distance from the sun. Large time variations in both the IMF and its fluctuations are observed. These are produced predominantly by dynamical processes in the interplanetary medium associated with stream interactions. Magnetic field variations near the sun are propagated to greater heliocentric distances, a process also contributing to the observed variability of the IMF. Temporal variations on a time scale comparable to or less than the corotation period complicate attempts to deduce radial gradients of the field and its fluctuations from the various observations. However, recent measurements inward to 0.46 AU and outward to 5 AU suggest that the radial component of the field on average decreases approximately as r−2, as was predicted by Parker, while the azimuthal component decreases more rapidly than the r−1 dependence predicted by simple theory. Three sets of observations are consistent with an r−1.3 dependence for |Bϕ|. The temporal variability of solar wind speed is most likely the predominant contributor to this latter observational result. The long‐term average azimuthal component radial gradient is probably consistent with the Parker r−1 dependence when solar wind speed variations are taken into account. The observations of the normal component magnitude |Bθ| are roughly consistent with a heliocentric distance dependence of r1.4. The observed radial distance dependence of the total magnitude of the IMF is well described by the Parker formulation. There is observational evidence that amplitudes of fluctuations of the vector field with periods less than 1 day vary with heliocentric distance as approximately r3/2, in agreement with theoretical models by Whang and Hollweg. In relation to total field intensity, the amplitude of directional fluctuations is on average nearly constant with radial distance, at most decreasing weakly with increasing distance, although temporal variations are large. There is evidence that fluctuations in field intensity grow in relation to those in field direction with increasing distance. More observations are needed to confirm these conclusions. The number of directional discontinuities per unit time is observed to decrease with increasing distance from the sun. The apparent decrease may possibly be caused by geometric or selection effects. The relationship between fluctuations of the field and the corotating stream structure is still not understood in detail, and therefore the origins of the various mesoscale and microscale features are at present uncertain.
Recent drought in California and western Europe
Authors: Namias Jerome
Published: February 2008

This paper relates the California and west European droughts of 1976 to contemporary and antecedent atmospheric and oceanographic factors. An observed anomalous warming of 3°–4°C from the surface to 10 km in the core of these droughts and diminishing relative humidities in the lower troposphere can be accounted for by subsidence of the order of several hundred meters per day. During winter, extremely strong high‐latitude westerlies and strong subtropical highs extended into western areas of the United States and west Europe. The hemispheric wave number increased from four in the winter of 1976 to five in the summer, the new troughs being formed in areas where lower‐boundary temperature contrasts existed. Newly derived seasonal teleconnections suggest that anomalous ageostrophic banking to the right of the high‐latitude westerlies, reinforced by sea surface temperature (SST) gradients, created the anomalous winter subtropical anticyclones. The summer drought‐producing circulation over west Europe, according to statistically derived teleconnections, was highly compatible with numerous remote anomalies but was probably forced largely by overlying and distant atmospheric responses to the strong central Atlantic SST gradient. Interannual lag correlations between sea level pressure patterns, as well as SST patterns, were unusually high between the winters and between the summers of 1975 and 1976 and appear to have increased over the past 5 years. It is theorized that these runs of recurrent circulations are due to atmosphere‐ocean coupling wherein subsurface anomalously warm or cold water, generated in the cold seasons over a deep mixed layer, has a tendency to be brought to the surface whenever wind stirring is enhanced. This usually occurs in the subsequent fall and winter.
Some properties of upper atmosphere dynamics
Authors: Mayr H. G. , Harris I. , Spencer N. W.
Published: February 2008

Composition and temperature data from satellite measurements and from radar backscatter observations show that dynamics is a major key in our understanding of the upper atmosphere. Individual gases are tracers of wind fields which in turn are driven by the energy and momentum sources of the complex magnetosphere‐thermosphere‐lower atmosphere system. As is shown with data from Ogo 6, ion drag effects on winds impose a magnetic field control on the thermospheric density structure. Differential heating manifests itself in day‐night and summer‐winter temperature contrasts and drives large‐scale circulation that redistributes the minor gases to account for the observed winter bulges in O and He (a factor of 40 larger in winter than in summer) and the large phase separations between atmospheric species in the diurnal tide. Large‐scale atomic oxygen transport within the thermosphere significantly enhances the annual temperature amplitude (by more than a factor of 2) and, through release of chemical energy, contributes to the mesospheric temperature anomaly. The latter phenomenon and the associated reversals in circulation are largely determined by the annual tide excited near 50 km and possibly by dissipation of gravity and planetary waves in the winter hemisphere. During magnetic storms, Joule heating and viscous dissipation drive winds that effectively deplete O and He in the auroral zones and accumulate them at lower latitudes. Mass transport of O amplifies and confines the temperature enhancement to high latitudes, compatible with the observed global response of mass density. The timing of wind and composition effects significantly contributes to the positive and negative phases in ionospheric storms. Owing to the rotational nature of ion drift momentum sources, their signatures in the atmosphere are comparatively weak and differ substantially from those associated with heat sources.
Paleomagnetism related to continental drift and plate tectonics
Authors: Van der Voo Rob
Published: February 2008

This brief review article deals with those aspects of paleomagnetism that are related to continental drift, plate tectonics, and polar wandering. It is a sequel to a previous review paper (Van der Voo, 1975) and will not repeat the bibliography of that paper dealing with the U.S. contributions prior to 1974.

The accomplishments and highlights of the past four years are reviewed below. This review will be followed by a rather personal assessment of the important open questions that are likely to be attacked in the next four‐year period. The bibliography contains a comprehensive listing of U.S. contributions in this field for 1974–1978, as well as selected publications from abroad. For a general treatment of paleomagnetism and plate tectonics the reader is referred to McElhinny (1973); recent listings of new paleomagnetic pole positions complement the data base of 1973 (McElhinny and Cowley, 1977, 1978; see also Hicken et al., 1972; Irving and Hastie, 1975; Irving et al., 1976a,b,c).
Physical properties of minerals and melts
Authors: Shankland T. J.
Published: February 2008

This review summarizes measurements and theoretical developments for those physical properties of primary interest in geophysical calculations. It includes thermal properties, electrical conductivity, diffusion in minerals and melts, with only slight mention of the corresponding properties of rocks. Elastic properties and acoustic velocities are discussed; however, related work on equations of state and on plastic deformation are covered by Bell and Tullis in other reviews in this series. Knowledge of physical properties provides the basis for interpreting geophysical measurements of seismic velocities, electrical conductivity, and temperature gradients in terms of unknown quantities, such as mineralogical and chemical composition, temperature, heat flow, and fluid contents at depth in the earth and moon.

The growth of this field as a specialty is signalled by several indications, for instance: books; Physics and Chemistry of Minerals and Rocks (Strens, 1976), High Pressure Research, Applications in Geophysics (Manghnani and Akimoto, 1977), each of which reports conference results; a new journal; Physics and Chemistry of Minerals; and topical meetings; the Mineral Physics Conference, Airlie, Virginia, October 1977.
Terpenoids in the atmosphere
Authors: Graedel T. E.
Published: February 2008

Terpenoids (terpenes and their oxygenated derivatives) are common tropospheric species. Information concerning the terpenoids and assessing their importance in atmospheric processes is sparse and widely distributed, however. This review presents chemical structure, physical property, and source information for 45 terpenoids known to be emitted into the atmosphere. Rate constants for the reactions of the terpenoids with atmospheric scavengers are presented, and typical terpenoid lifetimes are derived. Chemical product studies are used to derive plausible reaction mechanisms for selected acyclic, monocyclic, and bicyclic terpenes. The atmospheric cycle of the terpenoids is discussed, and it is concluded that inadequate information currently precludes quantitative assessments of the relative impact of terpenoids on local, regional, and global atmospheric processes.
Weather modification
Authors: Grant Lewis O. , Cotton William R.
Published: February 2008

A number of large weather modification experiments were completed and/or reported during the 1975–1978 period. These were, typically, experiments that were operated by relatively large groups of scientists and included the Bureau of Reclamation Colorado River Basin Pilot Project (hereafter referred to as CRBPP), NOAA's Florida Area Cumulus Experiment (FACE), the National Center of Atmospheric Research (NCAR) National Hail Research Experiment (NHRE), and the Metropolitan Meteorology Experiment (METROMEX). Other important but smaller cloud seeding experiments were also analyzed and reported: Israel's Confirmation Seeding Experiment (Israel II), the North Dakota Pilot Project, the Tasmania Experiment, and the Cascade Experiment emphasizing only physical studies as distinct from statistical experiments. Three broadly considered weather modification assessments were also published during this period.
Trace elements as quantitative probes of differentiation processes in planetary interiors
Authors: Drake Michael J.
Published: February 2008

Abundances of trace elements in extrusive igneous rocks may be used as petrological and geochemical probes of the source regions of the rocks if differentiation processes, partition coefficients, phase equilibria, and initial concentrations in the source region are known. The characteristic trace element signature that each mineral in the source region imparts on the magma forms the conceptual basis for trace element modeling. The task of the trace element geochemist is to solve mathematically the inverse problem. Given trace element abundances in a magma, what is the mode of its source region? The most successful modeling has been performed for small planetary bodies which underwent relatively simple igneous differentiation events. An example is the eucrite parent body, a planet which produced basalts at ⋍4.6 Gy. and has been quiescent ever since. This simple differentiation history permits the calculation of its bulk composition (a feldspathic peridotite) and has led to the tentative identification of asteroid 4 Vesta as the eucrite parent body. The differentiation of iron meteorite groups in parent body cores is amenable to similar treatment. Quantitative calculations are currently hampered by the paucity of experimentally determined solid metal/liquid metal partition coefficients. The ‘anomalous’ behavior of Cr, however, suggests that IIIA, B irons and main group pallasites equilibrated with troilite, spinel, ferromagnesian silicates, or some combination thereof. The moon has undergone more complex differentiation, and quantitative geochemical modeling is correspondingly more difficult. Nevertheless, modeling the two‐stage evolution of mare basalts raises the possibility that the primordial moon did not have chondritic relative abundances of such refractory elements as Ca, Al, U, and the rare‐earth elements. The nonchondritic element ratios are characteristic of planetary, not nebular, fractionation processes and are consistent with the derivation of the moon from a precursor planet, possibly the earth. Alternatively, they may be artifacts of our inadequate understanding of differentiation in a deep, rapidly convecting magma ocean. The enormous complexity of terrestrial evolution over geologic time generally precludes quantitative geochemical modeling of the earth. For example, calculations investigating the petrogenesis of calc‐alkaline andesites are restricted to limiting the range of plausible hypotheses. In cases where Nd isotopic systematics indicate that the source region of a basalt suite had an approximately chondritic Sm/Nd ratio (e.g., Columbia River Plateau), semiquantitative calculations of the nature of the mantle may be possible. Geochemical modeling may have predictive value for an unsampled planet such as Mercury which may have had a relatively simple thermal history.
Plasma instabilities in the solar wind: A theoretical review
Authors: Schwartz Steven J.
Published: February 2008

I present here a review of recent theoretical progress in the possible role of microturbulence in the solar wind. The solar wind is anticipated to excite plasma microinstabilities because of its transition from collision‐dominated to collisionless behavior. The applications of linear plasma theory that have been made in this field are extensively reviewed and discussed, along with our present understanding of nonlinear plasma phenomena. The solar wind is an excellent laboratory for studying many aspects of solar and plasma physics and may soon provide some answers to several fundamental questions.
The energetics of extratropical cyclones
Authors: Smith Phillip J.
Published: February 2008

The use of energetics analyses in studies of extratropical cyclones has received increasing attention over the past 15 years. Particularly significant have been analyses of the transport, generation, and dissipation of kinetic energy and the diabatic generation of available potential energy. In examining the energetics of extratropical cyclones this paper (1) reviews and distills the results of kinetic energy and available potential energy budget studies carried out over the past 15 years and (2) uses these results to establish the significance of the extratropical cyclone in the general circulation.
Long‐range weather forecasting: Value, status, and prospects
Authors: Nicholls N.
Published: February 2008

Progress in long‐range (1 month to 10 years) weather prediction over the past decade has been reviewed. A considerable body of research on long‐range forecasting has been carried out and published during this period. Many of these studies have produced encouraging results suggesting that some meteorological parameters can be predicted on a seasonal or monthly time scale, at least for certain regions and at certain times of the year. However, operational long‐range forecasts show, at best, only marginal skill and have not improved in recent years. It is suggested that this inability to transfer the level of skill obtained in some research studies into operational practice may be due to a requirement for national weather services to make predictions for all regions under their responsibility and for all times of the year (rather than restricting their forecasts to situations in which there appears to be a reasonable expectation that the forecast will be correct). A second factor that may cause operational forecast skill to be lower than that apparently feasible may be the use of inappropriate statistical techniques in the development of forecast rules.
Mechanical properties of snow
Authors: Salm B.
Published: February 2008

The investigation of the mechanical properties of seasonal snow cover aims mostly at applications in avalanche release and avalanche control but also at no less important problems such as vehicle mobility in snow, snow removal, or construction on snow. Primary needs are (1) constitutive equations, that is, relations between the stress tensor and the motion, and (2) fracture criteria which limit the region of validity of constitutive equations. Both can be tackled from the aspect of continuum theories and structure theories. With modern continuum theories the characteristic nonlinear behavior of snow can be taken into account and also the strong dependence on stress and strain history. When thermodynamics is introduced, more insight into the deformation and fracture processes can be gained. High initial deformation rates cause low dissipation, elastic behavior, and brittle fracture, whereas when dissipative mechanisms can develop, ductile fracture occurs. The advantage of structural theories lies in the immediate physical insight into deformation mechanisms, but the disadvantage is that only simple states of stresses acting macroscopically on a snow sample can be considered. Different approaches have been elaborated: for low‐density snow the concept of chains (a series of stress‐bearing grains) or the neck growth model (consideration of stress concentrations in bonds between grains) and for high‐density snow the pore collapse model (snow idealized as a material containing air voids). Structural constitutive equations were applied to the calculation of stress waves in snow. Recorded acoustic emissions, indicating intergranular bond fractures, can also be used for the construction of constitutive equations. Structural failure theories model brittle fracture with series elements, where the weakest link causes fracture of the entire body, and ductile fracture by parallel elements, where fracture of one element leads merely to a redistribution of stresses and only after a sufficiently high increase of the load to a total failure. In this method the statistical distribution of link strength plays an important role. The mechanics of wet snow (snow containing liquid water) is considerably different from dry snow mechanics. While deformation of dry snow is dominated by (slow) creep and glide of ice grains and bonds, the densification of wet snow is mainly due to the (fast) process of pressure melting at stressed contacts of a grain.
Stratospheric aerosols: Observation and theory
Authors: Turco R. P. , Whitten R. C. , Toon O. B.
Published: February 2008

We review current observational and theoretical knowledge of the stratospheric aerosols. These particles, which are composed primarily of sulfuric acid and other sulfates, are concentrated in a layer extending 20 km or more above the tropopause. The aerosols affect the chemistry of the stratosphere and the climatology of the earth. A number of important chemical and physical roles for the aerosols are discussed. We describe the properties of stratospheric aerosols as revealed by experimental data. Remote‐sensing optical instruments, both active (lidars) and passive (satellites), allow routine mapping of the global aerosol distribution. Extensive in situ measurements obtained by mechanical collection (filters and impactors) and scattered‐light detection yield the overall size dispersion of the aerosols. Laboratory analyses of preserved aerosol samples define the bulk composition (and possible origins) of the particles. Quantitative studies of aerosol precursor gases (SO2, OCS, and CS2) by wet chemical, cryogenic, and spectroscopic techniques reveal the photochemical sources of particulate mass. Theoretical aspects of the stratospheric aerosols are also reviewed. We discuss aerosol chemical reactions including those of gaseous precursors, those in aqueous solution, and those on particle surfaces. We also describe aerosol microphysical processes including nucleation, condensation/evaporation, coagulation, and sedimentation. Existing models of aerosols which incorporate these chemical and physical processes are outlined. Aerosol model predictions are appraised vis à vis observations. The simulations are shown to agree with measurements in many important respects. Areas requiring further investigation include the identification of the nucleation mechanisms for the aerosols and the characterization of the tenuous upper extent of the aerosol layer above ∼25 km. Estimates are presented for the potential aerosol changes attributable to the emissions of particles and gases by aerospace operations (aircraft and rockets) and industrial consumption of fossil fuels. It is demonstrated that although the climatic effects of existing levels of stratospheric aerosol pollution are negligible, potential increases in those levels might pose a future threat. Evidence for a major influence of massive volcanic eruptions on terrestrial climate is discussed. Model calculations of climate perturbations associated with past volcanic activity are summarized. In addition, detailed physicochemical simulations of the stratospheric clouds produced by the May 18, 1980, eruption of Mount St. Helens are shown to be consistent with experimental data collected in the clouds.
Coupling function between solar wind parameters and geomagnetic indices
Authors: Murayama Takashi
Published: February 2008

Results of past studies on the correlation of a function of solar wind parameters with a geomagnetic index are reviewed and examined to identify the most relevant coupling function among those hitherto proposed. For the AL index, three functions, BsV, BsV², and Akasofu's ε, are compared, where Bs is the southward component of the interplanetary magnetic field and V is the solar wind velocity, and the importance of BsV² is then confirmed by a new presentation of the prediction of each function and the AL index. For the Dst index, validities of the above three functions are also compared, but a new function, BsVP1/3, where P is the dynamic pressure of the solar wind, is proposed as the one that surpasses all of the other three functions in predicting Dst. Implications of the two coupling functions are discussed, and possible directions for future work on this problem are suggested.
Biomagnetic geomagnetism
Authors: Kirschvink Joseph L.
Published: February 2008

An article dealing with biomagnetism may at first seem strange to include in the IUGG quadrennial report, yet during the last four years a variety of interdisciplinary discoveries have been made that provide an area of common interest among these otherwise quite separate fields. Two definitions are in order to begin with. Magnetobiology is the branch of animal behavior (ethology) which is concerned with the influence of magnetic fields (both strong and weak) on living organsims. A related term, biomagnetism, is the study of magnetic fields produced by living systems without concern as to the effect of the field itself; Williamson and Kaufman [1980] provide a lucid review of three forms of biomagnetism which are produced electrically, paramagnetically, and by ferromagnetic contaminants. A new sub‐field of biomagnetism, biogenic ferrimagnetism, overlaps both of these and is the topic of concern here.
Physical oceanography of continental shelves
Authors: Allen J. S. , Beardsley Robert C. , Blanton J. O. , Boicourt William C. , Butman Bradford , Coachman L. K. , Huyer Adriana , Kinder Thomas H. , Royer Thomas C. , Schumacher James D. , Smith Robert L. , Sturges W. , Winant Clinton D.
Published: February 2008

Knowledge of the physical oceanography of continental shelves has increased tremendously in recent years, primarily as a result of new current and hydrographic measurements made in locations where no comparable measurements existed previously. In general, observations from geographically distinct continental shelves have shown that the nature of the flow may vary considerably from region to region. Although some characteristics, such as the response of currents to wind forcing, are common to many shelves, the relative importance of various physical processes in influencing the shelf flow field frequently is different. In the last several years, the scientific literature on shelf studies has expanded rapidly, with that for separate regions, to some extent, developing independently because of the variable role played by different physical effects.
Small‐scale physics of the ocean
Authors: Caldwell Douglas R.
Published: February 2008

The last quadrennial report combined internal waves with finestructure and microstructure, although the subjects were discussed separately within the review because “the direct linkage in the literature is not yet very strong” [Gregg and Briscoe, 1979]. The authors clearly expected, or at least hoped, that the connection would become stronger in the next four years. They pointed out that “there is at least a zeroth order steady state level for the internal wave field,” but that the rate of energy transfer into internal waves, and out of them into turbulence, was unknown. The intervening years have brought no great amount of progress in connecting internal waves with small‐scale processes, or in determining the rate of energy transmission.
Nonlinear interactions among internal gravity waves
Authors: Müller Peter , Holloway Greg , Henyey Frank , Pomphrey Neil
Published: February 2008

This paper reviews the nonlinear interaction calculations for the internal gravity wave field in the deep ocean. The nonlinear interactions are a principal part of the dynamics of internal waves and are an important link in the overall energy cascade from large to small scales. Four approaches have been taken for their analysis: the evaluation of the transfer integral describing weakly and resonantly interacting waves, the application of closure hypotheses from turbulence theories to more strongly interacting waves, the integration of the eikonal or ray equations describing the propagation of small‐scale internal waves in a background of large‐scale internal waves, and the direct numerical simulation of the basic hydrodynamic equations of motion. The weak resonant interaction calculations have provided most of the conventional wisdom. Specific interaction processes and their role in shaping the internal wave spectrum have been unveiled and a comprehensive inertial range theory developed. The range of validity of the resonant interaction approximation, however, is not known and must be seriously doubted for high‐wave number, high‐frequency waves. The turbulence closure calculations and the direct numerical modeling are not yet in a state to be directly applicable to the oceanic internal wave field. The closure models are too complex and rest on conjectures that are not demonstrably justified. Numerical modeling can treat strongly interacting waves and buoyant turbulence, but is severely limited by finite computer resolutions. Extensive suites of experiments have only been carried out for two‐dimensional flows. The eikonal calculations provide an efficient and versatile tool to study the interaction of small‐scale internal waves, but it is not clear to what extent the scale‐separated interactions with larger‐scale internal waves compete with and might be overwhelmed by interactions among like scales. The major shortcoming of all four approaches is that they neglect the interaction with the vortical (=potential vorticity carrying) mode of motion that must be expected to exist in addition to internal waves at small scales. This interaction is intrinsically neglected in all Lagrangian‐based studies and in the non‐rotating two‐dimensional simulations. The most promising approach for the future that can handle both arbitrarily strong interactions and the interaction with the vortical mode is numerical modeling once the resolution problem is overcome.
Jovian and Saturnian satellites
Authors: McKinnon William B.
Published: February 2008

The years 1983‐1987 follow mankind's epochal first spacecraft encounters with the giant planets Jupiter and Saturn. Possibly the most spectacular “discoveries” there were the diversity and level of geological activity on the satellites that circle each. And part of the excitement no doubt stemmed from rebuttal of pre‐encounter preconceptions, as the satellites of the inner solar system, while fascinating, are geologically dead. Consequently, an entirely new branch of solar system science has opened up, one that is fascinating in its own right, and one that promises to greatly aid understanding of the origin and evolution of the Earth, the solar system, and life itself.
Mantle convection and the state of the Earth's interior
Authors: Hager Bradford H. , Gurnis Michael
Published: February 2008

During 1983–1986, the four year period covered by this review, emphasis in the study of mantle convection shifted away from fluid mechanical analysis of simple systems with uniform material properties and simple geometries, toward analyzing the effects of more complicated, presumably more realistic models.
Marine tectonics: Processes at mid‐ocean ridges
Authors: Sempere Jean‐Christophe , MacDonald Ken C.
Published: February 2008

The use of multibeam echo‐sounders and various side‐looking sonar systems has greatly increased our knowledge and understanding of mid‐ocean ridge (MOR) processes. Since the last IUGG review on mid‐ocean ridge research [Macdonald, 1983], the extensive use of swath‐ mapping tools such as Sea Beam, Deep‐Tow, SeaMARC I and II, the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions. This review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid‐ocean ridges in the last four years. Certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews. Because of the exponential growth in the number of publications related to MORs during 1982–1986, only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text. References published prior to 1982 were added only where appropriate.
Review of hydromagnetic wave studies in the Antarctic
Authors: Arnoldy R. L. , Cahill L. J. , Engebretson M. J. , Lanzerotti L. J. , Wolfe A.
Published: February 2008

High‐latitude ULF waves at all frequencies are reviewed with emphasis on simultaneous measurements in both hemispheres. The seasonal variation of interhemisphere high‐latitude data is valuable in helping to understand the topology of the magnetosphere. The frequent occurance of Pc 1–2 pulsations at high latitudes and in the polar cap is discussed. Evidence for ground detection of flux transfer events via magnetic pulsations is reviewed. The correlation of high‐latitude pulsation data with other ground techniques of measuring particle precipitation is presented to better define the subset of high‐latitude ULF that is produced by local current systems fed by particle precipitation and field‐aligned currents. Finally, simultaneous ground and spacecraft measurements of ULF are reviewed which provide information on the propagation of ULF across such boundaries as the magnetopause and the ionosphere.
Gas transport in unsaturated porous media: The adequacy of Fick's law
Authors: Thorstenson D. C. , Pollock D. W.
Published: February 2008

The increasing use of natural unsaturated zones as repositories for landfills and disposal sites for hazardous wastes (chemical and radioactive) requires a greater understanding of transport processes in the unsaturated zone. For volatile constituents an important potential transport mechanism is gaseous diffusion. Diffusion, however, cannot be treated as an independent isolated transport mechanism. A complete understanding of multicomponent gas transport in porous media (unsaturated zones) requires a knowledge of Knudsen transport, the molecular and nonequimolar components of diffusive flux, and viscous (pressure driven) flux. The constitutive equations relating these flux components are available from the “dusty gas” model of Mason et al. (1967). This review presents a brief discussion of the underlying principles and interrelationships among each of the above flux mechanisms. Some aspects of these transport mechanisms are, to our knowledge, generally unrecognized in the Earth science literature. The principles underlying the transport mechanisms are illustrated with binary systems; the constitutive equations are then cast in forms thought to be most useful for the study of natural unsaturated zones. The viscous and diffusive fluxes are coupled in the constitutive equations through the Knudsen diffusivities; a knowledge of Knudsen diffusivities is necessary to calculate the viscous component of flux and pressure gradients. The Knudsen diffusivities can be calculated from measurements of the Klinkenberg effect. Two examples are presented showing that in natural systems, very small pressure gradients (1 Pa/m or less) can produce viscous fluxes greater than or equal to diffusive fluxes and that, conversely, pressure gradients of this magnitude can be generated by diffusive processes. The example calculations show that major concentration gradients can be developed for stagnant (zero flux, nonreactive) gases. A method is presented for approximating the viscous and diffusive flux components of gases in a multicomponent system from a knowledge of the concentration profiles of stagnant gases. In subsoil environments, argon and nitrogen are considered to be stagnant gases. Fick's laws are essentially, by definition, inadequate to deal with stagnant gases. In the examples presented, the error associated with estimating the total fluxes of nonstagnant gases by Fick's law, relative to stationary coordinates, ranges from a few percent to orders of magnitude.
A brief history of magnetospheric physics before the spaceflight era
Authors: Stern David P.
Published: February 2008

This review traces early research on the Earth's magnetic environment, covering the period when only ground‐based observations were possible. Observations of magnetic storms (1724) and of perturbations associated with the aurora (1741) suggested that those phenomena originated outside the Earth; correlation of the solar cycle (1851) with magnetic activity (1852) pointed to the Sun's involvement. The discovery of solar flares (1859) and growing evidence for their association with large storms led Birkeland (1900) to propose solar electron streams as the cause. Though laboratory experiments provided some support, the idea ran into theoretical difficulties and was replaced by Chapman and Ferraro's notion of solar plasma clouds (1930). Magnetic storms were first attributed (1911) to a “ring current” of high‐energy particles circling the Earth, but later work (1957) recognized that low‐energy particles undergoing guiding center drifts could have the same effect. To produce the ring current and aurora, plasma cloud particles required some way of penetrating the “Chapman‐Ferraro cavity”: Alfvén (1939) invoked an electric field, but his ideas met resistance. The picture grew more complicated with observations of comets (1943, 1951) which suggested a fast “solar wind” emanating from the Sun's corona at all times. This flow was explained by Parker's theory (1958), and the permanent cavity which it produced around the Earth was later named the “magnetosphere” (1959). As early as 1905, Birkeland had proposed that the large magnetic perturbations of the polar aurora reflected a “polar” type of magnetic storm whose electric currents descended into the upper atmosphere; that idea, however, was resisted for more than 50 years. By the time of the International Geophysical Year (1957–1958), when the first artificial satellites were launched, most of the important features of the magnetosphere had been glimpsed, but detailed understanding had to wait for in situ observations.
Magnetometer array studies, Earth structure, and tectonic processes
Authors: Gough D. Ian
Published: February 2008

This review presents results from magnetovariation fields recorded by two‐dimensional arrays of magnetometers. The emphasis is on the conductive structures mapped and studied and their tectonic implications. Eleven arrays were operated in North America between 1967 and 1985. A region of highly conductive uppermost mantle and/or lower crust, extending at least from 33°N to 54°N, has been shown to extend beneath much of the continent west of the Rocky Mountains. Two recent investigations are discussed in more detail: those of conductive structures under the Canadian Rockies and EMSLAB (Electromagnetic Sounding of the Lithosphere and Beyond) array results for Washington and Oregon, including a conductive strip beneath the Cascades volcanoes. Correlations with high heat flow and seismic parameters make it reasonable to attribute these regional conductors to partial melting and/or hot saline water. Within the craton the North American Central Plains conductor is discussed; this narrow, crustal feature is associated with a major fracture zone and age boundary, which may be a plate boundary of Proterozoic time. An array beneath the auroral electrojet, for study of the external currents, is noted. Results from four array studies in southern Africa are considered. Two of these relate to the Southern Cape Conductive Belt, which correlates not with high heat flow but with a large static magnetic anomaly. The magnetovariation, magnetic and gravity anomalies, and geological data can be accounted for if an accumulation of ophiolitic rocks including serpentine is present in the lower crust. Such an accumulation may have formed at a subduction in Proterozoic time. Two other arrays delineated a conductive belt associated with the southwestern end of the African rift system, in Namibia. Subsequent resistivity soundings located a conductor of resistivity 10 ohm m at less than 4 km depth. Two array studies in India follow, one in the north and one in the south. The array in the Himalayan foothills and Indo‐Gangetic plain mapped a conductor transverse to the regional strike; this may be a fracture zone produced in the interplate collision, with a rise of asthenospheric material such as fluids into the fractures. The southern Indian array reveals crustal conductors under the Indo‐Sri Lankan graben and another under the Comorin Ridge southwest of the tip of the subcontinent. Array studies in central and southeastern Australia and in Fennoscandia, in regions without large local conductivity anomalies, have been used to study conductivity variation with depth. A note on the Carpathian crustal anomaly is included as an example of combination of response parameters secured at different times to form a “virtual” array.
Multiphase flow and transport in porous media
Authors: Parker J. C.
Published: February 2008

Multiphase flow and transport of compositionally complex fluids in geologic media is of importance in a number of applied problems which have major social and economic effects. In petroleum reservoir engineering, efficient recovery of energy reserves is the principal goal. Unfortunately, some of these hydrocarbons and other organic chemicals often find their way unwanted into the soils and groundwater supplies. Removal in the latter case is predicated on ensuring the public health and safety. In this paper, principles of modeling fluid flow in systems containing up to three fluid phases (namely, water, air, and organic liquid) are described. Solution of the governing equations for multiphase flow requires knowledge of functional relationships between fluid pressures, saturations, and permeabilities which may be formulated on the basis of conceptual models of fluid‐porous media interactions. Mechanisms of transport in multicomponent multiphase systems in which species may partition between phases are also described, and the governing equations are presented for the case in which local phase equilibrium may be assumed. A number of hypothetical numerical problems are presented to illustrate the physical behavior of systems in which multiphase flow and transport arise.
A Comparison Study of the Occurrence of Equatorial Type Es and Daytime Blanketing Es in the Magnetic Equatorial Zone
Authors: Oyinloye J. O.
Published: February 2008

A study of the occurrence frequency of equatorial Es (Esq) and daytime blanketing Es at Ibadan (dip 6°S) and Zaria (dip 3°N) in Nigeria is presented. The period of study covers the years 1958 to 1965. Experimental results from the study reveal that Esq and blanketing Es are different phenomena and that a high incidence of Esq is usually accompanied by a low incidence of blanketing Es, and vice versa. In addition, the extent of the Esq belt in Nigeria is deduced from the relative occurrence of Esq and nonequatorial Es during the daytime at Ibadan.