bluuebunny/crossref_metadata_2025 huggingface dataset:
The charging of spacecraft surfaces
Authors: Garrett Henry Berry
Published: February 2008

The buildup of static charge on satellite surfaces is an important issue in the utilization of satellite systems. The analysis of this phenomenon has required important advances in basic charging theory and the development of complex codes to evaluate the plasma sheaths that surround satellites. The results of these theories and calculations have wide application in space physics in the design of systems and in the interpretation of low‐energy plasma measurements. In this review, those aspects of charge buildup on satellite surfaces relevant to the space physics community are summarized. The types of charging processes, models of charge buildup, satellite sheath theories, and charging observations are described with emphasis on basic concepts.
Properties of blowing snow
Authors: Schmidt R. A.
Published: February 2008

The size and shape of windblown snow particles determine not only the mass transported by turbulent fluxes but also the rate of phase change from ice to water vapor that occurs in this multiphase flow. These properties and particle densities dictate particle fall velocity and therefore the vertical distribution of mass and surface area, which strongly influence the gradients and fluxes of sensible heat and water vapor within the transport layer. Initial movement at the snow surface depends more on availability and impact forces of loose particles than on aerodynamic drag. Cohesion between surface particles and particle restitution coefficient are important properties that determine threshold wind speeds for snow transport. Threshold speeds for blowing snow vary over such a large range in nature that formulations predicting transport rate as a function of wind speed should include threshold speed as a parameter. The expression derived by Iversen et al. (1975) is compared with low‐level snow transport in the atmospheric boundary layer. Self‐similarity of wind profiles in blowing snow is a property of the flow that has been exploited for scale modeling of snow deposition around obstacles, both outdoors and in wind tunnels. Good quantitative results are obtained by careful attention to similitude requirements.
The role of metastable species in the thermosphere
Authors: Torr Marsha R. , Torr D. G.
Published: February 2008

Long‐lived or metastable excited states of various atoms and molecules in the thermosphere provide reservoirs for the temporary storage of a considerable portion of the solar EUV photon energy deposited in the thermosphere. These species permit the redistribution of energy via collision processes yielding kinetic or vibrational heating, ion formation, the formation of other metastable species and the nonlocal deposition of the energy, as opposed to spontaneous radiative decay. While thermospheric species such as O(¹S) have been studied for decades, and indeed provided the first evidence for forbidden transitions, others have a relatively short history. The body of information concerning metastable constituents of relevance to the thermosphere has grown considerably over the past decade, to the point where it is timely to consider the status and future needs of research in this area. In this paper we review the developments leading to the current photochemical picture of O(¹D), O(¹S), O+(²D), O+(²P), N(²D), N(²P), N+(¹S), N+(¹D), N2(A³Σu+), NO+(a³Σ), O2+(a4πu), and the vibrationally excited states of N2, O2, O2+, and N2+. Because a primary significance of these constituents is their role in the thermospheric energy budget, we quantify the major metastable channels by which solar EUV radiation is redistributed in the thermosphere. A few of the major highlights are as follows: A major fraction of the kinetic heating of the thermosphere takes place via the single constituent O(¹D); N2(A³Σu+) and vibrationally excited N2 also are important heating channels. O+(²D) is a primary factor in determining the thermospheric ionic composition. Species such as O+(²P) and N+(¹S) provide valuable ways in which to determine optically the concentrations of certain major species; measurement of emissions from the former yield the atomic oxygen concentration as well as the ion drift speed, and measurement of emissions from the latter provide the concentration of N2; N(²D) remains a major source of NO; and a recent finding is that vibrationally excited N2+ plays a vital role in converting N2+ into O+.
The structure of silicate melts: Implications for chemical and physical properties of natural magma
Authors: Mysen Bjørn O. , Virgo David , Seifert Friedrich A.
Published: February 2008

The structure of melts in binary metal oxide‐silica systems may be described in terms of monomers, dimers, chains, sheets, and three‐dimensional network structures. For the bulk compositions between orthosilicate and tectosilicate, three well‐defined ranges may be distinguished. For bulk nonbridging oxygen per silicon (NBO/Si) of about 2 or less, monomers, dimers, and chains coexist. In the range between metasilicate and disilicate there is usually a combination of monomers, chains, and sheets. Sheets are, however, uncommon or absent in systems where the field strength of the metal cation exceeds that of Mg2+. In those cases, monomers, chains, and three‐dimensional network units coexist. In the bulk compositional range of NBO/Si ≳1, sheets, chains, and three‐dimensional network structures coexist. In all systems the cations of high field strength show a preference for the most depolymerized structural units. Aluminum and probably ferric iron are tetrahedrally coordinated when charge balanced by a monovalent or divalent cation. Aluminate complexes thus formed show a preference for the most polymerized structural units in the melt. The degree of preference increases with decreasing field strength of the charge‐balancing cation. Ferrite complexes may form separate (MFe)4+‐O or (M0.5Fe)4+‐O clusters in the melts. Titanium and phosphorus are always tetrahedrally coordinated. These cations do not substitute significantly for Si4+ in tetrahedral coordination, but form separate clusters. The anionic structural model described above is consistent with viscosity and expansivity data for melts on binary metal oxide‐silica joins. The phase equilibrium data, such as the position of liquidus boundaries between mineral phases of different degress of polymerization on binary metal oxide‐silica joins, may be explained with the melt structure model. The observed expansion of immiscible liquid volumes on MO‐SiO2 joins with increasing field strength of the M cation is in accord with the enhanced stability of three‐dimensional network units in the melts as a function of increased field strength of the metal cation. Most volatile‐free natural magmatic liquids will contain chain, sheet, and three‐dimensional structural units. The proportion of sheet units in magmas with the same ratio of nonbridging oxygens to tetrahedral cations will decrease with increasing M2+/M+. The proportion of three‐dimensional structural units increases at the expense of chain and sheet units as the magma becomes more acidic. On the basis of the observed relationships between melt structure and physical properties the decreased compressibility and viscosity of basic magma compared with acidic magma may be explained. Application of this structural model to natural magma also explains why the pressure dependence of the viscosity of basic magmas is smaller than that of andesitic magmas.
Geodetic singularities
Authors: Bocchio F.
Published: February 2008

Both general and local coordinate systems for geodesy are usually defined in terms of the gravity vector and on the basis of the assumption of the ‘convexity’ of the equipotential surfaces of the gravity field, which ensures the uniqueness of the coordinates of geodetic type. Two formulations of the singularity condition which have been deduced starting from two different approaches to the geodetic singularity problem, that is, the local‐operational and the global‐geometrical approaches, are discussed. A geodetic singularity problem and the related inverse problem are also discussed for a homogeneous and a nonhomogeneous planet; in particular, the existence of geodetic singularities is shown in connection with a perturbing field with a very simple geometry, and the density distribution is deduced which gives rise to geodetic singularities in the external gravity field of the planet. The structure of the gravity field in the neighborhood of the singularities is investigated in detail together with the behavior of the gradients of the disturbances in the geodetic coordinates, and the scale of the perturbed zone is deduced in connection with a given perturbation.
Development of a turbulence closure model for geophysical fluid problems
Authors: Mellor George L. , Yamada Tetsuji
Published: February 2008

Applications of second‐moment turbulent closure hypotheses to geophysical fluid problems have developed rapidly since 1973, when genuine predictive skill in coping with the effects of stratification was demonstrated. The purpose here is to synthesize and organize material that has appeared in a number of articles and add new useful material so that a complete (and improved) description of a turbulence model from conception to application is condensed in a single article. It is hoped that this will be a useful reference to users of the model for application to either atmospheric or oceanic boundary layers.
Applications of deformation analysis in geodesy and geodynamics
Authors: Dermanis Athanasios , Livieratos Evangelos
Published: February 2008

The role of deformation analysis is discussed with respect to its existing or possible future applications in geodesy and geodynamics. Expressions for strain tensors are given in the more general case of Riemannian spaces and specialized for Euclidean spaces and the case of infinitesimal deformation. Among the various applications, special emphasis is given to the study of crustal deformations of the earth, deformations of the gravity field, and gravity field related deformations. Other applications are also considered.
Phase transitions and mantle discontinuities
Authors: Jeanloz Raymond , Thompson Alan B.
Published: February 2008

Density and elasticity data are consistent with, but do not require, a uniform upper‐ and lower‐mantle composition. Such data cannot at present resolve the small changes in physical properties that would be required to keep distinct mantle reservoirs dynamically separated. Alternatively, the issue of chemical stratification in the mantle can be addressed by analyzing the details of the phase equilibria of the appropriate minerals. In order to do this we construct an internally consistent pressure calibration scale which is based in part on the coesite‐stishovite transition pressure Ptr(GPa) = 7.45(±0.3) + 2.1(±0.3) × 10−3T(°C) according to our reanalysis of the available data. We conclude that a discontinuous reaction occurs in the olivine component (α+γ = α+β) of the mantle at the conditions of the 400‐km seismological discontinuity; however, no discontinuous reactions corresponding to the 670‐km discontinuity have yet been identified. The only reaction observed in diamond cell experiments at approximately the pressures existing at 670‐km depth, the breakdown of γ‐spinel to form a silicate perovskite assemblage, appears not to satisfy the observed sharpness of this discontinuity. Thus it may be necessary to invoke either a univariant reaction that has not yet been observed experimentally or a chemical discontinuity at this depth. As the mantle is likely to be at temperatures higher than those of the experiments (estimated to be near 1000°C), additional univariant reactions involving the silicate ilmenite or garnet phases that are predicted to occur may be significant. One possible interpretation is that the mantle is of uniform composition and that such (hypothetical) reactions produce the 670‐km discontinuity. This would imply that the phase assemblages so far studied in high‐pressure‐temperature experiments are not those occurring in the mantle. Alternatively, the mantle could be chemically stratified.
Planetary ring systems
Authors: Cuzzi Jeffrey
Published: February 2008

Planetary ring studies have evolved from observations of a single example, (Saturn), to related studies of a class of objects, in the last several years; in fact, this is the first IUGG review article on the subject. Therefore, it seems appropriate to cite at least review articles going back beyond 1979, if only as a guide to earlier literature (Alexander 1962, Bobrov 1970, Cook et al. 1973, Palluconi and Petengill (eds) 1973, Pollack 1975, Cook and Franklin 1977, and Cuzzi 1978; all of which deal only with Saturn's rings). More recent reviews have been written by Ip (1980 a,b); Cook (1980), Elliot (1982), and Goldreich and Tremaine (1982); also of interest are review articles in books to be published shortly; Saturn (Gehreis, ed.) and Planetary Rings (Brahic and Greenberg, eds.). Popular articles of interest have been written by Pollack (1978), Burns (1981) and Pollack and Cuzzi (1982).
New techniques
Authors: Pisacane Vincent L.
Published: February 2008

Many major advances in geodesy have been precipitated by the development of new or improved techniques for obtaining geophysical data. Geometrical geodesy, the study of the shape of the earth, has benefited from measurements of absolute and relative positions. Physical geodesy, the study of the gravity field, has benefited from measurements of the components of the absolute and relative gravity vectors. The significance of new techniques has been clearly recognized.
Electromagnetic induction studies
Authors: Hermance John F.
Published: February 2008

This report attempts to review recent developments involving electromagnetic induction studies of the lithosphere and asthenosphere. Activities of the last four years are emphasized, particularly those of U.S. workers. However, following the tradition of earlier reviews of this type (Filloux, 1979; Bennett and Filloux, 1975), for purposes of continuity and completeness we are not necessarily constrained by this time frame, nor by strict national boundaries. For example, certain aspects of Canadian research in this field is so inextricably related to that in the U.S., that it is appropriate to describe some of this activity with a few illustrative examples. Recognizing the interests of the readership of this journal, we have not gone into details of methods and technique, but have tended to emphasize those recent advances in the field which contribute to understanding some of the fundamental problems in contemporary studies of solid earth geophysics.
Urban hydrology
Authors: Delleur J. W.
Published: February 2008

The period of 1967–1974, in Urban Hydrology, was called the period of “tool making” by McPherson (1980) and was followed by the 1975–1978 period of “tool wielding”. The four years of 1979–1982 are characterized primarily by a greater attention to the problems associated with the runoff quality, by the extension and improvement of computer models for a better simulation of pollutant washoff and pollutant effects on receiving streams, by a better understanding of the limitations of detention basins, by the recognition that detention can contribute to pollution abatement and finally by the acquisition of a very much needed and extensive data base on urban rainfall runoff quantity and quality and practices of urban runoff pollution control through the US EPA/USGS Nationwide Urban Runoff Program. One of the effects of this latter program is that the concept of watershed‐wide management for environmental protection was sharpened in terms of the control of flooding and of the quality of urban runoff and of the impacts on receiving streams.

These last four years witnessed a maturing of urban hydrology which was manifest in the publication of a number of books on the subject. Kibler (1982b), Sheafer et al. (1982), Whipple et al. (1982), Novotny and Chester (1981), American Public Works Association (1981) and Lazaro (1979).
The geologic record of climatic change
Authors: Crowley Thomas J.
Published: February 2008

This paper reviews the principal results from paleoclimate studies and includes background material slanted toward climate modelers. The inferred temperature history of the last 4.6 billion years indicates major changes in the components of the earth's climate system. A secular change in global insolation receipt is due to a 20–30% increase in solar luminosity since the formation of the earth. A CO2‐H2O greenhouse effect may have offset the lower luminosity during early earth history. Inferred fluctuations of global temperature have occurred over a broad range of time scales. On time scales of 106–108years, paleogeographic factors (e.g., continental drift and sea level changes) have contributed significantly to temperature changes associated with transitions between nonglacial and glacial states. Preliminary modeling efforts indicate that additional factors (e.g., CO2, changes in atmospheric circulation) must also be considered in order to explain the origin of nonglacial climates. The origin of polar ice caps may result from ocean circulation changes that were caused by plate tectonic processes. Fluctuations of ice volume on a time scale of 10³–105years correlate with insolation variations caused by orbital perturbations. Feedback interactions within the land‐sea‐air‐ice system (e.g., ocean circulation changes and bedrock dynamics) have been responsible for a significant modulation of the orbital signal. Ice ages may be due to orbitally induced temperature changes superimposed on a global cooling of terrestrial origin.
Organic material in the global troposphere
Authors: Duce R. A. , Mohnen V. A. , Zimmerman P. R. , Grosjean D. , Cautreels W. , Chatfield R. , Jaenicke R. , Ogren J. A. , Pellizzari E. D. , Wallace G. T.
Published: February 2008

Interest in the global tropospheric chemistry of organic materials has been growing rapidly over the past decade. In addition to a basic concern about the fundamental biogeochemical cycles of organic matter, this interest has arisen largely because of concern about the oxidant‐forming potential of natural hydrocarbons, the possible importance of nonmethane hydrocarbons as a source for atmospheric CO, and the role played by organic material in the formation of secondary aerosol particles. In this review we consider the information presently available on concentration distribution, sources, sinks, and atmospheric transformation reactions of organic matter in the global troposphere. The data base for tropospheric organic compounds is very small. However, it is apparent that while anthropogenic sources often dominate the atmospheric chemistry of organic material in urban and near‐urban air, a key to understanding the global cycling of tropospheric organic substances is a clear understanding of the interaction of the atmosphere with the terrestrial and marine biosphere.
Lightning
Authors: Uman Martin A.
Published: February 2008

The previous review of U.S. lightning research for the IUGG covered the period 1971–1975 and was published by Uman et al. (1975). Although the present review is intended to cover the research of the last four years, 1979–1982, we will survey the total seven year period, 1976–1982, since the previous review. References to 82 articles were included in the 1971–1975 review, an average of 16 to 17 papers per year. Interestingly enough, the yearly average for 1976–1982 is 18, a value almost identical to the previous period. Many of these recent articles describe research performed as part of the Thunderstorm Research International Program (TRIP) hosted by the NASA Kennedy Space Center (KSC), Florida in 1976–1978 and by the New Mexico Institute of Mining and Technology in Socorro, New Mexico in 1979–1982.
Mesoscale meteorology
Authors: Emanuel Kerry , Sanders Frederick
Published: February 2008

The last four years have seen a considerable expansion in research on mesoscale atmospheric phenomena. The motivation is three‐fold: the prospect of greater forecast accuracy, an emerging ability to observe the mesoscale, and the challenge of understanding extremely complex physical mechanisms. The current level of accuracy of storm warnings and other local forecasts can be substantially advanced only by an improved ability to deal with structures smaller than the traditional synoptic scale. These structures are beginning to be described by analysis of special data and of routine surface observations.
Developments in digital seismology
Authors: Alexander Shelton S.
Published: February 2008

Seismology has entered the 1980s with increasing challenges and opportunities presented by advances in the technology for gathering and analysis pf digital data. These developments have resulted in: 1) a rapid increase in the amount of data routinely recorded; 2) a shift in data collection from primarily analog towards digital recording; and 3) the increasing application of advanced computer technology in seismological studies. There is clearly the potential to increase the scientific returns from seismic data of all types significantly, provided the data problems occasioned by these technological advances are overcome.

During the past four years there have been rapid advances in digital data storage and processing capability that are now making relatively sophisticated signal analysis simple to carry out even on microcomputers; minicomputers or mainframes that seismologists have used for many years are increasingly powerful and versatile. As a result of these developments high‐quality digital data sets are accessible in formats that are relatively easy to use, although standardized formats for data exchange are not universally agreed upon as yet. Unlike the situation only a few years ago, it is now feasible to analyze a large suite of seismic events in a typical study, rather than base conclusions or only a few events that can be digitized from analog paper or analog tape recordings. Moreover, the increased dynamic range afforded by modern digital systems (>120 db) allows one to study a large range of event magnitudes using the same source‐receiver combination.
Large scale thin‐skin tectonics
Authors: Seeber Leonardo
Published: February 2008

The lithosphere is, to a first approximation, a layered system. Generally, pressure, temperature and composition are strongly dependent on depth and vary relatively little laterally. These parameters can affect greatly the response to stress of rocks in the crust and upper mantle and are responsible for the stratification of many characteristics, such as seismic response, rheology and kinematics, in the lithosphere‐asthemosphere system (e.g., Chen and Molnar, 1983). On a smaller scale, lithology, which often is also horizontally stratified, plays a major role in determining strength (e.g., Engelder and Geiser, 1980) pore pressure can also greatly affect strength (Hubbert and Rubey, 1959; Suppe, 1981).
On the evolution of marginal basins
Authors: Taylor B. , Karner G. D.
Published: February 2008

This paper presents a critique of the models proposed to explain the formation of back arc basins: those marginal basins located behind active or inactive trench systems and whose origin is inferred to be subduction related. Several marginal basins are not generically back arc, but rather are related to the initiation of subduction, continental rifting, or plate boundary readjustments. Models of back arc basin formation must be consistent with the observed characteristics of back arc basins, which include the following: (1) the crustal structure and magnetic lineation patterns of back arc and major ocean basins are similar, implying that the processes of crustal accretion in both tectonic environments are also similar; (2) arc‐trench systems without currently spreading back arc basins are in the majority; (3) although petrographically similar to and within the compositional range of midocean ridge basalts (MORB), back arc basin basalts (BABB) show consistent geochemical differences from N‐type MORB and are in many respects transitional toward island arc tholeiites (IAT); (4) distinct BABB and IAT mantle sources may be in extremely close proximity during the initial rifting of an island arc; (5) rifting of the volcanic arc may occur on either side of the line of active volcanoes (±50 km) and may vary from one side to the other along strike; (6) a remnant arc is not always developed; (7) back arc spreading may be initiated above subducted lithosphere, but with time the center of spreading migrates away from the arc and no longer overlies a Benioff zone; and (8) there is no simple correlation between the timing of global plate reorganizations and the formation of back arc basins. The three main classes of models proposed to explain back arc basin formation are mantle diapirism, induced aesthenospheric convection, and global plate kinematics. Because the driving mechanism for the first two classes of models is provided by the local subducting slab, these models fail to explain the temporal and spatial distribution of back arc basins. The third class of models proposes that back arc basins should form whenever global plate interactions require divergence between the overriding plate and the trench line, the latter being observed to move only in a seaward direction with respect to a hot spot reference frame. However, the tectonic setting of several back arc basins suggests that they represent more than just a passive response to kinematic boundary conditions. For example, some dynamic back arc force seems required to move the New Hebrides, Tonga, and South Sandwich forearc plates seaward. Neither the local nor the global models adequately specify the necessary and/or sufficient conditions for back arc basin formation. A better understanding of the processes associated with the initiation of rifting and of subduction is required. Arc rifting and back arc spreading are both secondary phenomena to subduction, but they are also primary extensional phenomena, fundamentally analogous to continental rifting and the initial spreading of major ocean basins.
The spatial structure of different ULF pulsation types: A review of STARE radar results
Authors: Allan W. , Poulter E. M.
Published: February 2008

The Scandinavian Twin Auroral Radar Experiment (STARE) has proved useful in estimating the ionospheric electric fields of several types of ULF pulsation. These usually involve the propagation of hydromagnetic waves along the geomagnetic field lines. Reflection at the auroral ionosphere boundary can then result in standing wave resonances. Because of its good spatial resolution and coverage of this boundary, STARE provides unique data on the spatial variations of the pulsation fields. Background theoretical aspects and STARE observations are presented for three types of pulsation: impulsive or ringing Pc 5, monochromatic resonant Pc 5, and pulsations thought to be generated by instabilities in the ring current particle population. Since the ionosphere is resistive, it acts as an energy sink for the pulsations, and estimates of the ionospheric Joule heating are presented. Finally, some suggestions for future work are given.
Lightning: Estimates of the rates of energy dissipation and nitrogen fixation
Authors: Borucki William J. , Chameides William L.
Published: February 2008

The global rate of production of atmospheric NO is given by the product of the lightning energy dissipation rate and the NO yield per joule of discharge. A value for the global average energy dissipation rate is derived from the energy per flash and the global average flash rate; the latter is determined from satellite observations. The energy per flash determined from the optical measurements is in excellent agreement with that determined from measurements of electrical field changes; both give 4 × 108 J per flash. For a global flash rate of 100 s−1, the global average energy dissipation rate is estimated to be 4 × 1010 W; however, the uncertainty in this parameter is approximately a factor of 3. The NO yield is estimated to be (9 ± 2) × 1016 molecules/J, a value in good agreement with numerous other theoretically and experimentally derived yields. The production of NO from lightning is thus estimated to be 2.6 × 109 kg N yr−1 with a range caused by uncertainties of (0.8–8) × 109 kg N yr−1. Although lightning is a small source of fixed nitrogen to the biosphere, it appears to represent a major source of atmospheric NO to the remote troposphere.
Impact melt products of chondritic material
Authors: Rubin Alan E.
Published: February 2008

A large variety of objects in chondritic meteorites formed as a result of impact melting: shock veins, metal‐troilite mixtures, metal and sulfide nodules, melt pockets, vugs, agglutinates, glassy and crystalline spherules, and numerous types of melt‐rock clasts. The type of object produced in an impact event is related to the interaction of the shock waves with the particular target rock. Impact melting has also affected large portions of several chondrite breccias; many of these contain vugs and patches of silicate glass. Some workers have suggested that various iron meteorites (including groups IAB, IIICD, and IIE as well as several ungrouped irons) were formed from individual impact melt pools in chondritic regoliths. The Eagle Station Trio pallasites and several ungrouped meteorites (Bencubbin, Weatherford, Enon, Acapulco and Allan Hills A77081) may have formed from impact‐melted chondritic material. It is also possible that the parent magmas of ureilites were derived from impact‐melted metal‐rich carbonaceous chondrite material.
Sea surface temperature anomalies, planetary waves, and air‐sea feedback in the middle latitudes
Authors: Frankignoul Claude
Published: February 2008

The mechanisms that contribute to the generation and damping of large‐scale mid‐latitude sea surface temperature (SST) anomalies are discussed. The SST anomalies reflect primarily the response of the upper ocean to the changes in air‐sea fluxes that are associated with daily weather fluctuations. Heat flux forcing is dominant in the lower middle latitudes, while wind‐driven entrainment may be most effective in the high latitudes; advection by anomalous Ekman current is generally less important, and Ekman pumping is negligible. The SST anomalies decay in part because of entrainment effects associated with mixed‐layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere. The three approaches commonly used to model the evolution of SST anomalies are reviewed: case studies based on monthly or seasonal anomaly maps of the large‐scale SST and atmospheric anomalies, numerical simulations with one‐dimensional mixed‐layer models, and stochastic forcing models. We stress the similarities in the different approaches and discuss their main advantages and limitations. The response of the atmosphere to mid‐latitude SST anomalies is considered. First, we discuss the poorly known relationship between SST anomalies and diabatic heating. Using a crude assumption for the air‐sea coupling, we consider a two‐layer quasi‐geostrophic channel model and discuss the stationary wave response to SST anomaly forcing and the resulting air‐sea feedback. It is found that the back interaction of the SST anomalies onto the atmosphere causes a weak SST anomaly damping at large scales and a strong one at small scales; the air‐sea coupling should also act as an eastward propagator for the SST anomalies. The response of more realistic linear wave models to prescribed diabatic heating is then reviewed, and it is suggested that realistic mid‐latitude SST anomalies have a weak influence on the atmospheric circulation, corresponding to changes in the geopotential height of 10–30 m at most. This order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid‐latitude SST anomalies.
Isotopic modeling of the evolution of the mantle and crust
Authors: Turcotte D. L. , Kellogg L. H.
Published: February 2008

The geochemical reservoirs and cycles of the earth are discussed. Models involving the isotopic evolution of the enriched continental crustal reservoir and the complementary depleted mantle reservoir are considered. Analytic solutions for the fractionation factors f and isotope ratios ε are obtained using consistent approximations. The results are applied to data on the samarium‐neodymium, rubidium‐strontium, and thorium‐uranium‐lead systems. Using a model for instantaneous crustal differentiation, data on young rocks provide constraints on the mean age of the continental crust and on the mass of the depleted mantle reservoir. Although there are a variety of uncertainties, we favor a mean continental age of τc=2.1±0.7 Ga. A mass balance based on samarium‐neodymium and rubidium‐strontium data favors a mass for the depleted layer near the mass of the upper mantle. Mass balances for argon and helium, isotope correlations between strontium and neodymium and between thorium and uranium, and the substantial quantities of primordial helium and argon found in ocean island basalts (OIB) from Hawaii and Iceland favor the existence of a sizable near‐primitive reservoir. We conclude that the isotope data favor a near‐primitive lower mantle with a barrier to mantle convection at a depth of 650 km. Thus the isotope data favor layered mantle convection rather than whole mantle convection. Isotope data on older rocks provide information on the time evolution of the continents. An important question is whether significant volumes of continental crust are recycled back into the mantle. Isotope data on old continental rocks that can be associated with the depleted mantle appear to favor significant volumes of crustal recycling. We have also studied the implications of preferential recycling of either parent or daughter isotopes. Recycling of either isotope increases the age of the continental crust inferred from isotope data. Studies of lead isotopes in mid‐ocean ridge basalts (MORB) and OIB show that they evolved in uranium rich environments for several billion years. This is the “missing lead” paradox; we associate the missing lead with the lower continental crust. We conclude that the radiogenic lead evolved either in the depleted mantle reservoir or in the radiogenic upper crust. The isotopic heterogeneities of OIB are also considered; these are attributed to (1) entrainment of near‐primitive lower mantle rock and (2) inclusion of recently subducted and delaminated continental crust and mantle.
Strainmeters and tiltmeters
Authors: Agnew Duncan Carr
Published: February 2008

Despite steady effort over the last century, continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements. This article reviews the techniques and instrument designs that have been developed in this field. The continuous measurement of true tectonic motions, which have rates of 10−14 s−1, requires extremely high instrument stability, but more rapid motions (tides and seismic waves apart) are even smaller and not much more easily detectable. Much past effort has been spent improving the transducers used in these instruments, which usually measure small displacements; the commonest choices are optical (the most accurate), capacitive (the most sensitive), and inductive (the most rugged). Nowadays building a transducer is the easiest part; a much harder task, equally important to a good design, is attaching the instrument to the ground so that it can detect the signal wanted. This part of the design includes choosing a location. A large underground opening is thermally stable but distorting; a surface installation is easy to build but noisy because of soil weathering; and a borehole is inaccessible to weather but also to the operator. All such installations (and indeed the whole field of strain and tilt measurement) of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less; this is true for tides and seismic waves, but unproven for tectonic motions. Appropriate attachment techniques differ for each location, and many mundane details (such as cementing techniques for borehole instruments) remain to be worked out. The goal of measuring tectonic and tidal tilt has created many tiltmeter designs. Most are relatively small instruments that use some form of pendulum or bubble level; a few use a liquid surface to measure tilts over a long baseline. Repeated experience has shown the latter type, when well built, to be superior to the former, proving end‐monument motions to be a dominant source of noise. The same appears to hold true for strainmeters, the best results coming from long‐base laser instruments, though strainmeters using rigid or flexible material length standards are useful for special purposes, and borehole instruments show promise. Because achieving a good design has been so difficult, it is important to select the goals an instrument must meet and be prepared to compromise on others. The difficulty of validating results from this type of instrument makes comparison tests essential; such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details.
Dust and neutral gas modeling of the inner atmospheres of comets
Authors: Gombosi T. I. , Nagy A. F. , Cravens T. E.
Published: February 2008

This paper summarizes our present, preencounter understanding of the physical and chemical processes controling the inner (r < 1000 km) region of cometary atmospheres. Special emphasis was attached to compiling a self‐consistent set of governing equations. We are aiming this review at readers who want to understand the present status of the mantle and coma regions and/or who want to develop new, next generation models which will be needed as the large volume of new observational data will become available in the near future.
Numerical advection algorithms and their role in atmospheric transport and chemistry models
Authors: Rood Richard B.
Published: February 2008

During the last 35 years, well over 100 algorithms for modeling advection processes have been described and tested. This review summarizes the development and improvements that have taken place. The nature of the errors caused by numerical approximation to the advection equation are highlighted. Then the particular devices that have been proposed to remedy these errors are discussed. The extensive literature comparing transport algorithms is reviewed. Although there is no clear cut “best” algorithm, several conclusions can be made. The judicious use of simple finite difference schemes (second‐order time differences and even‐order ( >2) spatial differences) provides a minimum level of accuracy that is suitable for many atmospheric applications. More complex schemes can yield a significant improvement in accuracy, but sometimes at great computational expense. Spectral and pseudospectral techniques consistently provide the highest degree of accuracy, but expense and difficulties assuring positive mixing ratios are serious drawbacks. Schemes which consider fluid slabs bounded by grid points (volume schemes), rather than the simple specification of constituent values at the grid points, provide accurate positive definite results. The computer memory requirements of the volume schemes can be excessive. Recent attempts to maxmize accuracy while keeping cost low have lead to such useful schemes as the one proposed by P. K. Smolarkiewicz.
Hydrology—The computer revolution continues
Authors: Wallis James R.
Published: February 2008

Twenty years ago the use of computers in hydrology was minimal and consisted mostly of simple translations of existing pre‐computer algorithms. Later, it was realized that these machines could also be used to give more useful answers than were possible with the original algorithms. The race for computer code and algorithm modification was on, and computer usage in hydrology entered its second stage. Hydrology and water resources are now in the third phase of computer usage: problems are being routinely defined that could not even have been conceived without the existence of computers, and solutions and algorithms that are new and more powerful than their pre‐computer predecessors are omnipresent.
The Moon
Authors: Ryder Graham
Published: February 2008

S. R. Taylor [1982] wrote a book that summarized the Moon as we knew it at the start of the quadrennium. Since then lunar science has continued (perhaps to the surprise of many), and provided us with many new ideas and “facts” about the Moon and its past and present environment. Lunar science is not moribund. Some aspects have received insufficient attention despite the potential for advances.
Solar variability and oscillations
Authors: Hudson Hugh S.
Published: February 2008

Within this decade, observations of total solar irradiance have become good enough to permit us to study directly the solar luminosity variations on a wide range of time scales, up to several years. At the same time there has been considerable improvement in understanding the classical indicators of solar activity, such as UV and visible chromospheric lines, soft X‐rays, and radio fluxes. The observed variations include the effects of sunspots and plage (which induce “rotational modulation”), solar‐cycle effects, and signatures of global oscillations and convection. In addition new characteristic time‐scales (154 days and possibly 320 days) have been discovered but not explained. This review covers these developments and comments briefly on the subject of helioseismology, the study of the solar global oscillations.
Gravimetry
Authors: Moose Robert E.
Published: February 2008

This report of the developments in gravimetry in the United States for the period 1983–86 was compiled from the cited published papers and from information contributed by selected individuals concerning their particular activities.

The most significant development in gravity surveying during the last 4 years has been the utilization of the Global Positioning System (GPS) in all facets: land, sea and air of gravity data acquisition. Differential GPS is being used in land gravity surveys to provide accurate position and height information and carrier frequency Doppler observations are being used to accurately determine the velocity in moving base gravimetry. Using GPS, airborne gravity is now, and soon gradient measuring systems will be, able to map with ease previously inaccessible areas such as mountains, swamps and the arctic regions.
Metamorphic geology
Authors: Tracy Robert J.
Published: February 2008

T. P. Loomis noted in his review of metamorphic petrology in the preceding U.S. National Quadrennial Report to I.U.G.G. (1983) that metamorphic petrology was well on the way toward being a quantitative science, largely through advances in modelling thermodynamic and kinetic aspects of metamorphic mineral equilibria. This trend has continued through the most recent quadrennium and has even accelerated. There has been a blossoming of effort toward quantitative characterization of pressure‐temperature‐time paths during metamorphism, accompanied by much wider application of the Gibbs' Method for calculation of intensive parameters indicated by metamorphic mineral assemblages. Continued and expanded use of stable isotopes (especially those of carbon and oxygen) to monitor the processes of fluid‐rock interaction has produced efforts to coordinate petrologic and isotopic studies. Increasingly sophisticated experimental studies and thermodynamic analyses have greatly enhanced the data base for petrologic calculations, and have extended the application of mineral thermobarometric techniques to rock types and physical conditions previously inaccessible. The last four years have seen such advances in this last area that thermobarometry has become one of the more widely practiced, albeit controversial, fields in metamorphic petrology.
Continental margin tectonics: Submarine accretionary prisms
Authors: Moore J. Casey , Silver Eli A.
Published: February 2008

Submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted, deformed, and ultimately transformed to continental crust. Accretionary prisms develop at sites of lithospheric convergence, that is, subduction zones. Commonly accretionary prisms form along continental margins, although accretionary prisms may also occur adjacent to island arcs, which are ultimately coalesced into continental landmasses. Here, we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the United States.
Chemistry of the rock‐forming silicates: Ortho, ring, and single‐chain structures
Authors: Papike J. J.
Published: February 2008

The crystal chemistry of 21 ortho, ring, and single‐chain silicate structures is reviewed. Structure drawings are presented to portray the essential crystal chemical features necessary to correctly interpret chemical data for each mineral or mineral group. The groups considered are olivine, humite, zircon, sphene, garnet, vesuvianite, aluminosilicate, topaz, staurolite, chloritoid, epidote, melilite, beryl, cordierite, tourmaline, axinite, pyroxene, pyroxenoid, pectolite, sapphirine, and aenigmatite. Electron microprobe data for each group can be interpreted with various degrees of rigor, depending on whether H2O, Fe2+/Fe3+, and other elements not detected by the microprobe are present. Serious mineral chemists are encouraged to determine Fe2+/Fe3+ and H2O directly. Estimates of these values using microprobe data are usually imprecise and can lead to serious errors in interpretation of the chemical formula and thus any thermodynamic or petrologic inferences that are based on the correct formula.
A comparison of analytical and numerical models for steadily driven magnetic reconnection
Authors: Forbes T. G. , Priest E. R.
Published: February 2008

In this review we consider the role of boundary conditions in both analytical and numerical solutions of steadily driven reconnection. Recently, we developed a unified formulation for steady state reconnection in which different types of reconnection are produced by varying the inflow boundary conditions. Three families of solutions occur, namely, the slow‐mode compression, the hybrid expansion, and the flux pile up. The Petschek solution and a Sonneruplike solution occur as special cases separating the new regimes. We use this unified formulation to reinterpret the main numerical experiments of steadily driven reconnection and find that many previous contradictory features of the experiments are caused by the use of different boundary conditions. For example, the 1986 Biskamp experiment did not produce a Petschek‐like solution owing to the particular boundary conditions that were adopted rather than to any basic failure of the Petschek solution. The new solutions are used to derive conditions for the onset of impulsive, bursty reconnection in which a steady state regime goes unstable to secondary tearing and coalescence and which may be a prelude to fully turbulent reconnection. Our analysis suggests that the flux pileup solutions, which are relevant to magnetopause reconnection, are the ones most likely to be unstable in this way.