bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismic surface waves and crustal and upper mantle structure
Authors: Kovach Robert L.
Published: February 2008

Seismic surface wave data have been used to infer details of earth structure over various propagation paths. Experimental methods for measuring surface wave dispersion include the Fourier phase method, the time correlation method, the band‐pass filtering method, the group delay time method, and various digital ‘moving window’ techniques. Surface wave data exhibit distinctive observational characteristics for different tectonic provinces such as shields, aseismic continental platforms, rifts, oceans, and mountains. Inversion procedures used to determine velocity models from dispersion measurements utilize trial and error procedures or application of partial derivatives of phase and group velocity with respect to model parameters combined with linear inverse theory. The observed surface wave data emphasize that there are pronounced lateral variations in crustal and upper mantle structure and the continents and oceans are themselves inhomogeneous. Shield areas possess the highest values of shear wave velocities with depth and a relatively weak mantle low‐velocity zone. On the other hand, rift areas have much lower shear velocities and a very pronounced low‐velocity zone. Under the oceans the lid overlying the low‐velocity zone is variable in thickness and thickens with the increasing age of the ocean floor. The average velocity above 170–200 km is less under oceans than under continents. Surface waves propagating over oceanic paths are attenuated more than continental paths, but detailed regional studies are lacking.
Organization and structure of clouds and precipitation on the mesoscale and microscale in cyclonic storms
Authors: Hobbs Peter V.
Published: February 2008

Our current understanding of the organization and structure of clouds and precipitation in extra‐tropical cyclonic storms is reviewed. The regions of relatively heavy precipitation are organized into large mesoscale (∼ 10³–104 km²) rainbands which are classified into five types: warm‐frontal, warm‐sector, cold‐frontal (wide and narrow), prefrontal cold‐surge, and postfrontal bands. The rainbands themselves are composed of smaller mesoscale areas (∼ 10–10² km²) or ‘cores’ of precipitation. In some of the rainbands the precipitation cores often originate in higher‐level generating cells, probably produced by the lifting of potentially unstable air. The generating cells provide ‘seed’ ice crystals, which grow by aggregation and riming as they fall through lower cloud layers produced by large mesoscale or synoptic scale lifting of the air. In these cases the rainbands move with the velocity of the upper‐level winds at the levels of the generating cells and therefore tend to move through the cyclonic storm. Other rainbands have their origins in lower‐level convection. For example, narrow cold‐frontal bands are fed by moisture from a low‐level, southerly jet of air which the cold front progressively overtakes. The narrow cold‐frontal band is therefore anchored to the cold front. Appreciable precipitation on the mesoscale in cyclonic storms is invariably associated with high concentrations (∼ 1–100 1−1) of ice particles. Small hills may play an important role in triggering or enhancing mesoscale rainbands in cyclonic storms in regions where the air is unstable. The precipitation over and downwind of large mountain barriers, on the other hand, may be disrupted because the orography interferes with the low‐level, southerly flow of air which provides the front with its principal source of moisture.
Numerical and laboratory simulation of fault motion and earthquake occurrence
Authors: Cohen Steven C.
Published: February 2008

This paper reviews the simulation of earthquake occurrence by numerical and laboratory mechanical block models. Simple linear rheological elements are used with elastic forces driving the main events and viscoelastic forces being important for aftershock and creep occurrence. Friction and its dependence on velocity, stress, and displacement also play a key role in determining how, when, and where fault motion occurs. The discussion of the qualitative behavior of the simulators focuses on the manner in which energy is stored in the system and released by the unstable and stable sliding processes. The numerical results emphasize the statistics of earthquake occurrence and the correlations among source parameters.
Earthquake source mechanisms and plate tectonics
Authors: Kanamori Hiroo
Published: February 2008

This review and the accompanying references will be concerned mainly with earthquake source studies pertinent to plate tectonics. Studies on geological problems, lithospheric flexure and mantle convection are discussed in other reviews in this volume.

In the earlier stage of the development of plate tectonics, the distribution of earthquakes and the geometrical configuration of earthquake source mechanisms played an important role. As more sophisticated techniques for retrieving earthquake source parameters (synthetic seismogram method for both body and surface waves, inversion method, matching filter method, etc.) were developed, emphasis in the last four years was placed on the determination of not only the geometry of the source but also more quantitative parameters such as the stress drop, the amount of slip, the complexity, the strength of non‐isotropic components, and the spectral characteristics. Also significant emphasis was placed on intraplate earthquakes and events on continental plate boundaries.
Interplanetary type III radiobursts
Authors: Papadopoulos K.
Published: February 2008

Type III solar radiobursts are a form of sporadic solar radioemission originating throughout the solar corona and also in the interplanetary region, to heliocentric distances of 1AU and beyond. They are associated with fluxes of moderately energetic electrons (10–100 keV) which are accelerated either in flares or in active storm regions and which escape along magnetic field lines that penetrate the high corona. The bursts appear to have a frequency corresponding to twice the local plasma frequency (2ωe) (sometimes, the plasma frequency), their frequency drifts at a rate suggesting a source velocity of 1010 cm/sec. At a fixed frequency the duration ranges from < at the highest frequencies, to more than 1 hr at the lowest frequencies [Smith 1974; Fainberg and Stone 1974].
Are carbonaceous chondrites primitive or processed? A review
Authors: McSween Harry Y.
Published: February 2008

Carbonaceous chondrites, generally considered to be the most primitive surviving materials from the early solar system, form a distinctive group in terms of bulk Mg/Si, Ca/Si, and Al/Si ratios. The carbonaceous chondrites can be subdivided into five groups (CI, CM, CR, CO, and CV) based on a number of petrologic and chemical criteria. Petrographic observations indicate that most carbonaceous chondrites have been processed, either by thermal metamorphism in the case of CO and CV chondrites or by low‐temperature aqueous alteration in the case of CI, CM, and CR chondrites. Thermal metamorphism resulted in Fe/Mg exchange between chondrules, olivine and pyroxene grains, and matrix, changes in the compositions of metal grains, and textural integration. Aqueous alteration probably produced hydrated phyllosilicate matrix phases and resulted in alteration of chondrules and replacement and vein filling by secondary carbonates and sulfates. The changes incurred during these processes appear to have been largely isochemical. However, if certain constituents behaved as open‐system components, volatile elements or compounds may have been depleted during metamorphism, and isotopic patterns may have been changed during aqueous alteration. The recognition of two different types of postaccretional processes resulting in petrological modifications necessitates a reinterpretation of the classification system for carbonaceous chondrites.
Unsaturated‐zone water
Authors: Molz Fred J. , Davidson James M. , Tollner Ernest W.
Published: February 2008

The present theoretical base for mass transport in porous media rests mainly on empirical observations and resultant mathematical descriptions made at the macroscopic [pore size or above] level. Recently, several attempts have been made to extend the theoretical base to the molecular domain. Laroussi and De Backer [1975] derived the diffusion equation for soil moisture flow by considering the displacement of a fluid particle through an unsaturated porous medium as a Markov's stochastic process. However, Bhattacharya, Gupta and Sposito [l976a] point out that the Laroussi‐De Backer interpretation of the diffusivity is invalid because their analysis does not allow for Markovian coefficients that are space and time dependent.
Water resources systems
Authors: Loucks Daniel P.
Published: February 2008

The past four years have seen various statistical and optimization‐simulation modeling techniques of increased quality and usefulness developed and applied to water resources system design and operating problems. Older modeling approaches continue to be improved and newer methods continue to be developed for the comprehensive analysis of larger complex problems. What distinguishes the last four years from the past is the major increase in the number of successful and useful applications of these mathematical modeling techniques. If success can be measured by the impact models have on our understanding and management of hydrologie or water resource systems, then any review of the recent literature (especially of the proceedings of various symposia and conferences on this subject) will demonstrate that these methods of analyses have matured and are being successfully used throughout the world.
Scientific achievements from ten years of lunar laser ranging
Authors: Mulholland J. Derral
Published: February 2008

In the 10 years since lunar laser ranging became a reality the need to analyze the observations has motivated improvements in several aspects of the mathematical model of earth‐moon dynamics. Application of the data to improved estimates of the physical parameters of the earth‐moon system has yielded significant astronomical, selenophysical, geophysical, and cosmological results. The scientific impact, both in improved theories and in numerical applications, is surveyed. The underlying physics and major difficulties are discussed, as well as the scientific results.
On using satellite altimetry to determine the general circulation of the oceans with application to geoid improvement
Authors: Wunsch Carl , Gaposchkin E. M.
Published: February 2008

We describe the problem of combining hydrography with marine geodesy and satellite altimetry for the purpose of determining the general circulation of the oceans, defining the eddy field, and improving the marine geoid. The critical problem is to understand the error budgets of four fields: orbit, height measurement, geoid, and ocean water density. Corrections must be made for atmospheric load, tides, tropospheric water vapor, wave height, and other parameters. A general formalism for deducing the geoid and ocean circulation is obtained in terms of inverse theory and applied to some limited examples.
New advances in thermal plasma research
Authors: Chappell Charles R. , Baugher Charles R. , Horwitz James L.
Published: February 2008

It has been a decade since the comprehensive measurements made by the Ogo 5 satellite and by ground‐based whistler techniques have given us a picture of the plasmasphere as a dynamically changing region of ionospherically produced plasma. This image was at once comforting in its completeness and misleading in its simplicity. We found it easy to think of the plasmasphere as a region full of ‘cold’ plasma which was modulated by the magnetospheric convection electric field. At that same time, however, theory was predicting complex plasma distributions along the field lines which combined polar wind flow and diffusive equilibrium and which involved shock fronts and two‐stream instabilities. Today, with data from the Isee and Geos spacecraft we can begin to measure these complex distributions. The plasma is sometimes cold, but at times it is warm, and the influence of plasma flows combined with the effects of magnetic field line guidance opens an intriguing new world of thermal plasma studies. Such studies will be an essential element in the understanding of mass and energy interchange within the magnetosphere.
Linear viscoelasticity and dispersion in seismic wave propagation
Authors: Brennan B. J. , Smylie D. E.
Published: February 2008

The theoretical background to the application of linear viscoelasticity in describing the anelastic behavior of rocks is developed in this review. The constraints imposed on the behavior of the impulse response and system function of a linear system by the requirements that the system be causal and passive are examined. These include the existence of dispersion relations for the system function for causal systems and the role of the concepts of positive reality and minimum phase in passive systems. The uses of these linear system concepts in linear viscoelasticity and in the propagation of plane waves in an isotropic viscoelastic medium are considered. Finally, applications to seismology are presented, in particular the significance of the dispersion associated with a quality factor Q that is constant or varies as a power of frequency in comparisons of seismic data for different frequency ranges and in the evolution of the shape of propagating pulses.
Regional relationships among earthquake magnitude scales
Authors: Chung D. H. , Bernreuter D. L.
Published: February 2008

Various magnitude scales commonly used and the interrelationships among them are reviewed. It is shown that problems exist with all of the magnitude scales being used in the United States. When using regional catalogs, for example, it is often necessary to determine how the reported magnitudes were determined. Often such information is not available, although the potential errors are quite large. Both the MS and the mb scales were designed to be universal scales. However, both MS and mb magnitudes are often determined beyond the applicable range of the equations used to define the two scales. Furthermore, the MS magnitudes are not generally available for moderate to small earthquakes in most earthquake catalogs. The mb magnitudes are more generally available than MS values; however, there is also much greater variation in the way mb is determined. In particular, a significant change in the mb scale occurred in the early 1960’s when the World‐Wide Standard Seismograph Network (WWSSN) was established. This change in instrumentation used to determine mb values had a significant effect on estimated magnitudes (post‐1960 values are lower) and the saturation level of the mb scale. The older, longer‐period instruments recorded larger mb magnitudes than can be recorded with the WWSSN instruments. In addition, great care must be taken when selecting the mb magnitudes of western U.S. earthquakes, because the values are often in considerable error owing to the fact that they were determined at distances less than 25° and were not properly corrected for attenuation in the upper mantle, or asthenosphere. The seismic body wave magnitude mb of an earthquake is strongly affected by regional variations in the Q structure, composition, and physical state within the earth. Therefore because of differences in attenuation of P waves between the western and eastern United States, a problem arises when comparing mb values for the two regions. A regional mb magnitude bias exists which, depending on where the earthquake occurs and where the P waves are recorded, can lead to magnitude errors as large as ⅓ unit. There is also a significant difference between mb and ML values for earthquakes in the western United States. An empirical link between the mb of an eastern U.S. earthquake and the ML of an equivalent western earthquake is given by ML = 0.57 + 0.92(mb)east. This result is important when comparing ground motion between the two regions and for choosing a set of real western U.S. earthquake records to represent eastern earthquakes.
Review of surface friction, surface resistance, and flow of snow
Authors: Lang T. E. , Dent J. D.
Published: February 2008

Three related topics pertaining to surface properties of snow are reviewed: (1) surface friction between snow and other materials as applied to skis and sled runners, (2) surface resistance of snow to oversnow trafficability of vehicles, and (3) flow of snow over snow surfaces as occurs in avalanches. These topics were part of the presentations at the U.S.‐Canadian Workshop on the Properties of Snow held at Snowbird, Utah, April 1981. The review is an update of work in these areas since the dates of previous reviews and focuses, particularly, on the work reported by attendees of the workshop.
Global nature of field‐aligned currents and their relation to auroral phenomena
Authors: Saflekos N. A. , Sheehan R. E. , Carovillano R. L.
Published: February 2008

Low‐ and high‐altitude spacecraft carrying scientific magnetometers have probed the magnetic fields of the terrestrial magnetosphere. These measurements reveal that field‐aligned currents, possibly powered by dynamo action, flow over large regions of the earth's neighborhood. The purpose of this paper is to report on highlights of the U.S. contributions to the IMS effort in the area of understanding the global nature of the field‐aligned currents and their relation to auroral and ionospheric phenomena. It has been established now that field‐aligned currents flow on the same field lines connecting distant regions to low ionospheric altitudes. Similarly, currents flow on L shells extending over several hours of local time. However, it is becoming increasingly apparent that the sources of the currents in the various latitudes and longitudes are not the same. For this reason we discuss separately the following current‐laden regions: (1) the noon sector, (2) the dawn and dusk sectors, (3) the midnight sector, and (4) the polar cap. Special attention is paid to polar cap ionospheric irregularities and the relation of auroral kilometric radiation to field‐aligned currents and optical auroral emissions.
The elemental and isotopic composition of galactic cosmic ray nuclei
Authors: Mewaldt R. A.
Published: February 2008

Galactic cosmic rays represent a directly accessible sample of matter that originates outside the solar system. The elemental and isotopic composition of this sample of high‐energy matter contains a record of nucleosynthesis in other regions of the galaxy, and of subsequent nuclear and electromagnetic interactions that have altered its composition. There have recently been significant new advances in reading this record, brought about in large part by the launch of new high‐resolution instrumentation. In particular, measurements of the abundances of individual elements have now been extended into the upper 2/3 of the periodic table, and the individual isotopes of a number of heavy cosmic ray nuclei have recently been resolved.
Hydromagnetic waves in the magnetosphere
Authors: Hughes W. J.
Published: February 2008

The study of hydromagnetic waves in the magnetosphere has seen some notable advances over the last four years. We owe a large debt to the IMS observational programs both in space and on the ground. These programs have produced extremely valuable data sets which should be worked on for many years to come.

The improvement in instrumentation has been a major factor in observational work. The new generation of spacecraft are exemplified by the ISEE and GEOS missions, both of which have novel aspects. Both missions have played a large part in helping us understand how important heavy ions are in the propagation of hydromagnetic waves of all frequencies. The dual spacecraft, ISEE 1 and ISEE 2, are helping to unravel the spatial structure of these waves in space, while both missions are providing the first measurements of electric field oscillations associated with hydromagnetic waves. The ionospheric electric field measurements made by the STARE radar system have introduced a new dimension to the field, and help provide a link between ground based and spacecraft measurements. Several ground based magnetometer networks were either introduced or expanded, largely as a result of the IMS.
Inertial surveying and geodesy
Authors: Schwarz K. P.
Published: February 2008

Inertial survey systems offer a novel and, in many ways, unique approach to the geodetic problems of positioning and gravity field determination. This paper outlines the basic theory of using the output of an inertial measuring unit to obtain geodetically meaningful results. Emphasis is on the development of appropriate mathematical models and estimation procedures rather than on hardware aspects. A discussion of results achieved to date and an outlook on future applications concludes the presentation.
Atmospheric radiation: 1975–1983
Authors: Wiscombe Warren
Published: February 2008

Rarely, in the press of day‐to‐day scientific work, is there a quiet moment to stand back and survey our part of the geophysical landscape. These quadrennial reviews, it seems to me, are the ideal place in which to do so. But too often we have had a deadening recitation of details rather than a lively forum. I could not write that kind of review.
Geochemical evolution of the crust and mantle
Authors: DePaolo Donald J.
Published: February 2008

During the period 1979–1982 studies of the Internal evolution of the earth reflected a broadened perspective, due largely to the influence of a growing body of knowledge about planetary evolution which is based on studies of lunar rocks and observations of the other terrestrial planets. In addition, there has been a noticeable increase in the amount of communication between workers mostly concerned with the chemistry of planetary evolution and those mostly concerned with the physics. The results have been a sharper focusing of research directions and a feeling that unified models of planetary evolution, from accretion to senescence are now much closer to being within reach. The changing perspective has been accompanied by the emergence of experimental techniques that are yielding new basic information.
Recent progress in the application of satellite altimetry to observing the mesoscale variability and general circulation of the oceans
Authors: Fu Lee‐Lueng
Published: February 2008

Recent progress in the application of satellite altimetry from Seasat and GEOS 3 to the observation of the oceanic mesoscale variability and general circulation is reviewed. The lack of accurate geoid models has been the major obstacle in the study of the general ocean circulation from altimetry. The use of geoid‐independent methods that utilize the temporal differences in altimetric measurements taken at fixed locations, however, has made significant contributions to our knowledge of the mesoscale variability of the ocean. The mesoscale energies of the sea surface height and geostrophic current have been mapped on a global basis. Their distributions in wave number space have also been analyzed. Because of many of the deficiencies of existing altimeter data (short duration, inadequate orbit, poor accuracy, etc.) most of these results describe only a small portion of the frequency‐wave number spectrum of the variability, but they have nonetheless demonstrated the great value of an optimally designed altimetric mission in advancing our knowledge of the global mesoscale variability. The current technology allows satellite altimetry to detect oceanic variability at periods from a few days to 3–5 years, and wavelengths from 50 to 10,000 km. Determining the time‐averaged general ocean circulation from altimetry is more problematic because an accurate geoid is indispensable. The currently available global geoid models have useful accuracies only at wavelengths greater than about 7000 km. There have been several attempts at mapping the global ocean circulation at those scales using existing altimeter data and geoids. When these results are compared with hydrographic surveys, some qualitative agreement can be observed, but the quantitative differences are mostly inconclusive because of the geoid and orbit errors. It has been suggested, however, that an altimetric mission that is optimally designed with the current technology, when complemented by a state‐of‐the‐art gravimetric mission to map the earth's gravity field, is able to determine the ocean circulation quantitatively at scales from the ocean basin to about 200 km.
Surface albedo data for climatic modeling
Authors: Henderson‐Sellers A. , Wilson M. F.
Published: February 2008

The climate system is driven, primarily, by energy absorbed at the surface. Surface albedo sensitivity is incorporated into all types of climate models, and changes can lead to large feedback effects. For example, alterations in the extent and/or state of the cryosphere and large‐scale modification of vegetation cause significant perturbations in climate model results. The specification of surface albedo in general circulation climate models (GCM's) differs. An improved and agreed surface albedo data set is urgently required for climate modeling. It is likely that the most appropriate means of achieving consistent and credible surface albedos is by using well‐designed satellite surveillance to augment global inventories of soils and vegetation. However, retrieval of surface albedo values for all sky and surface conditions from satellite observations is difficult. Atmospheric distortion is especially hard to remove. Some of the sensitivity of GCM's to surface albedo values may be the result of inadequate parameterization of other climatic components. The accuracy of information demanded by climate modelers could be reduced and made more consistent. Recommendations are made for the implementation of a new global scale observational program with the aim of providing surface albedo data at an accuracy of ±0.05 within 5–10 years. Immediate initiation is urged.
Review of the critical ionization velocity effect in space
Authors: Newell Patrick T.
Published: February 2008

Laboratory experiments have shown under a variety of conditions that when a neutral gas passes through a magnetized plasma with a relative velocity perpendicular to the magnetic field that is greater than a critical velocity, anomalously high ionization of the neutrals occurs. The conditions under which the same effect is to be expected in space plasmas is still unclear. The experimental evidence for the occurrence of the critical ionization velocity effect in space is summarized, and various areas in which it has been proposed that the effect should be significant are discussed.
Convective cloud downdraft structure: An interpretive survey
Authors: Knupp Kevin R. , Cotton William R.
Published: February 2008

Observational and modeling studies dealing with different aspects of convective clouds are reviewed and interpreted to construct a generalized description of the structure, dynamics, and thermodynamics of convective cloud downdrafts. Observational studies reveal that downdraft speeds and sizes range from typical values of several meters per second and several hundred meters in nonprecipitating cumulus congestus clouds to typical values of 5–10 m s−1 and several kilometers in precipitating cumulonimbi. Maximum measured downdraft speeds appear to be limited to ∼20 m s−1. Different types of downdrafts appear to exist within precipitating convective clouds. Penetrative downdrafts common to nonprecipitating convective clouds and upper regions of precipitating convective clouds exhibit maximum horizontal dimensions of ∼1 km. These downdrafts emerge when subsaturated environmental air is entrained or mixed into the cloud. A second type, cloud edge downdrafts, appear in both observations and in cloud model results. Although their driving mechanisms are not fully understood, such downdrafts may be forced by cloud edge evaporational cooling and localized updraft mass flux compensation. Overshooting downdrafts comprise a third type and are typically associated with intense convection in which updraft air surpasses an equilibrium level of neutral buoyancy, cools upon further ascent, and then descends but remains within a few kilometers of cloud top. Finally, the precipitation‐associated downdraft is one forced at low levels by precipitation loading, evaporation, and melting. This downdraft may attain relatively large scales, of the order of the horizontal dimension of precipitating regions within the lowest several kilometers. Such large scales provide a clear distinction from (penetrative‐type) downdrafts of ∼1 km maximum scale within nonprecipitating convection. There is evidence from both observational and modeling studies that downdraft dynamical and thermodynamical processes are strongly influenced by static stability, wind shear profiles, cloud microphysical processes, and precipitation characteristics. However, the degree to which downdraft structure depends on such interrelated controlling factors has not yet been determined.
On optimal estimation of gravity from gravity gradients at aircraft altitude
Authors: Jekeli Christopher
Published: February 2008

Least squares collocation in physical geodesy is now a standard technique for estimating gravity‐related quantities from discrete observations in a limited region. It is an optimal method because estimation errors due to measurement noise and the discreteness and finite extent of observations are minimized. However, for large observation sets, the computational problem of collocation (i.e., the problem of solving a large, possibly ill‐conditioned, linear system of equations) is also well known and is very clearly illustrated with airborne gravity gradiometry. Natural alternatives to rigorous least squares collocation are therefore examined and are categorized as being either nonoptimal, suboptimal, or virtually optimal. All choices of estimation method are directed at reducing the computational requirements with an awareness of the desired estimation accuracy. An example of a nonoptimal procedure is the use of integral formulas of the Stokes or Vening‐Meinesz type; suboptimal estimation is exemplified by frequency domain collocation; and a case of virtual optimality is the approximate collocation estimator obtained with a few iterations of the conjugate gradient method used to invert the autocovariance matrix.
The inference of North Atlantic circulation patterns from climatological hydrographic data
Authors: Olbers D. J. , Wenzel M. , Willebrand J.
Published: February 2008

We present a review of β spiral techniques which have recently been developed for the determination of absolute velocity profiles from hydrographic observations. A specific technique is then designed and applied to the North Atlantic part of Levitus' (1982) climatological hydrographic atlas with the aim of estimating reference velocities and diffusivities for heat, salt, and potential vorticity. These quantities are determined on a 1° grid from the local gradients of temperature and salinity under the constraints of the thermal wind relations and the conservation of the respective tracers including diapycnic and isopycnic mixing terms. The estimation procedure includes the statistical framework of inverse modeling in the weighting of the constraints by the data noise variances and the determination of the covariances of the model parameters. The resulting circulation pattern bears strong resemblance to the classical view of the North Atlantic circulation as put foreward by Wüst (1935) and Defant (1941). The upper layers are dominated by the Gulf Stream/North Atlantic current system with a broad subtropical gyre recirculation. In the lower layer a western boundary current is fed from Norwegian Sea overflow penetrating the Gibbs fracture zone and partly circulating around the Labrador Sea. As a consequence of the climatological averaging the currents appear in broad shape with much reduced velocities, in particular in the upper layer. The vertical structure reveals an almost horizontal level of no motion pattern much along the concepts of Defant (1941). Diffusion coefficients were determined for an upper layer (depth of mixed layer to 800 m depth) and a lower layer (800 m to 2000 m). The spatial pattern of these coefficients correlates with maps of eddy activity, showing higher values in the strong current regimes and low values within the subtropical and subpolar gyre. Average values in the lower layer of the quiet regions are 10−5m²/s and 10² m²/s for the diapycnal and isopycnal diffusivity, respectively, and 10−1m²/s for the vertical diffusivity of vorticity (which yields 10² m²/s for the lateral diffusivity of potential vorticity). Toward the regions of strong currents and in the upper layer these values roughly increase by an order of magnitude.
Spherical shell tectonics: Effects of sphericity and inextensibility on the geometry of the descending lithosphere
Authors: Yamaoka Koshun , Fukao Yoshio , Kumazawa Mineo
Published: February 2008

The shape of a deep seismic zone is thought to represent that of the descending slab of lithosphere. The lithosphere before subduction is a spherical shell, and the shape of the descending slab is the result of the deformation of the spherical lithosphere at the subduction zone. Upon bending a spherical shell often deforms in a very different way from a simple plate. We examine whether the actual shape of the descending slab can be explained by a simple bending of an inextensible spherical shell, which shows little surface deformation under moderate stress. This examination is made region by region for most of the subduction zones in the world by means of an analogue method. The lithosphere is simulated by an inextensible spherical shell made of polyvinyl chloride resin. The Wadati‐Benioff zone is shaped by plaster by referring to the reliable hypocentral data selected from the International Seismological Centre (ISC) bulletins. The spherical shell is forced to fit the miniature of the Wadati‐Benioff zone. Fitting is first attempted only by bending. If a good fit is not attainable and if a discontinuity or gap in seismic activity is observed in the relevant region, the spherical shell is torn along this discontinuity or gap, and the goodness of fit is reexamined. The results of the analysis are summarized as follows: (1) The shape of the Wadati‐Benioff zone can be simulated largely by a simple bending of a spherical shell without surface deformation. (2) In almost all of the regions of poor fit with bending, a good fit can be achieved by tearing the spherical shell along the trace of low seismicity. The sphericity of the lithosphere and the inextensibility upon deformation are the two essential factors in controlling the slab shape. This means that the lateral constraint is most important for understanding the geometry of the downgoing slab of lithosphere and the stress state within it. Further, several problems related to the deformational characteristics of the spherical lithosphere are also reviewed and discussed in connection with subduction tectonics.
Earth Radiation Budget Experiment Scanner Instrument
Authors: Kopia Leonard P.
Published: February 2008

Orbital measurements of the earth's radiation budget are being made from several spacecraft launched in the latter part of 1984. Three sets of instruments have been designed to measure the incident solar flux, the earth's long‐wave emitted radiation, and the earth's reflected radiation more accurately than have been measured before. These instruments consist of a three‐channel narrow field of view scanning radiometer and a four‐channel wide field of view staring nonscanner radiometer and a solar channel. The instruments are collecting data on spectral, spatial, and temporal scales specified by scientists and researchers in the weather and climate discipline. The scanning radiometer, the subject of this paper, is designed to yield small‐scale definition for measurements taken by the nonscanner and thereby test convolution/deconvolution techniques used on wide field of view data. The scanning radiometer is also expected to yield bidirectional reflectance data as an aid in radiation transfer modeling calculations.
Inversion methods for satellite studies of the Earth's Radiation Budget: Development of algorithms for the ERBE Mission
Authors: Smith G. Louis , Green Richard N. , Raschke Ehrhard , Avis Lee M. , Suttles John T. , Wielicki Bruce A. , Davies Roger
Published: February 2008

The Earth Radiation Budget Experiment carries a three‐channel scanning radiometer and a set of nadir‐looking wide and medium field‐of‐view instruments for measuring the radiation emitted from earth and the solar radiation reflected from earth. This paper describes the algorithms which are used to compute the radiant exitances at a reference level (“top of the atmosphere”) from these measurements. Methods used to analyze data from previous radiation budget experiments are reviewed, and the rationale for the present algorithms is developed. The scanner data are converted to radiances by use of spectral factors, which account for imperfect spectral response of the optics. These radiances are converted to radiant exitances at the reference level by use of directional models, which account for anisotropy of the radiation as it leaves the earth. The spectral factors and directional models are selected on the basis of the scene, which is identified on the basis of the location and the long‐wave and shortwave radiances. These individual results are averaged over 2.5° × 2.5° regions. Data from the wide and medium field‐of‐view instruments are analyzed by use of the traditional shape factor method and also by use of a numerical filter, which permits resolution enhancement along the orbit track.
Acoustic tomography by Hamiltonian methods including the adiabatic approximation
Authors: Wunsch Carl
Published: February 2008

Long‐range acoustic propagation for ocean tomography is elegantly described by invoking a Hamiltonian formulation. Many results previously derived in an ad hoc manner emerge naturally from the use of the Hamiltonian. The cycling between the upper and lower ocean that is characteristic of oceanic sound propagation is treatable as a libration phenomenon. General perturbation methods, highly developed in astronomy and quantum mechanics, are immediately available for understanding both range independent and range dependent disturbances to a reference profile. The tomographic two‐point boundary value problem leads, in an analogy to the old Bohr quantum mechanics, to quantization of the action, although the more naturally quantized variable is the canonical angle. An adiabatic approximation merges naturally from the formalism. In the adiabatic approximation the range dependent bias problem in tomography can be fully understood and accounted for as long as the source and the receiver remain axial.
Remote sensing applications in hydrology
Authors: Schmugge Thomas
Published: February 2008

The physical basis of remote sensing depends on the inference of land surface characteristics from the measurement of the emitted or reflected electromagnetic radiation from the earth. The hydrologically related parameters studied using this approach include: surface temperature, evapotranspiration, soil moisture precipitation, snow, and components of the radiation balance. Significant progress has been made in determining these quantities using radiation at wavelengths from the microwave to gamma rays. The recent progress in several of these areas will be documented in this review.
Ring current and radiation belts
Authors: Williams D. J.
Published: February 2008

In this report we focus on the subject of the earth's ring current and radiation belts. Other particle results can be found in the presentations listed in the Index of this quadrennial (1983–1986) U.S. Report to the IUGG (see the SPR‐Magnetosphere and SPR‐Aeronomy sections for particle results pertaining, respectively, to the magnetosphere and the ionosphere/thermosphere). In the previous U.S. Report, ring‐current and radiation‐belt results through 1982 were included in a comprehensive presentation on near‐equatorial magnetospheric particles by Young [1983]. Since then, several volumes of conference proceedings and a book related to the subject at hand have appeared: Energetic Ion Composition in the Earth's Magnetosphere [Johnson, 1983], Solar‐Terrestrial Physics [Carovillano and Forbes, 1983], Progress in Solar‐Terrestrial Physics [Roederer, 1983], Quantitative Aspects of Magnetospheric Physics [Lyons and Williams, 1984], Space Plasma Simulations [Ashour‐Abdalla and Dutton, 1985], and Ion Acceleration in the Magnetosphere and Ionosphere [Chang, 1986].
Waves and instabilities
Authors: Inan Umran S.
Published: February 2008

This review concentrates on U. S. research activities in the area of waves and instabilities during the mid‐1982 to mid‐1986 period. Plasma waves and instabilities are phenomena that are central to the energization, acceleration, transport, and loss of energetic particles in magnetized plasmas. As such, they play a dominant role in almost all energy exchange phenomena that occur in planetary magnetospheres.

It is difficult to give a comprehensive review of the subject even for a limited period of four years; however, we note that several other articles in the U. S. National report to IUGG for the Solar Planetary Relationships (SPR) section discuss selected aspects of wave and instability phenomena. Specifically, numerical simulations are discussed by Ashour‐Abdalla [1987], phenomena in the magnetopause and bow shock by Elphic [1987], magnetospheric tail pheomena by Huang [1987], electric fields and currents by Mauk [1987], auroral phenomena by Gorney [1987], and planetary (Jupiter, Saturn, and Uranus) phenomena are covered by Connerney [1987]. We have attempted to avoid extensive overlap between these reviews and the present report.
Galactic cosmic rays and anomalous components in the heliosphere
Authors: McKibben R. B.
Published: February 2008

Studies of modulation of galactic cosmic rays by the sun and of the origin, acceleration, and modulation of the anomalous components are by definition long‐term undertakings. The time scale is that of the 11 (or 22) year solar activity cycle, and the system, the heliosphere, has a response time to changes of the order of a year. It is tempting to speculate that the tempo of research activity in the field may itself bear some relation to the solar activity cycle, with a phase lag appropriate to the time scales of data analysis and publication. If this speculation were true, since the last maximum in solar modulation occurred in 1981–82, the four years since the last review of modulation for the IUGG (Jones, 1983b) should have been a period of remarkable vitality and progress.
Geodetic theory
Authors: Colombo Oscar L.
Published: February 2008

Given the broad area of this review: “geodetic theory”, its material has been selected to cover as best as possible the work done in the last four years on basic ideas and methods, recognizing the fact that contemporary geodesy is a discipline with fast‐expanding and, therefore, rather fuzzy boundaries. For this very reason, a non‐too‐subtle selection criterion has been adopted, to avoid ending with an excessively long list of references. By and large, articles presenting mostly quantitative results, or outlining research plans and policies, or hardware developments, have been excluded, particularly those that clearly belong in another section of this Report. Those dedicated mostly to discussing basic concepts, or describing in detail the theories behind various methods, were chosen. The material has been arranged according to one classification scheme (others exist), which, while not being perfectly adequate for all the publications surveyed, may help the reader find those he might be interested in without too much difficulty.
Contemporary plate motion and crustal deformation
Authors: Stein Ross S.
Published: February 2008

The measurement of relative plate velocities during the past few years is a signal accomplishment in earth science, leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins. Regrettably, deformation premonitory to an earthquake has yet to be detected with confidence. Delineation of the spatial and temporal buildup of strain between earthquakes, however, has put limits on models of the earthquake cycle. A diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike‐slip faults. In contrast, the geometry of thrusts and normal faults, revealed by earthquake deformation, has been found to differ markedly from expectations. Geodetic observations have proved vital to monitor the ascent of magma through the Earth's crust and to predict volcanic eruptions at the Earth's surface. Episodic vertical and horizontal deformation in southern California remains a subject of dispute; if anything, it is less certain than it once seemed.
Status of the geopotential
Authors: Rapp Richard H.
Published: February 2008

Lerch (1982) has prepared the previous report on this topic. This discussion describes the developments reported during the period 1983 to 1986. Our definition of the geopotential is the description and determination of the earth's global gravity field. This is considered from current developments to results to be expected with future space missions.
Oceanographic and geophysical applications of satellite altimetry
Authors: Douglas B. C. , McAdoo D. C. , Cheney R. E.
Published: February 2008

Since the last quadrennial report, new satellite altimeter data have not been generally available. Nevertheless, important progress has been made from analyses of Geos 3 and Seasat data. The marine gravity field has been determined to an extraordinary resolution and accuracy, and important solid earth geophysical interpretations made. In the area of oceanography, statistical estimates of the variability of dynamic topography have been published, methods for incorporating altimeter data into numerical models have been developed and applied, and tentative, but interesting determinations of the mean circulation have been made. In addition, altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields. Finally, important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved.
Petrology of the igneous rocks
Authors: McCallum I. S.
Published: February 2008

During the period 1983 to 1986, the large number of papers, books, and monographs published on the petrology and geochemistry of igneous rocks reflects the vitality and continued growth of this central earth science discipline. While an attempt has been made to prepare a reasonably complete bibliography, the accompanying text, of necessity, reflects a subjective selection of topics. If some papers have escaped my net I apologize and assure the authors that the omissions are inadvertent. A list of books and monographs is provided in the first section of the bibliography. Papers dealing with isotopic and/or trace elements studies on igneous rocks are included in the bibliography if these papers also contain a significant petrologic component. The review by R. Carlson in this volume contains a complete reference list on this topic.
Volcanology
Authors: Self Stephen , Francis Peter W.
Published: February 2008

In the quadrennium 1983–1986 there has been an exceptional increase in studies concerning volcanoes. It has also been an active four years for the world's volcanoes, including some of the most devastating events known and major alerts at three of the world's calderas. The range of methods used to study volcanoes has also multiplied, embracing the use of many new techniques. All of this makes the task of selecting topics and papers for inclusion in this review extremely difficult. We cannot attempt to be comprehensive in such a short review. Our investigations for material stopped approximately in mid‐August, 1986. [Tilling and Newhall] (in press) are preparing a review of volcanology in 1987.