bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of Birkeland currents at auroral latitudes
Authors: Anderson Hugh R. , Vondrak Richard R.
Published: February 2008

After many years of languishing interest, field‐aligned currents (Birkeland currents) are now regarded as an important link between the magnetosphere and the ionosphere. We describe techniques that are used to measure them and then discuss in some detail measurements that have been interpreted as indicating the presence of Birkeland currents. We conclude that measurements substantiate the theory of large‐scale flow from the magnetosphere to the polar caps in a dawn‐dusk direction with opposite flow equatorward of the auroral zone connecting to the Alfvén layer. Sheet current flow in premidnight discrete aurora seems experimentally established also, but its connection with auroral acceleration and with the larger‐scale flow is not yet understood. The currents flowing during a substorm are not yet fully defined either.
Developments in stochastic hydrology
Authors: Matalas N. C.
Published: February 2008

Recent research has introduced a variety of stochastic models for simulating hydrologic processes, particularly streamflow, in time and space. The small sample properties of the model processes, as well as those of the marginal distributions of the processes, have been approached by Monte Carlo techniques. Models for the transfer of hydrologic information have formed the basis of algorithms developed for optimal design of data collection systems.
Geodetic theory
Authors: Chovitz B. H.
Published: February 2008

The planned new solution for the North American Datum has provided an impetus for research into improved techniques of network adjustment. Current state of the art is expounded by Dracup and Gergen [1974]. Refinements in general least squares are discussed by Fubara [1973] and Schmid and Schmid [1971]. Specific methods of adjustment which promise increased efficiency are covered by Zimmerman [1974], Schmid [1971a, 1973], Saxena [1974], and Pope [1974b]. Much work has gone into the problems of generalized inverses and singular matrices [Bossier, 1973; Uotila, 1974a]. A very general and complete presentation on adjustment techniques with a comprehensive bibliography can be found in a paper by Pope [1974a]. Also worth noting is a revised English version of the textbook by Hirvonen [1971].
Surface waters
Authors: Schaake John C.
Published: February 2008

Research in surface water hydrology made important advances in the areas of river mechanics and streamflow routing, experimental study of overland flow, surface runoff models, partial area processes, effects of land use on surface runoff, and probability, statistics and analysis of uncertainty. In each area there was a fundamental need to apply mathematical and computer methods, and this is reflected in the following review of progress in each of these areas.

A broad‐based effort went into developing numerical solutions of the Saint Venant partial differential equations for unsteady flow in open channels. Some papers suggested a numerical procedure; some looked at computational efficiency; some looked at convergence and/or stability properties; some looked at the importance of various terms; some looked at prediction accuracy; and some suggested procedures for branched or looped river networks. These papers offer testimony to widespread use in hydrology practice of models based either on the full Saint Venant equations or on one of many approximations to these equations, including both linear approximations with one or more terms neglected and nonlinear approximations with several terms neglected. Because some of these approximations have the same mathematical structure as certain well‐known hydrologic routing techniques, it is now possible to give clearer physical meaning to the better established hydrologic methods such as the Muskingum method. Hopefully, this will stimulate more intelligent use of all of these techniques (e.g., through new physically based criteria for applying the lag and route model or new criteria for judging when the full nonlinear Saint Venant equations must be used rather than some approximation, etc.). Following is a review of some specific contributions.
Water resource systems and relations
Authors: Schwarz Harry E.
Published: February 2008

The analyses of water resource systems and the application of mathematical statistics and operations research in the planning, operation, and management of water resource developments are continuing. Systems analyses as a tool of the hydrologist and water resource engineer are coming of age in the United States. In addition to the use of these techniques in analyzing and synthesizing physical systems, significant inputs are being made to broaden the analysis to social, economic, and environmental considerations.

Water resource systems analysis has come to mean the use of mathematical programing and simulation techniques in the study of large‐scale systems which control the movement of water on and under the surface of the earth. Included in the discussion which follows will be a review of surface water systems, groundwater systems, water quality systems, stochastic flow models, decision theory, and network theory.
Advances in magnetospheric physics: Aurora
Authors: Eather Robert H.
Published: February 2008

To write a brief review of progress in auroral physics of the last quadrennium 1971–1974 is akin to fitting 27 students in a Volkswagen—it can be done (Guiness Book of Records), but no one will be quite satisfied with the space he has. Auroral physics has not been spared from the science information explosion of recent years, and I make no claim to having read all relevant papers nor even being aware of the more significant advances in all of the various subsections of the field. Consequently, the writing of this review was preceded by a polling of auroral scientists for a short summary of their significant work over the last 4 years—to those few workers I may have inadvertently missed, I apologize; to those few workers who responded, I thank. It seems inevitable that some personal bias will enter a review of this nature but I hope that it is minimal. The approach adopted assumes a reader with a professional working knowledge of auroral physics as it was understood at the end of 1970.
Anomalies in the time‐averaged paleomagnetic field and their implications for the lower mantle
Authors: Merrill Ronald T. , McElhinny Michael W.
Published: February 2008

The proposal that the time‐averaged paleomagnetic field is not strictly that of a geocentric axial dipole but that of an axial dipole displaced slightly northward from the geocenter is examined in terms of spherical harmonic expansions. Standard procedures for spherical harmonic expansions such as are applied to the present instantaneous geomagnetic field are not necessarily applicable to paleomagnetic data. A technique is proposed that enhances the time‐averaging process that is a necessary part of determining the paleomagnetic field. This involves analyzing the inclination anomaly ΔI around latitude strips to determine the zonal harmonics and the declination anomaly ΔD around longitude sectors to determine the first nonzonal harmonics. The technique is applied to a carefully selected data set covering the last 5 m.y. All data are divided into normal or reversed sets providing 266 land‐based points (171 normal, 95 reversed) and 100 deep‐sea core results with inclination data only (50 normal, 50 reversed). These data demonstrate clearly that the time‐averaged field is not simply that of a geocentric axial dipole and also that it is different for the normal and reversed fields. With respect to the present field the zonal harmonics of the time‐averaged field are reduced less than the nonzonal harmonics, the indication being that westward and/or eastward drift of the nondipole field is dominant over 5 m.y. The magnitude of the second zonal harmonic suggests that on the average, paleomagnetic poles could be in error by about 3° when calculated by the usual geocentric axial dipole assumption. The data show clear asymmetries between the northern and southern hemispheres and possibly between the oceanic (Pacific) and continental hemispheres. Possible explanations of these asymmetries include variations in topography and/or temperature at the core‐mantle interface. Large‐scale asymmetries in the boundary conditions at this interface could affect the magnetic field through alteration of the convection pattern in the core. The asymmetries correlate with other global asymmetries such as the distribution of continents and oceans and the locations of subduction zones. They also apparently correlate with seismic velocity anomalies observed in the lower mantle. All these may reflect large‐scale inhomogeneities related to dynamic processes that have occurred in the lower mantle. Although all the Gaussian coefficients determined change sign when the axial dipole field reverses, there are significant differences between the normal and reversed fields, suggesting that the distribution of sources for these fields is not identical. This is consistent with the cyclonic convection models for reversal of the geomagnetic field proposed by Parker and Levy.
The 1976 Standard Atmosphere and its relationship to earlier standards
Authors: Minzner R. A.
Published: February 2008

The 1976 U.S. Standard Atmosphere, representing a mid‐latitude atmosphere for moderate solar activity, has recently been adopted by the Committee for the Extension of the Standard Atmosphere (COESA). For heights of 51 km and below, this standard is identical with its immediate predecessor, the 1962 U.S. Standard Atmosphere; above 50 km the 1976 standard completely replaces its predecessor. The new standard represents the latest in a century‐long history of model atmospheres, beginning in 1867 with a 10°C isothermal model. A comparison of the temperature‐height profile T(Z) of the 1976 standard with T(/2) of each of 11 important standards and models used during the preceding century traces the development of our knowledge of the earth’s atmosphere. Comparisons of the density‐height profile ρ(Z) of each of five earlier model atmospheres with that of the 1976 standard indicate an oscillation of ρ(Z) around the currently accepted average value. This oscillation is partly the result of true density changes related to the 11‐year cycle of solar activity and partly the result of uncertainty in earlier models. Number densities of each of six atmospheric species computed for the 1976 U.S. standard are compared over the height region of 0–1000 km.
Mathematical structure of transport equations for multispecies flows
Authors: Schunk R. W.
Published: February 2008

In this review we attempt to present a unified picture of transport in multispecies gas mixtures. To accomplish this task, it is necessary to outline the mathematical structure of the transport equations. Starting from Boltzmann's equation, we derive a general system of transport equations using an approach that is valid for flow situations in which there are large temperature and drift velocity differences between the interacting species. However, this system of equations, which is obtained by taking velocity moments of the Boltzmann equation, does not constitute a closed set, since the equation governing the velocity moment of order r contains the velocity moment of order r + 1. To close the system of transport equations, it is therefore necessary to adopt an approximate expression for the species velocity distribution function. For near‐equilibrium flows, various levels of approximation are considered, including the 5‐, 8‐, 10‐, 13‐, and 20‐moment approximations. The procedure for obtaining closed sets of transport equations for far‐from‐equilibrium flows is also discussed. When the transport equations are ordered with respect to the collisional mean free path, the result is the Euler, Navier‐Stokes, or extended Navier‐Stokes equations depending upon whether terms proportional to the zeroth, first, or second power of the mean free path are retained. For a collisionless plasma the analogous expansion using the Larmor radius yields the Chew‐Goldberger‐Low (CGL) equations to zeroth order and the extended CGL equations to first order.
Problems related to macroscopic electric fields in the magnetosphere
Authors: Fälthammar Carl‐Gunne
Published: February 2008

The macroscopic electric fields in the magnetosphere originate from internal as well as external sources. The fields are intimately coupled with the dynamics of magnetospheric plasma convection. They also depend on the complicated electrical properties of the hot collisionless plasma. Macroscopic electric fields are responsible for some important kinds of energization of charged particles that take place in the magnetosphere and affect not only particles of auroral energy but also, by multistep processes, trapped high‐energy particles. A particularly interesting feature of magnetospheric electric fields is that they can have substantial components along the geomagnetic field, as has recently been confirmed by observation. Several physical mechanisms have been identified by which such electric fields can be supported even when collisions between particles are negligible. Comments are made on the magnetic mirror effect, anomalous resistivity, the collisionless thermoelectric effect, and electric double layers, emphasizing key features and differences and their significance in the light of recent observational data.
Forced oceanic waves
Authors: Philander S. G. H.
Published: February 2008

This paper concerns the linear response of the ocean to forcing at a specified frequency and wave number in the absence of mean currents. It discusses the details of the forcing function, the general properties of the equations of motion, and possible simplifications of these equations. Two representations for the oceanic response to forcing are described in detail. One solution is in terms of the normal modes of the ocean. The vertical structure of these modes corresponds to that of the barotropic and baroclinic modes; their latitudinal structure corresponds to that of inertia‐gravity and Rossby waves. These waves are eigenfunctions of Laplace's tidal equations (LTE) with the frequency as eigenvalue. The description in terms of vertically standing modes is particularly useful if the forcing is nonlocal, because only these modes can propagate into undisturbed regions. The principal result is that it is extremely difficult for baroclinic (but not barotropic) disturbances to propagate horizontally away from a forced region. Instabilities of the Gulf Stream excite disturbances that are confined to the immediate neighborhood of the current; disturbances due to instabilities of equatorial currents do not propagate far latitudinally. A second representation of the oceanic response to forcing is in terms of vertically propagating, or vertically trapped, latitudinal modes. These modes are eigenfunctions of LTE with the equivalent depth h (not the frequency) as eigenvalue. Both positive and negative eigenvalues h are necessary for completeness. The modes with h > 0 consist of an infinite set of inertia‐gravity waves and a finite set of Rossby waves which either propagate vertically or form vertically standing modes. The latitudinally gravest modes are equatorially trapped and have been observed in the Atlantic and Pacific oceans. The modes with h < 0 are necessary to describe the oceanic response to nonresonant forcing. In the vertical this response attenuates with increasing distance from the forcing region. Because of the shallowness of the ocean the large eastward traveling atmospheric cyclones in mid‐latitudes and high latitudes force a response down to the ocean floor. Interaction with the bottom topography will result in smaller‐scale disturbances and will affect the frequency spectrum of the response when bottom‐trapped waves are excited.
Concise theory of radio transmission in the Earth‐ionosphere wave guide
Authors: Wait James R.
Published: February 2008

A concise review is given of the theory of propagation of electromagnetic waves in the earth‐ionosphere wave guide. A simple concentrically uniform model is adopted such that the earth's surface and the effective lower edge of the ionosphere are idealized by impedance type boundary conditions. Various representations of the field are discussed, and the relationships between them are pointed out.
Electron temperatures in the F region of the ionosphere: Theory and observations
Authors: Schunk R. W. , Nagy Andrew F.
Published: February 2008

The theory and observations relating to electron temperatures in the F region of the ionosphere are reviewed. The review is divided into three basic parts. In the first part the theory concerning electron heating, cooling, and energy transport processes is reviewed, and all the relevant expressions are updated. In the second part the behavior of F region electron temperatures, as measured by satellites, rockets, and incoherent scatter radars, is discussed. This portion covers electron temperature variations with altitude, latitude, local time, season, geomagnetic activity, and solar cycle. The third part is primarily devoted to a discussion of the various attempts to compare measured and calculated F region electron temperatures.
Thermodynamics and lattice vibrations of minerals: 2. Vibrational characteristics of silicates
Authors: Kieffer Susan Werner
Published: February 2008

General lattice vibrational properties of minerals, particularly those properties which strongly influence the thermodynamic behavior, are discussed in this paper (the second of a series relating thermodynamic and lattice vibrational properties of minerals). Infrared (IR), Raman (R), and inelastic neutron scattering (INS) data are summarized, if known, for the following minerals: halite (INS), periclase (INS), corundum (IR, R), brucite (IR, R, partial INS), quartz (R, IR, INS), cristobalite (IR, R), silica glass (IR, R, partial INS), stishovite (IR), rutile (R, IR, INS), albite (IR, R), microcline (IR), spinel (IR, R), muscovite (IR, R), jadeite (IR), diopside (IR, R), enstatite (IR, R), olivine (IR, R), zircon (IR, R), kyanite (IR), andalusite (IR), sillimanite (IR), pyrope (IR), andradite (IR), grossular (IR), and calcite (IR, R, INS). New high‐resolution infrared data are given for kyanite, andalusite, sillimanite, stishovite, coesite, jadeite, diopside, pyrope, andradite, and grossular. The data presented and summarized show that optic modes of vibration of silicates are spread over a range of frequencies, generally from wave numbers as low as 75 cm−1 to wave numbers as high as 1200 cm−1. The far‐infrared (low frequency) optic modes are particularly important in this study because they strongly influence the low‐temperature heat capacity and therefore the entropy. The mid‐infrared (high frequency) optic modes generally arise from the vibrations of tightly bound clusters within the structures and can generally be recognized as isolated bands in the vibrational spectrum. A method is given for enumeration of the fraction of total vibrational modes which are internal stretching modes. Inelastic neutron scattering data are reviewed to show the magnitude of anisotropy and dispersion of acoustic modes and of dispersion of optic modes in the minerals. The combined infrared, Raman, and INS data show that, excluding the stretching modes of quasi‐molecular clusters within the minerals, the optic modes do not appear to follow a simple recognizable distribution, such as a Debye distribution, but are rather uniformly distributed across a broad range of frequencies.
Planetary magnetism
Authors: Russell C. T.
Published: February 2008

The field of planetary magnetism has advanced rapidly over the last four years. In fact it was not deemed necessary to review this subject in the last quadrennial report. This advance has resulted both from new data and of refined analyses of existing data files. New data have become available from Mariner 10 at Mercury, from Venera 9 and 10 orbiting Venus, and Pioneer spacecraft flying past Jupiter.
Natural organic atmospheric aerosols of terrestrial origin
Authors: Zenchelsky Seymour , Youssefi Manoutchehr
Published: February 2008

Particulate matter in the atmosphere is a major source of contamination, having an impact upon visibility, health, and even climate. These aerosols are predominantly of natural origin. A minor component, the anthropogenic organic aerosol, has been studied extensively because of its relation to smog. Much less is known about the far more abundant natural organic aerosol. Estimates of the annual global production rate of the latter range between 75 and 1000 million metric tons. In contrast, the corresponding rate for man‐made organic aerosol is only between 0.2% and 17% of the natural rate. Thus the natural organic aerosol production rate is exceeded greatly only by that of natural sea‐salt aerosol and possibly by that of natural nitrate. By far the largest proportion of the natural organic aerosol is derived from vegetation by means of a photochemical reaction of its vapors, a process which is observed as haze formation. This reaction of olefins has been studied extensively and is believed to be identical with that involved in smog production by anthropogenic olefins. In fact, the resultant products in the two cases are virtually indistinguishable, although minor differences do exist. An additional possible source for natural organic aerosols is the release of waxy particles from the tips of pine needles by means of electrical brush discharge from clouds. Yet other small amounts come from biological cellular debris and possibly even from volcanos. The role of natural organic aerosols in condensation and precipitation has been studied. Claims for the effectiveness of organic aerosols as ice‐forming nuclei have been made. Natural organic aerosols have been suggested as possible sources of petroleum and of humus in the ground. Biodegradation mechanisms for this result have been considered. If it is verified, the impact upon pollution control strategies would be considerable.
Neutral thermospheric composition and thermal structure
Authors: Hedin Alan E.
Published: February 2008

Since the reviews by Carignan [1975] and Dickinson [1975], satellite and ground based programs have produced a wealth of new data on the composition and structure of the thermosphere, including the first extensive measurements of a number of minor constituents. These years have also been a period of consolidation and refinement, with data being incorporated in a number of semiempirical models which provide an increasingly accurate picture of thermospheric variations in usable forms. Our review of the published experimental work of the past four years has been organized into a number of overlapping categories which reflect the major activity areas. Empirical modelling is considered first, followed by solar activity variations, daily variations, magnetic storm variations, measurements of molecular oxygen and minor species, and miscellaneous temperature and density determinations.
Geochronology and radiogenic isotope research
Authors: Bickford M. E. , Van Schmus W. R.
Published: February 2008

During the four year period 1975–1978 research activity in the fields of geochronology and radiogenic isotopes has been alive and quite healthy. Geochronological laboratories have added greatly to our knowledge of time relations and patterns in the crust and others have applied studies of radiogenic isotopes to problems of the sources, genesis, and history of terrestrial and extraterrestrial materials. In this paper we will review progress in areas that are, in our judgment, the most exciting and that represent the greatest advances in earth science through application of isotopic studies. Much of the paper will be devoted to the development of the Sm‐Nd system and to the discovery of long‐term heterogeneity in the mantle.
Water quality
Authors: Steele Timothy Doak , Stefan Heinz G.
Published: February 2008

Significant contributions in the broad area of water quality over the quadrennium 1975–78 are highlighted. This summary is concerned primarily with physical and chemical aspects of water quality. The diversity of subject areas within the topic heading and the large volume of published research results necessitated the selection of representative contributions. Over 400 references are cited which are believed to be indicative of general trends in research and of the more important developments during this period. Many additional citations could have been made. Implementation of existing Federal legislation and continued passage of Federal legislation have stimulated numerous aspects of water‐quality research and regional studies. Dependence of physical‐based models on actual field data or detailed projections of future conditions have imposed, in specific cases, severe limitations on the extent to which such models can be used through requirement of environmental impact statements, to potentially control much of the economic development affecting ambient water quality. Research continues to improve the understanding of the role of water‐quality information in planning and management of water‐resources systems. Increasing limitations on research and development funds have stimulated the quest for real‐problem relevance in applying models or resource‐assessment techniques and in the development of guidelines for the applicability of data and other information for realistic and understandable solutions.
The Viking mission and the search for life on Mars
Authors: Klein Harold P.
Published: February 2008

Modern scientific hypotheses concerning the origin of life generally have as their central theme the idea that living systems arise through "chemical evolution," a process in which simple compounds are generally transformed under the influence of various energy sources into more and more complex molecules, ultimately resulting in a system of replicating molecules [Buvet and Ponnamperuma, 1971; Miller and Orgel, 1974]. Based upon comparisons between the chemical composition of terrestrial living systems and cosmic abundances [Frieden, 1972] as well as upon theoretical considerations [Wald, 1962], it is further assumed that the key substances in this evolution are all carbon‐based compounds. Given a planet with a "hospitable" environment, these processes continue until the stage is set for biological infestation of the planet and further biological evolution follows.

As it became clear that direct experimentation on other planets was technically feasible with the advent of spacecraft technology, attention turned to Mars as the most promising extraterrestrial object upon which to search for evidence of chemical evolution [Pittendrigh et al., 1966]. This view was reached despite significant gaps in our knowledge of that planet, most notably about the properties and composition of its surface. Even after the encounters by Mariners 4, 6, and 7 and the more encompassing Mariner 9 mission, virtually nothing was known about the chemistry of the Martian surface. Under these circumstances, the status of evolution of carbon compounds and particularly the question of the existence of life on Mars were entirely speculative.
Considerations on the origin and properties of the Antarctic aerosol
Authors: Shaw Glenn E.
Published: February 2008

Information pertaining to aerosols and to microparticles preserved in snow and ice on the high plateau of Antarctica is assembled and interpreted with a diffusive transport model. The boundary conditions for the problem involve the existence of a two‐mode microparticle size distribution function. The smaller (Aitken) mode likely consists of converted products from nucleation of trace gases; the particles are less than 2.3 days old and are produced locally over the ice caps at a production rate of 4 × 10−21 g cm−3s−1. The Aitken particles are present in concentrations of 10²–10³ cm−3 throughout the troposphere, except in the lowest few hundred meters within the turbulent boundary layer, where they are depleted. The Aitken particles are probably composed of converted sulfates and hydrocarbons. Large particles ∼0.4 µm in radius are also found in Antarctica, in concentrations of 0.5 cm−3; these particles dominate the aerosol mass. They are of great interest because they have apparently come from long distances and because they precipitate onto the surface and are incorporated into the polar ice in varying rates that can show a connection with past changes in terrestrial climate. The large particles are estimated to have come from (1) unidentified sulfate sources, (2) oceanic sources surrounding the continent, (3) arid regions in the southern hemisphere (Australia, Kalahari Desert, Atacama Desert), (4) extraterrestrial sources, and (5) oases on the continent—in that order of importance. Turbulent diffusion seems to be the primary particle transport mechanism, and diffusion models support the plausibility of the mentioned terrestrial sources and quantify their contributions. The transport by eddy diffusion from continental sources apparently is operating mainly within the middle and upper troposphere. Particles are removed over Antarctica by diffusing into the turbulent boundary region or by encountering clouds or hydrometeors. The major removal mechanisms are impaction on the surface (2.0 × 10−14 g cm−2 s−1), impaction onto snowflakes (1.6 × 10−14 g cm−2 s−1), impaction onto ice crystals (0.2 × 10−14 g cm−2 s−1), and nucleation (0.6 × 10−14 g cm−2 s−1). The Aitken particles are removed predominantly by diffusing to ice crystals (0.006 × 10−14 g cm−2 s−1) and by diffusing across the laminar layer to the surface (0.015 × 10−14 g cm−2 s−1). The many near‐surface removal mechanisms deplete aerosol mass loading by a factor of 5–10 in the turbulent boundary layer (making it a poor place to collect samples from). Changes in atmospheric circulation during the last third of the latest Wisconsin ice age may have increased desertification in the southern hemispheric mid‐latitude zones and caused greater amounts of dust to be deposited on the polar ice cap.
On charting global ocean tides
Authors: Schwiderski Ernst W.
Published: February 2008

This review article highlights the three‐century development of our scientific understanding of ocean tides, culminating through myths, paradoxes, and controversies in a global tide model that now permits the prediction of the instantaneous total tide anywhere in the open oceans with an accuracy of better than 10 cm. All major aspects of tidal research, including empirical, mathematical, and empirical‐mathematical methods, are considered. Particular attention is drawn to the most recently developed computerized techniques comprehending hydrodynamical dissipation and secondary tide‐generating forces, finite‐differencing schemes, geometric boundary and bathymetry modeling, and hydrodynamical interpolation of properly selected empirical tide data. Numerous computer experiments are mentioned that were carried out by various researchers in order to evaluate the magnitudes of the featured effects. Further possible improvements are mentioned, especially in nearshore areas, in the Arctic Sea, and near Antarctica, where empirical tide and bathymetry data are either rough or marginal.
Crust and upper mantle structure of the Eurasian continent from the phase velocity and Q of surface waves
Authors: Patton Howard
Published: February 2008

A review of studies using surface waves to determine crust and upper mantle structures of the Eurasian continent is presented. The results of these studies have assisted in the analysis of a new set of propagation data for lateral variation of phase velocity and Q on the continent. A Rayleigh wave phase velocity regionalization based on crustal conditions and topography is proposed involving five continental provinces: Indian Shield, Northern Platforms and Shields, Forelands and Coastal Plains, Tectonic, and Plateau. Phase velocities in the Indian Shield are 20% higher than velocities in the Plateau province at 26‐s period and 5% higher at 90‐s period. Stable platforms of northern Asia have significantly higher phase velocities than those of tectonic provinces out to 150‐s period. Shear velocity structures that incorporate published crustal structures and satisfy the regionalized dispersion curves and reported Sn velocities are presented. Surface wave amplitudes are shown to be strongly affected by horizontal refraction, causing focusing of ray paths, defocusing, and multipathing. Three very different average Rayleigh wave Q curves over periods of 25–60 s are obtained for stable northern platforms and tectonic provinces east and west of Central Asia. Interpretations of the observations are given in terms of intrinsic Q of the medium. The Q models as well as shear velocity models are discussed in the light of Eurasia's tectonic history.
Evidence in the auroral record for secular solar variability
Authors: Siscoe George L.
Published: February 2008

The historical record of aurorae is continuous and usefully dense for at least the last 2000 years. Revival of interest in the secular variability in solar activity motivates a review of the auroral record. The existence of secular variations in the auroral occurrence frequency has been known since the early 1700's, including the existence of a significant attenuation of auroral activity during the Maunder Minimum. Investigation of secular variations prior to the Maunder Minimum is now possible based on six auroral catalogs that have been published within the last 20 years. The catalogs cover the time period from the fifth century B.C. to the seventeenth century A.D. and combine both oriental and European observations. Features corresponding to the previously recognized Medieval Minimum, Medieval Maximum, and the Spörer Minimum are clearly evident in both oriental and European records. The global synchronicity of anomalies in the auroral occurrence frequency is used to argue that they are caused by changes in the level or state of solar activity. The combined catalogs provide a sufficient number of events in the Middle Ages to resolve a quasi‐80‐year periodicity in the recorded auroral occurrence frequency. Also in the unusually rich intervals of the Middle Ages, clear quasi‐10‐year periodicities appear in the recorded occurrence frequency wave form. These are most reasonably interpreted as manifestations of the 11‐year solar cycle and indicate that the solar cycle was then operative.
Exploratory data analysis in the geophysical sciences
Authors: Kleiner B. , Graedel T. E.
Published: February 2008

Exploratory data analysis (EDA) techniques are particularly relevant to the geophysical sciences, since geophysical systems typically possess multiple correlations of a variety of parameters on widely differing time scales, often in conjunction with temporal patterns of low intensity but high importance. In this article a variety of EDA techniques (robust statistics, scatterplots, histograms, stem‐and‐leaf diagrams, box plots, trend analysis programs, and quantile‐quantile plots) are applied to geophysical data to demonstrate the successful elucidation of information difficult or impossible to extract from the data by more formal and traditional statistical approaches.
The atmospheres of the outer planets and satellites
Authors: Trafton L.
Published: February 2008

This is a review of recent research results pertaining to the atmospheres of the outer planets and satellites. It includes the atmospheres of Pluto, Triton, Neptune, Uranus, Titan, Saturn, and Io. Io’s neutral torus and plasma torus are covered, but Jupiter and Jupiter’s magnetosphere are not. Jupiter is not included because of the number of specialized reviews which have recently become available for Jupiter. This review includes earlier Voyager 1 and 2 results for Io’s atmosphere and plasma torus as well as early Pioneer 11 results for Saturn and Titan. Neither ring systems nor atmosphereless bodies are reviewed here.
The nature of the lower continental crust: Inferences from geophysics, surface geology, and crustal xenoliths
Authors: Kay R. W. , Kay S. M.
Published: February 2008

Recent investigations of the lower continental crust have progressed along three relatively independent fronts: geophysics, field mapping, and study of xenoliths brought to the earth’s surface in volcanic and kimberlitic eruptions. The general results of these studies have increased our appreciation of the scale of lower crustal structural and compositional complexity, but not to the point where we can construct an accurate crustal cross section for even one locality. The first part of this review summarizes the results of crustal geophysical and geological mapping studies, which have provided both the broad framework and, more recently, some local detail for the continental crust. In the second part the role of crustal xenolith studies is outlined, and the occurrence of xenoliths is summarized by tectonic setting. In the course of this review, several generalizations about the lower crust are emphasized. First, compositional inferences based on matching of mean seismic velocities and rock types are not unique. For example, the occurrence of hydrous minerals at depth is indicated by some xenolith populations and perhaps corroborated by electrical conductivity studies. The lower velocities and densities of hydrous rocks allow consideration of less silicic mean compositions than were indicated by several recent estimates. Second, the occurrence of lower crustal metasedimentary rocks in several xenolith suites and in exhumed lower crustal sections indicates that mechanisms exist for burying surface rocks to great depths, presumably in thrust zones. Given the existence of metasedimentary rocks, however, one must still recognize the preponderance of igneous and metaigneous rocks, commonly of broadly basaltic composition, in lower crustal xenolith suites. Finally, the regional variability of the lower crust most probably correlates with tectonic setting and should temper extrapolations of lower crustal characteristics found in exposed lower crustal sections to other regions.
The ice cover in the Greenland and Norwegian seas
Authors: Wadhams Peter
Published: February 2008

The seasonal sea ice cover of the northern North Atlantic is reviewed, comprising the ice of the East Greenland Current, the ice cover around Svalbard, and the ice of the Barents Sea as far east as Franz Josef Land. The review considers various types of ice cover: (1) the fast ice along the coasts and in fjords, including ‘sikussak,’ or very old fast ice of exceptional thickness, (2) the transition zone between the fast ice and the main pack, including the positions and causes of recurring winter polynyas and the nature of the shear zone in NE Greenland, (3) the constitution, dynamics, and seasonal extent of the drifting pack ice, including interannual variations, (4) the processes of air‐ice‐ocean interaction which occur in the marginal ice zone, where the pack ice is influenced by an open ocean boundary.
Recent advances in the theory of the geodetic boundary value problem
Authors: Sanso’ Fernando
Published: February 2008

After a short discussion on the general meaning of boundary value problems in physical geodesy the most classical Molodensky’s problem is considered. Recent advancements in the study of this problem, in both the classical and the gravity space approach, are discussed. In particular, some new theorems are presented, one of which also refers to the dependence of the solution on variations of the choice of the telluroid. Geodetic boundary value problems of different types are mentioned: one of these, the altimetry‐gravimetry problem, is also of valuable practical importance.
The evolution of solar ultraviolet luminosity
Authors: Zahnle Kevin J. , Walker James C. G.
Published: February 2008

In view of the major role of the sun in defining the properties of planetary atmospheres, their evolution cannot be fully understood outside the context of an evolving sun. The ultraviolet radiation is especially interesting because of its strong interaction with planetary atmospheres. We use astronomical observations of stars that are analogous to the sun in order to reconstruct a tentative account of the evolution of solar UV luminosity. A wealth of evidence indicates that the young sun was a much more powerful source of energetic particles and radiation than it is today. While on the main sequence, solar activity has declined as an inverse power law of age (between t−5 and t−1.2) as a consequence of angular momentum loss to the solar wind. Recent IUE satellite observations of premain sequence stars suggest that before the sun reached the main sequence (at an age of about 50 m.y.), it may have emitted as much as 104 times as much ultraviolet radiation (λ < 2000 Å) than it does today. These results could impact our understanding of the photochemistry and escape of constituents of primordial planetary atmospheres.
The lunar regolith: Chemistry, mineralogy, and petrology
Authors: Papike J. J. , Simon S. B. , Laul J. C.
Published: February 2008

The lunar regolith, a several meter thick layer of unconsolidated debris, forms the interface between the moon and its space environment. The regolith forms from lithic sources by the destructional processes of comminution and the constructional processes of agglutinate formation. In this manner a steady state soil can develop and will remain in a type of dynamic equilibrium until the system is disturbed by burial or mixing with new soil. Mixing takes place mainly on a local scale (vertically through meters and horizontally over several kilometers). Lateral transport is a relatively inefficient process, and therefore most of the lunar soil components were derived locally. There is no evidence for preferential transport of the finer soil fractions relative to the coarser fractions. The truly ‘exotic’ (derived at distances of tens of kilometers) component is generally in low abundance (≪1%). Therefore remotely sensed data should provide a reasonably accurate picture of bedrock geology. The chemical composition of the regolith varies with grain size. The <10 µm fraction is chemically fractionated from the bulk soil. In most cases the <10 µm fraction is enriched in Al2O3, CaO, Na2O, K2O, light rare earth elements, and Th and depleted in MgO, FeO, MnO, and Sc. These systematics are largely a result of simple comminution, with feldspar and friable mesostasis from local source rocks concentrating in the finest fraction. There is evidence that agglutinate glass forms preferentially by fusion of the finest soil fractions. Therefore agglutinate glass, like the <10 µm soil fraction, appears to be fractionated from bulk soil compositions. Highland soils are distinct from mare soils both chemically and petrologically. Soil samples collected near mare‐highland contacts are mixtures of the two lithologies. Mineral chemical systematics of monomineralic fragments in the lunar soil provide important clues to soil provenance. They can, in some cases, sort out the highland/mare contributions and, in special cases, can even further pinpoint a lithic source. In theory, lunar regolith cores can serve as solar probes, recording the sun's activity over billions of years. In practice, this has generally not been the case. The formation and evolution of most cores is still poorly understood. For most, we have not established how they formed, for example, how many depositional and erosional events were involved, what the time span involved in the accretion of the sampled soil column was, and how long that soil column has remained in situ. Without this information it is difficult, if not impossible, to read the sun's record. More interdisciplinary studies on cores must be carried out before they can be used as solar probes.
Modern exospheric theories and their observational relevance
Authors: Fahr H. J. , Shizgal B.
Published: February 2008

A review and critique of present‐day kinetic theory models of planetary exospheres is presented. Models of ionized exospheres, specifically the solar and the terrestrial polar wind, are also discussed. The objective of the paper is to point out the need for a rigorous kinetic theory treatment of the atmosphere in the altitude region between the thermosphere and the exosphere. This is the region where the atmosphere undergoes a transition from a collision‐dominated to a collisionless situation. The various aspects of the exospheric problem are introduced and developed around this main theme. The exospheric problem and its considerable overlap with several related problems in physics and chemistry are noted. The calculation of the velocity distribution function of exospheric constituents with the spherically symmetric collisionless model is then presented. Various modifications of this standard model with regard to planetary rotation, nonuniform exobasic density and temperature distributions, and time‐dependent effects are subsequently discussed and compared. The extent to which collisionless models suffice to explain observational data of planetary exospheres is assessed. This assessment is given in terms of a comparison of density profiles or reduction factors determined with hydrogen and/or helium cells. A comparison of experimental measurements of the diurnal variation of terrestrial atomic hydrogen densities and theoretical models to explain the asymmetry is presented. The collisionless approach is criticized on theoretical grounds for the neglect of a consideration of the transition region and the resulting artificial boundary between the thermosphere and the exosphere. The aim of collisional models with regard to escape‐induced non‐Maxwellian effects, modifications of the temperature structure, nonthermal escape processes, and satellite particle populations from Monte Carlo simulations and/or kinetic theory models based on a Boltzmann equation is discussed, and the various results are compared. The various attempts to introduce collisional concepts are shown to be incomplete, each considering the problem with different objectives. Throughout, the importance of a more rigorous collisional treatment is stressed, in particular with respect to the description of nonthermal escape processes and satellite particle populations which cannot be considered in a collisionless context. The effects of charge exchange reactions, photoionization, and solar radiation pressure on satellite particles are examined. With regard to nonthermal escape processes, the absence of a detailed kinetic theory of product velocity distributions based on a collisional theory is also noted.
Progress toward the origin of the solar system
Authors: Weidenschilling Stuart J.
Published: February 2008

There has been considerable progress in recent years toward understanding the origin of our solar system. Beyond a broad concensus that the planets are derived from a nebular disk that formed with the sun itself, the differences between the various theories are generally more apparent than the similarities. Most of the disagreements derive from the assumed mass of the solar nebula, based on models for its formation. Estimates range from a few percent of the sun's mass, the minimum required to make the planets, up to one solar mass.
Flood frequency analysis: A review of 1979–1982
Authors: Greis Noel P.
Published: February 2008

In 1977, the Water Resources Council (WRC) probably had little idea that the endorsement of the log Pearson III (LP III) methodology would initiate such a period of activity within the hydrology community. The following review begins with a discussion of the studies which have appeared in response to the Council's action. These early studies questioned the underlying assumptions, suggesting improvements or alternatives to the LP III methodology. The work which followed took many directions.